tips and tricks for estimating energy savings - · pdf filetips and tricks for estimating...

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


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


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

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/


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


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%


• 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


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/


Benchmarking overall energy use

• Benchmark performance with EnergyStar (or other source), check against CBECS categories


Energy Disaggregation

• Measured or estimated equipment demand (kW, btuh) and operating hours per year

• Check against CBECS


• 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%


• Estimate % savings by measure

• Example - Chilled Water Plant Run Time Reduction, Hawaii State Capitol Building


• 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


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


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


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


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


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


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


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


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


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


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


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


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


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.

[email protected]

303-974-1200

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