Tips and Tricks for Estimating Energy Savings. Celeste Cizik, P.E. Project Manager E M C Engineers, Inc.

Transcription

1 Tips and Tricks for Estimating Energy Savings Celeste Cizik, P.E. Project Manager E M C Engineers, Inc.

2 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.

3 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

4 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

5 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

6 Getting Started with Analysis

7 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:

8 Applications Degree Day Calculations 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

9 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) ,441 2, , ,312 1, ,660 % Difference: 6% % Difference: -1%

10 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 Weather normalization - Targeting

11 Advantages Degree Day Calculations 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

12 Overview Disaggregation and Percent Savings Annual utility data Allocate energy use and demand Power measurements, trend data or estimates and hours of operation Commercial Buildings Energy Consumption Survey (CBECS): emeu/cbecs/

13 Disaggregation and Percent Savings Benchmarking overall energy use Benchmark performance with EnergyStar (or other source), check against CBECS categories

14 Disaggregation and Percent Savings Energy Disaggregation Measured or estimated equipment demand (kw, btuh) and operating hours per year Check against CBECS

15 Disaggregation and Percent Savings Estimate % savings for equipment overall energy savings % of Total Demand Cost % of Total Annual Energy Cost % kwh Equipment Demand Pk kw ($/month) Energy Total kwh ($/yr) Savings Savings $ Savings Fans 22% 30 $ % 179,400 $ 6,346 35% 62,790 $ 4,165 Mech Cooling 30% 41 $ % 143,520 $ 5,076 25% 35,880 $ 3,162 Heating 0% - $ - 0% - $ - 0% 0 $ - Lighting 22% 30 $ % 233,220 $ 8,249 15% 34,983 $ 2,070 Kitchen 0% - $ - 0% - $ - 0% 0 $ - Pumps 10% 14 $ % 89,700 $ 3,173 15% 13,455 $ 855 Plug Loads 10% 14 $ % 161,460 $ 5,711 5% 8,073 $ 412 Misc 6% 8 $ % 89,700 $ 3,173 5% 4,485 $ % 138 $ 2, % 897,000 $ 31, ,666 $ 10,898 % Savings: 18% 19%

16 Disaggregation and Percent Savings Estimate % savings by measure Example - Chilled Water Plant Run Time Reduction, Hawaii State Capitol Building

17 Disaggregation and Percent Savings Chilled Water Plant Run Time Reduction Equip. Chilled water plant run time baseline: 6,300 hrs Proposed: 2,860 hrs % Hours Reduction: 55% Electric - Demand Savings Allocated Demand (kw) Estimated % Demand Savings Demand Savings (kw) Electric - Energy Savings Allocated Energy Use (kwh/ yr) Estimated % Energy Savings Energy Savings: 418,885 kwh/yr Honolulu Electricity Cost: $ $/kwh Energy Cost Savings: $ 98,019 $/Yr Elec Energy Savings (kwh/yr) Measure #1- Reduce Chilled Water Plant Run Time Chillers 250 0% ,413 35% 328,445 CHW Pumps % ,438 55% 90, ,102,851 38% 418,885

18 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

19 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

20 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

21 Dry Bulb Bin (F) 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: Bin Inputs System Temps and Airflow OSA Damper Control Energy Totals Cooling Perimeter Perimeter Perimeter (1) Total Average Core Total Total Zone Core Zone Zone Total Core Zone Zone Fixed Mixed Outside Outside Sensible Bin Zone Zone Load 1 Load 1 Airflow Airflow Airflow Supply Air Supply Air Mixed Air Temp Airflow Airflow Load Cooling Hours Temp (F) (Btuh) (Btuh) (CFM) (CFM) (CFM) Temp (F) Temp (F) Temp (F) Used (F) (CFM) (%) (Btuh) kw (56,512) (28,256) 4,500 2,250 6, % (100,940) (53,845) (26,923) 4,500 2,250 6, % (95,742) (51,179) (25,589) 4,500 2,250 6, % (90,544) (48,512) (24,256) 4,500 2,250 6, % (85,346) (45,845) (22,923) 4,500 2,250 6, % (80,148) (43,179) (21,589) 4,500 2,250 6, % (74,950) (40,512) (20,256) 4,500 2,250 6, % (69,753) (37,845) (18,923) 4,500 2,250 6, % (64,555) (35,179) (17,589) 4,500 2,250 6, % (59,357) (32,512) (16,256) 4,500 2,250 6, % (54,159) (29,845) (14,923) 4,500 2,250 6, % (48,961) Heating Total Load (Btuh)

22 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 R 2 = 1: Perfect Correlation Beware of using relationships that don t correlate

23 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 User's Manual A B C Min Turndown AFor BI Inlet Guide Vanes ( ) % AF or BI riding curve ( ) 45% Constant Volume % FC riding curve % FC Inlet Guide Vanes ( ) % Variable Speed Drive ( ) % Vane Axial Variable Pitch Blades ( ) % % Fan Power = A + B *%CFM + C *%CFM^2

24 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 a b c d e f Capacity Correction CAPCOR1_* Performance Correction (Temp) PERCOR1_T_* PLR - % of total load Constant PLR PLR^2 T T^2 PLR* T T - delta between CHWT and CWT , Performance Correction (PLR) PERCOR1_P_* Capacity/Temp Performance Correction (%) = a + b*chwt + c*chwt 2 + d*cwt + e*cwt 2 + f*chwt*cwt Part Load (PLR) Performance Correction (%) = a + b*plr + c*plr 2 + d* T + e* T 2 + f*plr* T

25 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

26 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 Baseline Load Calculations Baseline Calculations Dry Bulb Bin 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 Zone Air Flow Supply Air Cooling Temp Air Flow Fraction Setpoint Input (F) (F) (cfm) (%) (F) (%) (%) (F) (F) (Btuh) (Btuh) (Btuh) (kw) , % 55 10% 10% (545,630) - (545,630) , % 55 10% 10% (553,261) - (553,261) , % 55 10% 10% (560,892) - (560,892) , % 55 10% 10% (568,524) - (568,524) , % 55 10% 10% (576,155) - (576,155) , % 55 10% 10% (583,786) - (583,786) , % 55 10% 10% (591,417) - (591,417) , % 55 10% 10% (599,048) - (599,048) , % 55 10% 10% (606,680) - (606,680) , % 55 10% 10% (614,311) - (614,311) , % 55 10% 10% (621,942) - (621,942) , % 55 10% 10% (629,573) - (629,573) , % 55 10% 10% (637,204) - (637,204) , % 55 10% 10% (644,836) - (644,836) 37.62

27 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 Proposed System Calculations Proposed Load Calculations Dry Bulb Bin 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 Zone Air Flow Supply Air Cooling Temp Air Flow Fraction Setpoint Input (F) (F) (cfm) (%) (F) (%) (%) (F) (F) (Btuh) (Btuh) (Btuh) (kw) , % 55 10% 63% , % 55 10% 68% , % 55 10% 74% , % 55 10% 81% , % 55 10% 89% , % 55 10% 100% , % 55 10% 100% (76,312) - (76,312) , % 55 10% 100% (152,624) - (152,624) , % 55 10% 100% (228,936) - (228,936) , % 55 10% 100% (305,248) - (305,248) , % 55 10% 100% (381,560) - (381,560) , % 55 10% 100% (457,871) - (457,871) , % 55 10% 100% (534,183) - (534,183) , % 55 10% 10% (644,836) - (644,836) 37.62

28 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

29 Checks and errors Weather Bin Calculations 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 Dry Bulb Wet Bulb Temp Temp Equations Used: Eq 1a Eq 1b Eq 1c Eq 1d Eq 1e Eq 1f Eq 1g Load Model Internal Cooling Load Envelope Cooling Load Cooling System Flag Cooling Load Fraction Load Delta-T (2-way Valves) Day of Ambient Cooling RH Week Enthalpy Load F F % Btu/lbm tons tons ON=1 tons % % 2.5

30 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

31 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

32 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

33 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 Temperature (deg F) Power (kw) and Load (Tons) Date/Time 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

34 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 Museum of Space History, Alamogordo, NM Weekly Building kwh Deviant Operation Cooling Degree Days Projected Normal Operation

35 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

36 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!

37 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.

38 Thank You! Celeste Cizik, P.E