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Celeste Cizik, P.E.Project ManagerE M C Engineers, Inc.
Tips and Tricks for
Estimating Energy Savings
Learning Objectives
1. Understand the pros and cons of various energy calculation
approaches.
2. Learn how to use trend data and utility bills to match calculations
with actual operation.
3. Learn the issues, errors, and limitations associated with
spreadsheet calculations.
4. Get tips on estimating savings for common RCx measures.
AIA Quality Assurance
Getting Started with Analysis
Overview of steps so far:
• Utility Analysis
• Field Survey and Data Collection
• Data Trending and Analysis
• Identification of Measures
• Analyze Energy and Cost Savings
Getting Started with Analysis
Defining the scope - Match the effort and detail with project requirements
• Expense of implementation, economic evaluation
• Potential rebates and program requirements
• Performance guarantees
• Client expectations
Getting Started with Analysis
Putting savings in perspective
• Project potential savings – base on total utility bill
• Energy Conservation Measure potential savings – base on total equipment energy use
• Spending $1,000 in consulting fees to save $100 in energy costs
Getting Started with Analysis
Degree Day Calculations
• Simplified form of historical weather data
• Heating Degree Days (HDD), Cooling Degree Days (CDD)
○How much (in degrees), and for how long (in days), the outside temperature was below (or above) the base temperature.
○Base temp - 65F typical, varies with building properties and internal loads (building “balance point”)
○Source for degree day data: http://www.degreedays.net/
Degree Day Calculations
Applications
• Monitoring and targeting energy consumption
• Rough calculation for energy savings
○Efficiency improvements
○Changes in heat transfer (envelope properties)
○Temperature setpoint adjustments
○Not applicable for most EBCx measures
Degree Day Calculations
Weather normalization - Monitoring
• Like-for-like energy comparison – different periods or places
• Is there really savings?
Average degree days: 2,027
Year
Total energy
consumption
(kWh/yr.)
Total heating
degree days/yr
kWh per
degree day
Normalized
kWh/yr (Avg
Deg Days)
2005 175,441 2,075 84.5 171,383
2006 164,312 1,929 85.2 172,660
% Difference: 6% % Difference: -1%
Degree Day Calculations
• Weekly or monthly energy data from past 1-2 yrs, corresponding degree days
• Linear regression of energy consumption
• New set of degree
days, what is the
expected energy use?
Weather normalization - Targeting
Degree Day Calculations
Advantages
• Easy to get, easy to work with – basic equations
• Good for normalization
Disadvantages
• Approximate calculations
○Base temperature varies - internal gains, setpoints
○Assumes 24/7 operation, only heating or cooling at any given time, no detailed control
• Not good basis for most EBCx energy savings measures
Disaggregation and Percent Savings
Overview
• Annual utility data
• Allocate energy use and demand
○Power measurements, trend data or estimates and hours of operation
○Commercial Buildings Energy Consumption Survey (CBECS): http://www.eia.doe.gov/emeu/cbecs/
Disaggregation and Percent Savings
Benchmarking overall energy use
• Benchmark performance with EnergyStar (or other source), check against CBECS categories
Disaggregation and Percent Savings
Energy Disaggregation
• Measured or estimated equipment demand (kW, btuh) and operating hours per year
• Check against CBECS
Disaggregation and Percent Savings
• Estimate % savings for equipment – overall energy savings
Equipment
% of
Total
Demand Pk kW
Demand
Cost
($/month)
% of
Total
Energy Total kWh
Annual
Energy Cost
($/yr)
%
Savings
kWh
Savings $ Savings
Fans 22% 30 463$ 20% 179,400 6,346$ 35% 62,790 4,165$
Mech Cooling 30% 41 631$ 16% 143,520 5,076$ 25% 35,880 3,162$
Heating 0% - -$ 0% - -$ 0% 0 -$
Lighting 22% 30 463$ 26% 233,220 8,249$ 15% 34,983 2,070$
Kitchen 0% - -$ 0% - -$ 0% 0 -$
Pumps 10% 14 210$ 10% 89,700 3,173$ 15% 13,455 855$
Plug Loads 10% 14 210$ 18% 161,460 5,711$ 5% 8,073 412$
Misc 6% 8 126$ 10% 89,700 3,173$ 5% 4,485 234$
100% 138 2,104$ 100% 897,000 31,728$ 159,666 10,898$
% Savings: 18% 19%
Disaggregation and Percent Savings
• Estimate % savings by measure
• Example - Chilled Water Plant Run Time Reduction, Hawaii State Capitol Building
Disaggregation and Percent Savings
• Chilled Water Plant Run Time Reduction
Energy Savings: 418,885 kwh/yr
Honolulu Electricity Cost: 0.2340$ $/kWh
Energy Cost Savings: 98,019$ $/Yr
Chilled water plant run time baseline: 6,300 hrs
Proposed: 2,860 hrs
% Hours Reduction: 55%
Electric - Demand Savings Electric - Energy Savings
Equip.
Allocated
Demand
(kW)
Estimated
% Demand
Savings
Demand
Savings
(kW)
Allocated
Energy Use
(kWh/ yr)
Estimated
% Energy
Savings
Elec
Energy
Savings
(kWh/Yr)
Measure #1 - Reduce Chilled Water Plant Run Time
Chillers 250 0% 0.0 938,413 35% 328,445
CHW Pumps 31.0 0% 0.0 164,438 55% 90,441
0.0 1,102,851 38% 418,885
Disaggregation and Percent Savings
Fast Savings Estimates: Energy Management Handbook, Turner and Doty
• Chilled water/condenser water temperature reset:
1-1.5% chiller energy (kW/ton) reduction per degree the chilled water temperature is raised or condenser water temperature is lowered
• Night setback: 1% savings per degree of setback, if kept there for at least 8 hours.
• Occupied setpoint adjustment: 2% savings per degree of setback for continuous operation
• Heating Water System Lockout: 30% gas savings compared with boilers idling all summer
Disaggregation and Percent Savings
Advantages• Good starting point for savings in general
• Gets within range of savings with limited effort
• Utility bill basis keeps estimates in check
• Works for projects/measures with:
○ Limited savings justification requirements
○ Low cost implementation, fast payback
○ Phased approach – rough estimate then detail
Disaggregation and Percent Savings
Disadvantages• Rough estimates
• No detail on specific equipment operation or measure interaction
• Often not acceptable for utility EBCx rebate programs
• Takes experience to appropriately disaggregate energy and assign appropriate savings
Weather Bin Calculations
• Common approach for EBCx analysis
○Detailed equipment control can be analyzed
○Not extensive effort
• Column by column calculations for equipment load at each temperature bin
• Hours in each bin used to get energy use and savings (Bin hour source: http://www.interenergysoftware.com/)
System Temps and Airflow
Dry Bulb
Bin (F)
Bin
Hours
Average
Zone
Temp (F)
Core Total
Zone Load1
(Btuh)
Perimeter
Total Zone
Load1
(Btuh)
Core Zone
Airflow
(CFM)
Perimeter
Zone
Airflow
(CFM)
Total
Airflow
(CFM)
Core Zone
Supply Air
Temp (F)
Perimeter
Zone
Supply Air
Temp (F)
(1)
Fixed
Mixed
Temp (F)
Mixed
Air Temp
Used (F)
Outside
Airflow
(CFM)
Outside
Airflow
(%)
Cooling
Total
Sensible
Load
(Btuh)
Cooling
kW
Heating
Total
Load
(Btuh)
99 1 72.0 (56,512) (28,256) 4,500 2,250 6,750 57.8 57.8 74.7 74.7 675 10% (100,940) 9.25 -
97 6 72.0 (53,845) (26,923) 4,500 2,250 6,750 58.5 58.5 74.5 74.5 675 10% (95,742) 8.78 -
95 10 72.0 (51,179) (25,589) 4,500 2,250 6,750 59.2 59.2 74.3 74.3 675 10% (90,544) 8.30 -
93 23 72.0 (48,512) (24,256) 4,500 2,250 6,750 59.9 59.9 74.1 74.1 675 10% (85,346) 7.82 -
91 64 72.0 (45,845) (22,923) 4,500 2,250 6,750 60.5 60.5 73.9 73.9 675 10% (80,148) 7.35 -
89 41 72.0 (43,179) (21,589) 4,500 2,250 6,750 61.2 61.2 73.7 73.7 675 10% (74,950) 6.87 -
87 70 72.0 (40,512) (20,256) 4,500 2,250 6,750 61.9 61.9 73.5 73.5 675 10% (69,753) 6.39 -
85 110 72.0 (37,845) (18,923) 4,500 2,250 6,750 62.5 62.5 73.3 73.3 675 10% (64,555) 5.92 -
83 103 72.0 (35,179) (17,589) 4,500 2,250 6,750 63.2 63.2 73.1 73.1 675 10% (59,357) 5.44 -
81 123 72.0 (32,512) (16,256) 4,500 2,250 6,750 63.9 63.9 72.9 72.9 675 10% (54,159) 4.96 -
79 148 72.0 (29,845) (14,923) 4,500 2,250 6,750 64.5 64.5 72.7 72.7 675 10% (48,961) 4.49 -
Bin Inputs OSA Damper Control Energy Totals
Weather Bin Calculations
Trend data regression• Correlate parameter with
outside air temperature
○ Fan, pump, chiller power
○ System temperatures –air/water supply and return, mixed air
• Use correlation equations in bin calculations
○ Y=mX+B
○ Parameter =slope*(OAT)+y-intercept
R2 = 1: Perfect Correlation
Beware of using relationships that don’t correlate
Weather Bin Calculations
Documented correlations• Fan/pump power vs. % flow (not
just fan/pump laws)○ ASHRAE 90.1 curves
○ DOE-2 curves
○ Manufacturer’s Data
• Use correlations for measures affecting motor variation and power○ Adjust min or operating % flow
○ Correct VFD operation
○ Adjust/reset static pressure setpoint
○ Reduce loads
Fan Curve Constants - ASHRAE Standard 90.1-1989 User's Manual
A B C
Min
Turndown
AFor BI Inlet Guide Vanes 0.584345 (0.579167) 0.970238 30%
AF or BI riding curve 0.227143 1.178929 (0.410714) 45%
Constant Volume 1.000000 0.000000 0.000000 100%
FC riding curve 0.190667 0.310000 0.500000 10%
FC Inlet Guide Vanes 0.339619 (0.848139) 1.495671 20%
Variable Speed Drive 0.219762 (0.874784) 1.652597 10%
Vane Axial Variable Pitch Blades 0.212048 (0.569286) 1.345238 20%
% Fan Power = A + B * %CFM + C * %CFM^2
Weather Bin Calculations
Documented correlations• Boiler and chiller efficiency vs. % load or operating
temperatures ○ Varies with chiller type
○ DOE-2 curves
○ Manufacturer’s data (hard to get)
• Measures affecting efficiency or part load○ Chilled water/condenser water setpoint adjust/reset, load reductions
DOE-2 Performance Curves - Centrifugal Chiller
Constant CHWT CHWT^2 CWT CWT^2 CHWT*CWT
1 45 2025 85 7225 3825
a b c d e f
Capacity Correction CAPCOR1_* -0.49737 -0.00956 -0.00060 0.04352 -0.00058 0.00096 1.02
Performance Correction (Temp) PERCOR1_T_* 1.15362 -0.03068 0.00031 0.00671 0.00005 -0.00009 0.99
PLR - % of total load Constant PLR PLR^2 ∆T ∆T^2 PLR*∆T
∆ T - delta between CHWT and CWT 1 1.00 1.00 40 1,600 40
Performance Correction (PLR) PERCOR1_P_* 0.2797 0.5738 0.2569 -0.0058 0.0001 -0.0035 0.97
Capacity/Temp Performance Correction (%) = a + b*CHWT + c*CHWT2 + d*CWT + e*CWT
2 + f*CHWT*CWT
Part Load (PLR) Performance Correction (%) = a + b*PLR + c*PLR2 + d*∆T + e*∆T
2 + f*PLR*∆T
Weather Bin Calculations
EXAMPLE – Optimize Economizer Operation
• 53,000 sq.ft. office building in Denver
• Occupied 3,380 hours/yr. (7am-8pm M-F)
• Outside damper control broken - fixed at 10% of 43,000 CFM (constant volume)
• Chiller operating year round
Weather Bin Calculations
Optimize Economizer Operation – Baseline• All cooling from chiller, no outside air free cooling
• Outside air measures good for weather bin calcs
Bin Temps and System Calculations Baseline Calculations
Baseline Load Calculations
Dry Bulb
Bin
Zone
Temp Air Flow
Air Flow
Fraction
Supply Air
Setpoint
OSA %
Min, No
Airflow
Mon.
OSA
Fraction
Used
MAT
With
OSA
%Used
Supply
Air
Temp
Actual
Unit
Heat/Cool
Load
Unit
Heating
Load
Unit
Cooling
Load
Cooling
Input
(F) (F) (cfm) (%) (F) (%) (%) (F) (F) (Btuh) (Btuh) (Btuh) (kW)
45 72.0 43,000 100% 55 10% 10% 69 55 (545,630) - (545,630) 31.83
47 72.0 43,000 100% 55 10% 10% 70 55 (553,261) - (553,261) 32.27
49 72.0 43,000 100% 55 10% 10% 70 55 (560,892) - (560,892) 32.72
51 72.0 43,000 100% 55 10% 10% 70 55 (568,524) - (568,524) 33.16
53 72.0 43,000 100% 55 10% 10% 70 55 (576,155) - (576,155) 33.61
55 72.0 43,000 100% 55 10% 10% 70 55 (583,786) - (583,786) 34.05
57 72.0 43,000 100% 55 10% 10% 71 55 (591,417) - (591,417) 34.50
59 72.0 43,000 100% 55 10% 10% 71 55 (599,048) - (599,048) 34.94
61 72.0 43,000 100% 55 10% 10% 71 55 (606,680) - (606,680) 35.39
63 72.0 43,000 100% 55 10% 10% 71 55 (614,311) - (614,311) 35.83
65 72.0 43,000 100% 55 10% 10% 71 55 (621,942) - (621,942) 36.28
67 72.0 43,000 100% 55 10% 10% 72 55 (629,573) - (629,573) 36.73
69 72.0 43,000 100% 55 10% 10% 72 55 (637,204) - (637,204) 37.17
71 72.0 43,000 100% 55 10% 10% 72 55 (644,836) - (644,836) 37.62
General Inputs
Weather Bin Calculations
Optimize Economizer Operation – Proposed• Reduced cooling - zone temp to supply air temp
• No mechanical cooling below supply air temperatureBin Temps and System Calculations Proposed System Calculations
Proposed Load Calculations
Dry Bulb
Bin
Zone
Temp Air Flow
Air Flow
Fraction
Supply Air
Setpoint
OSA %
Min No
Airflow
Mon.
OSA
Fraction
Used
MAT
With OSA
%Used
Supply Air
Temp
Actual
Unit
Heat/Cool
Load
Unit
Heating
Load
Unit
Cooling
Load
Cooling
Input
(F) (F) (cfm) (%) (F) (%) (%) (F) (F) (Btuh) (Btuh) (Btuh) (kW)
45 72.0 43,000 100% 55 10% 63% 55 55 - - - -
47 72.0 43,000 100% 55 10% 68% 55 55 - - - -
49 72.0 43,000 100% 55 10% 74% 55 55 - - - -
51 72.0 43,000 100% 55 10% 81% 55 55 - - - -
53 72.0 43,000 100% 55 10% 89% 55 55 - - - -
55 72.0 43,000 100% 55 10% 100% 55 55 - - - -
57 72.0 43,000 100% 55 10% 100% 57 55 (76,312) - (76,312) 4.45
59 72.0 43,000 100% 55 10% 100% 59 55 (152,624) - (152,624) 8.90
61 72.0 43,000 100% 55 10% 100% 61 55 (228,936) - (228,936) 13.35
63 72.0 43,000 100% 55 10% 100% 63 55 (305,248) - (305,248) 17.81
65 72.0 43,000 100% 55 10% 100% 65 55 (381,560) - (381,560) 22.26
67 72.0 43,000 100% 55 10% 100% 67 55 (457,871) - (457,871) 26.71
69 72.0 43,000 100% 55 10% 100% 69 55 (534,183) - (534,183) 31.16
71 72.0 43,000 100% 55 10% 10% 72 55 (644,836) - (644,836) 37.62
General Inputs
Weather Bin Calculations
Optimize Economizer Operation - Results
• Savings of 69,604 kWh/yr; 61% reduction in cooling energy
• Cost savings of $2,840/yr. (cooling energy and winter demand)
• Considerations for economizer measure:
o Match mixed air temperature setpoint with supply air temperature setpoint
o Possible humidity concerns above 55F OAT
Weather Bin Calculations
Checks and errors• Use utility data and disaggregation to check savings
• Consider measure interaction – stack proposed changes and/or use factors
• Beware ERRORS
○Most spreadsheets have errors – check carefully
○Organized, labeled inputs and equations, named cells –no hard coded values in equations
○Calculation templates
Legend
Input
ECM Parameter
Pasted Value
Calculated/Output
Equations Used: Eq 1a Eq 1b Eq 1c Eq 1d Eq 1e Eq 1f Eq 1g
Load Model
Dry Bulb
Temp
Wet Bulb
Temp RH
Day of
Week
Ambient
Enthalpy
Internal
Cooling
Load
Envelope
Cooling
Load
Cooling
System
Flag
Cooling
Load
Cooling
Load
Fraction
Load
Delta-T
(2-way
Valves)
F F % Btu/lbm tons tons ON=1 tons
68.0 66.0 90 2 30.7 106 0 0 0 0% 2.5
68.0 65.3 87 2 30.2 106 0 0 0 0% 2.5
Weather Bin Calculations
Advantages• System level detailed calculations with operating
parameters
• General accuracy around 20%, improves with higher outside air correlation
• Flexible, usable for most EBCx measures
• Accepted by utility EBCx rebate programs
• Manageable effort – less time than hourly spreadsheet or energy model
Weather Bin Calculations
Disadvantages• Loads and energy have to vary with outside
air dry bulb temperature only
○ Assumes constant internal gains – multiple bin models may be needed
○Humidity/solar loads can’t vary independently – not good for mild humid climates or solar driven loads
• Load response not well captured
• No exact time of day peaks
8,760 Hourly Models
Spreadsheet hourly models - Advantages• Similar to bin model, all hours of the year
• Multiple schedules possible – internal loads, equipment operation, setpoints, etc.
• Humidity, solar loads can be included – better for mild humid climates
• Actual time of day peaks
8,760 Hourly Models
Spreadsheet hourly models - Disadvantages
• Time consuming to create – more inputs and calculations
• Difficult to verify calculations with 8,760 lines –more errors, need charts to check
-
100
200
300
400
500
600
700
800
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
Po
we
r (k
W)
and
Lo
ad (
Ton
s)
Te
mp
era
ture
(d
eg
F)
Date/Time
MODEL - System Temperatures, Power, and Load
Dry Bulb Temp Chilled Water Supply Temp Chilled Water Return Temp
Condenser Water Supply Temp RH Total Chiller Load
All Chillers Power Evaporator Pumps Power Cooling Tower Fans Power
Condenser Pumps Power
8,760 Hourly Models
Full Building Energy Model (DOE-2/EQuest, Energy
Plus, etc.) – Advantages
• Detailed and accurate load modeling
• Allows measure interaction
• Can be used for ongoing Cx – expected operating correlations (kWh relative to cooling degree days)
Weekly Building kWh Versus Cooling Degree-Days
20000
22000
24000
26000
28000
30000
32000
34000
36000
38000
40000
10 30 50 70 90 110 130 150
Cooling Degree Days
We
ek
ly B
uil
din
g k
Wh
Deviant Operation
Projected Normal Operation
Museum of Space History, Alamogordo, NM
8,760 Hourly Models
Full Building Energy Model - Disadvantages
• Detailed building envelope and equipment inputs –not analysis of one system
• Difficult to calibrate to utility bills
• Not as flexible – designed for systems that work
• Most time consuming option, beyond typical EBCx
Museum of Natural History, Albuquerque, NM
Summary Statements
Key Tips
• Select appropriate calculation approach –match the effort with requirements
• Use utility bills and disaggregation for benchmarking and savings estimates/limits
• Incorporate operating characteristics and correlations
• Stay careful and organized, beware of ERRORS
• Be creative and continue to save energy and reduce operating costs!
AIA Quality Assurance
Portland Energy Conservation, Inc is a registered provider with The American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members are available on request.
This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
Thank You!
Celeste Cizik, P.E.
ccizik@emcengineers.com
303-974-1200
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