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1 Domestic Hot Water Research Research conducted by Bill Rittelmann Presented by Duncan Prahl Partners for High Performance Homes Meeting Westminster, CO, June 23, 2005

2 DHW Systems: Current Technologies

3 DHW Systems: Current Technologies

4 DHW Systems: Current Technologies Residential Domestic Water Heating Systems $7,000 Installed Cost - (USD) $6,000 $5,000 $4,000 $3,000 $2,000 $1,000 $0 0% 20% 40% 60% 80% 100% Source Energy Efficiency Gas Storage Electric Storage Heat pump Gas tankless Electric tankless Electric POU (cold water) Electric POU (warm water) Gas POU

5 Efficiency vs Inlet Water Temp

6 DHW Systems: Sizing Methods 3 60

7 DHW Systems: Event-Based Sizing Key Concepts Temperature-dependent flow The hot water flow rate depends on the temperature of the cold and hot water. This includes showers, baths, some clothes washers, hand washing, etc. Temperature-independent flow The hot water flow is constant regardless of cold and hot water temperatures. This is characteristic of most clothes washers & dishwashers

8 DHW Systems: Event-Based Sizing Key Concepts Energy Factor is not a constant The DOE Energy Factor is calculated under one set of laboratory conditions and does not account for different climates and usage. Inlet water temperature is not a constant Minimum annual inlet water temperatures vary more than 40 F across the country.

9 DHW Systems: Event-Based Sizing Key Concepts Event-based method is more universal The same event descriptions can be used to accurately size a water heater in Miami or Minneapolis. Although the resulting hot water demand will be quite different, the margin of error in the estimation is greatly reduced compared to demand estimation methods that use the same values regardless of water temperatures and end-use fixture descriptions.

10 DHW Systems: Event-Based Sizing Mid-August Temperature - (degrees F) Mid-February NREL (daily) NREL (monthly) 1985 ASHRAE (2 ft) 1985 ASHRAE (4 ft) Time - (Julian Days) Inlet (mains) Water Temperature

11 DHW Systems: Event-Based Sizing Inlet Water Temp. (degrees F) Hot Water Volume (gallons) Total flow = 2.5 gpm Duration = 8 minutes Total volume = 20 gallons Shower temp = 105 F 50% Tank Temperature (degrees F) Temperature-Dependent Flow

12 DHW Systems: Event-Based Sizing Average Hot Water Use - (GPD/occupant) Monthly per Capita Hot Water Use Jan Feb Mar Apr May Jun DOE standard usage rate = 28GPD Jul Aug Sep Oct Nov Dec

13 DHW Systems: Event-Based Sizing Use TRNSYS program to simulate DWH system Detailed Temperature Profile and Hot Water Flow Rate

14 DHW Systems: Event-Based Sizing Electric Water Heater Inlet Water Temp. 45 F, Tank Volume 50 Gallon

15 DHW Systems: Event-Based Sizing Electric Water Heater Inlet Water Temp. 45 F, Tank Volume 40 Gallon

16 DHW Systems: Event-Based Sizing Electric Water Heater Inlet Water Temp. 75 F, Tank Volume 30 Gallon

17 DHW Systems: Event-Based Sizing Electric Water Heater Inlet Water Temp. 75 F, Tank Volume 20 Gallon

18 DHW Systems: Event-Based Sizing T_inlet=60 F T_inlet=45 F T_inlet=36 F V = 30 gallon V = 40 gallon V = 50 gallon Summary of the Tank Size vs. Inlet Water Temp. (Electric)

19 Temperature Variance Temperature in different US cities City Yearly Average Temp. (ºF) T_min T_max Fairbanks, AK Anchorage, AK Duluth, MN Juneau, AK Fargo, ND Saint Cloud, MN Glasgow, MT Green Bay, WI Missoula, MT Burlington, VT Great Falls, MT Minneapolis - St. Paul, MN Casper, WY Concord, NH Madison, WI

20 DHW Systems: Event-Based Sizing City Yearly Average Temp. (ºF) T_min T_max Corpus Christi, TX Orlando, FL Tampa, FL Vero Beach, FL Phoenix, AZ Yuma, AZ Fort Myers, FL West Palm Beach, FL Miami, FL Honolulu, HI Key West, FL Temperature in different US cities

21 DHW Systems: Event-Based Sizing Preliminary conclusions from TRNSYS analysis: The size of the water heater is closely related to the cold water inlet temperature. Therefore, the sizing method should include climate zone consideration. The water usage pattern will influence the size of the water heater. The water schedule profile should be part of the sizing consideration.

22 DHW Systems: Piping losses Domestic Hot Water Piping "Stranded" heat loss, 30 feet of pipe Energy Lost In Pipe / Energy Consumed 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% 1 inch pipe 0.75 inch pipe 0.5 inch pipe inch pipe Draw Size (Gallon)

23 Efficient DHW Systems Factors that Impact Water Heater Energy Efficiency Fuel Conversion Efficiency Inlet (mains) Water Temperature Daily Standby Hot Losses Water Volume (Storage Volume) Tank Inlet (mains) Set Point Water Temperature Temperature Tank Ambient Set Air Point Temperature Temperature Occupant NAECA Minimum behavior Efficiency Standards

24 Efficient DHW Systems DOE Test Procedure First Hour Rating

25 Efficient DHW Systems Water Heater 90 Performance Volume (Gal.) Inlet Water Temperatures F 55 F 75 F 58 F Setpoint Temperature (degrees F) 50-Gallon Electric Water Heater Conventional Controls

26 Efficient DHW Systems Volume (Gallons) Control Strategy Conventional Energy Smart DOE Test Procedure Setpoint Temperature (degrees F) First-Hour Rating 50-gallon electric water heater

27 Efficient DHW Systems 70 Control Strategy 60 Conventional Energy Smart Volume (Gallons) DOE Test Procedure Setpoint Temperature (degrees F) 30-Minute Rating 50-gallon electric water heater

28 First Hour Ratings. Size Matters But Technology Matters More

29 Breaking the Limits of Efficiency Develop a non-solar electric DHW system with a source energy efficiency greater than 100%. (site to source multiplier is assumed to be 3.16) Identify efficiencies and limitations of earthcoupled heat pump systems adjacent to foundations. Quantify displacement of primary energy use relative to thermal storage capacity in a high performance home.

30 Non-Coincident DHW Heat Recovery ROOF MOUNTED HX WH Greywater Tank Passive Heat Recovery

31 Non-Coincident DHW Heat Recovery Annual Energy Savings 35% 30% Annual Energy Savings 25% 20% 15% 10% 5% Mean Annual Mains Temp.( F) % Heat Recovery Tank Size - (gallons) Passive Heat Recovery

32 Non-Coincident DHW Heat Recovery Impact of Heat Exchanger Size % % Energy - (kwh/yr) Recovered Energy WH Energy Use Savings 80-gallon 25% 20% 15% 10% Energy Savings % Heat Exchanger Pipe Length - (meters) Passive Heat Recovery 0%

33 Non-Coincident DHW Heat Recovery ROOF MOUNTED WH Source HX HX Load Outlet Inlet HP Inlet Outlet Greywater Tank Active Heat Recovery

34 Non-Coincident DHW Heat Recovery Annual Energy Savings 100% 90% 80% 70% 60% 50% 40% 30% 20% Annual Energy Savings vs. MWT and DW Tank Volume 63% 67% 68% Drain Water Tank Volume - (gallons) % 70% 70% Annual energy savings increase as mains water temperatures increase but drain water tank volumes beyond 80 gallons have little impact 69% 72% 72% 10% 0% HW Tank Volume = 80 gallons Annual Mean Mains Water Temperature - ( F) Active Heat Recovery

35 Non-Coincident DHW Heat Recovery Annual Energy Savings 100% 90% 80% 70% 60% 50% 40% 30% 20% Annual Energy Savings vs. MWT and HW Tank Volume 61% 67% Hot Water Tank Volume - (gallons) % 69% 70% 70% 71% 66% 63% Annual energy savings increase as mains water temperatures increase and HW tank volume is increased 10% 0% DW Tank Volume = 80 ll Mean Annual Mains Water Temperature - ( F) Active Heat Recovery

36 Non-Coincident DHW Heat Recovery Annual Energy Use - (kwh/yr) System Energy vs. Hot Water Tank Volume WH Energy HP Energy Total system annual energy use decreases as the volume of the hot water tank is increased to 80 gallons, but increases beyond that Annual Mean MWT = 55.4 F DW Tank Volume = 80 gallons Hot Water Tank Volume - (gallons) Active Heat Recovery

37 Non-Coincident DHW Heat Recovery Coefficent Of Performance - (C.O.P.) C.O.P.s vs. Drain-Water HX Piping Material Drain-Water HX Piping Material PEX Copper The thermal properties of the drainwater HX piping have little impact on system performance when HW tanks are 120 gallons or larger Annual Mean MWT = 55.4 F DW Tank Volume = 80 gallons Hot Water Tank Volume - (gallons) Active Heat Recovery

38 Earth-Coupled Heat Pump Water Heater Auxiliary Heat 353 kwh/yr WH ROOF MOUNTED HX Hot water load 72 gpd 4 showers and 1 load of laundry 5141 kwh/yr Load Outlet Inlet HP Outlet 70 F air Heat Pump 1620 kwh/yr Additional Heat Loss Inlet 1845 kwh/yr 69 F slab surface R-10 Source 51 F (normally 63 F) 49 F

39 ECHP Water Heater - Chicago Sub-Slab Earth-Coupled Heat Pump Water Heater Chicago, Slab-on-grade, R-10 under slab & vertical at perimeter Change in slab temperature is less than 1 F Coefficient of Performance - (C.O.P.) Whole-house C.O.P. increases when slab heat loss is beneficial Minimum temperature below slab is well above freezing Slab losses during heating season reduce whole-house C.O.P. Annual whole-house C.O.P. is 2.32 Heat Pump C.O.P. Heat Pump & Tank C.O.P Heat Pump, Tank & Slab C.O.P. Under slab Temp. with E-C Under slab Temp. no E-C Slab surface Temp. with E-C Slab surface Temp. no E-C 49 F Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Temperature - ( F)

40 ECHP Water Heater - Chicago Remote Earth-Coupled Heat Pump Water Heater Chicago Coefficient of Performance - (C.O.P.) Heat Pump C.O.P. Heat Pump & Aux. C.O.P Heat Pump, Aux. & Tank C.O.P. Temp. - Earth at EC loop Temp. - Earth surface Monthly aggregate C.O.P drops in summer due to unwanted heat losses from tank Annual aggregate C.O.P. is 2.05 EC fluid temperature is near freezing year-round 49 F Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Temperature - ( F)

41 ECHP Water Heater - Miami Sub-Slab Earth-Coupled Heat Pump Water Heater Miami, Slab-on-grade, R-10 under slab & vertical at perimeter Coefficient of Performance - (C.O.P.) Change in slab temperature is less than 1 F Whole-house C.O.P. soars when slab heat loss is beneficial Slab losses during heating season reduce whole-house C.O.P. Annual whole-house C.O.P. is 3.82 Heat Pump C.O.P. Heat Pump & Tank C.O.P Heat Pump, Tank & Slab C.O.P. Under slab Temp. with E-C Under slab Temp. no E-C Slab surface Temp. with E-C Slab surface Temp. no E-C Temperature - ( F) F Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 25

42 Domestic Hot Water Systems And that s how it works. Any Questions?