PO Box 2349

White Salmon, WA 98672 509.493.4468

www.newbuildings.org

COMMERCIAL ROOFTOP HVAC ENERGY SAVINGS RESEARCH PROGRAM

Final Project Report – Phase 2 March 25, 2009

Prepared by: Mark Cherniack – Senior Program Manager Howard Reichmuth PE – Senior Engineer

Prepared for: Northwest Power and Conservation Council

851 SW Sixth Avenue, Suite 11100 Portland, Oregon 97204

503.222.5161

ACKNOWLEDGEMENTS

The following organizations provided funding to make this phase of the ongoing research possible. They responded to an invitation to participate in this opportunity to further the potential for cooperative research partnerships among interested participants nationwide on small commercial HVAC system issues. Their contributions are much appreciated. From the Pacific Northwest through the Northwest Power and Conservation Council Avista Utilities Bonneville Power Administration Eugene (OR) Water and Electric Board Energy Trust of Oregon Idaho Power PacifiCorp (non-Energy Trust area) Puget Sound Energy Snohomish Public Utility District

From the Northeast Cape Light Compact (through Northeast Energy Efficiency Partnership-NEEP) Connecticut Light & Power (NEEP) Long Island Power Authority (NEEP) The United Illuminating Company (NEEP) Western Massachusetts Electric (NEEP) Efficiency Maine Efficiency Vermont National Grid New York State Energy Research and Development Authority NSTAR

TABLE OF CONTENTS

Introduction..................................................................................................................................... 1

Summary ......................................................................................................................................... 1

A. Economizer Controls Bench Test ............................................................................................. 3

B. In-Field Monitoring and Pilot Test of Protocol to Estimate Savings........................................ 3

Site Recruitment ......................................................................................................................... 3

Field Service/Repair Protocol..................................................................................................... 3

Field Measurement/Monitoring Plan and System ...................................................................... 4

Summary of Field Measurement Findings.................................................................................. 4

Discussion of Field Measurement Findings................................................................................ 5

RTU Electric Energy Signatures............................................................................................. 5

RTU Gas Energy Signatures ................................................................................................... 9

Enhanced Diagnostics ........................................................................................................... 11

C. Development of Annual Savings Methodology...................................................................... 14

D. Summarize Unit Characteristics from Program Data ............................................................. 17

E. Recommendations ................................................................................................................... 18

TABLE OF FIGURES

Figure 1. RTU Electric Energy Use Signature.............................................................................. 6 Figure 2. Two Cooling Episodes Approximately 1 Year Apart ................................................... 6 Figure 3. Economizer Effect ......................................................................................................... 7 Figure 4. RTU Gas Energy Signatures ....................................................................................... 10 Figure 5. Outside Air Map.......................................................................................................... 12 Figure 6. Economizer Control Temperature Map........................................................................ 12 Figure 7. Example of Irregular RTU Operation........................................................................... 16

TABLE OF APPENDICES Appendix A – June 2008 Bench Test Report Appendix B – C7650 to C7660 Comparison Appendix C – Research Site Data Appendix D – Research Field Service Protocol Appendix E - Research Plan Monitoring Appendix F – Research Case Study Appendix G – Research Site Monitoring Protocol Appendix H – Research Letter to Honeywell

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Introduction The Pacific Northwest (PNW) Regional Rooftop Working Group has been taking steps to

establish the potential energy and demand savings from utility-sponsored field service measures on small (typically 10 tons and under) commercial rooftop unitary (RTU) HVAC systems. An initial first phase led to the Phase 2 statement of work; the results are described in this report. The Phase 2 research also received important support from the Northeast Energy Efficiency Partnerships, a number of individual state and utility program administrators covering New England, New York and New Jersey. This research is part of an effort to develop a reliable RTU field service/repair (also known as “retrocommissioning”) protocol, along with a higher level of confidence in the associated energy savings necessary to justify RTU service programs. This report documents the results of the Phase 2 project, consisting of five main components:

A. Economizer Controls Bench Test B. In-field Monitoring and Pilot Test of Protocol to Estimate Savings C. Development of Annual Savings Methodology D. Summarize Unit Characteristics from Program Data E. Recommendations for Phase 3

Summary This project has resulted in recommendations on the following: • Honeywell Economizer Controller Sensor Change-out • Simplified Field Monitoring/Measurement Approach • Annualized RTU Energy Use Methodology • Fan Power Savings • Economizer Optimization • Performance Modeling • Shifting RTU Savings Approach from Repair to Retrofit

One significant outcome of the economizer sensor testing was development by

Honeywell Corporation of a highly accurate dry bulb sensor with advanced control capabilities. This was in direct response to the project finding a economizer control system design flaw that limited economizing operation under certain climate conditions. In addition, the results of the work have led to a cost-effective approach to field measurement for energy/demand savings evaluation, monitoring and verification requirements of the utilities and public policy energy analysts.

Through a newly designed and expanded application of the field protocol for further validation, unexpected and fruitful opportunities opened up in the Pacific Northwest which support implementing the Phase 3 recommendations, but within current and planned RTU-related research and field service demonstration projects in the region. Specifically, through the Premium Ventilation Package project being conducted by the Bonneville Power Administration,

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Eugene (OR) Water & Electric Board and Portland Energy Conservation, Inc., along with the Bonneville Power Administration’s plan for servicing up to 600 units in the Northwest and taking measurements on 20% of the systems. Both projects offer an unprecedented regional test bed opportunity for applying the recommended protocols.

In addition, the Research Team recommends initiation of a discussion on moving from the current RTU ‘service/repair’ paradigm to a deeper retrofit approach, that includes the appropriate service/repair package, along with ‘bolt on’ hardware that would significantly increase the efficiency of the RTU. The deeper energy savings would also bolster the business case for HVAC contractors, customers and utilities for a shift to a retrofit approach.

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A. Economizer Controls Bench Test

Bench testing confirmed a problem with a market-leading economizer controller (W7459) and sensor (C7650) combination manufactured by Honeywell (Appendix A). The 6-10°F deadband (hysteresis) designed into the sensor has the potential to limit economizer use in milder overnight conditions when the deadband is too wide for a more narrow overnight temperature swing to energize the economizer sooner in the morning, or at all. This is dependent on specific conditions. Honeywell verified the bench test findings. Project researchers implemented and tested a low-cost work-around using a contractor’s temporary thermostat. Honeywell would not support the work-around for technical reasons and requested recommendations from the research team on the design for a new sensor. In November 2008, Honeywell released a new sensor (C7660- Appendix B) with a 2°F deadband. This new sensor is easy to replace in the field on the W7459, has eight temperature settings including as low as 48°F for use in data center HVAC systems, and is easy to set correctly. The research team conducted limited testing on the new sensor and confirmed the new deadband.

B. In-Field Monitoring and Pilot Test of Protocol to Estimate Savings Site Recruitment

The research team recruited nine rooftop units (Appendix C) to monitor pre-and post-service/repair. The recruitment effort experienced difficulties in identifying units and clearing administrative hurdles for permission to access the units, all of which slowed monitoring activity. Ultimately, of the nine units, five had insufficient cooling loads to provide a useful data signal; only two of the remaining units had large cooling loads. Chances of improving recruitment are enhanced by a willing and cooperative building owner/manager, relatively easy physical access and internet access for monitored data transmission.

Field Service/Repair Protocol (Appendix D)

The procedure for checking out the RTU’s included visual inspection, functional testing and repair of faulty components as needed. Service and/or repair elements included:

• Thermostat including reset and/or replacement • Measured airflow through the evaporator • Economizer system check • Additional control potential • Refrigerant charge check/adjustment as needed

Coil cleaning was not done, although it is performed as needed by one of the research

subcontractors who also works with technicians in the Puget Sound Energy Premium Service Rooftop program.

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Field Measurement/Monitoring Plan and System

Field measurements were taken as described in the Field Measurement Monitoring Plan (Appendix E). The field monitoring collected data on 12 variables, including:

• RTU total power • RTU fan power • Gas burner status • Damper position • Condensate flow • Outdoor air temperature (2 measurements) • Return/mixed (4 measurements) temperatures • Supply air temperature Field measurements were taken as averages over a 15-minute data interval. The data

logger was sophisticated enough to take conditional as well as conventional averages. The monitoring data were taken from as many sites as were available in the period of summer 2007 through summer 2008. The damper position and the condensate flow were experimental variables and only at sites with favorable physical opportunity.

At the outset, it was planned to collect a wider number of variables than might ultimately be necessary to quantify annual energy use. However, the wider array of variables and the high resolution data collection (15-minute data interval) was intended to support auxiliary analysis of the RTU performance as needed. The collected data was to be stored at a web-based site; this was successful in most cases, but manual data collection was required in others.

Lagging site recruitment had a strong influence on the timing and measurement prospects at many sites. This resulted in leaving the monitoring equipment on some sites for almost a year, much longer than originally planned. While poor installation timing at some sites was initially a problem, the full year monitored data was compensated to an extent.

Summary of Field Measurement Findings Field measurements were pre-processed in a data template which examined the data in

time series and in various parameter vs. parameter plots intended to test for reasonableness and as a quick screening look at performance (Appendix C). As is usually the case initially, the data appeared somewhat variable and inconclusive. A closer look at detailed case study data (Appendix F) provided a basis for examining patterns in the data from regularly operated sites. This appendix examines the details of summer RTU operation and provides a clear-cut example of economizer operation.

Useful data from this project was much less than originally planned. However, there was sufficient data to develop a workable RTU field monitoring and measurement approach to support development of an annualized savings methodology. More data from additional sites would have enabled better characterization of individual measure savings. The findings from this work are as follows:

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Finding 1. An RTU on a building with a regular operating schedule has distinct electrical and gas energy use signatures which are seasonally stable and precise enough to show differences in individual RTU operating characteristics.

Finding 2. An RTU energy signature can be derived from field measurements and short-term monitoring of two key variables during warm weather including at least 10 days (14 is better) with average daily temperatures above 60°F:

• Outside air temperature • Heating unit gas burner status (necessary for winter condition monitoring only) • RTU total power

The signature for electric energy use can be derived from approximately two weeks of

warm weather monitoring. The RTU gas energy signature will require a third measurement (gas burner status) and must be derived from monitoring for about two weeks of winter weather with a mean 24-hour temperature of 50°F or lower.

Finding 3. RTU energy signatures can be diagnostic of operational problems. In general, the signature from a regularly and well operating building will be a tightly coherent pattern of points that expresses an easily recognized, stable operating pattern. However, other RTU energy signatures can show deviations from this prototypical operating pattern that reveal the presence of anomalies and inefficiencies. After an RTU on a regularly operating building has been properly treated by a rooftop service protocol, it should display a proper operating pattern.

Finding 4. RTU energy signatures can be used along with an annual average day temperature histogram to develop estimates of RTU annual energy use without the need to consider other specifics and energy end use of the building or the associated space details. The calculation of annual energy use and savings from RTU energy signatures, along with a brief description of the associated site monitoring protocol is in Appendix G.

Finding 5. The key RTU operating parameters - interior and economizer set points, percent of outside air and de facto schedules - can be measured and mapped with the addition of four sensors to the site monitoring package. This information goes beyond the energy signature and into economizer performance diagnostics.

Discussion of Field Measurement Findings

RTU Electric Energy Signatures Figure 1 summarizes one year of RTU field monitoring on a well-controlled building.

The data, when aggregated as 24-hour averages, show an orderly pattern. More detailed analysis using hourly, 15- or 1-minute intervals can show various operating characteristics of the RTU. These include percentage of outside air and economizer inside/outside control setpoints. However, such detailed analysis is usually inconclusive because it is strongly complicated by thermal transients associated with large outdoor air temperature changes throughout day.

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RTU Electric Energy Performance Map - BI1 Unit 1

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Figure 1. RTU Electric Energy Use Signature

It is noteworthy that the operating data are grouped fairly tightly. This data was

assembled from one year’s operation and shows limited effects of seasonal variation. Note however, the several points below the main line in the range of 60-80°F. These are all from the same cooling episode - the first “hot” spell after winter. It indicates that this portion of the building had lower cooling requirements for a few days as the building warmed to typical summer wall and structure temperatures. It is notable that there was so little seasonal thermal noise of this sort. It is also notable that the sloping portion of the energy signature is so nearly linear with temperature.

Figure 2 shows two smaller subsets of this same data separated by almost a year.

RTU Electric Energy Performance Map - BI1 unit 1

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Figure 2. Two Cooling Episodes Approximately 1 Year Apart

In both periods the economizer was working well, but the fan power was slightly lower

by about 50 watts in the earlier 2007 data. The 2007 signature does appear slightly lower,

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perhaps due in part to the slightly lower fan energy coupled with the 24-hour fan usage in this unit. Detailed data were reviewed for other explanations of the difference; none were found. In Figure 2, the low temperature component of the signature was synthesized from available winter operating data, but it could as easily have been derived from one-time measurement of fan energy extrapolated to 24-hour operation. Most importantly, Figure 2 shows the full year RTU energy signature can be derived from about 10 days of cooling season operating data with 24-hour mean temperatures in excess of 65°F.

The interpretation of an RTU energy signature can lead to a useful practical understanding of the components of RTU energy use and savings. This RTU energy signature is interpreted as follows:

Cooling Balance Temperature. This is the temperature at which the almost horizontal low temperature component of the signature changes to the upward sloping portion with the higher temperatures. In Figure 1, this temperature is about 57°F. This indicates the average 24-hour temperature at which compressor cooling just begins to be needed. This temperature can vary with each RTU depending on the internal load served by the RTU. This balance temperature would be lower for a case with higher internal gains and could be higher where there is less internal gain.

A significant empirical finding from this work shows that the balance temperature is also increased a few degrees by the action of an economizer. The action of an economizer is potentially complex, often regarded as complex enough to defy a simple understanding of the overall economizer effect, thus relegating economizer effects to the province of more complex modeling. However, this research shows an empirical measurement of the economizer impact that is clearly evident in a simple geometric fashion.

RTU Electric Energy Performance Map - BI unit 2

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Figure 3. Economizer Effect

Figure 3 shows a different RTU than Figure 1, but significantly, an RTU serving a

regularly operated space.

The experimental situation underlying Figure 3 was achieved by disabling a properly functioning economizer. In the “econo” case, the dampers opened at the proper times to admit about 80% outside air. For the “no-econo” case, the dampers were set to admit a fixed minimum

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outside air which turned out to be high, about 30% outside air. The results show that the economizer lowers the amount of cooling energy at all average daily temperatures above 55°F.

Effectively, the economizer has increased the cooling balance temperature by about 5°F. A detailed review of the situation revealed that on hot days the economizer was used just after midnight at the end of the compressor cooling for the day, and in the early morning by 9:00 am as the store was opening. It is notable here that the magnitude of energy savings from the economizer is nearly constant for all the average daily temperatures in the range of 65-80°F. Detailed data showed the economizing opportunities were not strongly dependent on the average outdoor temperature. They were present each day as the outside temperature transited the “economizing window.” In practice, the aggregate effect of the economizer was to increase the balance temperature a few degrees by preempting the use of compressor cooling.

It is also noteworthy that the slope of the blue line through the “economizing” points is about the same as the slope of the red line through the “no-economizer” points. This is because the economizer does not affect site-dependent fundamentals impacting Dx cooling: compressor COP vs. temperature, the interior load, the minimum % OSA, or thermal conduction. For practical purposes, the effect of the economizer has been to shift the temperature origin of the sloping portion of the RTU signature to a temperature about 5°F higher. It is likely the small change in slope on the economizer line relative to the no-economizer line is due to the fact that the economizing window is more limited as the daily outdoor temperature increases.

The particular situation illustrated in Figure 3 is a minimal expression of the economizer effect; there was no attempt to pre-cool the space that would have increased the economizer effect. At this particular RTU, there was also a tight deadband set in the cooling control that limited the use of the economizer. The data for this unit does not support an estimate of how much more economizing effect would have been achieved by more aggressive economizer control. This question should be directly addressed in further research and field work.

Horizontal Baseload Slope. In Figure 1, at temperatures below about 57°F the daily

RTU electric energy use is almost independent of the temperature. It is almost entirely for fan energy because the fan was run 24 hours a day. A closer look shows slightly more energy use at colder temperatures, for example 20°F, than at warmer temperatures near 50°F. This small increase in daily RTU energy is due to increased use of the fan in the heating mode where fan energy increases due to the increase in the volume of heated air.

It is important to note that this portion of the RTU energy signature can be estimated without monitoring from a one-time measurement of the fan power in various operating modes, and from the operating schedule. From a monitoring standpoint, it is particularly important to be able to synthesize this portion of the curve to be synthesized from site measurements because this portion of the curve may not be evident in a monitoring test conducted during a prolonged hot spell. The most informative monitoring data will have some cooler weather data as well as warm weather.

Figure 1 has been derived from full-year data that a practical short-term field test protocol will not have. This horizontal portion is a very important part of the energy signature because in the frequent cases with 24-hour fan operation the fan energy is the largest part of annual energy use.

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Another important operating pattern is for an RTU fan that operates only when there is heating or cooling to supply; it has no fan-only ventilation energy use. We do not have data on such a probable case, but in this case it is likely that this “horizontal” portion of the curve will not be a simple horizontal line. It will have a small slope at low temperatures representing the heating fan energy, and at mid-season temperatures (50-65), it will show economizer fan activity, if there is any.

Compressor Cooling Slope. In Figure 1, the pattern of points above 57°F shows the increase in daily energy use for the additional compressor-based cooling. The slope of this portion of the signature depends on many site specific factors such as refrigeration system efficiency vs. temperature, percentage of outside air, conduction cooling load to the served space, etc. In a regularly operated building these factors remain relatively constant. The relatively stable case illustrated in Figure 1 shows that empirically these factors will resolve into an approximate linear relationship to average daily temperature that is consistent throughout the cooling season.

The key finding is that the electric energy signature pattern can be used with a temperature histogram to estimate the annual energy use (and the annual energy savings from a separate pre- and post-service measurement) for a particular RTU without the necessity of examining the other aspects of the building and its operation. In other general work pertaining to HVAC operation, the annual temperature histogram is given in 5°F temperature bins so it can be used with observed HVAC efficiencies observed in each of the temperature bins from other research results. The same procedure could work well for estimating annual RTU energy use.

It is important to recognize that this pattern is the consequence of a regularly operated building (in this case a big box store). An estimate of annual energy use or savings for a less regularly-operated building may not be possible at all except to speculate that it would probably be less than that for a fully operated building. Fortunately, Figure 1 is close to the ideal shape for an RTU performance signature. A shape such as in Figure 1 is what a model of a properly operating RTU would show. Most RTU signatures will have a general shape like the ideal, but they may have clusters of points removed from the ideal shape. These clusters point to operational irregularities.

RTU Gas Energy Signatures The RTU gas energy use showed the pattern illustrated in Figure 4.

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RTU Gas Energy Performance Map - BI1 Unit 1

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Figure 4. RTU Gas Energy Signatures

The data in this figure shows a general pattern, but it is not as coherent as the data in Figure 1 observed for the electric use of the same RTU over the same period. While this data shows more scatter, it also suggests there are days with significantly higher or lower heating efficiencies or thermal loads. The red line on Figure 4 shows the limiting pattern for the high energy (low efficiency situations), and the blue line shows the predominant performance. The slopes are proportional to the overall heat delivery efficiency including furnace efficiency, ventilation requirements, burner efficiency, net thermal load and duct efficiency. In this example the low efficiency days are operating at about 65% of the predominant overall efficiency, a significant deterioration.

This data covered the whole heating season. It was reviewed in detail for some indication of what caused the rather large differences in energy use. Outdoor temperature, thermal lag, interior temperature, day type, and ventilation %OSA were ruled out as causes for the scattered data.

The most probable correlation for the higher energy points is a higher proportion of the daily heating during the occupied day. The detailed data shows that the portion of the building conditioned by this RTU becomes significantly thermally stratified. When the lights come on in the morning the upper space from which the return air is drawn heats up by 3-5°F within about 30 minutes. When the heating comes on, the upper space reaches almost the temperature of the supplied hot air. This situation is probably caused by duct irregularities allowing the heated supply air to short-circuit the space The heating is effectively less efficient under these circumstances as the hot stratified air is exhausted and replaced by cold ventilation air. Figure 4 shows that variations on the energy signature can indicate subtle operational interactions. In this case, the operational problem is large, subtle, and it is probably caused by incorrect duct work that is not directly part of the example RTU.

The primary elements of the gas energy signature illustrated in Figure 4 are as follows:

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1) Heating Balance Temperature. The temperature below which heating initially becomes necessary is the heating balance temperature. In Figure 4, that temperature is about 60°F. This temperature may be somewhat unique to each RTU because it depends on the thermal load of the served space net of the internal gains to the space. If the internal gains of the space were higher for the same thermal load, the balance temperature would be lower, and similarly if the thermal loads of the space were higher for the same internal gain the heating balance temperature would be higher.

2) Heat slope. The slope of the cluster of heating points with decreasing temperature is

dependent on the burner (or heat pump) efficiency, the thermal load, the duct efficiency, and the ventilation rate.

Enhanced Diagnostics The site monitoring went beyond the three measurements required for the energy

signatures alone. The monitoring included four other sensors in an effort to collect performance data in greater depth to support additional diagnostics. The extra sensors included:

• Return air temperature • Mixed air temperature, (average of four temperatures) • Supply air temperature • Damper position as measured with a string potentiometer

The addition of the return and mixed air measurements was to support the capability to

estimate the fraction of outside air induced into the system. The damper position measurement provided a positive means of classifying the operating mode, and the supply air temperature supports the calculation of the thermal output and COP of the RTU. Acting together these sensors were able to provide two key maps of control performance as shown in Figure 5 and Figure 6.

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Figure 5. Outside Air Map

Economizer Control Map - BI unit #2

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Figure 6. Economizer Control Temperature Map

Figure 5 is intended to quantify the amount of outside air being admitted through the

economizer dampers. The amount of outside air admitted is given as a ratio: the percent of the unit air total flow that is outside air. The percentage of outside air is indirectly shown in Figure 5 as the slope of the mode line. Figure 5 shows the percent outside air for economizing (Stage 1), circulation only, and compressor operation (Stage 2). This is the conventional presentation for deriving the percentage of outside air from temperature measurements. However, unique in

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Figure 5 is the use of the damper position to classify modes that leads to a useful empirical estimate of the outside air admitted in each mode of operation. This eliminates the scattered points usually portrayed on this type of graphic view. From the slopes of the mode lines in Figure 5, the RTU was admitting about 80% outside air in stage 1, and it was admitting about 11% outside air in the recirculation and compressor stages. It is also evident that there were times during the compressor mode that the economizer could have been used but it was not engaged.

In Figure 6, the damper position indicator is used to define the times when the economizer dampers are either driven open (on) or closed (off), and to note the return and outside air temperatures at those times. In an attempt to simplify the monitoring, the return air temperature is used as a proxy for the thermostat temperature in this figure. At night, shown here when the outside air temperatures are in the range 47-56°F, this proxy is probably accurate and it shows that the economizer (stage-1 cooling) turned on at about 72°F and turned off at about 71°F. These on-off temperatures were about the same for all outside air temperatures in the range of 47-56°F.

However, after the full building lights come on, the space tends to stratify temperature-wise and to distort the proxy measurement with a temperature increase of about 3-5°F. In these cases, it is assumed that the thermostat on/off temperatures observed at night are the accurate ones. The upshot of this control temperature map is to show that the economizer was operating for a range of outdoor temperatures from 47-74°F. And it shows that the economizer was turned on when the thermostat temperature reached about 72°F and it was turned off at temperatures below about 71°F.

For this example RTU the observed range of outdoor temperatures will support active economizer operation. However, the range of observed thermostat temperatures (deadband) is too narrow for the best economizer operation. It is very common to have a tight deadband such as the one observed, but it is a holdover from a pre-economizer control paradigm. The action of an economizer is much gentler thermally than that of a compressor. For best operation it needs to begin admitting cool ventilation earlier and to continue admitting ventilation air longer than is typical with compressor control. In this example, the economizer would too often come on in the morning late and operate as an economizer for only about an hour before the compressor would come on and the economizer turn off. The economizer could have forestalled the compressor for another hour if it had come on at a few degrees lower interior temperature. Similarly, at night, the economizer would cease operation when the building had cooled to about 71°F. This effectively limits pre-cooling; the economizer should be controlled to a several degrees lower temperature for best results.

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C. Development of Annual Savings Methodology The principal overall finding from the field measurements is that the RTU energy

signatures, derived from short term summer monitoring, can be used along with an annual average day temperature histogram to develop estimates of the particular RTU annual energy use. Further, these annual energy use estimates can be develped without the need to consider the other energy end uses of the building or the associated space. This finding assumes that the RTU and the associated space have been operated consistently for the full year.

The development of an annual energy savings methodology involves a close and necessary coordination between the specifics of the monitored data and its subsequent analytical treatment. This project has led to the development of a brief monitoring protocol and the associated analytical methods (Appendix G). The value of this protocol is that it is based on a tested process that has linked the monitored variables to orderly analytical outputs. The challenge in all M&V is to link monitored data, which almost always is inherently disorderly, to clear and reasonable conclusions. In general a monitoring protocol will involve specification of the types of variables to be monitored, monitoring methods, and the analytical process of aggregation, filtering, plotting, and engineering necessary to reduce the monitored data to usable information.

The process of developing this protocol has showed that only a minimal data set is necessary to sustain the essential RTU annual energy estimates, with the additional monitored variables leading to a more detailed understanding of the RTU operation. The monitoring protocol considers a full range of monitored variables and itemizes the incremental information attained by the added variables. In this way two levels of monitoring have been specified: Level 1, a minimal level intended to document savings and simple enough for economic application to larger samples, and Level 2 a more detailed and costly level intended to support problem diagnosis in monitored RTUs and to support comparison with savings modeling efforts.

The initial review of the monitoring data showed that a reliable RTU electric energy signature could not be drawn exclusively from the daily energy vs average temperature in a short term (2-3 week) data set; there was usually too much variability to justify fitting one function versus another. But further analysis showed that a more confident fit could be made to the data by including analytical inspection of the detailed data to help define the functional form. This requirement for data inspection increases the analytical effort from what was intended to be a brief statistical procedure to a mini case study for each site. At this point, a consistent methodology has been devised for estimating energy and demand savings for a specific operating RTU, but it requires engineering judgment on a case by case basis. The principal focus (and challenge) of the analytical effort is to devise a reasonable RTU energy performance function in terms of average daily temperature.

The annual savings methodology is a three step process: 1) describe the RTU performance as a function of average daily temperature, then 2) evaluate this function at each of the average daily temperatures for a normal year to get the daily energy use for each day of the normal year, and 3) sum the daily energy use from each day into a yearly total. . If the principal interest is cooling operation then the model and the savings need only consider the cooling portion of the year.

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This perspective on the annual energy use (or savings) immediately provides some insight into the relative savings afforded by the various component measures of the RTU service protocol. The most important perspective on RTU energy use is with regard to the relative energy use of the fan and the compressor. It is tempting to regard the compressor energy use as the dominant energy use because when the compressor is operating, the power is high, of the order of several kW. However, in practice the compressor is powered only for several hours a day for fewer than about 90 days a year. By contrast, many installations use the fan 24 hours per day for all 365 days of the year. In this case a small change in fan power can be equivalent to a large change in compressor power.

Many rooftop service protocols include an adjustment of airflow toward a nominal target of 300-400 cfm/ton in order to improve compressor efficiency. It is important to recognize in these cases that the energy savings from the improved compressor efficiency for a limited number of days in the year are likely to be significantly offset by the increased fan energy that will be present for the full year. A perspective on the RTU whole year energy use argues for very careful treatment of fan energy in any rooftop service protocol. This is an important consideration when the intention of the RTU treatment protocol focuses on summer savings, but may burden the operation in other seasons.

It should also be noted that a thermostat adjustment can have a similar effect as an economizer by delaying the onset of compressor operation until later in the day. The effect of thermostat adjustments can be very significant, and should not be overlooked. The action of the thermostat and the economizer have a complex relationship such that the increase in cooling set point can reduce (and replace ) economizer activity unless a pre-cooling strategy is employed.

This savings methodology has been derived from RTUs operating on buildings that have a regular weekly schedule such as retail and occupied offices. In reality, many buildings will not be this regular. Either they will be irregularly operated or they will have regular operation, but with a malfunctioning HVAC system. It is likely that irregular operation will be a significant source of RTU energy savings. A comparison of the irregular operating signature to an idealized operating pattern can be a useful diagnostic. Figure 7 shows an RTU electric energy signature that is “messy” along with an idealization of the same signature.

In this figure, the electric energy use approximately corresponding to the average temperature of 50°F appears higher than the idealized signature. A point-by-point inspection of this case showed that the compressor was coming on when there was outside ventilation available. This is a clear failure of the economizer control system on some particular days, but not all days. If the service treatment were to succeed, these high points would be on the idealized slope in the post-retrofit period.

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RTU Electric Energy Performance Map - BI2 unit 2

0.000

20.000

40.000

60.000

80.000

100.000

120.000

30.0 40.0 50.0 60.0 70.0 80.0 90.0

Mean 24 Hour Temp, deg F

RTU

Ele

ctric

Ene

rgy,

kW

h/da

y

Figure 7. Example of Irregular RTU Operation

Note the points corresponding to the temperatures in the 70-80°F range. These scatter about the idealized line. An inspection of these points showed that some of the scatter is due to changes in the day to day average temperature of the order of 3°F. In extreme cases, where the average day temperature changed more than 5°F (a significant day-to-day change), the scatter is probably due to residual thermal transients. It is likely that a scatter plot such as is Figure 7 will be the best that can be typically expected from this 24-hour data averaging method.

The patterns found in the energy signatures of the irregular cases of a large enough sample would constitute a usable assay and quantification of the current state of RTU energy use and control that goes beyond prior studies such as the Jacobs study that were one time inspection based and did not lead to annual energy use estimates.

A preferred outcome for estimating annual savings would be to model the savings, but the modeling must be calibrated to the empirical findings by casting the modeling into an average temperature vs. daily energy format as found in this field research work. This research has identified that there is an energy signature pattern to which to true the models. However, modeling is essential to confirm and possibly modify the functional form of the idealized energy signature. Therefore, the monitoring protocol includes data collection that supports a comparison of the empirical data with modeling.

17

D. Summarize Unit Characteristics from Program Data A preliminary task to the bench test effort was review of available field experience to

identify the most commonly used control items for test. Accordingly, researchers reviewed available characteristics from data collected as part of Puget Sound Energy (PSE) Premium Service Rooftop program. To be eligible for the program, an RTU must have an economizer. This represented a fairly large set of data expected to be typical of installations in the Northwest. Out of 223 systems with economizers, the following characteristics were noted:

• 70% had the Honeywell controller/sensor combination being tested • 41% used enthalpy sensors with unknown drift and calibration, although only dry-

bulb sensing is necessary in our climate • 56% had only a single stage of cooling wired, which significantly curtailed

economizer use • 73% used a single changeover point (one outdoor sensor and no return air sensor) • 27% used a differential changeover strategy Taken together, these statistics suggest that about 60% of units were operating below par.

The main reason is the predominant use of single-stage control. A secondary reason is the unnecessary use of enthalpy sensors in this climate. One manufacturer (Honeywell) has provided the basic controller (W7459) used throughout the last several decades by most HVAC manufacturers–with an estimated 85% market share. Recently, other companies have developed their own products. However, this particular controller is ubiquitous among existing installations that would be candidates for retrofit repairs.

18

E. Recommendations The results of the project were not fully anticipated.

• The initial Bench Test component resulted in an improvement in economizer control

accuracy through a partnership with Honeywell Corporation and development of a sophisticated dry-bulb sensor for new and retrofit rooftop HVAC unit application.

• The Research Project Team made recommendations to Honeywell (Appendix H) for a new, basic economizer controller with advanced features, including a number of features recommended for the Advanced Rooftop Unit. Honeywell is developing a new controller product with a number of the recommended features.

• The difficulty in site recruitment and individual circumstances of the sites which limited data availability measurement all worked to restrict the number of sites for analysis, but not the findings.

• RTU energy signatures can be used along with an annual average day temperature histogram to develop estimates of RTU annual energy use and savings without the need to consider other energy end uses in the building or the associated space.

The following recommendations are made with the expectation that additional discussion

and research will be required. At the outset of Phase 2, there was a discussion among the Pacific Northwest regional stakeholders about taking the field measurement and field service protocols developed in Phase 2 and applying them to a larger number of units. The number 60 was noted. However, rather than propose a new phase of field research as a discrete follow-up to Phase 2, it is recommended that the proposed field measurement protocol and annual savings methodology be applied to existing and new RTU service-related research and pilot projects in the Pacific Northwest, regardless of the service protocol. Specifically, the recommended protocols should be applied in the Premium Ventilation Package project and the 600 RTUs planned for servicing through the Bonneville Power Administration. This will provide further opportunity to substantiate the usefulness and accuracy of the protocol and provide additional field data that can be used to further sharpen the methodology for substantiating energy savings. Economizer Controller Sensor Change-out and Elimination

a) Existing and planned RTU service programs in the Pacific Northwest and other regions where the Honeywell C7650 sensor is in widespread use should initiate replacement with the C7660 sensor through any utility-supported field service work. This recommendation is specifically aimed at the Premium Ventilation Package project and the large Bonneville-sponsored field service project. It is likely that this controller sensor combination is in widespread use in California and the Southwest states.

b) Utilities likely to have the C7650 sensor in its RTU population, and still coming in, should immediately write a performance or a prescriptive specification for units being incentivised through utility high efficiency HVAC programs that requires a sensor with no more than a 2°F deadband. This would not impact any other sensor products in this market and would stop the use of stocks of old sensors that OEMs will use until exhausted.

c) The Regional Technical Forum should reach out to promote the sensor-related findings and recommendations to utility and energy efficiency public benefits organizations in the Northwest, California and the Southwest, including the NW Energy Efficiency Alliance, the

19

Energy Trust of Oregon, the California Energy Commission, Western Cooling Efficiency Center, and the Southwest Energy Efficiency Project. The American Heating and Refrigeration Institute should be informed of these findings and recommendations to potentially influence its members to switch to the new sensor immediately.

d) Honeywell, the supplier of the new sensor (C7660), has discussed a potential region-wide bulk purchase of new sensors to achieve the best unit pricing. This offer should be actively followed up on, especially with regard to the large field service project that Bonneville will be implementing.

Field Monitoring/Measurement Approach. The Pacific Northwest Regional Technical Forum should consider adopting the field monitoring approach described in this report as the core approach for RTU savings measurement in the Pacific Northwest, including in the Premium Ventilation Package Project and upcoming Bonneville project involving up to 600 RTUs, and any other RTU savings-related field monitoring that will be done in the Pacific Northwest.

Utilities in the Northeast are likely to find a similar energy signature, but with different

cooling slope and balance temperature. The annualized energy use methodology should be applicable in the Northeast; however, some Northeast region-specific measurement is recommended to verify the measurement protocol and methodology.

The Research Team recommends that utilities in the Northeast identify several RTUs for service and implement the measurement protocol at each of the three recommended levels of data collection/analysis to provide experience and confidence with the protocols at each level. The number of units to be field monitored is a local option.

If field measurements are taken within a consistent framework, results from on-going or planned field studies can be readily aggregated into a statistically robust perspective. Persistence measurements using the methodology are recommended at annual intervals for at least five years on a limited sample of regularly operating buildings. It is expected that any field measurement effort may include additional measurement values beyond the minimum recommended. Fan Power Savings. More attention should be given to fan power in designing an RTU service package. Issues include 24-hour fan operation, along with features of the Premium Ventilation Package project including: variable speed control, morning ventilation lockout, and differential economizer control. Increased air flow adjustments for the purpose of optimizing refrigeration cycle performance can increase overall annual fan energy use and erase savings realized from other measures. Economizer Optimization. Where economizers are working at all, they typically could be further optimized with incremental improvements that increase energy savings. Improvements include: wider control setpoints with more aggressive use of pre-cooling and night flush. Performance Modeling. Existing modeling approaches related to RTU performance should be reconciled to empirically-derived RTU energy signatures by formulating the modeling results into the average day vs. average energy format of the energy signatures.

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Rooftop Unit Work Group. The Pacific Northwest Regional Rooftop Research Working Group (RTUG) should be revitalized to work on other activities, including:

• Review the research report Findings and Recommendations. • Seek RTF approval of the recommended protocol and other approaches if warranted. • Plan for scheduled periodic review of evaluated results of all RTU-related programs. • Develop and obtain approval for a Regional Technical Forum deemed savings calculator

for RTU savings programs. • Actively seek collaborative activities on HVAC energy efficiency with interested energy

efficiency-related organizations and agencies in California, the Northeast and Southwest. RTU Savings Program Paradigm Shift. The RTUG should engage in discussions within the region and with colleagues from the Northeast focused on the future of utility RTU energy efficiency programs. The topic for consideration is a shift in the standard utility RTU ‘service’ approach (including basic controls/thermostats, airflow/refrigeration diagnostics/repair, duct leakage assessment/repair, economizer assessment/repair, et al.) to a more comprehensive ‘retrofit/upgrade’ approach. This approach includes the standard service package as the initial retrocommissioning step, followed by adding retrofit items including among a number of other options:

• Expanded control functions being tested in the Bonneville Premium Ventilation Package Project

• Electrically commuted fan motors • New motor technology such as NovaTorque (www.novatorque.com). • Evaporative condenser pre-cooling • Embedded fault detection and diagnostics with remote communication capability • Duct redesign/revision • Outdoor air sensor upgrade • 5-bladed fan blade These options along with other ‘bolt-on’ improvements could be packaged in a utility-

supported existing RTU service/retrofit/upgrade program. This approach could significantly increase the utility’s potential for kWh and kW savings. The magnitude of expected savings beyond the standard service package approach would bolster the business case for HVAC contractors to participate by up-selling hardware upgrades. Most contractors make the majority of their revenue from selling equipment, not service. The retrofit package could provide a new, potentially substantial revenue stream. The savings potential of the upgrade approach should have a noticeable positive impact on the customer’s utility bill compared with a service-only package, where bill savings may be difficult to identify. At least in the near term, this approach could be more attractive to customers given the mounting economic stress driving increased customer interest in repairing or perhaps upgrading existing RTUs rather than purchasing new equipment. Finally, the expected increase in kWh/kW savings will substantially improve utility benefit-cost ratios and should provide in market aggregate, significant savings across the fleet of existing RTUs.

APPENDIX A

Commercial Rooftop HVAC Energy Savings Research Program

Bench Test Report

June 2008

Prepared by: Mark Cherniack – Senior Program Manager Howard Reichmuth PE – Senior Engineer

Prepared for: Northwest Power and Conservation Council

851 SW Sixth Avenue, Suite 11100 Portland, Oregon 97204

(503) 222-5161

Acknowledgements Acknowledgements

The design and set up of the testing chamber, testing of the components/systems, and initial data assessment was completed by David Robison, P.E., Stellar Processes, Bob Davis, Ecotope and Dennis Landwehr, P.E. under subcontract to New Buildings Institute (NBI). NBI staff is responsible for the final report and conclusions.

The following organizations provided funding to make this phase of the ongoing research possible. They responded to an invitation to participate in this opportunity to further the potential for cooperative research partnerships among interested participants nationwide on small commercial HVAC system issues. Their contributions are much appreciated.

From the Pacific Northwest through the Northwest Power and Conservation Council

Avista Utilities Bonneville Power Administration Eugene (OR) Water and Electric Board Energy Trust of Oregon Idaho Power PacifiCorp (non-Energy Trust area) Puget Sound Energy Snohomish Public Utility District

From the Northeast

Cape Light Compact (through Northeast Energy Efficiency Partnership-NEEP) Connecticut Light & Power (NEEP) Long Island Power Authority (NEEP) The United Illuminating Company (NEEP) Western Massachusetts Electric (NEEP) Efficiency Maine Efficiency Vermont National Grid New York State Energy Research and Development Authority NSTAR

The Project Team also acknowledges the responsiveness of Honeywell Product Manager Adrienne Thomle and her engineering staff for making recommendations that strengthened the research, as well as responding with new product designs that will allow economizers to fully function as intended in saving energy.

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Executive Summary This work has been done as part of the Commercial Rooftop HVAC Energy Savings Research Program which includes four interdependent elements: 1) bench testing of economizer controls, 2) field testing of repair protocols, 3) devising an appropriate measurement and verification (M&V) approach and 4) developing a savings prediction methodology based on prototypical buildings. Taken together, these elements are intended to lead to the development of a reliable field repair protocol with a higher level of confidence in the associated energy savings. This document summarizes the results of only the first of the four elements, the bench testing of economizer controls. This document is also an interim summary of results because the bench testing capability is being retained and will be used further during the project.

The bench testing research was applied to the most typical type of dry bulb economizer controller using controlled environmental chambers to determine the environmental and control factors that influence the operation of the economizer. The principal findings are:

• The sensors and economizer controller system exhibits an operational pattern (deadband) that can significantly interfere with expected economizer operation by limiting the economizer potential during seasons with warm nights. We refer to this as “hysteresis” in this report.

• The sensor and controller components tested exhibited a consistent low bias in temperature. Environmental temperatures that are supposed to activate the controller do not correspond to those specified by the manufacturer. The apparent wide sensor and controller tolerance leads to loss of economizer energy savings potential.

• The enthalpy sensors tested appear initially to be more accurate than the dry-bulb sensors tested. However, this stage of research did not measure sensor response over the range of humidity that would be necessary to fully test enthalpy sensors. Some “hysteresis” is present with enthalpy sensors as was exhibited in the dry-bulb sensors tested, but the magnitude of the deadband across a range of conditions is not yet bounded by the available data. Additional testing of the enthalpy sensor is still underway.

• A dual differential economizer strategy was tested and compared to the single changeover strategy as a potential improvement. The differential control strategy used in conjunction with a 2-stage thermostat has the potential for a more sophisticated control than a simple single change point strategy. However, test results showed only modest improvement from this control strategy. This strategy may be more complex to execute in a simplified and consistent field procedure. It also requires a 2-stage thermostat, which is recommended in any case for effective economizer performance.

• A proposed “work-around” solution in the field would substitute an inexpensive contractor’s thermostat (<$10) for the temperature sensor commonly in use. This combination operates with very little hysteresis and is expected to increase the amount of economizer operation. This work around is amenable to a simple and consistent field procedure.

• Honeywell personnel provided helpful feedback on the testing protocol. They do not support the proposed work around due to concerns about high feed-in amps to the controller, even though a resistor could be added the circuit.

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• The test apparatus was successful in providing an inexpensive set of controlled environmental chambers.

Taken together these findings cast significant doubt on the capability of existing economizers, specifically with the Honeywell C7650 dry bulb/temperature sensor, to perform according to their potential. Given that economizers have been embodied in building codes on the assumption of performance consistent with their specification, there is an urgency to apply corrective measures. Accordingly, the immediate recommendations are:

• A dialog has been opened with Honeywell, the controller/sensor manufacturer, concerning the findings in this report and the proposed work-around. These findings suggest that a significant group of existing economizer controls currently in operating RTUs cannot access the full economizer potential. This is a major functionality problem with significant kWh waste that needs addressing and it is important to continue to access the knowledge of the equipment manufacturer in this regard.

• Honeywell, in response to the bench test results that provided important ‘customer’ input to the sensor/controller product manager, has developed a new, advanced dry-bulb sensor that should resolve the field problem. Honeywell has committed to sending several beta stage sensors for bench and field testing in July. If this new sensor works as expected, further discussions about a field retrofit package for utility programs will be held with Honeywell. Commercial availability is expected 3rd quarter of 2008.

• Utilities should assess the impacts of identifying the economizer controller sensor equipment described in the report, that may be installed in new RTUs that are receiving financial incentives through current or planned utility energy efficiency/DSM programs. If the particular Honeywell sensor product is present in these new units, a decision must be considered about including a modification to the equipment at installation time so as to not install the problem sensor. A field work-around employing the contractor’s thermostat or snapdisk could be used in lieu of the problematic temperature sensor. The work-around should be based on the single change point control and not use the differential control. The implementation of the work around should be viewed as temporary until the new Honeywell sensor is commercially available. Alternately, utility high efficiency RTU incentive programs could at least flag those systems for a follow up sensor retrofit.

• The bench test has been expanded to include Honeywell enthalpy-based economizer controls. It is could be expected that the hysteresis effects observed for dry bulb temperature sensors would not be as significant in the case of enthalpy sensor otherwise, the use of economizing in the more humid eastern US will also be limited relative to its potential. At the time of this report, data is still too sparse from the enthalpy sensor tests for reporting conclusions.

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Introduction The principal conservation benefit from using an economizer proceeds from using cooler outside air for space cooling instead of air-conditioning when conditions permit. Unfortunately, detailed monitoring revealed that economizing is often ineffective. One cause of this problem is due to a known problem with the economizer control system, referred to here as “hysteresis.” In the typical control mode, the controller must sense a sufficiently cold outdoor temperature before economizing is allowed – this temperature is typically 10ºF cooler than the indoor temperature. This required temperature is referred to as the nominal changeover temperature. Earlier monitoring studies have shown that this “hysteresis” effect prevented economizing during warm summer months in mild climates because the coldest nighttime temperatures were not cold enough to allow economizing. The same problem was not observed in climates with a larger diurnal temperature swing and colder night temperatures.

The purpose of the current investigation is to test a typical controller system, identifying the extent to which hysteresis or poor sensor calibration might limit full operation, and to develop and test a “work-around” solution as part of the development of the field service protocol that will be implemented in Phase 3 of the overall project. This preliminary task has been limited to testing the controller apparatus within a set of controlled environmental chambers in order to quantify the problem and verify the potential solution. A future task, and part of the field testing portion of the larger project, will be to implement the proposed solution in the field and to verify the energy impact on HVAC equipment in actual service. This bench testing alone is not sufficient to quantify the full energy impact of economizing because that is a complex function of specific site characteristics and operations. The full energy impact of economizing requires building modeling guided by these lab results and by the field test results. The necessary modeling and field testing are a coordinated part of the larger project.

It is usually not necessary to bench test commercial equipment. However, the current status of this type of controller has been shrouded in conflicting anecdotal observations and incomplete knowledge of the inner logic of the control system. In the view of the research project oversight committee, the intended research needed to be based on a precise understanding of the control system performance that could not be assessed from existing research or from the specifications provided by the manufacturer.

This initial report discusses observations regarding the dry-bulb economizer control operations as observed in an indoor test chamber. This type of economizer operation is important in the Pacific Northwest and Rocky Mountain areas where humidity is generally low. Enthalpy controls for economizers will be assessed at a later time as part of the project since they are important for utilities supporting this research in the Northeast, where humidity has a greater impact.

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Previous investigations have attempted to quantify the savings from repair of existing packaged HVAC units1. These HVAC units are numerous in small commercial buildings, but conservation options have been difficult to justify due to the costs necessary to reach these small customers. Demonstration of cost and benefits will assist agencies in designing conservation outreach programs.

Background A preliminary task to the bench test effort was to review available field experience to identify the most commonly used control items for test. Accordingly, we reviewed available characteristics data collected as part of Puget Sound Energy (PSE) Premium Service Rooftop program. To be eligible for the program, an RTU must have an economizer. This represented a fairly large set of data expected to be typical of installations in the Northwest. Out of 223 systems with economizers, the following characteristics were noted:

• 70% had the controller that we are testing • 41% used enthalpy sensors with unknown drift and calibration, although only dry-

bulb sensing is necessary in our climate. • 56% had only a single stage of cooling wired, which significantly curtailed

economizer use. • 73% used single changeover point (one outdoor sensor and no return air sensor),

27% used a differential changeover strategy.

Taken together these statistics suggest that about 60% of the units were operating below par. The main reason is the predominant use of single stage control. A secondary reason is the unnecessary use of enthalpy sensors in this climate. One manufacturer (Honeywell) has provided the basic controller (W7459) used throughout the last several decades by most HVAC manufacturers – with about 85% market share. Recently, other companies have developed their own products. However, this particular controller is ubiquitous among existing installations that would be candidates for retrofit repairs. For that reason, we targeted this particular controller as the subject of study. The particular items bench tested are itemized below.

Item/Function Manufacturer Model /Part # Economizer Controller Honeywell W 7459

Dry bulb Temperature Sensor Honeywell C 7650

Contractor’s Thermostat, (<$10)

Temp-Stat TS-65

Snap Disc Thermostat (~$25) Service First SEN00235A Model 20602L4-B74

Table 1 – Items Tested

1 Small Commercial HVAC Pilot Program Market Progress Evaluation Report, No. 1, http://www.nwalliance.org/research/reports/135.pdf

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The initial understanding of the particular control logic was somewhat general and informed principally by the manufacturer’s product cut sheets and application guide. At the outset, controller operation is generally understood as follows: The important part of the controller is a potentiometer that compares conditions and modulates the economizer dampers in response to control parameters. Those parameters include 1) installer-adjusted set points for the outside air temperature which triggers economizer operation (A, B, C, D settings), 2) a reference condition that is usually a set resistor, but an indoor temperature sensor is used for differential control, and a 3) a sequence to assure that supply temperature is not overly cold. When there is a call for cooling and economizing is possible, the controller sends 24 volt current to the damper motor, which simultaneously opens the outside air dampers and closes the return air dampers. An LED light indicates this condition. When there is no current, the LED turns off and the motor resets by spring action to a minimum amount of outside air needed to meet indoor air quality guidelines. This example can be described as a single changeover strategy since operation change is controlled by a single outside air sensor referenced to the controller set points. Notice that this idealized description of the control logic does not mention any hysteresis effect in the cut sheets, though it is mentioned in a note in the applications guide. After the detailed testing conducted here, a precise apparent control logic diagram was devised and is shown in Figure 3 (pg.9).

Component Testing Results The bench testing was done in a testing facility, described in Appendix A, set up specifically for this purpose. The initial bench tests were intended to reveal the specific operation of the control system on a limited number of controllers and sensors, hence the results are essentially anecdotal and are not intended to be statistically rigorous samples.

Two controllers and four temperature sensors were purchased for testing purposes. Eugene Water and Electric Board (EWEB) staff also provided a number of working but used sensors retrieved from various repair jobs. The test equipment recorded the position of the economizer actuator arm and the status of the LED indication light. Both are conditions that indicate the controller is operating in economizer mode. Both of these conditions agreed closely with each other – typically the actuator arm moved within a few seconds of the indicator light.

The manufacturer’s cut sheet for sensors2 indicates that control operations and sensor ma output are expected to follow a linear response to outdoor temperature. This manufacturer’s specification is referred in this report as the “reference”. Of course, the reference range of operation also depends on the installer-adjusted set points (A, B, C, D settings).

Initial tests of sensors and controllers were directed at the electrical properties of the components compared to temperature. These initial tests revealed that the controller and temperature sensors were biased toward low temperature readings. That is, sensors activated operation at temperatures lower than actual temperature. The tests also showed that the temperature sensor output exhibits sensitivity to the excitation voltage. However, measurements on the individual components, such as current versus temperature in the temperature sensors, led to inconclusive results due to lack of knowledge of the electronic details of the control approach. Accordingly, an overall control test protocol was devised that treated the sensor and controllers as a single component. This overall control test protocol is described and discussed in Appendix B.

2 Figure 3. C7650 Temperature Sensor Output Current of C7650 Sensor Manual 63-2499-1, 1996.

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Implied Controller Temperature Points

20

30

40

50

60

70

80

90

100

Deg

FReference

7650 TestResult

D C B/C B

Figure 1 - Test of Controller Settings

Reference ObservedDeg F Deg F

D ON 45.0 39.1 OFF 54.6 48.1 C ON 59.1 51.0 OFF 68.7 60.5 B/C ON 65.5 59.2 OFF 74.8 70.1 B ON 71.9 61.5 OFF 80.9 71.0

Table 2 - Reference and Observed Change Points

Figure 1 and Table 2 show the response of one typical sensor at different controller set points under the testing protocol as described in Appendix B. For this sensor, all the tests results are biased lower than the specified reference. For example, at setting B/C, economizing is expected to occur within the range of 65 to 75ºF ambient temperature. In fact, the operation occurred within a range of 59 to 70ºF. The result is a constraint on economizing operation. Using this example at setting B/C, night temperatures will have to fall to below 59ºF so that economizing will take place the next day. Obviously, this rules out economizing during much of the summer in a mild climate. Thus, even such a small error can result in a serious reduction of economizing. The test results agree with previous field monitoring that showed ineffective economizing in locations with warm night temperatures. An evident difficulty is that the installer, relying on the manufacturer’s reference documentation, will not be able to select an appropriate setpoint due to the undocumented bias of the components, which appears to be variable among sensors.

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Previous studies have observed that the controllers are typically shipped from the factory set at setting D. Figure 1 demonstrates that this setting assures little or no economizing. As a result, the repair programs have recommended that installers change the setting to B or C. Based on PSE program data, installers are following that recommendation and typically adjust the setting to midway between B and C. Accordingly, B/C was used as the typical setting for subsequent testing.

Example of Controller Operation

40

50

60

70

80

90

8:20

11:40

15:00

18:20

21:40 1:0

04:2

07:4

011

:00

Time

Tem

pera

ture

, deg

F

OnOff

Figure 2 - Example of Controller Operation Figure 2 shows an example of typical test runs that illustrate the hysteresis effect. In this first part of the example, the chamber starts at a temperature near 70ºF, so the controller quickly turns economizing “off”. Economizing remains “off” until the temperature falls to 60ºF; then it turns “on” again. As the temperature rises, economizing remains on until the temperature reaches about 70ºF. The important point is that the controller does not initiate operation until the temperature falls to the “reset” point of about 60ºF. Then, economizing continues until the temperature rises again to the high limit. At that point, economizing is halted until the “reset” temperature is again experienced. This operation continues through any number of similar cycles. This example duplicates the problem observed in the field – economizing will not occur unless night time temperatures fall to the low set point, which may not happen under milder nighttime conditions.

There was concern that the installer may not do A, B, C, D settings consistently. The set potentiometer is small and difficult to read in the field, and the potentiometer is continuously variable, with no physical ratchet for the A, B, C, D points. So one question tested was: how reproducible are the settings? Multiple attempts to set at the A, B, C, D settings were fairly repeatable.

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APPARENT ECONOMIZER LOGIC

Set reference temps, ref low and ref high, with ABCD potentiometer

Is OSA less than ref low?

Turn on reset indicator

Is OSA less than ref high?

Is reset indicator

on? Turn off reset indicator

Is supply temp

greater than 55°?

24 volts to actuator LED is on, damper is opened

full or controlled to maintain 55F supply

No voltage to actuator, LED is off and damper returns

by spring to minimum setting

yes no

yes no

yes

yes

no

no

Figure 3 - Control Logic Diagram Based on these observations, Figure 3 shows a diagram of the control logic as determined from the bench test results. Of course, the controller is only operational when there is a call for cooling.

Both controllers tested performed identically. This suggests that it might be possible to set the controller at a setpoint to compensate for the observed temperature bias in the sensors. However, the sensors exhibited some variability in the amount of bias. Figure 4 and Table 3 show how several sensors performed with the controller at the same B/C setting each time. Such variability makes it difficult to define a standard offset that would compensate for the biased measurements. More important, this compensation approach does not solve the hysteresis problem.

Figure 4 and Table 3, show the performance of the four new C7650 sensors and six older C7650 sensors. Initially, we were concerned that older sensors might drift off calibration and be less accurate. Disassembly of the sensors in Figure 5 shows that, although the model number has not changed, the manufacturing design has changed. The new sensors utilize different internal components than the old ones. While our sample is small, it suggests that there is little difference in performance between new and older sensors.

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Implied Controller Temperature Points, Setting B/C

4045505560657075808590

DegF

Reference

NewSensorsUsedSensorsContractorTstatSnapdisk

Figure 4 - Comparison of Sensors

New Sensors Used Sensors DegF DegF DegF

ON B/C Reference

65.5 #2 59.2 E#1 64.1

OFF 74.8 70.1 72.7 ON #1 61.6 E#3 63.6 OFF 71.3 72.0 ON T-statA 63.3 #3 60.7 E#4 63.7 OFF 65.3 70.3 73.6 ON T-statB 64.2 #4 59.3 E#6 61.1 OFF 65.9 69.8 71.0 ON SnapdiskA 64.5 E#7 60.7

OFF 75.7 69.9 ON SnapdiskB 66.6 E#2 62.1

OFF 77.2 70.3

Table 3 - Observed Change Points by Sensor

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Figure 5 – New (not the 2008 replacement model) and Older Sensors The C7650 sensors output a current signal in milliamps (mA) to the controller. This is an advantage in control applications since resistance in a long wiring run has less effect on current based sensor than a resistance based one. The internal components of the sensor are necessary to generate the required current signal. It was suggested that there may be a field measurement of resistance that installers could make to verify sensor accuracy. However, measurements found that the sensors exhibit no measurable resistance. That is, the internal electronic components do not pass current without the excitation voltage.

Recognizing that the built-in hysteresis (deadband) limits operation, testing focused on finding and testing a work-around solution. The research team investigated the use of a simple thermostat (close-on-fall thermostat) to substitute for the outdoor temperature sensor. Replacing the usual sensor with an on/off closure has the effect of providing a satisfying temperature input that overrides any control constraints. The closure switch is a possible workaround for the imprecision of the controller and sensors. Essentially, it bypasses the A, B, C, D settings and provides an on/off control instead.

We tested two snapdisks (cost ~ $25) and found them to be highly repeatable and close to specifications. However, these are relatively expensive, and they still show a significant 10 degrees of hysteresis deadband.

Two low-cost “contractor’s thermostats” (cost <$10) were tested and found to be equally accurate and repeatable. These thermostats are connected in place of the sensor and then bypass the changeover logic. Figure 5 shows the temperature control points for these options as well. Either the snapdisk or the thermostat provides a solution to the sensor temperature accuracy problem. But the preferred choice is the contractor’s thermostat because it has a narrow

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deadband and it is relatively inexpensive. It permits economizing when temperatures are 63ºF and below and continues until temperatures rise to 65ºF – the narrow deadband of this thermostat is preferred because it will increase the use of economizing. This thermostat is also available in other temperature ranges. Figure 6 shows the snap disc on the left and contractors thermostat, right, that were tested.

Figure 6. Snapdisk and Contactor's Thermostat

It was suggested by the manufacturer that enthalpy sensors are more accurate than the dry-bulb sensors tested. We briefly checked an economizer using an enthalpy sensor with a single changeover strategy (i.e. with the reference resistor in place instead of an enthalpy sensor in the return air). Air in the environmental chamber was quite dry and it was necessary to apply control setting D in order to have any control response at all from the enthalpy sensor. As shown in Figure 7, this particular sensor demonstrated a better response -- with operation for outdoor air Temperature at a range of 67 to 77ºF. This suggests the enthalpy sensor tested may have better accuracy than the dry-bulb sensors tested. However, the same deadband hysteresis still occurs with the enthalpy sensors. Also it is known that this sensor is responsive to humidity as well as temperature, and we are reluctant to extrapolate this performance to field conditions without a more thorough test of response to a wider variety of temperature/humidity conditions. Ongoing, limited testing of the C7400 enthalpy sensor is continuing until there is sufficient test point data to assess and report on.

- 14 -

Enthaply System, Setting D (dry air)

4045505560657075808590

OA

T, d

egF

LED OnLED OFF

Figure 7 - Operation with Enthalpy Sensor

Differential Control Strategy A dual differential control was also tested. Under this strategy, the controller is set up to compare outdoor air temperature (OAT) to the return air temperature (RAT). This strategy is expected to provide for more economizer operation when the indoor temperature is warmer than the temperature implied by the reference resistor. This strategy requires that the controller be set to the D setting. A test of the differential control requires that the two control parameters, outside air temperature, and return air temperature, be varied in an orderly way to test the control system under its full range of conditions. For this test, we cycled the outdoor temperature repeatedly while maintaining the return air temperature at a specific point. The test was then repeated with a different temperature set for the return air sensor. Results are shown in Figure 8.

Implied Differential Controller Temperature Points

20

30

40

50

60

70

80

90

100

DegF

7650 TestResult

65 72 75 79

Figure 8 - Differential Control Results In general, one observes that the initiation temperature or “turn-on” point increases when return air is warmer. This is consistent with allowing economizing to continue longer since the building

- 15 -

can benefit from cooling even at higher outdoor temperatures. However, the high limit of “turn-off” temperature does not appear to be affected. Test results in Figure 8 are somewhat variable due to noise in the experimental measurements. The results of these tests are simplified in Figure 9 showing generalized economizer “turn-on” and “turn-off” temperatures as a function of return air temperature.

Generalized Differential Operation

50

60

70

80

65 70 75 80

Return Temperature, degF

Out

door

Tem

pera

ture

, de

gF OnOff

Figure 9 - Generalized Differential Operation Benefits from differential control are likely to be modest. First, because the decrease in the “hysteresis” deadband is modest. Second, because the amount of economizer cooling from outdoor air will be small when outdoor temperature is close to indoor temperature. Note that the “single changeover” operation described earlier is a special case of the differential control. With single changeover, the reference resistor results in a mA signal that would be the equivalent of the RAT sensor reading a high indoor temperature. Thus, the constraints related to RAT are “locked in.”

Progress with Honeywell In 2006, prior to the start of the project’s research phase, NBI staff had communicated the potential deadband problem that researchers in the Northwest had identified earlier to Honeywell’s product manager for the economizer controller and sensor of interest. In response, the product manager noted that the C7650 does indeed act as described and was not recommended for use for dry bulb applications. It was suggested that the utility service programs could simply replace the C7650 with the C7400 enthalpy sensor.

This recommendation to substitute enthalpy sensors was rejected by the research team for two reasons: 1) a sensor based on humidity measurement is not compatible with the generally lower humidity levels in the Northwest, and 2) there is anecdotal evidence indicating that enthalpy sensors are not particularly accurate and may suffer from drift and/or calibration problems. A study of humidity sensors conducted by the Iowa Energy Center indicated widespread low accuracy in the sensors currently available in the market. Honeywell staff noted that new automated calibration techniques will be instituted for enthalpy sensor production that will result in higher accuracy sensors.

- 16 -

Naturally, there was interest from the research team as to how this sensor came to be so widely used if the manufacturer now does not recommend its use. As was learned, Honeywell had designed the controller to be paired with an enthalpy sensor. In responding to its customers, the HVAC manufacturers, to provide a lower cost sensor solution, the enthalpy sensor was replaced with the C7650 sensor. The unfortunate result has been a limitation on the availability of economizer cooling in the Pacific Northwest and elsewhere in the country under temperature conditions where nighttime summer temperatures are elevated and the deadband limits the changeover point to activate the economizer damper. There is no estimate possible of the kWh savings lost from the use of this sensor with the W7459 controller and potentially other controllers across tens of thousands of rooftop units.

As a result of the developing relationship and ongoing communications with the Honeywell, the research team was asked to provide recommendations to Honeywell on the parameters of a more effective temperature sensor and economizer controller. Some of the recommendations referenced the features defined in the California Energy Commission’s Public Interest Energy Research project for the Advanced Rooftop Unit (ARTU). One of the ARTU features was a controller sensor with a 2°F deadband.

The recommendations of the research team provided support to the Honeywell product manager internally to accelerate the development of a new dry-bulb sensor and updated economizer controller. A new controller design will include DCV input capability, a startup check test sequence for the installer and other features that have not been disclosed.

In late May 2007, research team members including representatives from the Bonneville Power Administration, Ecotope, New Buildings Institute, Northwest Energy Efficiency Alliance Northwest Power and Conservation Council, Portland Energy Conservation, Inc., and Stellar Processes, met with the product manager and engineering staff in Portland, OR to discuss the design and features of the new sensor. The sensor is field retrofittable having the same form factor of the C7650 and is connected by the existing wiring leads. The new sensor that was presented had six optional temperature ranges, from 48°F to 78°F. The lowest temperature level addresses market needs for providing adequate cooling for data centers/rooms. The settings are activated by dipswitches. This setup provides the HVAC installer with a positive signal that they have set the unit’s changeover range where they meant to. The sensor has onboard logic and will actually control the controller. The A-B-C-D setting ‘pot’ in the W7459 will be inoperative. Team members recommended 63°F for the factory default setting. Honeywell will be sending beta samples of the sensor for the research team to bench and field test. There was also a discussion of the development and potential large-scale field deployment of a retrofit package in the Northwest. Detailed discussions will take place once commercial availability and pricing is known. The research team will stay fully in touch with the Northeast projet partners on this developing activity.

Honeywell expects to obsolete the C7650 sensor as the means of removing it from market availability and expects a commercial launch of the new sensor in October 2008. No information has been provided yet on sensor pricing.

Significantly, the utilities are now being viewed by this Honeywell product manager, as an important customer group that has specific product functionality needs, in addition to the traditional Honeywell customer base consisting primarily of the HVAC manufacturers, whose product value needs are not necessarily consistent with utility and ratepayer needs. This is a significant opening for utilities and energy efficiency organizations to be involved with

- 17 -

fundamental energy efficiency-related product development and design. This relationship with Honeywell needs to be actively maintained and supported further as appropriate. There are other energy performance and hardware-related opportunities that must be explored with the HVAC manufactures directly. These will be further elaborated to the utility partners involved in this project.

- 18 -

Appendix A– Description of Test Facility The test apparatus was required to meet the following specifications:

• Three independent temperature controlled test chambers. o Dry bulb temperature controllable in the range 40-80 ºF.

• Equipment test bench o Log on/off status of at least 8 digital variables. o Log 8 analog sensor outputs, 0-5 V, and 4-20 mA, o Log economizer actuator output signal.

• Communication system integration sufficient to store and archive test results both analog data and digital data as appropriate.

o Log test conditions for dry bulb temperature and relative humidity

The chambers consist of three insulated boxed installed in a residential freezer as shown in Figure 10.

Figure 10 - Environmental Chambers Each box contains a small air circulation fan to maintain a uniform temperature. A computer control system senses the temperature in each box and adds heat (by turning on a small light bulb) as needed to maintain the specified temperature regime, as shown in Figure 10. Each box can be programmed for a specified temperature regime, such as a specified change rate and temperature range. For example, Figure 12 shows a program that varies temperature from about 44 to 72 ºF and back at a rate of about 1 degree per minute. This is a typical program to represent the “outdoor” temperature range or OAT. While there is some fluctuation in the controller temperature, the system can maintains an average temperature within about 0.1 ºF.

- 19 -

Figure 11 - Inside of Chamber The test protocol alluded to in this report consisted of following a sensor/controller system through a range of OAT temperature changes similar to that shown in Figure 12. We then recorded the temperature points at which the controller operation changed to either economize or not economize. These control points represent the “turn on” or “turn off” points described in the report such as in Figure 1 and Figure 8.

T e m p e ra tu re in C h a m b e r

4 04 55 05 56 06 57 07 5

12:26:0

0

12:41:0

0

12:56:0

0

13:11:0

0

13:26:0

0

13:41:0

0

13:56:0

0

14:11:0

0

14:26:0

0

14:41:0

0

14:56:0

0

15:11:0

0

15:26:0

0

DegF

Figure 12 - Example of Environmental Chamber Temperatures

- 20 -

With multiple chambers, it is possible to investigate alternative strategies. For example, we test the differential strategy by programming one chamber to represent the “return air” temperature while another chamber represented the “outdoor” one. In this case, the test protocol specifies that the chamber that represents OAT to follow a similar program to that shown in as described earlier. At the same time, another chamber that represents RAT operates through a temperature range that would vary between something like 65 to 75 ºF. We then record the temperature points at which the controller operation changed to either economize or not economize. This protocol then allows documentation of the conditions when economizer operations start and stop as shown in Figure 1.

We built the apparatus with capability to measure other parameters, such as the mA sensor output. That is because, at the onset, we were not sure what measured parameters might turn out to be important. While we recorded mA outputs, it turned out that the controller operations could be easily described using temperature measurements. The equipment is also capable of measuring relative humidity although current work has focused only on dry-bulb controls. Future work will investigate enthalpy controls.

Figure 13 shows a schematic of the test apparatus. The three environmental chambers are indicated by different colors.

25W

- DS 18B20 Sensor

- AD 590 Sensor

NBI ECONOMIZER TESTING SET-UP

Laptop w/Energy Answer

USBHub

DS Adapter

MCC USB – 1208FS

A/D *4 Port ADigital 1/0 Outputs*16

Analog Port BInputs Outputs

To ’s

AC Relayx 4

To Bulbs

TEST CHAMBERS

Honeywell7650

sensor

FreezerAmbient

HoneywellW7459

Controller

24vac

24v AC

Relay

To 10V DC

To MA Input

1

PhotoDiode

LED

DigitalInput

To ’s

W7415Actuator

On120V Plug Strip

Off

10 VDC

24 VAC

20 VDC

To 3 ACRelays

24V AC

120 V

To W 7459Input 1

Arm

0 1 2 3 Multiplexer4 x 8 input

Inputs0A – 0H 1A – 1N 2A – 2H 3A – 3HDC Volt DC-MA ‘D igital’ AD590Inputs Inputs Inputs Sensors

1

2

ToMA Input

50

Figure 13 - Test Apparatus Schematic Diagram

- 21 -

Appendix B - Overall Economizer Control Test Description and Discussion

Purpose - This test is intended to establish the outside air temperatures associated with economizer open and close points. This test is intended to be used with dry bulb temperature sensors. In general, the economizer control may have several components (temperature sensors, controller, actuator) that interact in the overall control function. Measurements on the individual components, such as mA vs. temperature for the temperature sensors, lead to inconclusive results due to lack of knowledge of the electronic details of the control approach. Regardless of the electronic specifics of the controls, (or any sub component), all economizer controls ultimately do the same thing: they open and close dampers at certain outside air, return air, and supply air temperatures. This test seeks to quantify the performance of the economizer control system as a whole. A principal complexity of existing economizer controls is that the control points may depend on the direction of change of the outside air temperature, increasing or decreasing. The control also differs depending on whether or not the outside temperature has reached a sufficiently low temperature trigger point. This dependency on a low temperature trigger point is referred to as control hysteresis. The control test must be capable of identifying the circumstances leading to the control points. General Method - In general, the testing method seeks to vary the principal control parameters in an orderly way, sufficient to exercise and observe the control system over the full range of control conditions it can be expected to encounter. Here this is referred to as traversing the control domain. Single outdoor dry bulb sensor control - The simplest case involves a single dry bulb outdoor temperature control. In this case, traversing the control domain consists only of varying the outdoor temperature in both directions between upper and lower limits. This test uses a test setup with a temperature controlled test chamber. The outside air temperature is simulated in the test chamber, enclosing the outside air temperature sensor. This simulated outside air temperature will be cycled from a high temperature, higher than the highest control temperature for the subject control (usually 80-90ºF), to a low temperature, lower than the lowest control temperature (usually about 45ºF). As the outside air temperature is cycled, the status of the control output is recorded, open dampers (LED on), or close dampers (LED off).

- 22 -

Thermal Delay in Sensors

62

63

64

65

66

17:53

17:59

18:05

18:11

18:17

18:23

18:29

Tem

pera

ture

, deg

F

62.80

EnvironmentTemperature

Program

Sensor Response

Figure 14 - Thermal Delay in Sensor Response We found that the sensors exhibit a large time response in responding to temperature changes. Figure 14 exhibits an example. The test is programmed for step temperature change as shown by the black line. The actual temperature in the environment boxes follows closely as shown by the green data points. However, the response from the sensor, shown by the red line, exhibits a long thermal decay response in adjusting to the temperature change. (The sensor output is actually in mA but has been calibrated here to match the temperature units shown.) In this example, it takes about 12 minutes for the sensor to fully equilibrate to a 1ºF temperature change. Given this long delay, we elected to operate the tests with a full hour to allow for thermal equilibrium. Our initial tests failed to recognize the importance of allowing for full thermal equilibrium. Note that a long response is not necessarily an error in controls – it avoids control “chatter” if there is rapid temperature cycling around the control point.

Economizer Response Test - differential control

40

45

50

55

60

65

70

75

0 60 120 180 240 300 360 420 480 540 600 660 720 780 840

Increasing Time, minutes

Out

side

Air

or R

etur

n Air

Tem

pera

ture

, deg

F

ON OFF

Figure 15 - Economizer Response Test

- 23 -

The real problem in testing a control system is that there is often a very wide range of control possibilities and the purpose of the controls test is to examine a broad enough range of control possibilities that the full operation of the control is well understood. The challenge is to find simple ways of presenting the multiple test results. For the simple case of a single outdoor dry bulb temperature control, the test results are worked into a graphical format such as Figure 15. The advantage of Figure 15 is that it maps the results of an automatic test sequence consisting of hundreds of individual tests conducted in an orderly sequence and range of conditions. For example, this figure shows that the dampers open whenever the temperature is below about 56ºF. It also shows that the dampers are open at outside air temperatures of 56 to 72ºF, but only if the temperature has been increasing from a temperature below 55 ºF. It also shows that the dampers close at about 72ºF, and that the dampers will remain closed in the range of 56 to 72ºF until the temperature again reaches 55ºF or below. For the simple single sensor test, there need be only a few temperature cycles, not the many cycles shown in Figure 12. The operationally useful outputs from Figure 15 are the low ON control point (about 56ºF), the high OFF control point (about 72ºF), and the recognition of the hysteresis pattern such that a temperature of 55ºF or lower must be encountered in order for the dampers to open. Figure 15 shows a simple single change point situation. Ideally, the outside air temperature should have been cycled to a higher temperature to show operation of the control at temperatures above the upper control point. In early tests, to limit duration of the test, the test control limited the upper outside air test points to the high control point. Enthalpy Sensor Control – This is a potentially complex control system to test because it involves varying the humidity as well as the dry bulb temperature. Traversing the control domain for this situation will involve traversing the psychrometric chart in a manner that is experimentally achievable to establish a performance surface. The resulting data will then need to be interpolated and reassembled to express the control system performance compared with the parameters of interest.

C7660 Dry BulbTemperature Sensor for

Economizers

How the New C7660 Compares to the C7650

Appendix B

2

Enthalpy Setpoint Selection

• A, B, C, D Setpoints are used to select air temperature and humidity for free cooling

CONTROLCURVE

ABCD

CONTROL POINTAPPROX. F ( C)

AT 50% RH73 (23)70 (21)67 (19)63 (17)

12

14

16

1

8

20

22

24

2

6

28

30

32

3

4

36

38

40

4

2

44

46

90100

8070

6050

40

30

20

10

ENTHALP

Y—BTU P

ER POUND D

RY AIR

85(29)

90(32)

95(35)

100(38)

105(41)

110(43

35(2)

35(2)

40(4)

40(4)

105(41)

11(43

45(7)

45(7)

50(10)

50(10)

55(13)

55(13)

60(16)

60(16)

65(18)

65(18)

70(21)

70(21)

75(24)

75(24)

80(27)

80(27)

85(29)

90(32)

95(35)

100(38)

APPROXIMATE DRY BULB TEMPERATURE — F ( C)

A

A

B

B

C

C

D

D

M11681

RELA

TIVE

HUM

IDIT

Y (%

)

1

1

HIGH LIMIT CURVE FOR W7459D.

3

Background of C7650 Operation

4

Background of C7650 Operation

5

Models Overview

2 degree dead band 10 degree dead band

-40 to 149°F (-40° to 65° C) shipping temp

-40°F to +150°F (-40°to 66°C) shipping temp

-40 to 149°F (-40° to 65° C) ambient temp

35°F to +100°F (+4°C to +38°C) ambient temp The device remains operational after exposure to extremes of –40°to 125°F (-40°C to 52°C)

8 Selectable changeover temperatures

Dry bulb changeover based on A, B C and D setting on economizer module

Underwriters Laboratories Inc. Flammability Rating: UL94-5V

Underwriters Laboratories Inc. Flammability Rating: UL94-5V

2 models2 models

C7660C7650

6

Models Overview (cont)

Microprocessor based control with +/- 1 degree F hysteresis

Analog circuit based on C7400 circuit

4 OR 20 mA output signal to economizer control; At 4 mA not OK to economize, 20 mA OK to economize

10 to 20 mA output signal to economizer logic module

C7660C7650

7

Selectable Temperature Options

APPENDIX C

Table 1. Summary of Site Treatments and Data Collection Site Name

Unit Size, ton

flow, cfm/ton

Location Economizer Description Repair History

Retrofit Status Comment Useful Data

1 JLS #1 5 246 Beaverton, OR

enthalpy, bad actuator at initial visit; replaced; changeover at D

on roof id #10 serves main entry, York D7CG060N09946EBA S/N=GM036027, MFD 03/98

repaired 6/7, no economizing

retrofit 7/7/07 data useful but operation is variable

Have power/day, %OSA

2 #2 5 272 enthalpy, OA damper not hooked up on arrival; changeover at D

on roof id #7 serves display area, York D7G060N09946EBA, SAME AS #10

repaired 6/7, no operation

retrofit 7/7/07 No useful operation so far

Have power/day, no useful operation

3 GS1 #1 5 310 Clackamas, OR

enthalpy; Set at A

Rheem; don't have M/N or age; serves Lottery Lighthouse

Not useful little operation

4 #2 5 274 snapdisc; econo not fully checked out

Carrier 48TME006A5, guess 5 YO, serves drywall tool store

no RAT Not useful No useful operation

5 GS2 7.5 427 enthalpy; D; operation not fully checked

Rheem RKKBA090CL, 8 YO serves health club, AC only, no gas connected

no power measurement, no dipper or damper position

Not useful Johnson Controls disabled, no useful operation

6 BI1 #1 7.5 223 Redmond, OR

snapdisc; set on B*

Trane YCD090A3H (18 YO) general retail-- store room, unit #6

working economizer

Retrofit 6/4/08, Changeover 55>65

Useful Data

7 #2 5 304 snapdisc; set on B

Trane YCD060A3H (18 YO) general retail-- break room, unit #1

working economizer

Retrofit 6/4/08, Changeover 55>65

Useful Data

8 BI2 #1 5 335 Madras,OR DIP- 60 F (Precedent unit)

Trane YCD060A3H (6 YO) general retail-- break room

no economizing,

Retrofit 6/4/08, Changeover 55>65

Useful Data

Site Name

Unit Size, ton

flow, cfm/ton

Location Economizer Description Repair History

Retrofit Status Comment Useful Data

9 #2 7.5 319 DIP- 60 F (Precedent unit)

Trane YCD090C3L (6 YO) general retail-- store room

MA sensor replaced during set up visit, working economizer

Retrofit 6/4/08, Changeover 55>65

Useful Data

10 BI3 #1 5 374 Washougal, WA

econo changeover temps of 55 F

Both units orig. run air handlers 24/7.

Heating3/14/08Retrofit Changeover 55>65 6/20/08

Insufficient pre/post data due to uncooperative weather

Lost power measurements, have temps

#2 10 273 econo changeover temps of 55 F

Both units orig. run air handlers 24/7.

Heating3/14/08Retrofit 6/20/08, Changeover 55>65

Insufficient pre/post data due to uncooperative weather

Lost power measurements, have temps

11 Capstone #1 5 257 Camus, WA

econo changeover of about 65 F, high static

Air handlers set on CIRC which means they operated about 30% of time regardless of heating/cooling, serves office ~5000 sqft

Retrofit 6/21/08, Changeover 65>73

Useful Data

#2 4 453.5 econo changeover of about 65 F

Air handlers set on CIRC which means they operated about 30% of time regardless of heating/cooling cooling , serves office ~5000 sqft

Retrofit 6/21/08, Changeover 65>73

Useful Data

all units gas packs; note GS2 doesn't have gas piped to unit *unsure if setting makes any difference in operation

Data Observations -- JLS This was a small office building that proved to have irregular operations and modest loads. Unit 1 did not do any cooling but operated in fan-only ventilation mode. On Unit 2, we restored economizing but the data show little evidence of any impact. The air mix plots appear to show a slight increase in the amount of economizer Outside Air fraction but no change in changeover temperature.

Figure 1. Energy Signature JLS Unit 1

Figure 2. Energy Signature JLS Unit 2

Unit 1 Daily Total

15

25

35

45

40 50 60 70 80 90

OAT

KWh/

d

0

1

2

3

Gas

Dut

y/d RTU.Pwr.1

Post PwrGas.Duty.1Post Gas

Unit 2 Daily Total

15

25

35

45

55

65

40 50 60 70 80 90

OAT

KWh/

d RTU.Pwr.2post Pwr

Figure 3. Percent Outside Air, JLS Unit 1

Figure 4. Percent Outside Air, JLS Unit 2

OSA % vs Outemp

0%

10%

20%

40 45 50 55 60 65 70 75 80 85 90 95 100 105 110

Outemp deg F

OS

A %

PrePost

Figure 5. Economizer OSA, JLS Unit 2

Economizer Operations

0.00

0.01

0.01

0.02

0.02

0.03

0.03

40 45 50 55 60 65 70 75 80 85 90 95 100 105 110

Outemp deg F

Econ

omiz

er C

oolin

g, th

erm

al

kWh/

h PrePost

Figure 6. Economizer Operation, JLS Unit 2

Data Observations – BI1 The BiMart buildings typically had one RTU in high use (#1) and one serving the breakroom (#2) that was not under high loads. In these cases, the change should have restored economizer operation. If so, impact should be most apparent where average daily temperatures are still cool (60-70 deg). However, there is little evidence in the energy signatures. The air mix plots show that an increase to more OSA was accomplished.

Figure 7. Energy Signature BI1 Unit 1

Figure 8. Energy Signature BI1 Unit 2

Unit 1 Daily Total

0102030405060708090

100

20 30 40 50 60 70 80 90

OAT

KW

h/d

02468101214161820

Gas

Dut

y%/d RTU.Pwr.1

Post kWhGas.Duty.1Post Gas

Unit 2 Daily Total

01020304050607080

20 30 40 50 60 70 80 90

OAT

KWh/

d

0

1

Gas

Dut

y/d RTU.Pwr.2

Post kWhGas.Duty.2

Figure 9. Percent Outside Air, BI1 Unit 1

Fan Only Air Handler Temperatures, Pre OSA = 30%, Post OSA = 30%,

Pre Econo = 55%, Post Econo = 85%

-20

-15

-10

-5

0

5

10

-50 -40 -30 -20 -10 0 10 20 30

OAT-RAT, deg F

MAT

-RAT

, deg

F

Pre MAT-RAT Post MAT-RAT Pre OSAPost OSA Pre Econo Post Econo

Figure 10. Percent Outside Air, BI1 Unit 2

Figure 11. Economizer OSA, BI1 Unit 1

Figure 12. Economizer Operation, BI1 Unit 1

Figure 13. Economizer OSA, BI1 Unit 2

Figure 14. Economizer Operation, BI1 Unit 2

Data Observations – BI2 In these cases, the change should have restored economizer operation. If so, impact should be most apparent where average daily temperatures are still cool (60-70 deg). However, there is little evidence in the energy signatures. The air mix plots show that an increase to more OSA was accomplished. Unit 1 continued to run in compressor mode throughout so there are no useful plots. Air mix was not changed significantly in Unit 2.

Figure 15. Energy Signature BI2 Unit 1

Figure 16. Energy Signature BI2 Unit 2

Unit 1 Daily Total

0

10

20

3040

50

60

70

0 10 20 30 40 50 60 70 80 90

OAT

KW

h/d

0

1

Gas

Dut

y/d

RTU.Pwr.1Post kWhGas.Duty.1

Unit 2 Daily Total

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60 70 80 90

OAT

KWh/

d

0

1

Gas

Dut

y/d RTU.Pwr.2

Post kWhGas.Duty.2

Figure 17. Percent Outside Air, BI2 Unit 1

Figure 18. Percent Outside Air, BI2 Unit 2

OSA % vs Outemp

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

110%

40 45 50 55 60 65 70 75 80 85 90 95 100 105 110

Outemp deg F

OS

A % Pre

Post

Figure 19. Economizer OSA, BI2 Unit 2

Economizer Operations

0.00

0.10

0.20

0.30

0.40

40 45 50 55 60 65 70 75 80 85 90 95 100 105 110

Outemp deg F

Econ

omiz

er C

oolin

g, th

erm

al

kWh/

h PrePost

Figure 20. Economizer Operations, BI2 Unit 2

Data Observations – BI3 In these cases, the change shown is the addition of a thermostat to enable fuel savings during morning warmup. Weather did not cooperate – we had little heating post and little cooling prior to the change so there is insufficient data for comparison. No change in air mix is apparent, as would be expected. A drop in fan power occurred, for which we do not have an explanation. The economizer retrofit occurred later but, due to measurement failure, no power measurements and mode determination are available for the period following that change.

Figure 21. Energy Signature BI3 Unit 1

Figure 22. Energy Signature BI3 Unit 2

Unit 1 Daily Total

0102030405060708090

100

20 30 40 50 60 70 80 90

OAT

KW

h/d

0

5

10

15

20

25

30

Gas

Dut

y/d RTU.Pwr.Pre

Gas.Duty.PostRTU.Pwr.PostGas.Duty.Pre

Unit 2 Daily Total

0

50

100

150

200

250

20 30 40 50 60 70 80 90

OAT

KWh/

d

0

5

10

15

20

Gas

Dut

y/d RTU.Pwr.Pre

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Figure 23. Percent Outside Air, BI3 Unit 1

Figure 24. Percent Outside Air, BI3 Unit 2

Data Observations – Capstone In these cases, the change should have encouraged more economizing. It is possible that some improvement occurred since the climate is a milder one. If so, it is more apparent in the temperature regime of 60-70 deg for Unit 1. Change in heating operation for this unit is not meaningful since the weather warmed. It is noteworthy that this building did occasional morning warmup even on days that averaged relatively warm.

Figure 25. Energy Signature Capstone Unit 1

Figure 26. Energy Signature Capstone Unit 2

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Figure 27. Percent Outside Air, Capstone Unit 1

Figure 28. Percent Outside Air, Capstone Unit 2

Figure 29. Economizer OSA, Capstone Unit 1

Figure 30. Econoimizer Operations, Capstone Unit 1

Figure 31. Economizer OSA, Capstone Unit 2

Figure 32. Economizer Operations, Capstone Unit 2

APPENDIX D General Description of In-field Rooftop HVAC Unit Service/Repair Protocol

The procedure used to check out rooftop package units in the research project included visual inspection, functional testing, and repair of faulty components (as needed). Site detail is described in Appendix C. Thermostat Operational settings and basic functionality are checked. Type of thermostat is noted (commercial vs. residential; single/2-stage). Jumpers that circumvent economizing noted and (usually) removed. Airflow Flow rate through evaporator is measured with TrueFlow plates. Economizer System Controller and sensors are checked for functionality (outside air (OA) damper drives open on cooling call when outside temperature is suitable or OA damper can be forced to operate under simulated suitable outside temperature. Output of outside air and mixed (discharge) air sensor is checked vs. manufacturers’ tables. Sensors are cleaned or replaced as needed. Air flow through economizer at minimum and maximum settings is measured with TrueFlow and adjustments made as needed. Dampers repaired as needed. Other Controls In some cases, the system is checked to see if morning warm up can be enabled. This procedure shuts down minimum outside air to zero during morning recovery from setback to save heating energy, primarily natural gas. Extra control (24V) wires and a relay or a new thermostat (2-stage) are needed for this to work. Refrigerant Charge Charge is checked in cooling mode for systems that have at least 300 CFM/ton of system airflow. Adjustments are made as needed based on superheat and/or subcooling measurements using industry standard metrics and calculated by hand. Coil Cleaning In the regular Puget Sound Energy Premium Service Program, condenser coils are cleaned once per year. This was not done in this research project because of the challenges involved with cleanup.

APPENDIX E

Research Contractor Field Measurement/Monitoring Plan This plan describes the monitoring to be applied to individual HVAC rooftop units to

validate a package of energy saving tune-up measures. The general approach to this monitoring is to identify the changes in the operating characteristics of the unit by capturing detailed performance data at least one week pre- and one week post-retrofit. An associated analysis of the data will identify and describe the changes in the operating characteristics of the unit attributable to the energy savings measures. The descriptions of the changes in operating characteristics in engineering terms will then be used with an annual energy usage model to estimate the annual energy savings attributable to the treatment. The monitoring, the associated analysis, and the annual savings model are all analytically related. Therefore, this monitoring plan will include a description of the monitoring data collection as well as the intended associated analysis. Data Collection Objectives The performance data to be collected from a monitored unit is intended to provide a complete description of the unit operation as follows: 1) Economizer operation – Identify the operation of the economizer subject to changes in controls.

2) Mode of operation – Identify hours of operation in each of possible operational mode.

One-time Measurements Make auxiliary measurements necessary to the analysis of the monitoring data and the annual energy use model as follows:

• Measure true power • Measure power factor and the corresponding operational power levels for all fan and

compressor operating levels. This information may be used on three phase systems to correlate the monitored power on one phase to the full power.

• Identify each level of fan and compressor operation for set up of data logger to accurately bin the temperatures associated with different fan and compressor power levels.

• Measure total airflow through the unit for different fan speeds and damper settings before and after the treatment.

• Logged Measurements. Logged temperature and power measurements as shown in Figure 1 will be taken on 15-minute data averaging intervals.

All measurements will be conditional on each level of fan and compressor power so that the air temperature measurements can be associated with the corresponding fan and compressor power levels in the subsequent analysis. Each conditional measurement will be associated with a duty cycle measurement for that power level. This level of monitoring will result in a large accumulation of data in the course of the one month monitoring duration. In the event that the accumulated data may be expected to exceed the data storage capability, the data will be collected at one-hour intervals and the maximum total power will be logged to examine the electrical demand impacts of the treatment.

Figure 1. Logged Temperature and Power Points Data Analysis Methods This monitoring project is structured as a “case study” approach -- each site will be considered for its own specific conditions and results.

1) Economizer operation

Characterize economizer operation will be characterized by deriving the percent outside air and the economizer effect. The objective of the percent outside air measurements is to determine the minimum and maximum outside air percents before and after the treatment

2) Energy Signature Analysis

Plot average daily power and fuel usage for weekdays. Determine if there is sufficient resolution to verify an improvement in energy efficiency following known changes to the operational controls.

3) Annual savings estimate

The proposed methodology is based on a table of expected efficiency improvements developed by an engineering simulation of prototypical buildings. The objective is to compare the monitored cases with the table to verify the methodology. If the table approach is successful, the table can be used to predict savings over the entire course of the year based on verification during a short observation period.

Field Measurement/Monitoring Approach Energy Answer (EA) is a Windows PC-based data acquisition and analysis system. It

uses proven off-the-shelf hardware combined with powerful data acquisition software developed specifically for energy-use monitoring in buildings. A group of additional software modules are included to allow users to access data and control the data collection system from and internet-connected PC. The laptop PC and system hardware are packaged in a lockable aluminum briefcase for easy portability and professional appearance in the field.

Hardware

The heart of the system is a laptop computer. They have 300 MHz Intel processors, 6 Gig Disks, 128 MB of RAM, and Floppy Disk drives. Additionally they are supplied in this program with external 4-port USB hubs, 10/100 Ethernet Network Adapters and wireless network (WiFi) adapters (80211b or b/g). The AC adapters are included, as are the stock internal batteries, which may not have much useful capacity at this point. Also included with each system is an external Uninterruptible Power Supply with a lead-acid rechargeable battery expected to carry an unattended system through power outages up to several hours long. Software

The laptops are loaded with licensed copies of MS Windows 2000 Professional, the predecessor of Windows XP Professional which was chosen because the memory and hard drive capacity of these older machines is better suited to the older version. Software includes programs for secure networking, remote computing and automatic time correction to National Institute of Standards and Technology clock. Each system has the standard Windows 2000 accessory programs such as WordPad, Excel, HyperTerminal, Internet Explorer, Zip file compressing and extracting utilities, Acrobat reader, and necessary drivers. Finally but most importantly, each system will have a licensed and supported copy of EA. EA is an integrated system to interrogate sensors of various types, display the current and accumulated measurements, and archive the periodic results in an easily accessible format. EA is a powerful system optimized for energy-use data collection. Available measurements include:

• True AC Power, with AC Volts x AC Amps Temperature with Dallas/Maxim 1-wire bus system

• Temperature with HCZ wireless transmitter and receiver • Digital status (relay contacts or DC Volts) • Frequency (anemometer, etc.) • Counts (pulses from utility electrical or gas meters, etc.)

Other analog parameters (0-5V, 4-20 mA, etc.)

Each EA system can handle 1 high frequency input plus up to eight status or low (10 Hz) pulse or frequency inputs. Each system has four analog inputs; three are used for AC Volts, Compressor Current/Power, and Fan Current/Power. The fourth is available for an additional power measurement or other analog channel. Expansion Modules are available to allow up to 32 analog measurements.

The EA software acquires the digitized signals from the various hardware sources, converts each signal to engineering units (Volts/Amps/Degrees...). For some measurements specific measurements are mathematically manipulated: for each power measurement 128 Voltage samples are multiplied by 128 current samples which were taken over the same 1/60th of a second, and the results averaged to compute an average power over one power line cycle. The Point List file defines the measurements to be made, how each hardware point is connected, the slope and intercept to be applied to the raw data to convert it to engineering units (CT size, for example), and other parameters for the particular measurement. In addition to the various hardware types, there are many computed point types. For example, the on/off status of the compressor is computed based on the momentary power indicated by the power hardware measurement.

The Sampling Interval defines how often the program interrogates each sensor and calculates the various results. If the system detects that it cannot complete a pass through the Point List in the time specified, the Sampling interval will be increased appropriately. The Storage Interval (here 3600 Seconds or 1 Hour) defines how often the EA system stores the averaged or summed data. The use of computed channels as discussed below allows the less-frequent storage of summary data, ready for advanced analysis.

APPENDIX F

RTU Savings Research Case Study- BI #1, Unit#2

This detailed analysis is directed at finding and quantifying economizer events in the monitoring data. This particular case has a positive measurement of damper position that can help to reveal the operating economizer control logic. It also provides a clear view of how the monitoring variables change during an economizer event.

In this case study, a properly functioning economizer was disconnected and the dampers were set to a fixed minimum outside air setting. The building was regularly occupied during weekdays and Saturdays. The outside air temperatures were suitable for economizing, hot enough at midday to elicit cooling, yet cool enough to at other times to offer low energy ventilation cooling. This case also offers a measurement of the damper position as well as the key RTU temperatures. Finding a representative test situation. This case is analyzed in terms of pre- and post- operating energy. During both the pre- and post-operations, the indoor thermostat setting remained the same and the internal occupancy heat gain also was the same. This is a well controlled flip-flop case and both the pre- and post- monitoring data had regular repeating patterns that showed some difference pre to post.

A comparison of the pre/post activity is provided by a one-day operation comparison for pre- and post-days with similar outdoor temperatures. The temperatures for the pre- and post-comparison days are shown in Figure1.1

Pre and Post Temperature Conditions

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Figure 1 Pre and Post Economizer Operating Test Temperatures

The ideal comparison cases would be identical, but Figure 1 shows that these comparison cases had almost identical day time high temperatures and almost identical return (interior)

1 OAT-outside air temperature; RAT-Return Air Temperature; MAT-Mixed Air Temperature; SAT-Supply Air Temperature

temperature profiles. The physical difference between these cases is the operation of the economizer as all other conditions are the same. Comparing the Outside Air. To assess the status of the outside air during these pre and post cases, the RTU temperatures were plotted in an outside air diagnostic diagram as in Figure 2. This figure shows that in the pre case, (the black points), the outside air was at 30% at all times as shown from the slope of a line fitted to the pre temperature points. The post case temperature points fall into two patterns: the low slope pattern shows 10% outside air when the dampers are closed, and the high slope pattern shows 80% outside air when the dampers are open. Points scattered between these patterns are an artifact of 15 minute monitoring periods that show the dampers in one position for part of the 15 minute period and in the other position for the rest of the 15 minute period. Other analysis shows that in fact the dampers are predominantly either open or closed; they do not loiter in the intermediate positions.

Outside Air Fraction - temperature analysis

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Figure 2 Outside Air Temperature Analysis Diagram

The important observation from Figure 2 is that the pre outside air is about 30% regardless of the outside air temperature, and the post minimum outside air is 10%. This difference in the minimum air has a strong effect on the compressor energy as the increased outside air is cooled. Figure 3 shows the total RTU energy for the pre and post cases.

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A closer look at the key RTU temperatures is given in Figures 4 and 5.

RTU Temperatures - no economizer

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RTU Temperatures - economizer

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Note in Figure 4 that the blue line for the supply air temperature shows a temperature of between 40 and 50 deg F for several hours continuously. The unit is essentially “maxxed out” in the late afternoon as it deals with the 30% outside air. In Figure 5 the supply air temperature is constantly varying between 50 and 60 deg F throughout the occupied hours.

Some of the notable events evident in Figure 5 are the economizer operations. These are the wiggly blue and violet lines at about 0800 and 2400. In both these, cases the economizer is opening and closing the dampers when it should be leaving the dampers open. Detailed inspection of the monitoring results shows that this is ultimately caused by a very narrow deadband at the thermostat for turning the economizer on and off. This detailed inspection, along with the, positive information relating to damper position, allowed an economizer control map to be prepared: Figure 6. This control map shows the thermostat and outside air conditions under which the economizer opens and closes.

It is apparent in this figure that the economizer turns on at a temperature in the low 70s and turns off at a temperature about 1 deg lower. This is a very narrow deadband and it serves to maintain the control temperature, but it severely limits this economizer from pre-cooling this building.

This figure also shows apparent economizer activity with thermostat temperatures in the range of 73-76 deg F. This activity at higher temperatures is an artifact of the monitoring situation: the thermostat temperature is not directly measured; it is inferred from the return temperature. At night, the economizer on/off activity is at thermostat temperatures of 71-72 deg F. However, in the early morning, the economizer activity appears to be at higher thermostat (return air) temperatures. In these morning cases, something has warmed the return air. It is likely the warm air that has stratified in the top of the conditioned space as the building activity (lighting especially) starts in the morning. It may also include some solar gain on the RTU.

Economizer Control Map - BI unit #2

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Figure 6 Economizer Control Map An Economizer Control Map. This map shows that the economizer is responding to two different temperatures, one at the thermostat, and to the outside air temperature. The thermostat determines the cooling call, and opens the economizer at about 72 deg F and closes the economizer at 71 deg F. It also shows that the economizer will respond to a cooling call for outside air temperatures in the range of about 50-72 deg F.

Figure 6 does demonstrate a diagnostic plot of economizer control that is possible if a positive measurement of damper movement is available. In the field monitoring, the damper position was measured by a string potentiometer attached to the damper with a small powerful magnet. While this measurement is simple in principle, and could be quite reliable, it was not successful on most of the sites monitored here.

Finally an overall performance plot of the operation of this unit for 21 days is given in figure 7. This figure shows 11 days with no economizer and 10 days with an economizer. In both the cases, with and without economizer, the data assumes the familiar sloping line to describe the daily RTU energy versus the average daily outside air temperature. In the figure, the line for economizer operation indicates a lower daily RTU energy at any given temperature. In this particular example it appears that the economizer is saving of the order of 10 kWh/day at all daily average temperatures greater than about 55 deg F.

The savings are dependent on the specifics of the situation. The savings would have been larger if the building had been pre-cooled (which was not possible because of the tight control dead band), and the savings would have been smaller if the fixed outside ventilation air of 30% had been lower, such as 15-20%.

RTU Electric Energy Performance Map - BI unit 2

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Figure 7 RTU Performance Plot

APPENDIX G

Recommended Site Monitoring Protocol for Measuring RTU Performance Introduction

This monitoring protocol will specify the general measurements and associated analytical treatment for empirically deriving RTU performance models that can be used to estimate annual RTU performance, in terms of electric energy, electric demand, and natural gas use. The field measurements and estimated annual performance will reflect the performance of that particular RTU serving a repeating internal load pattern that is reasonably consistent for a full year. The field monitoring portion of this protocol is intended to capture the essential performance parameters of the unit in a minimum amount of time that requires that the monitoring and retrofit be coordinated with appropriate weather for testing. In practice, site recruitment and monitoring scheduling are vital associated activities essential for monitoring success.

Timing The timing of events is the dominant theme of RTU site monitoring. Derivation of

an accurate electric cooling RTU performance model will require that the monitoring be done in the warm part of the year. Practical experience suggests that about 7-10 days with daily average temperatures above 60°F is required to realize an adequate amount of compressor run data. This will require about 2-3 weeks of monitoring in the months of June through September to accumulate this necessary amount of data. With careful timing, it is possible that a particular suite of monitoring equipment could capture 5-6 RTU performance signatures in a single summer monitoring season. With scheduled retrofits of the RTUs, it would be possible for a suite of monitoring equipment to support two pre/post performance measurements in the course of a single summer season.

The winter heating portion of the RTU performance model is similarly constrained by

seasonal timing. However, most recent emphasis has been on the summer performance of RTUs which can be derived from short term summer tests. Winter heating performance measurement requires similar separate wintertime tests.

Monitoring Level An objective of this site measurement protocol is to minimize M&V

costs. Accordingly, this protocol recognizes varying levels of monitoring effort leading to increasingly detailed results. Table 1 shows three levels of RTU monitoring with increasing levels of complexity and cost. Each level builds upon the prior level to produce increased insight into RTU performance.

Monitoring

Level Variables Site Observations Outputs

Level 1: Basic 1. Hourly RTU Energy 2. Hourly Max RTU power 3. Hourly Average Temperature

Note Internal gain sources; Note occupancy regularity; Note t-stat schedules

1. Mode Demand Map 2. Operating Day Profiles 3. Energy Performance Map

Level 2: Diagnostic

Add: 1. Hourly Return air temp, and @ max power 2. Hourly Mixed air temp and @max power 3. Economizer control signal 4. Fan power & fan power at max unit power 5. Hourly supply air temperature and @ max power

1. Percent outside air by mode 2. Economizer control temperature map 3. Fan power profiles

Level 3: Research

Add: 1. Airflow transducer 2. Condensate flow 3. Relative Humidity on air temps

Air flow @ calibrated fan power or flow transducer

1. COP, thermal efficiency 2. Energy balances 3. Fan/compressor performance diagnostics

Table 1. RTU Performance Monitoring Levels What is most important to note is that the Basic and simplest level will produce the

essential energy and demand information necessary to quantify savings. The other more detailed levels can add more performance information, but the essential energy and demand information is fully achievable in Level 1. Level 2 is intended to collect the extra information necessary to diagnose RTU performance and to document operational conditions for comparison to modeling. Levels 1 and 2 are described in this protocol. Level 3 is included in the Table to show the broad range of RTU monitoring scope, and to show that the essential measurements necessary to document RTU savings can be achieved without the full, more costly research compliment of instrumentation.

Note also that at all levels, the monitored variables take two forms: the hourly averages of

the variable as well as the value of the variable at maximum hourly (or other interval) power. This measurement of the variables at maximum power is for screening purposes and has been found necessary to produce the clear signatures in the Mode Demand Map and the Percent Outside Air Map. In a sophisticated data logger, these measurements at maximum interval power are the result of “conditional logging”. In simpler data logging systems, the same effect can be approximated by logging with small averaging intervals such as 1 -5 minutes. The smaller intervals have the advantage in permitting analysis of detailed operating cycle profiles, but they also produce very high volumes of data and associated data management and analysis issues. When using the smaller intervals in lieu of conditional logging, the intervals should be no longer than 5 minutes. 15 minute intervals will work, but there is excess noise that justifies the shorter interval.

It should also be noted that levels 1 and 2 of this protocol have worked well using air dry

bulb temperature only. This definitely simplifies the monitoring and analysis. In the western US situations that have been monitored, the dry bulb temperature has been the dominant variable. Humidity undoubtedly plays a role, but thus far the analysis for western US locations with generally low humidity has proceeded successfully without considering humidity as an explicit variable. However, Northeastern and Southeastern US locations, with much higher humidity, may require a modification of this protocol that includes humidity or enthalpy as variables. Level 1 Monitoring

The overall objective of the Level 1 monitoring is to derive an annual RTU energy use estimate from the actual operating conditions. The annual RTU energy and demand estimates will need to be derived with reference to all three analytical outputs of Level 1 monitoring. In theory, only one output, the RTU energy performance map alone, should be sufficient, but such clean data is rare and the other information needs to be used to develop a confident understanding of the RTU performance. In practice, Level 1 monitoring takes the form of a brief case study for each RTU, and critical engineering judgment is required to put the pieces together.

One Time Site Observations

A great many site details may be collected, but in the interest of minimizing Level 1 site monitoring overhead, only the essential observations are noted here

• RTU nameplate and site specifics. • Approximate estimate of internal loads served by the monitored RTU, i.e., 2400 ft2

office or retail; note special internal loads/gains such as cooking, computer servers etc.

• Subjective estimate of the weather • Description of the space served by the RTU that is operating on a regular

daily/weekly schedule during the pre- and post-service periods. • Thermostat type and schedules.

Site Monitoring

• Outdoor temperature recorded as 1-5 minute samples rolled up into one hour averages and further rolled up into 24-hour daily averages. Outdoor temperature measurements require some care: the temperature sensor must be protected from biased measurements by shading from direct sunlight and infrared radiation, and it must not be mounted inside the economizer hood because air convecting up through the unit at night when the unit is off will bias the night temperature readings. The preferred mounting for the outdoor air sensor is in a shaded vented enclosure on the shady side of the unit. It is best to avoid a single outdoor air sensor serving several monitored units because the rooftop temperatures can vary from place to place with time of day.

• RTU total power recorded as average 1-5 minute interval power rolled up into hourly power and further rolled up into 24-hour summed daily energy and maximum power in each of the one hour analysis intervals. This is commonly measured with a logger capable of conditional measurements, but as an alternative, the power can be logged in one or two minute intervals, and the maximum observed in an hour can be taken as the maximum hourly power.

• RTU heating status recorded as the fraction of each logged hour that the heating is on. This measurement is rolled up into heating hours per day. This heating status measurement is only necessary in addition to the other two measurements when monitoring for gas heating performance.

Analysis Approach

Step 0: Organize and aggregate the data into an hourly time sequence for average RTU power, average outside air temperature, maximum hourly RTU power. In preparing this aggregation, it is important to include indexing so that individual 24-hour profiles of RTU power and temperature can be readily reviewed as needed. In practice, there is often extensive checking of unusual data points and it is important to be able to readily find and plot the fundamental data points.

Step 1: Assess the RTU power by mode. This is done with a Mode Map prepared by

plotting the max power for all hourly intervals versus the average outside air temperature for the interval. The result will be a reasonably precise graph as in Figure 1 even if the site operations are not very regular. Figure 1 was compiled from one minute data.

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operation and to the first and second stages of compressor cooling. In these fairly precise groupings, it is possible to see that the post retrofit demand is generally higher than the pre-retrofit demand, and that the peak demand has increased by about 400 Watts. This provides an estimate of the demand savings associated with the retrofit. Now, having identified the

operational modes, it is important preparation to review the time sequenced hourly data for the circumstances (time, temperature, etc.) associated with the operation of each mode.

Step 2: Aggregate the hourly data for RTU power and outside air temperature into 24-hour

averages, and plot the daily average temperatures versus the daily average power as in Figure 2. Note in Figure 2, that the line marked “no econo” has an angle in it corresponding to a temperature here referred to as the “cooling balance point.” This point is defined as the intersection of the sloping line showing the compressor cooling energy and the horizontal line referred to as the fan only portion.

Step 3: Construct an RTU Electric Energy Performance Map. The full broken line function

is the Electric Performance Map that will be used to estimate the annual energy use. This Performance Map is constructed by fitting a simple broken line function to the pre- and post-retrofit data. The analytical effort consists of deriving the following functional parameters:

1) A horizontal portion. This portion represents the daily fan only energy use that will

occur at temperatures low enough not to require any compressor cooling. Often this will be directly evident in the data, but in monitoring periods of predominantly warm weather, there may be no such points. In these cases, the detailed hourly data should be reviewed for incidents of fan only operation and for evidence of the fan operating schedule. This information can then be synthesized into a reasonable estimate of the daily total fan only RTU energy. It is common for unintended or unnecessary compressor operation to take place at lower average daily temperatures. It is important to recognize these points as control aberrations and to base the horizontal portion on the true fan only situations.

2) A balance point temperature. This point is the average daily temperature below which

compressor operation is not necessary in typical operation. Often this point is clearly evident in the data, but in exceptionally warm monitoring periods, the days will not be cool enough to reveal this point. When this point is not evident in the data, then it is because all the data points are warm day points that offer a good chance of fitting a line to this sloping portion of the data that can then be used to define the balance point. In this case, the balance point temperature is the intersection of the horizontal portion and the sloping portion. The balance point is strongly influenced by thermostat set points and by economizer operation, and it has a significant effect on the estimated annual energy. Because this point is so significant in the results, it is important to examine the detailed hourly data to confirm that the point is reasonable. When there is no balance point evident in the data and no reasonable fit to the sloping line, then the site is not usable for the analysis. It is common to find cases of very low RTU energy at well above the balance point temperature, usually associated with un-occupied periods. In these cases, it is important to recognize that there are two patterns: one for the occupied periods and one for the unoccupied periods.

3) A sloping portion. This portion represents the increasing daily RTU energy at higher

daily average temperatures caused by the increased operation of the compressor. The number of points in this sloping portion will depend strongly on the weather conditions of the monitoring period. If the weather has not been warm enough to trigger at least 5 days of reasonably significant compressor operation, then the site is not usable. In most cases, there will be a clearly

evident sloping pattern to the points to which a sloping line can be confidently fitted. However, even with several days of significant compressor operation, the points may resemble a cluster rather than the ideal tight line. In this case, the high and low points for similar temperatures should be examined in detail for evidence of operational irregularities. If no irregularities can be found then the sloping portion should be considered as the line proceeding from the balance point temperature and through the cluster of points. If there is a cluster of points it is because different internal gain from one day to the next and a line from the balance point through the cloud will be a reasonable average for this irregular operation.

The resulting function must be considered an idealized performance map because aberrant points may have been omitted in constructing the map. The idealized form will resemble the classic broken line form that has been noted on long term observations of a properly functioning RTU on a regularly operating site. In a good situation and with sufficient data, this is the form the data appears to take. A comparison of the idealized performance map to observed points will show cases where the RTU did not operate properly, and these aberrant points should be examined as preparation for modifying the idealized performance map to an as-operated performance map.

The ideal performance map must now be modified as necessary to reflect the as-observed

operation. In most cases, very little modification will be required. However, in cases where regular occupancy lapses are identified or where unusual system operation is identified, then one or more of the three parameters specifying the performance map must be modified to reflect the as observed performance. If these modifications cannot confidently be done, then the site must not be used.

RTU Electric Energy Performance Map - BI unit 2

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econono econo

Figure 2. Pre- and Post-Service RTU Electric Energy Performance Maps

In figure 2, the post retrofit data does not include any points for average daily temperatures below about 62°F. It is probable that the post retrofit data has a horizontal fan-only portion that would have been evident at lower temperatures. For calculating annual post retrofit energy use, a horizontal fan-only portion will need to be synthesized from evidence from the power by mode map and from evidence of the fan run modes in the reviewed hourly data.

Step 4: Verify the apparent savings (or lack thereof) evident in Figure 2 by isolating pre- and post-service days with similar daily temperature profiles, and plot the corresponding hourly average power profiles as in Figure 3.

Comparison Day RTU Energy

01

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rgy,

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Figure 3. Daily RTU Power Profiles for Similar Days In Figure 3, it is evident that the savings are being achieved through suppressing compressor operation before 12 PM. This pattern is probable in cases of economizer operation or thermostat resets; this case looks more like thermostat reset because the fan is not evident in suppressing the compressor operation. The savings also proceed from using stage one cooling instead of stage 2. This step is a “due diligence” check on savings that are indicated in the RTU Electric Performance Map in Figure 2 to confirm that the savings have a real physical basis and are not statistical aberrations.

Step 5: Use the RTU Electric Energy Performance Map with an annual outdoor temperature histogram to estimate the annual energy use. It will be necessary to assume the horizontal portion extends toward the lower temperatures in order to have a complete annual RTU energy map. When the energy map is used with an annual histogram, it is important to recognize in cases of 24-hour fan operation that most of the annual temperatures may be low enough that the horizontal fan energy portion of the energy map will constitute a very significant portion of the annual energy.

The annualizing process starts with the average day temperature histogram for the site as in Figure 4.

Annual Average Day Temperature Histograms

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10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70 70-75 75-80 80-85 85-90

Temperature Bin, deg F

Num

ber o

f Day

s pe

r Nor

mal

Yea

r

Pdx Boise

Figure 4. Annual Temperature Histograms for Average Daily Temperatures – 5°F Temperature Bins

Figure 4 shows average day temperature histograms in 5°F bins for two example sites: Portland, Oregon, and Boise, Idaho. Note for example, that for the Portland site there are more than 210 days in the moderate temperature range of 45-65°F and for the Boise site there are about 100 days with average daily temperatures above 65°F.

To estimate the RTU annual electric energy, the RTU electric energy performance map is evaluated at the temperature of the center of each of the temperature bins and the sum for all the bins is taken as the annual RTU electric energy. Figure 5 shows the distribution of annual energy by temperature bins for a retrofit in Portland. This example is a very significant retrofit and achieves about 8,900 kWh/yr savings.

RTU Annual Energy

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Daily Average Temperature Bin

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ual R

TU E

nerg

y, k

Eh

PostPre

Figure 5. Pre/Post RTU Electric Energy Use by Temperature Bin for Portland, Oregon Level 2 Monitoring

The overall objective of the Level 2 diagnostic monitoring is to provide empirical information necessary to identify key economizer related operating patterns of the RTU. This information will help to diagnose operating problems at the RTU, and it will document the operating circumstances necessary to support a modeling comparison to the empirical observations.

The operating circumstances to be documented in Level 2 monitoring are:

• Percent outside air induced at the outside air dampers • De-facto set points for the thermostat and the economizer • Fan power and schedules

These enhanced diagnostics do not include any refrigerant charge-related measurements

and do not address the issue of the adequacy of the refrigerant charge. However, it should be noted that the effects, energy and demand, of any refrigerant charge-related activities will have been included in the savings estimates developed through level 1 monitoring. Level 2 Site Monitoring. This expanded set of monitored variables is in addition to the variables monitored for Level 1. And as in Level 1, these variables should include two measurements for each variable: the average value for the monitoring interval, and the value of the variable coincident with the maximum RTU power in each monitored interval. The analysis interval should be one hour. If the variables are monitored in short intervals, such as 1 minute, the values coincident with RTU maximum hourly power can be established in the aggregation phase during post data processing, otherwise the monitoring for the hourly coincident maximum power variables will require conditional logging.

The expanded monitoring variables are as follows:

1) Return air temperature. This temperature is used as a proxy for the zone thermostat temperature. A single sensor in the return duct easily monitors this well mixed airstream. However, it should be noted that this return temperature would be different than the zone thermostat temperature. The reality of building air flow is that the warmer air will stratify somewhat when there is a source of heat to the zone. This may increase the return air temperature by a few degrees Fahrenheit when the lighting comes on and it may increase by 10°F or more when heat is supplied to the zone. The return air temperature can be a reasonable proxy for the thermostat at night, but not during heating cycles. On the other hand, the increase of the return air temperature is an important indicator of significant thermal stratification and building occupancy.

2) Mixed air temperature. This temperature is the key to solving for the percent outside air. It is generally difficult to measure correctly because the mixed air region is relatively small and the warm return air and the cold outside air have not fully mixed. It is common to find plumes of unmixed air. The approach to getting a reasonable mixed air temperature is to measure the mixed air temperature at three or ideally four points in the mixed air region and to take the average. The rational is that if one measurement is in an unmixed plume the other temperatures will not be in the same plume. An average of four temperature points has worked reasonably well, but a special average temperature sensor in the form of a several foot long flexible transducer could work as well or better. The best results will be achieved when the outside air, return air, the mixed air, and the supply air sensors have all been calibrated together.

3) Supply air temperature. This measurement plays a role in calculating the thermal output of the cooling and heating systems. It can also serve as a check on the mixed air temperatures and can assist in examining operating modes and related setpoints. This measurement is easier to make than the mixed air temperature measurement, and with appropriate correction and screening it can be used in lieu of the mixed air temperature measurement for estimating the percent outside air when the compressor and heating is off. It cannot be used to estimate percent outside air except at least 10-15 minutes after the cooling or heating has ceased.

4) Damper position. This measure is a positive measurement of damper position. In practice it can be readily achieved by the use of a string potentiometer attached to the damper by means of a sheet metal screw or magnet. The measurement only gives a relative position of the damper. However, most importantly it gives a clear indication of when the damper has started to open and when it closes. This clear indication of damper motion significantly improves the classification of operating modes. An alternative to this variable is the first stage cooling signal which can be used to classify operating modes. Ideally both the damper position and the first stage cooling signal could be monitored.

5) Fan power. This measure will be used when considering changes to the fan control or power. Changes to fan power which persist all year can have significant savings. Fan power and scheduling is also explicitly needed in constructing RTU performance models for comparison to the empirical observations. Evidence of the fan power will be in the RTU total power measurement, and in cases with constant speed fans this may be sufficient to establish fan schedule and power without monitoring. However, fan power will need to be monitored in cases of variable speed fans.

Data Analysis

The analysis of the data generally consists of screening the data to prepare plots that show the operating conditions clearly. There are many other plotting possibilities that can be developed but two essential plots are shown as examples below.

The damper position is used to identify the de-facto operating modes as illustrated in the

Figure 6. This figure was derived with information from the damper position measurements, but the same could have been derived using the coincident, (with RTU max power) return and mixed air temperatures.

Temperatures by mode

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-10

-5

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5

-30 -20 -10 0 10 20 30

Oat-Rat

Mat

-Rat stage1

stage2circ

Figure 6. Percent Outside Air Map

This figure is the standard temperature based approach to solving for the percent outside air. Typically, this presentation will show a scatter of points in between the lines for stage 1 and circulation that are artifacts of partial or mixed mode activity in the monitoring interval. This presentation eliminates those multi-mode points by using the positive mode identification afforded by the damper position sensor, or the return, outside air and mixed air temperatures at the hourly maximum power.

The second diagnostic from the enhanced monitoring is to identify the critical

economizer control temperatures. Two temperatures control an economizer. The interior temperature at the zone thermostat will typically energize economizing usually as the first stage of cooling. The temperature sensor at the economizer measures outside air temperature and selects a range at which economizing will be allowed. Positive damper position measurement allows a clear measurement of both the interior and exterior temperatures when the damper changes position. These change point temperatures can be mapped as in the accompanying figure to show the action of the economizer control.

Economizer Control Map - BI unit #2

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Return Air Temp, deg F

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Figure 7. Economizer Control Map

Note in this economizer control map that the economizer turns off at a temperature only a degree cooler that it turned on. This is typical of most thermostats and it substantially limits economizer effectiveness for pre-cooling. Notice also the shift in the higher outside temperature points toward a higher return temperature.

This map is intended to portray the interior thermostat temperature vs. outside air

temperature. However, the difficulty of running a wire to the thermostat leads to the use of the return air temperature as a proxy for interior thermostat temperature. The displacement of the higher temperature points is an indication of thermal stratification in the zone. Thermal stratification is a favorable event in the case of cooling because it drives out internal gains before they have completely mixed with the zone air. However, in heating mode, stratification is an unfavorable event because it discharges air that is already warmer than the zone air.

APPENDIX H

January 9, 2008 To: Adrienne Thomle, Honeywell From: Mark Cherniack, New Buildings Institute Adrienne: In response to your specific questions (12/17/07) about design considerations for a new controller/sensor product, I polled members of our technical working committee and offer the following responses.

1. What is the desired control range for a dry bulb sensor? e.g., 45-70F, 50-75F, 40-65F, etc.? OSA range needs to be set for changeover, 55F to 80F, expanded by the differential needed for control. 2. Should control point be adjustable or fixed? We have seen so many cases in the field where the adjustable dial was set so low that the economizer was effectively cancelled out. We also feel contractors will find the unit easier to install if the changeover set point is fixed. In the two sensor or differential configuration, the adjustment potentiometer will result in incorrect operation unless set at “D.” We have also seen dials that short or open at the end points. Honeywell should leave the pot off the circuit board and plug the hole in the case. For the analog unit, the need for adjustability for a single sensor arrangement may be able to be met with different resistors in the return air sensor position. Having an adjustment in the field just leads to technician error. 3. If a dry bulb sensor had a test pad for the technician to set the change over temperature accurately, how accurate would the temperature setting need to be? 1F, 2F, .5F? If this is a separate test unit the technician plugs in to simulate a temperature, then adjustability to at least 2F is desired. A test procedure in a DDC-type thermostat would be much preferable, like the test selections in the Honeywell VisionPro 9000 series. 4. What is the desired hysteresis for the temperature? 2F is fine for OSA difference economizer changeover. Anything less will react too quickly to wind direction changes and brief cloud cover. Anything in the 2F to 4F range would be acceptable, although the ARTU committee wanted 2F maximum. 5. What is the resolution for temperature? We support the CEC PIER ARTU Feature described on pg. 21 of the ARTU Features Definition Report:

“Feature # 11-01 Unit controller will utilize an analog to digital resolution no less than 8 bits. Level: 2

Comments: Eight-bit resolution assures that the analog signal received by the controller from various sensors is converted into enough discrete digital signals for processing to ensure that sensor accuracy is not lost. Eight bits gives 256 discreet steps of digital signal and is readily available. This feature relates mainly to diagnostic features. Using an analog controller limits the ability to develop diagnostic capability. Providing a digital microprocessor will add cost, but reduce the cost of diagnostics because the processors can be combined. This feature is not meant to require or enable 256 discreet steps of economizer positioning. Rather, the intent is to achieve an acceptable resolution in sensor measurement. For example, with an eight-bit controller, an outdoor air temperature that varies from 0 to 102°F can be resolved into steps of 0.4°F.”

Acceptable resolution is something less than 1.0°F for economizer OSA selection. If a standardized temperature sensor is used for the unit with 8-bit resolution, with a range from -40F to 140F (desirable if OSA will be displayed on an indoor thermostat) the resolution is 0.7F. This wide range allows a standard sensor to be used for three different applications: outside air, discharge air over the full range of air conditioning and heating, and space temperature. If a narrower range is acceptable (OSA will not be displayed on the thermostat), say 40F to 140F (to show discharge air temperature in furnace heating) then resolution will be 0.4F with standard sensors. While selecting different sensors for OSA, space, and DA, could improve resolution, especially for space temperature, a standardized sensor (at least for OSA & discharge air) is probably desirable to avoid field wiring errors and reduce inventory costs. Please also note features 11-02 and 11-03 in terms of critical diagnostic capability.

Additional Comments We would also like to submit the following regarding the Draft Bench Test Report. We intend to summarize your suggested edits on the report as a separate note. I’ll send the summary to you for review prior to finalizing. We appreciated your suggested comments on the draft Bench Test Report. However, it is our opinion that enthalpy control is not necessary to achieve significant economizer savings here in the Pacific Northwest. Based on better reliability and simpler troubleshooting for dry bulb sensors, we feel strongly that a dry bulb differential option needs to be made available for the Western United States. We also think there is a strong preference on the part of western HVAC contractors for the dry bulb sensors. If an independent study shows that the maintenance cycles are the same for enthalpy sensors, then we may reconsider this position. In any event, we do not see enough additional savings in the west to justify enthalpy sensors with their inherent higher cost (2x) and field reported reliability issues. We have not yet seen, but would like to, a study (preferably published) of enthalpy sensor reliability and accuracy in field use. If Honeywell has this type of information to share, we would be most appreciative.

Economizer Product Development Priority

In addition, the committee has further comments on economizer and sensor product development and deployment, in order of priority.

1. A dry bulb solution that can be retrofitted in the field with either:

a) a redesigned sensor with the hysteresis (changeover reset differential) reduced to the range of 2degF by a redesign of the dry bulb sensor alone (without a controller redesign) assuming the redesigned sensor can work properly with existing controllers in the field. Advantage of a redesigned sensor is that the differential sensor option can be retrofit on existing controllers. If the hysteresis cannot be reduced without controller redesign, then this item should wait until the controller is redesigned (see comments below) and priority be given to a smarter digital solution, or

b) a dry bulb “snap disk”-type (including the contractors thermostat that’s been tested) OSA sensor solution packaged in the black box with a resistor to limit current is our first choice. It would retrofit the W7459 controller and reduce hysteresis to an acceptable range as noted. We would very much like to see this available as an optional Honeywell product. This would have a 2F differential, and would open above somewhere around 68F to 70F and close to 2F lower. The important point is that it needs to be a solution for the significant number (x thousands) of existing W7459 controllers out there that need to be upgraded. It would come with instructions making it clear that a 2-stage cooling thermostat is required and the main control sensor needs to be located downstream of the cooling coil (discharge air) not in the mixed air position. The advantage of this product is its simplicity, quickness to market, and that it overrides any adjustment without removing the ABCD dial from the controller.

As a committee representing PNW utilities and related HVAC professionals, we feel it is important to have a retrofit/tune up solution for existing installations of the W7459. We think that to change the temperature differential may require redesign of the controller, not just the sensors, so the redesign solution would require replacement of the entire controller and that is not likely as part of a utility RTU tune-up program.

If a simple sensor retrofit was made available without the need of a new controller, we would recommend regionwide changes in current enhanced economizer specifications to allow it, as long as the thermostat had a unique stage for economizer operation. In the PNW, DSM programs that follow the enhanced spec include: Bonneville Power Administration, Eugene Water & Electric Board, and NBI’s Advanced Buildings Core Performance.

The 2-stage thermostat is a very real issue. HVAC service contractors working with Avista Utilities (Spokane, WA) and Southern California Edison found rooftop units with respectively 20% and 22% using single-stage, residential-type thermostats that precluded proper economizer function. And this was only one of the problems reducing economizer performance.

2. The committee felt that after retrofittable snap disks or improved dry bulb sensors were created, the next priority would be to come up with a completely different smart economizer control system rather than putting effort into redesigning the low-end electronic controller. This would likely be in the form of a control module and a high-end programmable thermostat that is an upgrade to the VisionPro IAQ system; in fact many of the requested features can be accomplished today by programming features of the VisionPro. Even though the VisionPro target market is residential, we see a number of contractors installing the VisionPro in commercial settings, as the large screen has

good customer acceptance and this line has an attractive price point. We suggest the upgraded unit have the following features:

a. Differential dry-bulb economizer control using OSA and space temperature for changeover. When the OSA is 5F to 2F (settable) lower than space temperature, the economizer is enabled. This approach eliminates the return-air sensor, but should provide effective control. It provides effective differential control with the same number of sensors as single sensor changeover.

b. All the logic could reside at the thermostat, but this requires many wire pairs up to the unit (OSA damper; OSA; DA; H1; C1, etc.). A better approach for retrofit would be a separate module on the roof that could use existing wiring to install. This wiring configuration would be similar to the VisionPro IAQ. Since communication modules are built in, it would make networking the units a good future option.

c. The economizer should be controlled directly from the thermostat or rooftop control module, and not require a separate module. A 0-10 V damper motor output (for M72**, MS75** or M9*** with Q7230) similar to the more modern economizer controllers (W72**) makes sense. An adapter should be provided to allow operation of older economizer motors (M7415, M7405 and M8405).

d. A night flush algorithm. Honeywell published research in the ASHRAE Research Journal a few years ago on a reasonable delta T to run a night flush cycle on, but we have yet to see a packaged product with this option. There is enough research showing this sequence provides viable savings, and in fact produces demand savings. That should make the sequence very attractive in the California and other markets. If we’ve paid for the bulk of the economizer package, it makes sense to add night flush. The 4 periods on the typical thermostat (contractors install residential thermostats in commercial settings as noted above) would change from Wake/Leave/Return/Sleep to 3 periods: prepare/ occupied/ unoccupied. A low ventilation setpoint during the prepare period during the summer would allow night flush to be activated. Doing night flush right would be preferable, and we can provide input on details of workable sequences we have been running in DDC for several years.

• Inputs for occupancy sensor and/or CO2 sensor input for ventilation control.

• For heat pumps, strip heat lockout above 30F OSA, adjustable.

• Optional - A duty cycle function for heat pumps or electric heat so that during warm up units are on 40 minutes and off 20. This provides an important demand limiting function, and could operate off the thermostat clock without networking the thermostat; you would select duty cycle A, B, or C at each thermostat during setup.

• Optional: some basic ARTU diagnostics if there is any room left on the chip. Extend the VisionPro startup testing to include an economizer test.

• Optional: Holiday scheduling would be desirable, with infrared programming via PDA.

• For application in the Eastern US, a differential enthalpy version could use space enthalpy and outdoor enthalpy for changeover.

We realize this is more expensive than the low end W7459 economizer, but it adds far more control features and savings and has some demand saving items attractive to the California market. It should be more reliable. When an economizer installed at the time a rooftop unit is replaced, utilities often pay a rebate for a new programmable thermostat anyway. Due to increased reliability, utilities should be willing to promote and rebate this as a replacement for existing analog economizer controllers. It seems this system may be able to use less expensive thermistors rather than the current sensors and also avoid sensor connection polarity issues.

3. If the above suggested upgraded integrated thermostat/economizer control is significantly more expensive than a 2-stage, high-end (holiday scheduling and occupancy sensor input) programmable thermostat and economizer controller together, then it may be desirable to redesign the W7459 controller and dry bulb sensors. If the controller needs to be reworked, then we suggest:

a. The ABCD adjustment dial should be eliminated. Adjustment should be able to be achieved for single-sensor control (in the rare case where it is needed) by using ABCD resistors in place of the return air sensor. The factory-installed resistor should establish a changeover at 70-68F outside with instructions to use a 2-stage cooling thermostat (dedicated stage for economizer).

Note that if the hysteresis issue is resolved through an improved dry-bulb sensor design, EWEB will continue to prefer a dry-bulb differential in its premium economizer specification. This is also the present Advanced Buildings Core Performance (NBI) specification.

b. In a simplified design, the changeover relay could be eliminated since there is very little savings from using a single-stage thermostat with the changeover set around 55F or 60F (either economizer or mechanical cooling but no integrated operation). Stage one cooling would wire to the economizer (currently tab 1), and stage two cooling would wire to the compressor. For units with 2 stages of mechanical cooling a 3-stage thermostat could be used, or a delay on make time delay relay could be used to bring on the second mechanical stage when the zone temperature remained unsatisfied after 5 minutes.

c. An alternative would be to rework the changeover relay so it could be used with a heat pump where currently an auxiliary relay driven with the reversing valve signal is required to know when the “Y” signal is cooling vs. heating. We have a lot of commercial heat pumps in the northwest and wiring these up properly seems to be a challenge for a number of service technicians. In some cases it is straightforward to select the right controller, but it would be much easier for everyone and help provide expected performance, if controllers were clearly labeled so that it was obvious which one is needed for a heat pump application.

d. If the unit were redesigned, using a T-shaped, 2-conductor spade for the sensor connections that are supplied with the controller would reduce polarity errors and be in line with the ARTU specification.