Tips and Tricks for
Estimating Energy Savings
Celeste Cizik, P.E.
Project Manager
E M C Engineers, Inc.
AIA Quality Assurance
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.
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
Total energy
Normalized
consumption Total heating
kWh per
kWh/yr (Avg
Year
(kWh/yr.)
degree days/yr degree day
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
Weather normalization - Targeting
• 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?
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
Fans
Mech Cooling
Heating
Lighting
Kitchen
Pumps
Plug Loads
Misc
% of
Total
Demand
22%
30%
0%
22%
0%
10%
10%
6%
100%
Pk kW
30
41
30
14
14
8
138
Demand
% of
Cost
Total
($/month) Energy
$
463
20%
$
631
16%
$
0%
$
463
26%
$
0%
$
210
10%
$
210
18%
$
126
10%
$ 2,104
100%
Total kWh
179,400
143,520
233,220
89,700
161,460
89,700
897,000
Annual
Energy Cost
($/yr)
$
6,346
$
5,076
$
$
8,249
$
$
3,173
$
5,711
$
3,173
$
31,728
%
Savings
35%
25%
0%
15%
0%
15%
5%
5%
% Savings:
kWh
Savings $ Savings
62,790
35,880
0
34,983
0
13,455
8,073
4,485
159,666
18%
$
$
$
$
$
$
$
$
$
4,165
3,162
2,070
855
412
234
10,898
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
Chilled water plant run time baseline:
Proposed:
% Hours Reduction:
6,300 hrs
2,860 hrs
55%
Electric - Demand Savings
Allocated Estimated Demand
Demand % Demand Savings
(kW)
Savings
(kW)
Equip.
Measure #1 - Reduce Chilled Water Plant Run Time
Chillers
250
0%
0.0
CHW Pumps
31.0
0%
0.0
0.0
Energy Savings:
Honolulu Electricity Cost: $
Energy Cost Savings: $
Electric - Energy Savings
Elec
Allocated Estimated Energy
Energy Use % Energy Savings
(kWh/ yr)
Savings (kWh/Yr)
938,413
164,438
35%
55%
328,445
90,441
1,102,851
38%
418,885
418,885 kwh/yr
0.2340 $/kWh
98,019 $/Yr
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/)
Bin Inputs
Dry Bulb
Bin (F)
99
97
95
93
91
89
87
85
83
81
79
System Temps and Airflow
Bin
Hours
1
6
10
23
64
41
70
110
103
123
148
Perimeter
Average Core Total Total Zone Core Zone
1
1
Zone Zone Load
Load
Airflow
Temp (F) (Btuh)
(Btuh)
(CFM)
72.0
(56,512)
(28,256)
4,500
72.0
(53,845)
(26,923)
4,500
72.0
(51,179)
(25,589)
4,500
72.0
(48,512)
(24,256)
4,500
72.0
(45,845)
(22,923)
4,500
72.0
(43,179)
(21,589)
4,500
72.0
(40,512)
(20,256)
4,500
72.0
(37,845)
(18,923)
4,500
72.0
(35,179)
(17,589)
4,500
72.0
(32,512)
(16,256)
4,500
72.0
(29,845)
(14,923)
4,500
Perimeter
Zone
Airflow
(CFM)
2,250
2,250
2,250
2,250
2,250
2,250
2,250
2,250
2,250
2,250
2,250
OSA Damper Control
(1)
Perimeter
Zone
Fixed
Mixed Outside
Total Core Zone
Airflow Supply Air Supply Air Mixed Air Temp Airflow
(CFM)
Temp (F) Temp (F) Temp (F) Used (F) (CFM)
6,750
57.8
57.8
74.7
74.7
675
6,750
58.5
58.5
74.5
74.5
675
6,750
59.2
59.2
74.3
74.3
675
6,750
59.9
59.9
74.1
74.1
675
6,750
60.5
60.5
73.9
73.9
675
6,750
61.2
61.2
73.7
73.7
675
6,750
61.9
61.9
73.5
73.5
675
6,750
62.5
62.5
73.3
73.3
675
6,750
63.2
63.2
73.1
73.1
675
6,750
63.9
63.9
72.9
72.9
675
6,750
64.5
64.5
72.7
72.7
675
Outside
Airflow
(%)
10%
10%
10%
10%
10%
10%
10%
10%
10%
10%
10%
Energy Totals
Cooling
Total
Heating
Sensible
Total
Load
Cooling
Load
(Btuh)
kW
(Btuh)
(100,940)
9.25
(95,742)
8.78
(90,544)
8.30
(85,346)
7.82
(80,148)
7.35
(74,950)
6.87
(69,753)
6.39
(64,555)
5.92
(59,357)
5.44
(54,159)
4.96
(48,961)
4.49
-
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
AFor BI Inlet Guide Vanes 0.584345
AF or BI riding curve 0.227143
Constant Volume 1.000000
FC riding curve 0.190667
FC Inlet Guide Vanes 0.339619
Variable Speed Drive 0.219762
Vane Axial Variable Pitch Blades 0.212048
% Fan Power = A + B * %CFM + C * %CFM^2
B
(0.579167)
1.178929
0.000000
0.310000
(0.848139)
(0.874784)
(0.569286)
C
0.970238
(0.410714)
0.000000
0.500000
1.495671
1.652597
1.345238
Min
Turndown
30%
45%
100%
10%
20%
10%
20%
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
-0.49737 -0.00956 -0.00060 0.04352 -0.00058
0.00096
CAPCOR1_*
Performance Correction (Temp) PERCOR1_T_* 1.15362 -0.03068 0.00031 0.00671 0.00005
-0.00009
∆T
∆T^2
PLR - % of total load
Constant PLR
PLR^2
PLR*∆T
∆ T - delta between CHWT and CWT
1
1.00
1.00
40
1,600
40
Performance Correction (PLR)
0.2797 0.5738 0.2569 -0.0058 0.0001
-0.0035
PERCOR1_P_*
2
2
1.02
0.99
0.97
Capacity/Temp Performance Correction (%) = a + b*CHWT + c*CHWT + d*CWT + e*CWT + f*CHWT*CWT
Part Load (PLR) Performance Correction (%) = a + b*PLR + c*PLR2 + d*∆ T + e*∆ T2 + 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
General Inputs
Dry Bulb
Bin
(F)
45
47
49
51
53
55
57
59
61
63
65
67
69
71
Zone
Temp
(F)
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
Air Flow
(cfm)
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
Air Flow Supply Air
Fraction
Setpoint
(%)
(F)
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
Baseline Calculations
Baseline Load Calculations
OSA %
MAT Supply
Min, No
OSA
With
Air
Temp
Airflow Fraction OSA
Mon.
Used %Used Actual
(%)
(%)
(F)
(F)
10%
10%
69
55
10%
10%
70
55
10%
10%
70
55
10%
10%
70
55
10%
10%
70
55
10%
10%
70
55
10%
10%
71
55
10%
10%
71
55
10%
10%
71
55
10%
10%
71
55
10%
10%
71
55
10%
10%
72
55
10%
10%
72
55
10%
10%
72
55
Unit
Heat/Cool
Load
(Btuh)
(545,630)
(553,261)
(560,892)
(568,524)
(576,155)
(583,786)
(591,417)
(599,048)
(606,680)
(614,311)
(621,942)
(629,573)
(637,204)
(644,836)
Unit
Heating
Load
(Btuh)
-
Unit
Cooling
Cooling
Load
Input
(Btuh)
(kW)
(545,630)
31.83
(553,261)
32.27
(560,892)
32.72
(568,524)
33.16
(576,155)
33.61
(583,786)
34.05
(591,417)
34.50
(599,048)
34.94
(606,680)
35.39
(614,311)
35.83
(621,942)
36.28
(629,573)
36.73
(637,204)
37.17
(644,836)
37.62
Weather Bin Calculations
Optimize Economizer Operation – Proposed
• Reduced cooling - zone temp to supply air temp
• No mechanical cooling below supply air temperature
Bin Temps and System Calculations
General Inputs
Dry Bulb
Bin
(F)
45
47
49
51
53
55
57
59
61
63
65
67
69
71
Zone
Temp
(F)
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
72.0
Air Flow
(cfm)
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
43,000
Air Flow Supply Air
Fraction Setpoint
(%)
(F)
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
100%
55
Proposed System Calculations
Proposed Load Calculations
OSA %
Min No
OSA
MAT Supply Air
Unit
Airflow Fraction With OSA Temp
Heat/Cool
Mon.
Used
%Used
Actual
Load
(%)
(%)
(F)
(F)
(Btuh)
10%
63%
55
55
10%
68%
55
55
10%
74%
55
55
10%
81%
55
55
10%
89%
55
55
10%
100%
55
55
10%
100%
57
55
(76,312)
10%
100%
59
55
(152,624)
10%
100%
61
55
(228,936)
10%
100%
63
55
(305,248)
10%
100%
65
55
(381,560)
10%
100%
67
55
(457,871)
10%
100%
69
55
(534,183)
10%
10%
72
55
(644,836)
Unit
Heating
Load
(Btuh)
-
Unit
Cooling
Load
(Btuh)
(76,312)
(152,624)
(228,936)
(305,248)
(381,560)
(457,871)
(534,183)
(644,836)
Cooling
Input
(kW)
4.45
8.90
13.35
17.81
22.26
26.71
31.16
37.62
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
Equations Used: Eq 1a
Eq 1b
Eq 1c
Load Model
Eq 1d
Eq 1e
Eq 1f
Eq 1g
Legend
Input
ECM Parameter
Pasted Value
Calculated/Output
Dry Bulb Wet Bulb
Temp
Temp
F
F
68.0
66.0
68.0
65.3
Day of
Week
RH
%
90
87
2
2
Internal Envelope Cooling
Ambient Cooling Cooling System
Enthalpy
Load
Load
Flag
Btu/lbm
tons
tons
ON=1
30.7
106
0
0
30.2
106
0
0
Cooling
Load
tons
0
0
Cooling
Load
Fraction
0%
0%
Load
Delta-T
(2-way
Valves)
2.5
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
MODEL - System Temperatures, Power, and Load
100.0
800
90.0
700
80.0
Temperature (deg F)
500
60.0
50.0
400
40.0
300
30.0
200
20.0
100
10.0
0.0
-
Date/Time
Dry Bulb Temp
Condenser Water Supply Temp
All Chillers Power
Condenser Pumps Power
Chilled Water Supply Temp
RH
Evaporator Pumps Power
Chilled Water Return Temp
Total Chiller Load
Cooling Tower Fans Power
Power (kW) and Load (Tons)
600
70.0
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
40000
Deviant
Operation
Weekly Building kWh
38000
36000
34000
32000
30000
28000
26000
24000
Projected Normal
Operation
22000
Museum of Space History, Alamogordo,
NM
20000
10
30
50
70
90
Cooling Degree Days
110
130
150
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
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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