Heat Pump Water Heaters: A Key Energy Technology for California Passive House California April 2018 Danny S. Parker A Research Institute of the University of Central Florida
Heat Pump Water Heaters (HPWH): What Are They? How Do They Work? 2
What You ll learn What are heat pump water heaters? How well do they work in the laboratory? How well do they work in the field? What describes best units? What are some non-water heating issues/advantages? How do they compare with a natural gas water heater? What are the impacts on Greenhouse Gases? What are impacts on cost? What are new technologies? Improved compressors & UEF PV assisted HPWH
Hot Water Systems (HWS) Laboratory FSEC: Cocoa, Florida 4
Florida Solar Energy Center Hot Water Systems Laboratory Plumber s nightmare! Evaluated Most Popular Hot Water Systems 2014 More HPWH s /Hybrids 2012 Evaluated Hybrids PV HPWH 2016 - Present
Averaged 1-Year Performance of Water Heaters and 1 st Gen. HPWH in Laboratory (Cocoa, FL) Annual Performance 0.71 Modern HPWH Energy Factor or UEF 2.27 [2.35] [0.83] Heat Pump WH Nat Gas Tankless 0.56 Typical operating efficiencies for standard water heaters [0.59] Nat Gas 40 Gal. 0.85 [0.91] 50 Gal. Electric 0.00 1.00 2.00 3.00 Daily efficiencies (COP) First Generation Nos. Now UEF (like COP) of 3.7 or greater 6
50 Gal. Heat Pump Water Heater Efficiency COP 4 3.5 3 2.5 2 1.5 1 0.5 0 40 50 60 70 80 90 100 Average Daily HWS Lab Interior Temperature (F) Where HPWH located matters! 7
Simulated Performance of HPWH in U.S. Where HPWH located matters! 8
What Can we learn from the field? 60 measured FL homes; red=hot water 9
Heat Pump Water Heaters Dependable savings vs. electric resistance water heaters, in 10 homes changed out 80 gal. models: 4+ person households 68% overall savings (5.3 kwh/day) 80 gal: 74% savings (7.6 kwh/day)
Northeast HPWH Study (Massachusetts and Rhode Island) HPWH Capacity (gal) Rated EF Avg. COP % Savings General Electric 50 2.35 1.82/ 1.61 44-55% AO Smith 60/80 2.33 2.12 58% Stiebel Eltron 80 2.51 2.32 61% GE Units = 10, Stiebel Eltron = 2, AO Smith = 2 Cost Effectiveness; simple payback 5.7 yrs (avg.) - Range of 3.2-10.5 yrs @ $0.17/kWh Only four HPWH left at default setting 120 F (others 122 140F) 11
How Does this Compare to PG&E? Gas Water Heating major part of PG&E GHG emissions Water heating is BIG: 90% of PGE customers = gas water heat Gas use from 2009 RASS survey 195 therms or 3,169 kwh if electric Our spreadsheet estimates 203 therms/2885 kwh for San Jose 4.6 million res customers= 4.72 million Tons CO 2 per year! What are overall cost & CarbonImpacts? Annual Carbon Impact & $Cost for Water Heating 2500 2000 1500 1000 500 0 Nat. GasTank Nat Gas:Tankless ElecResistance HPWH PV_HPWH lbs CO2/yr $Dollars/yr
Lessons learned from Multi-Family Housing Installations Transfer Grills facing kitchen and laundry Service Door common exterior hallway HPWH in confined small volume closet (<100 ft 3 ) 13
HPWH Survey Response Five Multi-Family Complexes 720 HPWH Units installed in Multi-family homes throughout Florida Generally hi-acceptance Isolated complaints Fan noise Some complaints of insufficient hot water Few ask higher T stat set +5 deg (125 ⁰F) One case reported having turn space heat ON because of cold air by HPWH Other : Quarterly maintenance for air Filter, Drainage check 14
Laboratory Testing to Re-create Field installations in confined space Closet Temperature (F) or RH(%) 80 75 70 65 60 55 50 45 40 0 3 6 9 12 15 18 21 24 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Condensate (Pint) RH Closet T Cond. Pints 15-minute data intervals 15
HPWH Confined in Closet Performance Analysis Days Avg. kwh/day Avg. COP Avg. Inlet (F) Avg. Outlet (F) HPWH in conditioned lab 6 2.050 2.64 74.78 118.47 HPWH in conditioned + confined space (92.5 ft 3 ) 7 2.342 2.30 74.21 117.49 Percent increase of electric 14% 0.292 Volume Draw use Percent COP reduction 13% 50 gal./day 16
HPWH cools the space where located Can provide free cooling or slight increases to heating if located inside -Like small room air conditioner - Running 2 hrs in the morning Potentially free cooling in summer Otherwise cooler garage/utility room Some dehumidification as well Recommend utility room install. Why? - Extra heat in that space (Dryer/washer) - Isolated often from rest of home Important to locate away from thermostat 17
HPWH Air Ducting/Noise Issue Most manufacturers on 3 or 4 th generation Of HPWH. Much more quiet For instance Rheem unit claims Only 49 db for latest unit Others now much more quiet 18
Tested Airflow Pathways Airflow Configuration East FRTF Building Measured Airflow (cfm) West FRTF Building Measured Airflow (cfm) Building Pressure Impact During HPWH Operation Garage to Garage (7 ) 160 160 None Indoor to Indoor (16 ) 160 157 Neutral Outdoor to Indoor (19 ) 147 148 Positive
Space Cooling Energy Savings (~ 1 year pre and 1 year post) # of Occu pants Config. HPWH Energy Post (kwh/day) Cooling Energy Pre (kwh/day) Cooling Energy Post (kwh/day) Cooling Savings (kwh/day) Cooling Savings (%) AC SEER Site 1 4 Interior 2.1 16.3 14.5 1.8 10.8 13.0 5 2 Ducted 2.7 44.7 43.0 1.7 3.8 13.0 9 2 Ducted 3.2 11.5 10.0 1.5 13.2 < 13 13 2 Interior 2.6 6.8 6.1 0.7 10.7 15.5 26 5 Ducted 3.5 11.5 10.1 1.4 12.3 17.0 50 4 Ducted 2.7 18.5 17.8 0.7 3.9 17.0 51 2 Ducted 1.3 15.0 14.2 0.8 5.6 16.0 56 3 Interior 3.1 18.9 18.7 0.2 2.7 10.0 Avg. 3 N/A 2.6 17.9 16.8 1.1 7.9 Med. 2.5 N/A 2.7 15.6 14.3 1.1 8.2
New Tech: PV-Assisted HPWH 80% + Energy savings vs. Electric resistance - No more daily energy use than a refrigerator Large reductions to Green House Gas Emissions relative to electric or gas water heaters
FSEC s PV-HPWH: Prototype Use Current Generation HPWH 80% + energy savings Dedicated 620 W PV & micro-inverters Mixing/Anti-scald valve: set @125 ⁰C Smart Controls & programmed for added thermal storage -Normal thermostat set: 125 F -When solar availability = High, Autoset thermostat to 160 ⁰F -Overall COP = 5.4 (Florida) Competitive; parts cost ($2000) retail Conventional solar water heaters often >$7000- $10,000 installed 310 W PV + 310 W PV 60 gal HPWH 300-watt Microinverters
PV-HPWH Performance Example
PV-Driven HPWH vs Standard Electric 50 gallon Water Heater Average = 7.18 kwh/day Hot Water @ 125⁰F = 54.4 gpd Average = 1.23 kwh/day Hot water @ 125 ⁰F = 57gpd
Advantages of PV-HPWH Superior performance to solar thermal No net-metering agreement Much lower cost than (perhaps half solar thermal) Simple & fast install: No plumbing, light-weight modules Better winter performance: no freeze protection PV output higher in winter, no piping losses Solid state= More reliable/longer life lower maintenance than solar thermal Stores 2.3 kwh thermal/day above set@ no cost Produces hot water even in a power outage Better future performance available HPWH COPs now 3 3.5 vs. prototype compressor (2.2) PV module efficiencies increasing = smaller module footprint Seasonal tilt tracking possible given small size Disadvantage: not yet manufactured
Spreadsheet to Estimate All This for You Only a few inputs: fairly sophisticated estimation of water demand; size of household and ages Yes, research shows teenagers use 3x as much hot water
A Little Summary HPWH install: Building location important Garage may reduce winter efficiency Locate away from thermostat Interior location can provide helpful summer cooling When ducting air, know where air is coming from Compressor operation limited w/ ambient temps below 40 ⁰F. Not big limitation in CA HPWH is ideal for mild U.S. climates Large GHG reductions HPWH best technology for water heating in an all electric home Future PV-HPWH technology promises less water heating energy than a refrigerator 27