PG&E Assessment Projects on Heat Pump Water Heaters. Sherry Hu, Ph.D, PE Robert Davis, PE Pacific Gas & Electric May 13, 2010

Transcription

1 PG&E Assessment Projects on Heat Pump Water Heaters Sherry Hu, Ph.D, PE Robert Davis, PE Pacific Gas & Electric May 13, 2010

2 Agenda 1. Introduction of Heat Pump Water Heaters 2. Overview of PG&E Assessment Projects 3. Project 1: Energy Simulation 4. Project 2: Lab Evaluation of AirTap A7 and Rheem HP50 5. Project 3: Lab Evaluation and Field Study of GE GeoSpring Hybrid Water Heater 2

3 Introduction HPWH Operation Typical refrigeration / heap pump cycle Heat Rejected (to the water in a HPWH tank) Condenser Expansion Valve Compressor Evaporator Electric Energy Heat Absorbed (from ambient air) 3

4 Introduction HPWH units Add-on and Integrated HPWHs AirTap 50 Rheem HP50 GE GeoSpring Hybrid 4

5 Introduction Results from Simple Analyses 50 Gal electric residential storage water heater, gas residential storage water Heater, HPWH in a single family home Water Heater Technology Comparison PG&E Weighted Climate Zone, Single Family Home, 50 Gal Water Heater using PG&E E-1 Code H All Electric Rates Water Heater Type Energy Factor Installed Cost Annual Energy Use (kwh/therm) Yearly Energy Cost Retrofit Simple Payback CO2 Emission Electric Resistance Water Heater 0.86 $750 3,581 $772 Baseline Baseline Gas Water Heater 0.57 $ (therm) $ % Rheem Integral HPWH 2.00 $1,600 1,540 $ % Add On HPWH (Retrofit) 2.00 $800 1,540 $ % GE Integral HPWH 2.50 $1,600 1,232 $ % PG&E has app. 5.3 million residential customers and 9% use electrical water heaters. Assuming 10% market penetration, HPWHs can bring 114GWh and 25 MW energy savings, which are app. 10% of PG&E annual energy saving and demand saving goals. 5

6 Overview of PG&E Assessment Projects 1. Energy Simulation Project - Investigated the HPWH performance and interaction with building HVAC operations and assessed overall energy impacts to single family homes. 2. Laboratory evaluation of AirTap A7 and Rheem HP50 Investigated the operating characteristics of the units and evaluated product energy performance, installation, operation, control, maintenance, and other characteristics. 3. Lab Evaluation and Field Study of GE GeoSpring Hybrid Water Heater. Continue the assessment through lab and field testing of the new GE HPWHs. Planned to complete by June

7 Energy Simulation Project - Background If a HPWH is located within a conditioned space, the air cooling effects generated by the HPWH evaporator can affect the building s HVAC system operations. During HVAC cooling operations, the HPWH cooling effects can reduce HVAC load and generate additional energy savings. However, the HPWH cooling effects will increase HVAC system energy consumption during its heating operations. 7

8 Project Methodology Detailed building and HPWH system energy impact analyses using both equest modeling and EXCEL spreadsheet analysis. 8

9 Project Methodology 9 PG&E climate zones, CZ01 through CZ05, CZ11, CZ12, CZ13, and CZ16 2 vintages, old existing homes 1975 (v75) and homes built after 2005 (v11) in the DEER 2008 Each vintage model includes 4 prototype buildings and 5 HVAC control schedules A total of 360 cases were investigated 9

10 Project Methodology COP performance data provided by Rheem for the HP50 model considered in the analysis. The correlation equation is obtained to allow automatic calculation of COP based on hourly ambient conditions from the equest model output. Rheem HP50 HPWH Performance Data Dry-bulb Temperature Relative Humidity % HR Energy Factor (COP) 10

11 Project Results The initial investigation considered setting the HPWH into resistance water heating mode during winter months to avoid heating energy penalties caused by the HPWH cooling effects. Based on calculated source energy efficiencies, we concluded that the heat pump mode is more efficient than the electric resistance mode, even when HVAC system heating penalties are included. For the final energy impact analysis, HPWH systems were set to operate under heat pump mode throughout the year for all climate zones. 11

12 PROJECT RESULTS Annual Energy Savings for HPWH Baseline: Residential Electric Storage Water Heater Climate Building Source Energy Zone Vintage kwh kw Therms MMBtu CZ01 Before CZ01 After CZ02 Before CZ02 After CZ03 Before CZ03 After CZ04 Before CZ04 After CZ05 Before CZ05 After CZ11 Before CZ11 After CZ12 Before CZ12 After CZ13 Before CZ13 After CZ16 Before CZ16 After Average Source Energy represents the total amount of raw fuel that is required to operate a system and it incorporates all transmission, delivery, and production losses. 1 therm = MMBtu Source Energy 1 kwh = MMBtu Source Energy 12

13 PROJECT RESULTS Annual Energy Savings for HPWH Baseline: Residential Gas Storage Water Heater Climate Building Source Energy Zone Vintage kwh kw Therms MMBtu CZ01 Before CZ01 After CZ02 Before CZ02 After CZ03 Before CZ03 After CZ04 Before CZ04 After CZ05 Before CZ05 After CZ11 Before CZ11 After CZ12 Before CZ12 After CZ13 Before CZ13 After CZ16 Before CZ16 After Average

14 PROJECT RESULTS The source energy efficiency analysis clearly indicates that an electric resistance storage water heater has the lowest source energy efficiency. Therefore, HPWH should always run in heat pump mode even during the winter heating season. Table 3 Source Energy Efficiency of Water Heaters Water Heater Type Source Energy Efficiency Gas 57% Electric 29% HPWH 64% no HVAC Interaction 67% Positive Cooling Interaction 104% Negative Heating Interaction 44%[1] [1] This is based on the assumption that space heating fuel source is natural gas. 14

15 Key Takeaways HPWHs are energy saving retrofitting option to existing electrical resistance water heaters. 15

16 Purpose of Testing Program (Projects 2 & 3) Laboratory Understand operating characteristics of actual HPWHs Advantages / limitations Cooling effects Evaluate accuracy and applicability of energy efficiency ratings Issues with current test procedure (DOE 10CFR430) Field Gather performance data under real load profiles Record user impression Goal to develop work paper for potential incentive program based on expected energy and demand savings 16

17 Evaluated Systems AirGenerate AirTap A7 Add-on unit for standard water heater (55 gallon electric heater used) Immersion type condenser R-22 Operation of resistance elements independent Rheem HP50 HP Integral with 50-gallon tank Pumped circulation between tank and condenser R-410a Allows concurrent operation of 2 heat sources (2kW) GE GeoSpring HP Integral with 50-gallon tank Tank jacket condenser coil (like desuperheater) R-134a Only one heat source in operation at a time (4½kW) Currently testing 1 lab, 1 field 17

18 Laboratory Testing Issues Controlled Environmental Rooms Unavailable Unable to thoroughly describe sensitivity to air temperature and humidity Ambient Range: Fdb & 36-49%RH (53-58 Fwb) Did not measure airflow rate Cooling effect evaluated as difference between heating capacity and power input Did measure air temperatures 18

19 Findings Operation Mode Choices HP Only (Highest Efficiency) Resistance Only (Fastest Recovery) Normal / Hybrid (Heat Pump Priority) EnergyGuide Label may be misleading EF is for HP Only Mode, FHR is for Resistance Mode HP Operating Temperature Upper Limit Rheem: 130 F, AirTap: 135 F, GE: 140 F (?) High Efficiency but Long Recovery Times for Heat Pump Mode 19

20 First Hour Rating with HP Only F First Hour Rating: 34.3 Gallons F F Six Tank Thermocouples ( F) Average Tank Temperature ( F) Water Inlet Temperature ( F) Water Outlet Temperature ( F) Water Flow Rate (GPM) Power (kw) GPM or kw Gallons Average / StDev / Max-Min Dry Bulb Temperature ( F): Relative Humidity (%): Wet Bulb Temperature ( F): Hours 20

21 HP Performance Derived from FHR Test Water Heating Air Cooling COP Power Heating & Cooling Capacity (1,000 Btu/hr) & COP Power (kw) Average / StDev / Max-Min Dry Bulb Temperature ( F): Relative Humidity (%): Wet Bulb Temperature ( F): Average Tank Water Temperature ( F) 21

22 Power Demand Trends 1,300 1,200 1,100 Rheem Heat Pump Power (Watts) 1, AirTap 600 GE Average Tank Temperature ( F) 22

23 Relative Heating Capacity 30,000 25,000 40,000 Btu/hr Burner Input 70% Recovery Efficiency 20,000 Heating Capacity (Btu/hr) 15,000 10,000 4,500 Watt Heating Element 98% Recovery Efficiency Cool Tank Heat Pump Only Capacity Hot Tank 5,000 0 Standard Gas Standard Electric Rheem AirTap GE 23

24 DOE Energy Factor Test F F F EF: F F F F Six Tank Thermocouples ( F) Average Tank Temperature ( F) Water Outlet Temperature ( F) Water Inlet Temperature ( F) Water Flow Rate (GPM) Power (kw) GPM & kw Heater does not fully recover after each draw. May inflate EF because of efficiency improvement at lower water temperatures Hours 24

25 Conclusions Recommend that tank temperature setpoint should set at the lowest tolerable level to minimize both power demand and standby loss Default for Rheem & GE is 120 F End users may increase the setpoint to increase stored energy to compensate for slow recovery Reports Available at: 25