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Heat Pump Water Heater Modelingin EnergyPlusBuilding America Residential EnergyEfficiency Stakeholder MeetingEric WilsonCraig ChristensenMarch 1, 2012NREL/PR-5500-54318NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Heat Pump Water Heater Modeling MotivationModelingIssuesResults2

Photos by Kate Hudon, NREL/PIX 18675, NREL/PIX 18671, NREL/PIX 18667,NREL/PIX 18676, and NREL/PIX 18919Gap: Existing analysis tools cannot accuratelymodel HPWHs with reasonable runtime.3

What have we achieved so far?Field Monitoring14 xPhoto from Steven Winter Associates, Inc.Laboratory EvaluationsPhotos by Kate Hudon, NREL/PIX 18675, NREL/PIX 18671,NREL/PIX 18667, NREL/PIX 18676, and NREL/PIX 189194

Closing the GapField Monitoring14 xPhoto from Steven Winter Associates, Inc.Laboratory Evaluations6 sec timestepPhotos by Kate Hudon, NREL/PIX 18675, NREL/PIX 18671,NREL/PIX 18667, NREL/PIX 18676, and NREL/PIX 18919hourly timestep5

Why is modeling important? Performance varies:Can’t just use EF System interactionooHPWH affects buildingheating and coolingSpace conditionsaffect HPWHperformance6

Modeling Goals Manage RisksAccuracyo Run timeo Occupant satisfactiono Flexibility to explore the effects of:Tank location, volume, setpointo Hot water use patternso HPWH vs. all other measures(optimization)7

Heat Pump Water Heater Modeling MotivationModelingIssuesResults1) Tank Stratification2) Draw Profile3) Performance Maps4) Sizing8

1) Tank StratificationExisting ModelEnergyPlus HPWH mixed tankMixedtankTmains9

1) Tank StratificationExisting ModelEnergyPlus HPWH mixed tankRealistic PerformanceStratified tankMixedtankTmainsStratifiedtankTmains10

1) Tank StratificationExisting ModelEnergyPlus HPWH mixed tankRealistic PerformanceStratified tank1) Colderwater suppliedImplications ofusing a mixedtank model MixedtankStratifiedtank2) warmer coil worse performanceTmainsTmains11

1) Tank StratificationNew ModelTwo tanks in SeriesRealistic PerformanceStratified tankMixedtankTmainsMixedtankStratifiedtankTmains12

2) Draw ProfileExisting ModelSmooth Draw ProfileHourly TimestepHPWH PowerHot Water Use13

2) Draw ProfileExisting ModelSmooth Draw ProfileHourly Timestep14

2) Draw ProfileExisting ModelSmooth Draw ProfileHourly TimestepRealistic PerformanceDiscrete Draw Events6 Second Timestep 4.5 kWIf these draw profiles are used for an annual simulation HPWH EnergyHPWH Energy14 MBtu/yr23 MBtu/yr 1.0 kW15

2) Draw ProfileNew ModelHourly Averaged Discrete DrawsHourly TimestepRealistic PerformanceDiscrete Draw Events6 Second Timestep 4.5 kW 1.0 kW16

2) Draw ProfileNew ModelRealistic PerformanceHourly Averaged Discrete DrawsHourly TimestepDiscrete Draw Events6 Second Timestep 4.5 kWHourly Time SeriesTotal Hot Water Flow Rate (cfm)0.100.080.060.040.020.009101112February131415 1.0 kW17

2) Draw ProfileNew ModelHourly Averaged Discrete DrawsHourly TimestepRealistic PerformanceDiscrete Draw Events6 Second Timestep 4.5 kW(element)With the new model draw profile, annual results match:HPWH EnergyHPWH Energy 23 MBtu/yr23 MBtu/yr 1.0 kW(heat pump)18

3) Performance MapsExisting ModelConstant Performance?Constant Performance?19

3) Performance MapsExisting ModelConstant Performance?Realistic PerformanceManufacturer SpecificMfgr 1Mfgr 2Mfgr 3Constant Performance?(constant 67 F, 50% RH air)20

3) Performance MapsNew ModelGeneric Normalized Performance MapRealistic PerformanceManufacturer Specific(equals 1 at rating point)Mfgr 1Mfgr 2Mfgr 3(constant 67 F, 50% RH air)21

3) Performance MapsNew ModelUse rated values to getspecific performance map:Realistic PerformanceManufacturer SpecificMfgr 1Mfgr 2Mfgr 3(constant 67 F, 50% RH air)22

4) HPWH SizingExisting Model No existing method forHPWH sizingTank Volume (gal)Conventional Electric WH Sizing:706050403020100Range f(# baths)1234# Bedrooms523

4) HPWH SizingExisting ModelRealistic Performance No existing method forHPWH sizingTank Volume (gal)Conventional Electric WH Sizing:706050403020100Range f(# baths)1234# Bedrooms5AprilReduced capacity to meet DHWdemand (vs. conventional WHs)Function of:Climateo # bedroomso Tank Volumeo Setpoint Temperatureo24

4) HPWH SizingNew Model“Percent Unmet Showers”OptionRealistic PerformanceDisplay VariableAprilReduced capacity to meet DHWdemand (vs. conventional WHs)Percent Unmet ShowersFunction of: Function of climate, # bedrooms, tank volume, setpoint Estimate of shower time 110 F Helps users select acceptable options Sensitive to hot water use patterns so will vary fromone set of occupants to the nextClimateo # bedroomso Tank Volumeo Setpoint Temperatureo25

Heat Pump Water Heater Modeling MotivationModelingIssuesResults26

Model CalibrationCalibrated to TRNSYS results 5%12 cases: Chicago, Houston;1, 3, 5 BR;50, 80 gal27

Model CalibrationDaily System COPChicago, 50 galUnfinished BasementDaily Draw Volume (gal/day)28

Model CalibrationDaily System COPChicago, 50 galUnfinished BasementDaily Draw Volume (gal/day)29

Model CalibrationDaily System COPHouston, 50 galGarageDaily Draw Volume (gal/day)30

Model CalibrationDaily System COPHouston, 50 galGarageDaily Draw Volume (gal/day)31

BEoptE Modeling ResultsHPWH vs. Electric ResistanceWith Cooling Impact (Air-Source HP)Model: A-BSetpoint: 120-140 FLocation: Conditioned, Unconditioned32

BEoptE Optimization ResultsSpace Conditioning Air-Source Heat PumpMaximum Energy Savings(state average utility rates,Nat’l avg Source/Site ratio)Lowest Life-Cycle Cost1 BR3 BR5 BR1 BR3 BR5 c/HPElec/HP(“HPWH” includes various models/volumes, locations, and setpoints)Space Conditioning Gas FurnaceMaximum Energy SavingsLowest Life-Cycle Cost1 BR3 BR5 BR1 BR3 BR5 Gas” includes: standard, premium, tankless, or tankless condensing.)33

ConclusionsHPWH model for EnergyPlus/BEopt Market Benefits:ooooIntegrated with existing toolFastFlexibleAccurate34

ConclusionsLessons Learned Rated EF for HPWHs not good indicator of performanceDon’t use “smooth” BA HSP draw profile for HPWH testingControl logic mattersSizing HPWHs for adequate HW delivery: many factorsRemaining Issues Better draw profiles for HPWH modeling/testing Performance in enclosed spaces35

For more information:Laboratory Testing Report:Sparn, B.; Hudon, K.; Christensen, D. (2011). Laboratory Performance Evaluation ofResidential Integrated Heat Pump Water Heaters. 77 pp.; NREL Report No. TP-550052635.TRNSYS Modeling Results:Maguire, J. (2011). A Parametric Analysis of Residential Water Heaters. Master’sThesis. Boulder, CO: University of Colorado.

Hot water use patterns HPWH vs. all other measures (optimization) 8 . Motivation Results . 1) Tank Stratification 2) Draw Profile . 3) Performance Maps . 4) Sizing Modeling Issues . 9 . 1) Tank Stratification . Mixed tank . T. mains. Existing Model . EnergyPlus HPWH mixed tank . Stratified tank . 11 1) Tank Stratification Mixed tank T .