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Design & Engineering Services
FIELD SURVEY OF RTU FAN EFFICIENCY AND
OPERATION PATTERNS
HT.11.SCE.020 Report
Prepared by:
Design & Engineering Services
Customer Service Business Unit
Southern California Edison
December 2012
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page i Design & Engineering Services December 2012
Acknowledgements
Southern California Edison’s Design & Engineering Services (DES) group is responsible for
this project. It was developed as part of Southern California Edison’s HVAC Technologies
and Systems Diagnostics Advocacy Program (HTSDA) under internal project number
HT.11.SCE.020. Jay Madden, P.E. conducted this technology evaluation with overall
guidance and management from Jerine Ahmed. Western Cooling Efficiency Center (WCEC)
and Davis Energy Group (DEG) designed and conducted the field surveys, tabulated the
data, and prepared the report for this project. For more information on this project, contact
jay.madden@sce.com.
Disclaimer
This report was prepared by Southern California Edison (SCE) and funded by California
utility customers under the auspices of the California Public Utilities Commission.
Reproduction or distribution of the whole or any part of the contents of this document
without the express written permission of SCE is prohibited. This work was performed with
reasonable care and in accordance with professional standards. However, neither SCE nor
any entity performing the work pursuant to SCE’s authority make any warranty or
representation, expressed or implied, with regard to this report, the merchantability or
fitness for a particular purpose of the results of the work, or any analyses, or conclusions
contained in this report. The results reflected in the work are generally representative of
operating conditions; however, the results in any other situation may vary depending upon
particular operating conditions.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page ii Design & Engineering Services December 2012
EXECUTIVE SUMMARY
This study focuses on small commercial rooftop unit (RTU) supply air fans and how the
thermostats controlling these supply fans are configured. According to the 2006 California
Commercial End Use Survey, supply fans in the more than one million RTUs in California
contribute 11.9% of total statewide commercial building electrical consumption. This
compares to the cooling component (compressor and condenser fan) which represents
14.9% of total statewide electrical consumption. From this context, addressing supply fan
energy efficiency is an important future research area. To evaluate the energy savings
potential of any potential supply fan efficiency opportunity, the baseline operating
characteristics need to be quantified based on actual field conditions.
The goal of this project was to field survey small commercial building establishments to
assess in-situ RTU supply fan electrical demand, and to record how the thermostat
controlling the RTU is programmed, if at all. In addition to defining occupied and unoccupied
periods of the day/week, a review of the thermostat configuration allows one to document
whether the supply fans are operating continuously or cycling in response to a thermostat
call for cooling or heating.
Field surveys were completed during summer 2012 at 216 RTUs in northern and southern
California, with rooftop field measurements of supply fan power at a subset of 58 RTUs.
Complete data sets were not obtained for every RTU surveyed as the access provided by
each of the 98 surveyed commercial sites varied, resulting in different pieces of data
recorded at each site. This is why many of the analyses have data set populations less than
the full 216 records. The survey team gained access to commercial establishments by
coordinating with HVAC contractor service calls, coordinating with building owners and
municipal/public entities, and by cold-calling commercial establishments. Nameplate RTU
data were collected at the 58 units, allowing RTU supply fan power characterization in terms
of a kW/nominal ton metric.
The survey results indicated that the supply fans ran continuously at about 40% of the
surveyed RTUs serving commercial buildings. The other 60% cycled with calls for cooling or
heating. In a third of the surveyed units, the supply fan operated continuously during
unoccupied hours, with another 36% of the fans cycling during unoccupied hours. Table 1
summarizes these results. While these proportions varied by building type, the sample sizes
for each building type were not sufficiently large to make conclusions that are more
detailed.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page iii Design & Engineering Services December 2012
TABLE 1: FAN OPERATION PATTERNS FOR OCCUPIED AND UNOCCUPIED STATES
ROOFTOP UNITS (N=193)
FAN OPERATION PATTERN OCCUPIED UNOCCUPIED
Continuous 39.4% 32.1%
Cycles 58.5% 36.3%
Off 0.0 29.5%
Unknown 2.1% 2.1%
Measured supply fan power in this survey as presented in Table 2 was slightly lower than
results from the datasets in the Bonneville Power Administration RTU Pilot Servicing
Program and the California Energy Commission (CEC) Small HVAC System Design Guide.
Direct-drive supply fans were found to consume less energy per nominal ton of capacity
relative to belt-drive fans. However, direct-drive fans were not observed in RTUs above 5
tons nominal capacity.
TABLE 2: COMPARISON OF MONITORED SUPPLY FAN POWER DENSITY
STUDY FAN POWER DENSITY (KW/NOMINAL TON)
SCE Survey 0.15
Bonneville Power Administration RTU Pilot Servicing Program 0.18
CEC Small HVAC System Design Guide 0.18
Based upon the survey observations, RTU potential supply fan energy efficiency measures
should not assume continuous supply fan operation during occupied hours. This assumption
would result in calculated energy savings higher than actual results. It is also difficult to
draw a conclusion regarding fan energy savings during unoccupied hours. One-third of the
RTUs were observed to be operating continuously at night, some of which could possibly be
due to thermostat programming errors. Theoretically, the programming errors should be
corrected before fan energy measures are applied to these buildings.
The survey found programmable thermostats or EMS at a majority of the RTUs, which
provides the opportunity for features like programmed operation and night setback
operation. However, lack of understanding of these controls resulted in bypassing these
opportunities. Better awareness could result in better comfort levels in the conditioned
spaces as well as lower energy consumption.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page iv Design & Engineering Services December 2012
ACRONYMS
AC Air Conditioning Unit
ACM Alternative Calculations Method
ASHRAE American Society for Heating Refrigeration and Air Conditioning
BPA Bonneville Power Administration
CA California
CEUS California Commercial End-Use Survey
CFM Cubic Feet per Minute
DEG Davis Energy Group
DOE Department of Energy
EMS Energy Management System
HVAC Heating, Ventilation, and Air Conditioning
IAQ Indoor Air Quality
kW kiloWatt
PNW Pacific Northwest
RTU Rooftop Unit
RTUG Regional Rooftop Working Group
SCE Southern California Edison
UC University of California
WCEC Western Cooling Efficiency Center
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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CONTENTS
EXECUTIVE SUMMARY ________________________________________________ II
INTRODUCTION ____________________________________________________ 1
BACKGROUND ____________________________________________________ 2
Ventilation Code Requirements ................................................. 2
Bonneville Power Administration RTU Pilot Servicing Program ....... 3
California Commercial End-Use Survey (CEUS) ........................... 8
Small HVAC System Design Guide ........................................... 10
METHODOLOGY __________________________________________________ 11
Survey Protocol..................................................................... 11
Survey Schedule ................................................................... 12
RESULTS_________________________________________________________ 13
DISCUSSION _____________________________________________________ 28
CONCLUSIONS ___________________________________________________ 30
REFERENCES _____________________________________________________ 31
APPENDIX A: SURVEY DATA COLLECTION FORM _________________________ 32
APPENDIX B: SURVEY DATA BY SITE ___________________________________ 35
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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FIGURES
Figure 1: RTU evaporator fan kW per ton (BPA study) ...................... 4
Figure 2: Capacity of Surveyed RTUs ............................................. 5
Figure 3: RTU Fan Hours per Day .................................................. 6
Figure 4: Compressor runtime vs. fan runtime ................................ 8
Figure 5: Survey sites by county ................................................. 14
Figure 6: Survey sites by facility type and county .......................... 15
Figure 7: Number of RTU “in building” surveys by facility type and
region ....................................................................... 15
Figure 8: Number of RTUs per site by region (N or S) and facility
type (individual site values shown in black) .................. 16
Figure 9: Observed RTU nameplate nominal capacity ..................... 17
Figure 10: Thermostat manufacturers by facility type .................... 18
Figure 11: RTU manufacturers by facility type ............................... 18
Figure 12: Fan operation characteristics during occupancy by
region and facility type ............................................... 20
Figure 13: Fan operation characteristics during non-occupied
periods by region and facility type ................................ 20
Figure 14: Hours of continuous fan operation by facility type .......... 21
Figure 15: The average number of business hours per business
day by facility type ..................................................... 22
Figure 16: Ratio of average daily available cooling hours to
business occupancy hours ........................................... 23
Figure 17: Measured supply fan kw/ton by site ............................. 24
Figure 18: Fan power per ton by drive type versus RTU tonnage ..... 24
Figure 19: Measured supply fan kw/ton by region and facility type .. 26
Figure 20: Individual site occupied thermostat setpoints (by
region-facility-schedule type)....................................... 27
Figure 21: Individual site unoccupied thermostat setpoints in black
(by region-facility-schedule type) ................................. 27
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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TABLES
Table 1: Fan operation patterns for occupied and unoccupied
states ........................................................................ iii
Table 2: Comparison of monitored supply fan power density ............ iii
Table 3: RTU fan categorization sorting rules .................................. 7
Table 4: Comparison of fan operation in multiple studies .................. 9
Table 5: Thermostat operation ( CEUS study) ................................. 9
Table 6: Types of programmed RTU operation .............................. 13
Table 7: Characterization of fan operations in terms of occupancy
state, system setting, and fan setting ........................... 19
Table 8: Fan operation patterns for occupied and unoccupied
states ....................................................................... 19
Table 9: Average fan power per ton by drive type and RTU
tonnage .................................................................... 25
Table 10: Supply Fan Power Density ............................................ 28
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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INTRODUCTION
This study focuses on small commercial rooftop unit (RTU) supply air fans and how the
thermostats controlling these supply fans are configured. The information in this study
assists in understanding the actual energy consumption and savings potential of
conservation strategies that reduce supply fan energy and/or reduce fan operating hours.
To evaluate the energy savings potential of any technology, the baseline operating
characteristics of the device or system need to be quantified, documented, and based on
actual performance. One often overlooked energy consuming component in commercial
buildings is the supply air fan found in the ubiquitous commercial rooftop unit (RTU). From a
statewide perspective, the operation of RTU supply air fans is of particular interest because
the more than one million RTUs in California contribute to associated annual ventilation
energy use totaling 11.9% of statewide commercial building electrical consumption. This
compares to the cooling (compressor and condenser fan) annual energy end use estimate of
14.9% [1]. Supply fan annual energy use is dependent upon average operating hours,
which varies widely depending on the facility type, space conditioning loads, comfort
preferences, and how the RTU fan is controlled.
Although both the RTU compressor(s) and supply fan are controlled by the same
thermostat, the thermostat can operate the supply fan independently. The thermostat is set
to one of the following settings:
“Auto” where the supply fan cycles with the compressor operator
“On” where the fan operates regardless of compressor operation
Programmable thermostats and energy management systems (EMS) may be programmed
to operate the fan on a schedule, such as during occupied hours only, to meet building
ventilation needs. Therefore, surveying thermostat settings is required to gain
understanding of typical operation patterns of RTU supply air fans.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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BACKGROUND
By law, mechanical ventilation is required in all buildings, but a significant percentage of
buildings that rely on RTU supply fans for ventilation do not program the fan to provide
ventilation during all occupied hours. As a result, ventilation is only provided when the fan is
running to satisfy a thermostat call for heating or cooling. Conversely, some fans operate
continuously even in unoccupied buildings. Additionally, the average fan power consumed in
RTUs is impacted by the fan design and the resistance of its ductwork.
It is difficult for a utility program to estimate the energy savings for fan efficiency or fan
controls when the baseline run-time and power consumption is unknown. Southern
California Edison (SCE) and Western Cooling Efficiency Center (WCEC) searched for existing
literature for commercial buildings with which to evaluate and compare supply fan
operation, supply fan power consumption, or both.
VENTILATION CODE REQUIREMENTS
Ventilation design in commercial applications is code-driven and regulated to balance
the competing goals of maintaining improved air quality with building energy
consumption.
California’s most recent Building Energy Efficiency Standards (2008) states that
occupied spaces in new buildings must be ventilated mechanically one hour before
occupancy and during all periods in which the space is usually occupied, with the rate
of ventilation varying by use and occupant density [2]. This requirement dates back
to California’s first version of the Building Energy Efficiency Standards published in
1978 [3], which based requirements on the American Society for Heating
Refrigeration and Air Conditioning (ASHRAE) standard 62-73. Regulations in other
states vary but most, if not all, are based on the International Code Council’s
International Mechanical Code, which is based on ASHRAE’s current version of the
ventilation standard 62.1, which requires mechanical ventilation in occupied
commercial buildings.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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BONNEVILLE POWER ADMINISTRATION RTU PILOT SERVICING
PROGRAM
The Bonneville Power Administration (BPA) is the federal marketing agent for power
to all of the federally owned hydroelectric projects in the Pacific Northwest. The
Pacific Northwest (PNW) Regional Technical Forum, through the Regional Rooftop
Working Group (RTUG), surveyed and monitored approximately 150 RTUs in the
greater Seattle area during the summers of 2009 and 2010. Survey data compiled
from this literature review included RTU cooling capacity (tons), evaporator fan kW,
thermostat settings, and thermostat schedules. The RTUG measured and logged RTU
power consumption for at least two weeks before intervention by a servicing
program. Power data were reported as average power in hourly increments. A
summary sheet and raw power data for each RTU are available on the Internet [4].
It is important to note that the BPA data comes from the greater Seattle area, where
ventilation requirements are similar to California’s Title 24 regulations for building
standards. For example, in Seattle, ventilation is currently required for all occupied
spaces, but only during the actual operating hours, not one hour proceeding
occupancy, as in the California code.
The BPA measured and analyzed evaporator fan power measured on 122 units, as
reported on the summary sheet [4]. The service technician measured and reported
the fan power when installing the monitoring equipment and again after performing
the service on the unit. To be included in this data set, the fan power reading on the
first visit had to match the fan power reading on the second visit to within 10%
(three data points failed this criterion). The remaining 119 data points were binned
by fan power per nominal ton (Figure 1). The population mean is estimated as
0.185±0.011 kW/ton with 95% confidence. The following factors affect the fan
power:
Resistance of ductwork in the distribution system
Resistance of air filters
Fan and motor efficiency
Supply air flow rates
The Air-Conditioning, Heating, and Refrigeration Institute’s Standard 340/360-2007
[5] specifies that, based on nominal tonnage, the calculated fan power should be 365
W per 1000 CFM [226 W/m3/s] of indoor air circulated for both heating and cooling.
At a typical supply fan flow rate of 400 cfm per nominal ton, this is equivalent to
0.15 kW/ton. On average, the surveyed RTU fan power (0.185 kW) consumption is
27% higher than the modeling assumption of 0.15 kW/ton at 400 cfm/ton. This is
due to higher airflow rates, greater resistance, or reduced fan/motor efficiencies.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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FIGURE 1: RTU EVAPORATOR FAN KW PER TON (BPA STUDY)
The most commonly surveyed unit in the BPA study are the 5-ton RTU, followed by
7.5 ton capacity RTUs, as shown in the “8” bin in Figure 2. Eighty percent of units
surveyed were 10 ton capacity or less with no correlation between fan power per ton
and unit size.
0%
5%
10%
15%
20%
25%
0.02 0.06 0.1 0.14 0.18 0.22 0.26 0.3 0.34 0.38 0.42 0.46 0.5
Per
cen
t of S
amp
le
Measured Evaporator Fan kW per Ton of Rated Cooling
Population mean = 0.185 ± 0.011 kW/ton (95% Confidence)Sample size n=119
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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FIGURE 2: CAPACITY OF SURVEYED RTUS
An analysis of the BPA monitoring data from 136 RTUs determined the average
number of fan run-hours per day, and whether the fan operated continuously,
continuously during occupied hours only, or cycled with the compressor. The fan was
considered “on” when the average power over a one hour monitoring logging interval
was observed to be 20-120% of the technician measured fan power. The compressor
was considered to be “on” when the total unit power rose above 120% of the fan
only power. This approach will overestimate fan hours, since some short air
conditioner cycling intervals will be included in the 20-120% category and be
counted as the fan running for an entire hour.
Since the service technician changed the operating pattern of the fan for
approximately 10% of the units, only the data used before servicing is included in
the results. Figure 3 shows that the fan operated continuously to provide ventilation
approximately 40% of the time. An analysis of the power data estimated the fan and
compressor run-times, and the average fan and compressor run-hours per day for
each bin is shown above each bar in Figure 3. For fan run-hours of 20 hours per day
or less, fan run-time increases as the average cooling run-time increases.
0%
5%
10%
15%
20%
25%
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Per
cen
t of S
amp
le
Rated Tonnage for RTUs Surveyed
Population mean = 7.94 ± 0.82 tons (95% Confidence)Sample size n=119
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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FIGURE 3: RTU FAN HOURS PER DAY
The type of controller for the RTU was recorded for 107 of the RTUs surveyed. The
thermostat was a programmable thermostat 73% of the time and an energy
management system (EMS) 27% of the time. The study reported no manual
thermostats. Setbacks of cooling and heating setpoints were generally reported
during unoccupied hours.
An initial method was developed to categorize RTU fan operation as shown below:
The fan is “continuous” if it runs 24 hours a day.
The fan is “occupied” if it runs during occupied hours only.
The fan is “cycling” if the fan only runs when there is a call for heating or cooling.
The RTUs are categorized by evaluating the power draw of the RTU over the course
of a week. This method was subjective, error-prone, and time consuming, so the
following rules were developed to sort each RTU into the appropriate category as
shown in Table 3:
The fan is “continuous” if the fan is running 90% of the time.
The fan is “occupied” if the compressor run time percentage divided by the fan
time percentage is less than 0.75 and the fan runs less than 90% of the time.
The fan is “cycling” if the compressor run time percentage divided by the fan time
is at least 0.75 and the fan runs less than 90% of the time.
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
0-4 4-8 8-12 12-16 16-20 20-24
Per
cen
t of S
amp
le
Fan Run Hours Per Day
Sample size n=136
Avg. fan hrs/day=10.1
Avg. comphrs/day=7.0
Avg. fan hrs/day=6.2
Avg. comphrs/day=4.0
Avg. fan hrs/day=13.8
Avg. comphrs/day=7.3
Avg. fan hrs/day=17.9
Avg. comphrs/day=11.3
Avg. fan hrs/day=22.7
Avg. comphrs/day=12.3
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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While 0.75 may be lower than expected, it is required to account for the difficultly in
determining the difference between fan and compressor operation in hourly averaged
data. For example, extra “fan only” hours are in many cases full RTU operation for a
partial hour. Selecting 0.75 as the cutoff between cycling and occupied-only use
resulted in the closest match to a subjective graphical analysis done previously.
Applying these parameters, 40% of the RTU fans surveyed ran continuously, 27%
operated only with the compressor when providing cooling, and 33% ran during
occupied hours regardless of the cooling state (Figure 4).
TABLE 3: RTU FAN CATEGORIZATION SORTING RULES
FAN OPERATION CATEGORY EQUATION
Continuous:
Occupied:
Cycling:
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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FIGURE 4: COMPRESSOR RUNTIME VS. FAN RUNTIME
CALIFORNIA COMMERCIAL END-USE SURVEY (CEUS)
The California Commercial End-Use Survey of 2003 estimates the magnitude of
electricity end-usages in commercial buildings [7]. The survey included a sample of
2,790 commercial facilities from the service areas of Pacific Gas and Electric (PG&E),
San Diego Gas & Electric (SDG&E), Southern California Edison (SCE), Southern
California Gas Company (SCG), and the Sacramento Municipal Utility District
(SMUD). The objective of the study is not specific to RTUs, but several details about
RTUs were gathered as part of the survey. Because of privacy concerns, this report is
not publicly available, so SCE provided an analysis of the survey data for their
service territory only.
The CEUS had significantly more classifications for the fan operation than did the
BPA study, and classified the fan operation during both occupied and unoccupied
hours. Table 4 shows that the sample of 568 RTUs and associated thermostats
indicate continuous operation of fans in 9.3% of units and continuous operation
during occupied hours in 44.9% of the units. The measured fan hours in the 2003
CEUS study is significantly less than measured during the 2009 BPA Rooftop Unit
Servicing Program, with the fan operating less during both occupied and unoccupied
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Co
mp
ress
or
run
tim
e [%
]
Fan Runtime [%]
cut-off
Continuous
Occupied
Cyclic
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hours. The CEUS data also shows that programmable thermostats and EMS were
significantly less prevalent in 2003 as shown in Table 5.
TABLE 4: COMPARISON OF FAN OPERATION IN MULTIPLE STUDIES
Fan Operation
Pattern
BPA ROOFTOP UNIT SERVICING 2009-
10 (N=133)
CEUS 2003
(N=568)
Occupied Hours
Unoccupied
Hours Occupied Hours
Unoccupied
Hours
Continuous 73% 40% 44.9% 9.3%
Cycles 27% 60% 51.5% 31.9%
Manual 0.0 0.0 3.5% 1.6%
Off 0.0 0.0 0.0 42.8%
Night Cycles 0.0 0.0 0.0 9.3%
Unknown 0.0 0.0 0.1% 5.1%
TABLE 5: THERMOSTAT OPERATION ( CEUS STUDY)
CONTROL TYPE PERCENT OF SAMPLE (N=568)
Unknown 9.4
Always On 3.6
EMS 6.1
Manual 41.4
Programmable 31.3
Time Clock 8.1
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SMALL HVAC SYSTEM DESIGN GUIDE
The Small HVAC System Design Guide, published by the CEC, evaluated several
parameters that effect RTU efficiency, including fan energy consumption [7]. The
2003 report presented average airflow and power measurements for evaporator fans
in 79 RTUs in California, a subset of the 215 total units monitored for the study. The
average measured airflow was 325 cfm/ton and the average measured fan power
was 0.18 kW/ton. This is in agreement with the BPA study from 2009, which
suggests that fan power averages are not specific to geography and did not change
between 2003 and 2009.
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METHODOLOGY
The goal of this survey was to collect data relevant to supply fan operation from over 200
thermostats, with a target subset of over 50 “on-roof” data points. On-roof data includes
RTU nameplate information and fan power measurements. Various strategies were
developed to gain access to commercial buildings and their roofs. Rooftop data were more
difficult to obtain. Permission from the tenant or building owner to access the roof was
required. To disaggregate the data collection sample, the team collected data from different
types of commercial buildings in northern and southern California, including restaurants,
retail stores, small offices, medical facilities, warehouses, and schools.
A two-fold approach was undertaken to collect survey sites for the in-building thermostat
portion of the project. In southern California, the project team connected with several
commercial HVAC contractors that operate in the greater Los Angeles area. The team
briefed the contractors on the nature of the work and coordinated the site visits. One of the
HVAC contractors cooperated fully and scheduled site visits directly through the dispatch
coordinator. Each day, the dispatcher informed the field survey team about the next day’s
schedule of site visits, which allowed the field survey staff to gain access to the building or
rooftop. A key advantage in this strategy was that the field survey staff could gain access to
the building and often to the rooftop in coordination with the HVAC service technician. The
field survey team also tried this approach with a HVAC contractor in the Sacramento area,
but the level of coordination and the availability of appropriate sites resulted in limited
opportunities.
The Davis Energy Group (DEG) and the Western Cooling Efficiency Center (WCEC) used
local contacts in Davis, CA to arrange some “on-roof” surveys at a commercial office park,
City of Davis public buildings, and a city public school.
SURVEY PROTOCOL
DEG worked with WCEC and SCE to develop a Field Survey Recording form to help
the team gather the appropriate data. A copy of this form is in Appendix A. The first
page of the form provides space to enter “in building” characteristics and the second
page provides space to enter “on-roof” data.
The “in building” section of the survey focused on the following:
Characterizing the facility by commercial building type
Defining the normal occupancy period for the building for each day of the week
Documenting thermostat type and model
Reviewing thermostat programming (occupied and unoccupied schedule of
temperatures, fan scheduling)
Assessing any comfort or Indoor Air Quality (IAQ) issues with the building contact
(anecdotal information)
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The “on-roof” section of the survey focused on the following:
Documenting the RTU manufacturer and model number (model number includes
nominal cooling capacity information)
Documenting the RTU physical characteristics (condenser configuration, number
of compressors, presence of economizer, refrigerant type)
Documenting supply fan data (nominal horsepower, belt or direct-drive, and
measured supply fan kW)
Manufacturer model numbers were used to research and document nominal
equipment capacities, and then added to the online survey form. Whenever possible,
photos were taken to document the building exterior, thermostat, and RTU physical
characteristics. Electrical measurements were completed using a Fluke 1735 three-
phase power logger, which is commonly used in conducting energy studies and basic
power quality logging. The accuracy of power measurement of the Fluke 1735 is
specified as 1.5% of the measured value, not including errors from the current
transducers. The current transducers were I5A/50A Clamp PQ4, for which the
accuracy varies by the measured current, with the range being 2.5% of measured
value below 2.5 amps and 0.5% of the measured value above 25 amps.
The completed surveys were uploaded to a GoogleDocs site to allow the project team
to access them.
SURVEY SCHEDULE
Field activities began in late June 2012 and continued until late September 2012.
DEG hired an engineering intern to complete most of the “in building” survey work
and some of the “on-roof” data. After an initial training period in northern California,
the intern completed site surveys in Los Angeles on July 18-31, 2012 and on
September 4-12, 2012. DEG engineering technicians also gathered “on-roof” data,
and then completed all “on-roof” power measurements. The intern and engineering
technicians worked closely with the southern California mechanical contractor to
facilitate access to the chosen sites.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
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RESULTS
To assess the differences between RTU and fan behaviors, the team completed surveys at
98 different sites in different climate zones and sampled 216 RTUs. Not all of RTUs were
independently controlled with their own thermostats. Some of the thermostats only
displayed the current temperature and the temperature setpoints were programmed in a
building management system. In this survey study, there were four different types of
programmed RTU operation, and the types and percentages in the sample are summarized
in Table 6.
TABLE 6: TYPES OF PROGRAMMED RTU OPERATION
PROGRAMMED RTU OPERATION TYPE PERCENT OF SAMPLE (N=212)
Programmable Thermostat 83.0%
Building Management System 9.9%
Manual 0.9%
Time-Clock 6.1%
Surveys were also completed in multiple climate zones to provide a preliminary assessment
of potential differences between RTU and fan behaviors throughout California. At a subset of
the survey sites where occupancy and thermostat data were collected, rooftop access was
also provided, allowing for collection of RTU physical data (manufacturer, model number,
number of compressors, condenser coil configuration, etc.) and measurement of the supply
fan power during operation. This section of the report summarizes the results. Full site
tabulations of the data can be found in Appendix B.
The team completed site surveys in Los Angeles, Orange, and Riverside in southern
California, and Yolo and Solano in northern California. The graphs in this section provide
basic descriptive information about the survey sites. Figure 5 shows the total number of
sites surveyed in each county.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 14
Design & Engineering Services December 2012
FIGURE 5: SURVEY SITES BY COUNTY
Approximately two-thirds of the total sites in northern California are in or around Davis, CA.
Within each of these counties, seven main types of commercial buildings are used in this
study, including food/liquor, health care, office, restaurant, retail, and school. Miscellaneous
commercial sites, such as theaters and automotive repair shops, are included in the study.
Figure 6 shows 83% of the survey buildings were retail, restaurant, and office sites.
Figure 7 presents the number of “in building” surveys by building type and location. Fast
food restaurants represent close to half of the “in building” surveys; office and retail sites
represent one-third of the building types.
0
5
10
15
20
25
30
35
40
45
50
55
60
Yolo Los Angeles Orange Riverside Solano
Nu
mb
er
of
Site
s
County
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Southern California Edison Page 15
Design & Engineering Services December 2012
FIGURE 6: SURVEY SITES BY FACILITY TYPE AND COUNTY
FIGURE 7: NUMBER OF RTU “IN BUILDING” SURVEYS BY FACILITY TYPE AND REGION
13
1
9
6
1
1
1
11
9
12
5
4
2
29
1
2
Los Angeles
Orange
Riverside
Solano
Yolo
Co
un
ty
Facility Type
0
10
20
30
40
50
60
70
80
90
Restaurant Office Retail Store Misc School Food/Liquor Health Care
Nu
mb
er
of
RTU
s
Northern CA Southern CA
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Southern California Edison Page 16
Design & Engineering Services December 2012
Figure 8 plots the number of RTUs per site surveyed “on-roof”, by location (N=northern
CA, S=southern CA) and building type. Each black dot represents an individual data point;
the red dot and line represents the mean value and the standard error of the mean.
Interestingly, for each of the facility types, southern California sites always had more RTUs
per site than northern California. This could be an artifact of the small dataset. Nameplate
data (make and model number) collected during the “on-roof” survey were researched on
the Web to derive nominal equipment capacity (in tons).
FIGURE 8: NUMBER OF RTUS PER SITE BY REGION (N OR S) AND FACILITY TYPE (INDIVIDUAL SITE VALUES SHOWN IN BLACK)
Figure 9 provides a breakdown of observed RTU capacities. The majority of the RTUs
surveyed were found to be between four and ten tons per RTU, with capacity ranging from 3
to 25 tons. Average capacity for the 115 RTUs was 6.50 tons, with a standard deviation of
3.33 tons.
0
2
4
6
8
10
12
14
16
RTU
s/Si
te
Data Point Avg. for Facility TypeError Bars Denote One
Standard Error of the MeanN = northern CaliforniaS = southern California
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 17
Design & Engineering Services December 2012
FIGURE 9: OBSERVED RTU NAMEPLATE NOMINAL CAPACITY
Figure 10 and Figure 11 characterize the distribution of thermostats and RTU manufacturers
surveyed in the sample. Although Honeywell thermostats were by far the most common (63
observations), the total number of different thermostat manufacturers (22) was greater
than anticipated. In terms of RTU manufacturers, Lennox, Trane, and Carrier were the most
commonly observed (representing two-thirds of the units), with the remaining one-third
comprised of six other manufacturers.
0%
5%
10%
15%
20%
25%
30%
35%
40%
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Pe
rce
nt o
f Sam
ple
Rated Tonnage for RTUs Surveyed
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Southern California Edison Page 18
Design & Engineering Services December 2012
FIGURE 10: THERMOSTAT MANUFACTURERS BY FACILITY TYPE
FIGURE 11: RTU MANUFACTURERS BY FACILITY TYPE
1
1 7
10 4
1 1
2 17 31 12 1
1
11 3
15 2
2
1
2
1
1 1 2 3
1
1
2
1
1
2
9 3
1 2 4
1 4
4 5 1 13 11
1
1
8
14
2
63
1
14
17
4
1
7
2
1
2
1
1
2
12
7
5
25
1
1Source
Braeburn
Carrier
Emerson
Honeywell
Invensys
Johnson Controls
Lennox
Lux
Lux1500
LuxPro
Maple Chase
Nest
Novar
Proliphix
Ritetemp
Robert Shaw
TCS Basys Controls
Totaline
Venstar
White-Rodgers
York
Food/Liquor Health Care Misc. Office Restaurant Retail School Total
The
rmo
stat
Man
ufa
ctu
rer
Facility Type
4 2 2
2
5 3
4 10 9 2
2
1
7
6 20 1
8 3
3 3 20
1
8
2
8
26
9
27
11
26
1
American Standard
BDP
Bryant
Carrier
Goodman
Lennox
Rheem
Trane
York
Food/Liquor Health Care Misc. Office Restaurant Retail School Total
RTU
Man
ufa
ctu
rer
Facility Type
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 19
Design & Engineering Services December 2012
The descriptive data presented up to this point characterizes the sites, building types, RTU
characteristics, and thermostat manufacturer. To investigate the energy implications of the
supply fan and thermostat control, the data need to be evaluated from a quantitative
perspective by defining operational characteristics of the RTU supply fan based on
field-observed thermostat programming. Table 7 defines potential fan operation states
based upon whether the building is occupied or not, the thermostat is programmed or
operated manually, and whether the fan setting is “auto” or “off”. For example, continuous
fan operation can occur in either occupied or unoccupied conditions, but the thermostat
must be scheduled for operation, with the fan set in the “on” mode.
TABLE 7: CHARACTERIZATION OF FAN OPERATIONS IN TERMS OF OCCUPANCY STATE, SYSTEM SETTING, AND FAN SETTING
OCCUPANCY STATE SYSTEM SETTING FAN SETTING
FAN OPERATION OCCUPIED UNOCCUPIED SCHEDULE MANUAL AUTO ON
Continuous
Cycles
Manual – Auto
Manual – On
Off
Unknown
Similar to the results shown in Table 4: Comparison of fan operation in multiple studies
Table 4, Table 8 presents the results, for the six categories, found from the RTU survey
data. Figure 12 and Figure 13 summarize the data based on this classification for both
occupied periods of the day and unoccupied. The data are categorized by region and facility
type with the x-axis label including the total number of sites per category, and the columns
denoting the number of sites within each category. Overall, 76 out of 193 sites were found
to operate the supply fans continuously during occupancy. During non-occupied periods,
132 of 193 sites were found to have the supply fan cycling in response to cooling operation,
with none of the supply fans operating continuously.
TABLE 8: FAN OPERATION PATTERNS FOR OCCUPIED AND UNOCCUPIED STATES
ROOFTOP UNITS (N=193)
FAN OPERATION PATTERN OCCUPIED UNOCCUPIED
Continuous 39.4% 32.1%
Cycles 58.5% 36.3%
Off 0.0 29.5%
Unknown 2.1% 2.1%
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 20
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FIGURE 12: FAN OPERATION CHARACTERISTICS DURING OCCUPANCY BY REGION AND FACILITY TYPE
FIGURE 13: FAN OPERATION CHARACTERISTICS DURING NON-OCCUPIED PERIODS BY REGION AND FACILITY TYPE
Figure 14 summarizes the hours of fan operation by facility type for the 76 RTUs that
operated the supply fans continuously, either with manual or scheduled thermostat control.
For manually control thermostat, the number of daily fan operating hours was determined
to be equal to the occupancy period of the day; for scheduled RTUs, the fans were assumed
to operate 24 hours per day.
23
3
16 36
21 1
106 7
6
11
23
5
2 2
53
1
291
1 3 1
9
31
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%P
erc
en
t o
f Sa
mp
le
Unknown
Manual - On
Manual - Auto
Cycles
Continuous
N = northern CaliforniaS = southern California
2 2
5 4
1
32
1
19
23
3
1636
2
1 1
106
7
6
11 23
5
31
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Pe
rce
nt
of
Sam
ple
Unknown
Cycles
Continuous
Off
N = northern CaliforniaS = southern California
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 21
Design & Engineering Services December 2012
FIGURE 14: HOURS OF CONTINUOUS FAN OPERATION BY FACILITY TYPE
For RTUs that do not operate the supply fans continuously, both the length of the business
day and control of the thermostat (manual control vs. programmed cooling setpoints)
dictate the number of supply fan operating hours. Figure 15 plots the average number of
business hours per business day for each of the facility types in both northern and southern
California. Many commercial buildings operate their systems both before and after normal
building occupancy times to accommodate unusual schedules, as well as to ensure that the
building is conditioned prior to occupancy.
02468
1012141618202224
Ho
urs
of
Fan
Op
era
ton
Data Point Avg. of Facility Type Error Bars Denote OneStandard Error of the Mean
N = northern CaliforniaS = southern California
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 22
Design & Engineering Services December 2012
FIGURE 15: THE AVERAGE NUMBER OF BUSINESS HOURS PER BUSINESS DAY BY FACILITY TYPE
The following series of graphs explore the thermostat programming in terms of variations in
cooling setpoints during occupied and unoccupied periods by facility type and location.
There are three different kinds of temperature and occupancy schedules as follows:
Manual (M): A manual cooling schedule is the result of the varying comfort
level of the business or the limitations of the thermostat, i.e.
non-programmable. When a thermostat is turned on, set, and adjusted while
the business is occupied, it is assumed that cooling is on during normal
business hours only. This assumption is made because there is no way to
determine whether business operators, with manually operated cooling,
habitually turn off or increase the temperature set-point to prevent
unnecessary cooling during unoccupied hours.
Daily (D): A daily cooling schedule is programmed in the thermostat and can
vary on an hourly basis throughout the day.
Weekly (W): A weekly cooling schedule is programmed in the thermostat
and can vary on an hourly and daily basis.
It was important to note that thermostat and cooling programs could be overridden by the
end user at any point in time, which introduced error into the analysis.
Figure 16 plots the ratio of actual conditioned hours divided by occupied hours for each of
the building types. A value of 1.0 would suggest space conditioning only occurring during
occupied periods. Values less than 1.0 represent facilities where the cooling system is only
enabled (by schedule or manually) for a fraction of the full day. Values greater than 1.0
indicate extended conditioning hours.
8
10
12
14
16
18
20
22
24
26
Ho
urs
/Day
Data Point Avg. for Facility TypeError Bars Denote One
Standard Error of the MeanN = northern CaliforniaS = southern California
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 23
Design & Engineering Services December 2012
FIGURE 16: RATIO OF AVERAGE DAILY AVAILABLE COOLING HOURS TO BUSINESS OCCUPANCY HOURS
Supply fan power readings allowed the characterization of fan energy use according to a
kW/nominal ton metric, based on the RTU nameplate data. Supply fans are either belt-drive
or direct-drive, so additional disaggregation was warranted. Figure 17 shows the range of
measured fan power per nominal ton, depending on the drive method. On average, the belt-
drive supply fans draw 0.154 kW/ton (standard error of the mean of 0.009 kW/ton) and the
direct-drive supply fans drew 0.139 kW/ton (standard error of the mean of 0.008 kW/ton).
Although the minimum power per ton measurements are close for the two drive methods,
the maximum measurements differ significantly. This difference could be due to properties
other than the motor, such as a high resistance distribution system, dirty air filters, etc.
Figure 18 plots belt-drive and direct-drive fan kW/ton, as a function of RTU capacity (tons)
and Table 9 provides similar data in a tabular form. For the sample of units surveyed, the
direct-drive fans are limited to RTUs of 5 tons or less, representing 58% of the surveyed
RTUs in the <= 5 ton size range. For both drive types, Table 9 shows almost no trend. It
appears that the fan kW/ton remains constant except for the 8.5 tonnage data. However,
given there are only two 8.5 ton belt-drive datapoints, there is no statistical basis to
indicate a trend without further data. The limited sample of larger RTUs (10 tons and
greater) also does not suggest a clear trend in the larger sized units. Due to the limited
numbers of RTU data points that have both tonnage and fan power readings, it is difficult to
determine with adequate certainty if there is a valid correlation between average fan power
per ton and RTU tonnage. Further study in this area is warranted to determine if units in the
5 to 10 size range might be preferred candidates for potential fan efficiency measure
strategies.
0
0.5
1
1.5
2
2.5
3
Rat
io
Data Point Avg. Ratio Error Bars Denote OneStandard Error of the Mean
D = Daily, M = Manual, W = Weekly
N = northern CA, S = southern CA
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 24
Design & Engineering Services December 2012
FIGURE 17: MEASURED SUPPLY FAN KW/TON BY SITE
FIGURE 18: FAN POWER PER TON BY DRIVE TYPE VERSUS RTU TONNAGE
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Belt Direct
kW/t
on
Data Point Avg. for Drive Type Error Bars Denote One Standard Error of the Mean
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0 5 10 15 20 25 30
kW/t
on
Tonnage
Belt
Direct
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 25
Design & Engineering Services December 2012
TABLE 9: AVERAGE FAN POWER PER TON BY DRIVE TYPE AND RTU TONNAGE
BELT DIRECT
CAPACITY (TONS) COUNT AVERAGE [KW/TON] COUNT AVERAGE [KW/TON]
2.5 0 0 1 0.12
3 2 0.11 6 0.12
4 6 0.15 4 0.13
5 11 0.15 14 0.15
6 2 0.15 0 0
7.5 11 0.16 0 0
8.5 2 0.32 0 0
10 10 0.14 0 0
12.5 1 0.14 0 0
15 1 0.06 0 0
25 1 0.14 0 0
Another investigation examined the variation in fan power measurements at different
facilities and regions. The fan power per ton was categorized into the seven facility types
and then further filtered for northern and southern California. In Figure 19, individual data
points are plotted as open circles, the mean is shown with a solid red circle, and the error
bars represent the standard error of the mean. For this limited dataset, surveyed southern
California restaurant sites demonstrated a higher kW/ton than other facility types. This
observation, although anecdotal at best, is indicative for the need for further study.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 26
Design & Engineering Services December 2012
FIGURE 19: MEASURED SUPPLY FAN KW/TON BY REGION AND FACILITY TYPE
The thermostat setpoints during the occupied and unoccupied periods for each facility type,
location, and thermostat type (M, D, or W) are shown in Figure 20 and Figure 21,
respectively. As seen in Figure 20, some of the designated daily and weekly schedules
appear to be inaccurate. Because these survey data were collected throughout the summer,
it is reasonable to expect that very few commercial businesses would be maintaining
setpoints during occupied periods at temperatures above 78°F, let alone 80°F1. It was
observed that of the 136 thermostat schedules, 25 may well have been programmed
incorrectly. “Incorrect” was defined as irregular temperature setpoints and schedules or
abnormally high temperature setpoints, such as a thermostat programmed with lower
cooling setpoints in the middle of the night, and higher setpoints during “normal” mid-day
occupancy periods. Many of these thermostats were operated manually, apparently
indicating that the building occupants were not able to correctly program the thermostat.
For example, if a cooling setpoint steadily decreases to 72°F, jumps to a setpoint of 80°F for
fifty minutes, and then returns to 72°F, the schedule is not programmed properly.
Conversely, in Figure 21, it is not practical for some of the businesses to cool the
conditioned space during unoccupied hours. For instance, some of the restaurants, offices,
and schools were operating their air conditioning systems to maintain temperature setpoints
below 75°F during unoccupied periods. The extreme case of cooling during unoccupied
period was one of the northern California offices that had a daily unoccupied setpoint of
1 One particular bar/restaurant establishment did have a corroborated mid-day setpoint of 80°F. They
operated numerous ceiling fans in lieu of lower cooling setpoints for much of the day. Later at night
when occupancy increased, the setpoints were lowered.
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
kW/t
on
Data Point Avg. for Facility TypeError Bars Denote One
Standard Error of the MeanN = northern CaliforniaS = southern California
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 27
Design & Engineering Services December 2012
62°F. This facility can save energy by reprogramming the thermostat or at least turning it
off while the facility is unoccupied. This may also work for other sites.
FIGURE 20: INDIVIDUAL SITE OCCUPIED THERMOSTAT SETPOINTS (BY REGION-FACILITY-SCHEDULE TYPE)
FIGURE 21: INDIVIDUAL SITE UNOCCUPIED THERMOSTAT SETPOINTS IN BLACK (BY REGION-FACILITY-SCHEDULE TYPE)
55
60
65
70
75
80
85
90
95
100
Tem
pe
ratu
re [F
]
Data Point Avg. Setpoint Error Bars Denote One Standard Error of the Mean
D = Daily, M = Manual, W = WeeklyN = northern CA, S = southern CA
55
60
65
70
75
80
85
90
95
100
Tem
pe
ratu
re [F
]
Data Point Avg. Setpoint Error Bars Denote One Standard Error of the Mean
D=Daily, M=Manual, W=Weekly
N = northern CA, S = southern CA
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 28
Design & Engineering Services December 2012
DISCUSSION
The survey results indicated that the supply fans ran continuously of 40% of packaged RTUs
serving commercial buildings. The other 60% cycled with calls for cooling or heating. In
one-third of the surveyed units, the supply fan operated continuously during unoccupied
hours, another 36% of the fans cycled during unoccupied hours, and the remainder of the
fans were set to off. While these proportions varied by building type, the sample sizes for
each building type were not sufficiently large to make more detailed conclusions.
Measured supply fan power in this survey was slightly lower than results from previous
studies. Table 10 compares the results of this study with those of previous works. Direct-
drive supply fans were found to have a lower demand per nominal ton than belt-drive
supply fans. However, direct-drive fans were not observed in RTUs above 5 tons nominal
capacity.
TABLE 10: SUPPLY FAN POWER DENSITY
STUDY FAN POWER DENSITY (KW/NOMINAL TON)
SCE Survey 0.15
Bonneville Power Administration RTU Pilot Servicing Program 0.18
CEC Small HVAC System Design Guide 0.18
Observations from the field survey team provide additional insights into how commercial
building owners and occupants interact with their RTU. The surveyed sites include a range
of building occupants including restaurant franchises, owner-occupied commercial sites,
tenant-occupied sites, and public buildings. The best-maintained and operated RTUs tended
to be those owned by a city, public entity, or larger organizations that have an institutional
focus on maintenance, as well as the financial allocation in the budget for regular upkeep.
Typically, the larger commercial sites need to manage and regularly schedule RTU
maintenance because of the sheer number of the systems and all the potential issues that
can arise. These larger operations also tended to control and monitor unit operation
remotely through building management systems and are therefore were better equipped to
quickly identify and fix performance problems. Among owner-occupied establishments,
there was a perceived wide range of understanding about how the RTU is controlled and
maintained. Some people were very much in tune with both the RTU and control settings,
while others were not. For the tenant-occupied establishments, the landlord or property
management company generally handles maintenance issues and the tenants often have
little knowledge about the process. The feedback from the field suggests that some
landlords seem to monitor and maintain RTUs regularly, while others only fix issues when
there are significant complaints from the employees or clientele. In the latter category,
some of the RTUs on older buildings had been repaired repeatedly to the point of being
barely serviceable.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 29
Design & Engineering Services December 2012
A fair number of people interviewed on-site were not aware how the thermostats in their
establishment were set up. This was most true for tenant-occupied buildings. Examples
included verbal reporting of fan settings or cooling setpoints that didn’t match reality, e.g.
employees stating the fan is set to Auto not On, and the fan setting (on the thermostat) was
found to be set to On. Another example was one employee would state that the system is
not programmed, while a second employee stated that the system does have a program.
Despite seeing a large number of newer, programmable thermostats, most were not
programmed at all or were programmed incorrectly. In many of these cases it looked as
though someone had tried programming the thermostat but either gave up or decided to
run the system manually. Among the smaller business establishments surveyed, the
majority used their thermostats as on/off switches, turning them to Auto when they started
to feel warm (often around 12-1 PM) and then switching them to Off at the end of the
business day.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 30
Design & Engineering Services December 2012
CONCLUSIONS
Survey results indicated that the supply fans ran continuously during building occupancy at
about 40% of the surveyed RTUs. The other 60% cycled with calls for cooling or heating. In
a third of the surveyed units, the supply fan also operated continuously during unoccupied
hours, with another 36% of the fans cycling during unoccupied hours. During occupied
periods, the SCE survey data is consistent with the CEUS data, with a slightly greater
weighting of supply fan cycling operation relative to continuous fan operation. During
unoccupied periods, the SCE data indicate a much greater occurrence of continuous fan
operation relative to the CEUS data (32.1% vs. 9.3%). Cycling fan operation was found in
36.3% of the surveys, which is slightly lower than the combined “cycles” and “Night cycles”
data from the CEUS study. Relative to the BPA study results, the SCE findings show much
less continuous fan operation during occupancy, and 30% “fan off” during unoccupied
periods relative to zero observed operation in the BPA study.
The measured supply fan power in the SCE survey was slightly lower than results from the
previous BPA and CEC studies. Additionally, the SCE survey results found that direct-drive
supply fans were found to have a lower demand per nominal ton than belt-drive supply
fans. This area may warrant further study.
The survey found programmable thermostats or EMS at a majority of the RTUs, which
provides the opportunity for features like programmed operation and night setback
operation. However, lack of understanding of these controls resulted in bypassing these
opportunities. Better awareness could result in better comfort levels in the conditioned
spaces as well as lower energy consumption.
Based upon the observations made during this survey, RTU supply fan energy efficiency
measures should not assume a continuous fan operation during occupied hours. This
assumption would result in calculated energy savings higher than actual results.
Calculations of fan energy savings should assume that the fan is operating when there is a
call for heating or cooling in addition to supply fan operating hours run independent of
compressor operation, which varies highly throughout the sample.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 31
Design & Engineering Services December 2012
REFERENCES
[1] Itron, Inc., "California Commercial End-Use Survey," California Energy Commission, Sacramento, 2006.
[2] California Energy Commission, "2008 Building Energy Efficiency Standards," December 2008. [Online].
Available: http://www.energy.ca.gov/title24/2008publications/CEC-400-2008-003/CEC-400-2008-003-
CMF.PDF. [Accessed 21 October 2012].
[3] California Energy Commission, "Past Building Energy Efficency Standards," 26 July 1978. [Online]. Available:
http://www.energy.ca.gov/title24/standards_archive/1978_standards/CEC-400-1978-001.PDF. [Accessed 31
October 2012].
[4] Northwest Council, "BPA Rooftop Unit Pilot Servicing Program," 2010.
[5] AHRI, "http://www.ahrinet.org/," October 2011. [Online]. Available:
http://www.ahrinet.org/App_Content/ahri/files/standards%20pdfs/ANSI%20standards%20pdfs/ANSI%20AHRI
%20Standard%20340-360-2007%20with%20Addenda%201%20and%202.pdf.. [Accessed 21 October 2012].
[6] Itron, Inc., "California Commercial End-Use Survey," California Energy Commission, Sacramento, 2003.
[7] Architectural Energy Corporation, "Small HVAC System Design Guide," California Energy Commission,
Sacramento, 2003.
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 32
Design & Engineering Services December 2012
APPENDIX A: SURVEY DATA COLLECTION FORM
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 33
Design & Engineering Services December 2012
Survey Site Business Name
Survey Site ID # (DDMM-X)
Survey Site Contact Name
Survey Site Contact Phone
Facility Type (Take photo of
exterior)
Circle One: School (room), (office) or (public area);
Small office (office space), (public area);
Retail (sales area), (office);
Convenience Store;
Restaurant;
Health Care;
Warehouse;
Other (describe)
~ Age of Building & RTU Bldg RTU (estimate, if possible)
Normal Business hours (circle
days)
Open from: to: On Days: M T W R F S S
Open from: to: On Days: M T W R F S S
Open from: to: On Days: M T W R F S S
RTU Programmed Operation 24 hour, time-clock, building management system
Fan Control Mode On or Auto
Programmed Cooling Setpoint
Temperature (enter time period,
days of week, and temperature
setting during unoccupied
periods)
Temp from: to: Days: UnOcc T:
Thermostat Manufacturer (Take Photo of Thermostat)
Thermostat Model #
Any comfort or IAQ complaints?
RTU service interval (if
information available)
Select from: Only when problems; annual service; monthly
service; or _______ times per year
Photo Checklist Outside Front___ Interior Space ___ Thermostat___
Interior Exposed Ductwork ____
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 34
Design & Engineering Services December 2012
Assess whether site contact seems amenable to future energy efficiency projects
( Yes / No / Uncertain )
RTU Make (Photo of RTU)
RTU Model #
Refrigerant type (nameplate)
Condenser coil configuration Circle those that apply: 1 sided, 2 sided, 3 sided, 4 sided, flat
or “V”
Economizer installed? (Photo of economizer)
If yes, comment on condition Does economizer appear to be operational?
Number of compressors
Supply Fan nominal hp (nameplate)
Supply fan drive Select from: belt drive, direct drive, VFD option
Photo Checklist RTU(s)– capture condenser coil views___ Economizer___
Compressors ___ Exposed Rooftop Ductwork ____
Field Measurements
Supply fan Watts Watts or kW
Supply fan amps Amps
Supply fan voltage & phase
(single, 3)
Volts, phase
Field Survey of RTU Fan Efficiency and Operation Patterns HT.11.SCE.020
Southern California Edison Page 35
Design & Engineering Services December 2012
APPENDIX B: SURVEY DATA BY SITE
Appendix B.pdf
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