Results from Heat Pump Water Heater (HPWH) Laboratory Experiment Second Annual Residential Energy Efficiency Technical Update Meeting Bethany Sparn & Kate Hudon August 10, 2011 NREL 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.
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Results from Heat Pump Water Heater (HPWH) Laboratory Experiment
Second Annual Residential Energy Efficiency Technical Update Meeting
Bethany Sparn amp Kate Hudon
August 10 2011
NREL is a national laboratory of the US Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy LLC
Introduction to Heat Pump Water Heaters (HPWHs)
Benefits of HPWH Technology Significant Energy Saving Potential
- A heat pump is an air conditioner in reverse heat from the air is transferred into the water
- HPWH Energy Factors (EF) range from 2-235 in contrast to traditional electric water heaters with EF=090-095
HPWHs can be used in retrofit applications - Integrated HPWH can easily replace a conventional
water heater in many applications
Oil Prices
Oil
Pric
e ($
bar
rel)
1950 ndash 1955 Initial 1973 ndash 1986 2000 ndash 2011 RampD Two
Prototypes Tested Reemergence of
HPWH RampD Strong Market
Presence NATIONAL RENEWABLE ENERGY LABORATORY
Five Integrated HPWHs Tested All integrated HPWHs currently on the market were tested Experiment Objectives
- Map performance over wide range of operating conditions - Evaluate operability and usability
GE GeoSpring HPWH
50 Gallons
Rheem HPWH AO Smith Stiebel Eltron Air Generate Airtap 50 Gallons Voltex HPWH Accelera 300 HPWH Integrated HPWH
80 Gallons 80 Gallons 66 Gallons
NATIONAL RENEWABLE ENERGY LABORATORY 3
Experimental Set-up amp Test Plan Testing took place at NRELrsquos Advanced Thermal Conversion Laboratory
- Established HVAC Laboratory (accurate wide range best-inshyclass speed of testing)
- Allowed for precise control of air and water conditions
Air-sealed insulated plenum for testing two units side-by-side
Test Plan Summary Test Name Dry bulb (F) RH Inlet Water (F) Outlet Water Airflow Operating Mode
(F) 1 OPERATING MODE TESTS
OM‐67 675 50 58 135 100 All Factory Modes OM‐95 95 40 58 135 100 Hybrid Modes Test Plan Included OM‐47 47 73 58 135 100 Hybrid Modes
2 DOE STANDARD RATING POINT TESTS
DOE‐1hr 675 50 58 135 100 Factory Default - DOE Standard Tests DOE‐130‐1hr 675 50 58 130 100 Factory Default DOE‐140‐1hr 675 50 58 140 100 Factory Default - Operating Mode Tests DOE‐24hr 675 50 58 135 100 Factory Default
3 DRAW PROFILES - Performance Mapping DP‐2 675 50 45 120 100 Factory Default DP‐3 675 50 45 120 100 Factory Default - Draw Profiles 4 COP CURVE DEVELOPMENT - PERFORMANCE MAPPING
COP‐47 47 73 35 135 100 Compressor Only COP‐57 57 61 35 135 100 Compressor Only - Reduced Airflow COP‐67 675 50 35 135 100 Compressor Only COP‐77 77 40 35 135 100 Compressor Only COP‐85 85 42 35 135 100 Compressor Only COP‐95 95 40 35 135 100 Compressor Only Each unit was in the test stand for
COP‐95 dry 95 20 35 135 100 Compressor Only COP‐105 105 42 35 135 100 Compressor Only
COP‐105 dry 105 16 35 135 100 Compressor Only ~5 weeks 5 REDUCED AIRFLOW
AF‐13 675 50 35 135 66 Compressor Only AF‐23 675 50 35 135 33 Compressor Only
4NATIONAL RENEWABLE ENERGY LABORATORY
DOE Standard Test Results
Purpose - Verify that Manufacturerrsquos Ratings for
First Hour Rating (FHR) and Energy Factor (EF) are reasonable
- Determine if set point has an effect on First Hour Rating
Procedure - DOE 1 hour test and 24
hour test were followed per Federal Register 10 CFR Part 430 Subpart B Appendix E
Results - Results were similar to
manufacturerrsquos ratings - Set point temperature
had effect on FHR for some units but not all Control logic could be responsible Note NRELrsquos Advanced Thermal Conversion Laboratory is NOT A RATINGS LABORATORY Results
from the DOE standard tests presented here are ESTIMATES and should not be used as ratings
5NATIONAL RENEWABLE ENERGY LABORATORY
Operating Mode Test Results
Purpose Operating Mode Test Summary Table Determine control logic for each HPWH in each mode of operation
Procedure - Starting with a tank of hot water
draw water until heat pump turns on - Allow unit to recover to set point
temperature - Draw water until electric resistance
elements turn on - Repeat for each mode of operation
Results Unique control logic for each HPWH
- Upper lower or combination of both thermistors used to control heating
- Temperature drops ranged from 05degC to 10degC before heating is initiated
GE Rheem A O Smith Stiebel Eltron Air Generate Most efficient Mode eHeat EnergySaver Efficiency On Econ Heat pump Yes Yes Yes Yes Yes Control logic to turn on heat pump
ΔTupper = -05degC
Tlower = 22degC ΔTtank = -5degC ΔTupper = -2degC ΔTlower = -10degC
Resistance elements No Yes No Yes No
Control logic to turn on heating elements
- Tlower = 22degC - ΔTupper = -10degC -
Hybrid Mode Hybrid Normal Hybrid NA Auto Heat pump Yes Yes Yes - Yes Control logic to turn on heat pump
ΔTupper
= -05degC Tlower
= 22degC ΔTtank
= -5degC - ΔTlower = -10degC
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper
= -10degC Tlower = 22degC
ΔTtank
= -10degC - ΔTupper = -10degC
Additional Mode High
Demand NA NA NA NA
Heat pump Yes - - - -Control logic to turn on heat pump
ΔTupper
= -05degC - - - -
Resistance elements Yes - - - -
Control logic to turn on heating elements
ΔTupper
= -3degC - - - -
Resistance-only Mode Electric Only Electric Only Electric Only NA Heater
Heat pump No No No - No Control logic to turn on heat pump
- - - - -
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper = shy05degC
Tlower = 20degC ΔTtank
= -2degC - ΔTupper = -10degC
- Various control strategies for electric resistance elements
NATIONAL RENEWABLE ENERGY LABORATORY 6
Coefficient of Performance (COP) Test Results
NATIONAL RENEWABLE ENERGY LABORATORY
COP Curves for All HPWHs at Twb = 14degC (67degF)
7
Purpose Map heat pump performance over a wide range of inlet air conditions
Procedure - Set HPWH to operate using only
the heat pump - Fill tank with cold (~3degC) water - Heat water until highest set point
temperature is reached - Calculate ten-minute running
average COP
Results - COP increases with increasing air
temperature - COP decreases with increasing
water temperature - Icing limits heat pump operating
range for some HPWHs for low air and water conditions
Typical Operating Range
Beyond Typical Operating Range
COP Curves for AOSmith HPWH
Coefficient of Performance (COP) Test Results
Typical Operating Range
Beyond Typical Operating Range
COP Curves for Rheem HPWH COP Curves for GE HPWH
COP Curves for Stiebel Eltron HPWH COP Curves for Air Generate HPWH
8NATIONAL RENEWABLE ENERGY LABORATORY
Draw Profile Test Results Purpose DP1 Results for the Air Generate HPWH Determine realistic HPWH performance using two Draw Profiles DP1 ndash Morning and Evening Draws DP2 ndash Series of Short Draws
Procedure Run draw profile with air and water conditions held constant
Results for DP1 Outlet water temperature fell below lsquohotrsquo value of 405degC depending on storage tank size and control logic Draw Profile COP
- HPWHs with 80 gallon tanks did not have issues maintaining outlet temperature using the heat pump
- HPWHs with smaller tanks dropped below lsquohotrsquo outlet temperature and relied on electric resistance elements thus reducing performance
HPWH COP
(DP1 ndash Morning) COP
(DP1 ndash Evening) COP (DP2)
GE 12 18 35 Rheem 14 26 25
AO Smith 36 34 26 Stiebel Eltron 39 54 31
Air Generate 17 28 NA
9NATIONAL RENEWABLE ENERGY LABORATORY
Preliminary TRNSYS Model Results - HPWH model developed in TRNSYS - Annual simulations run in 6 climate regions in conditioned and
unconditioned space bull Effect on space conditioned was included bull Simulations ran for new homes Existing homes is next step
- Initial results show HPWH technology is applicable in any climate region for electric resistance water heater replacements
- TRNSYS modeling has some limitations including bull Performance map based on data Extrapolation used for conditions not tested bull Home models include simple foundation and infiltration models
- Future modeling efforts will develop an Energy Plus HPWH model for use in NRELrsquos Building Energy Optimization software BEopt
Water Heater Annual Source Energy Consumption in Conditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐53 54 Chicago IL ‐30 42 Houston TX 36 63 Los Angeles CA 70 54 Phoenix AZ 33 58 Seattle WA ‐32 40
Water Heater Annual Source Energy Consumption in Unconditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐025 50 Chicago IL ‐37 37 Houston TX ‐23 35 Los Angeles CA ‐24 35 Phoenix AZ ‐20 35 Seattle WA ‐21 42
These homes have the HPWH located in the basement In all other homes the HPWH is in the garage
NATIONAL RENEWABLE ENERGY LABORATORY 10
Homeowner Concerns Recovery Rate Installation
- Installation location must be large enough to accommodate
1 Size of a HPWH 2 Air flow rate of heat pump
Cost - Units currently range from $1300 to $2600 - Installation costs are expected to be in-line
with conventional water heaters HPWH Cooling Capacity vs Average Tank Temperature
Performance - Cold Climate Performance A HPWH will
perform best in warmer climates but significant energy savings can be achieved in cold climates as well
- Recovery Rate Significantly reduced relative to an electric resistance water heater A larger storage tank will help mitigate this issue
- Cooling Effect Between 02 and 07 tons of refrigeration in typical operating range
11NATIONAL RENEWABLE ENERGY LABORATORY
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Introduction to Heat Pump Water Heaters (HPWHs)
Benefits of HPWH Technology Significant Energy Saving Potential
- A heat pump is an air conditioner in reverse heat from the air is transferred into the water
- HPWH Energy Factors (EF) range from 2-235 in contrast to traditional electric water heaters with EF=090-095
HPWHs can be used in retrofit applications - Integrated HPWH can easily replace a conventional
water heater in many applications
Oil Prices
Oil
Pric
e ($
bar
rel)
1950 ndash 1955 Initial 1973 ndash 1986 2000 ndash 2011 RampD Two
Prototypes Tested Reemergence of
HPWH RampD Strong Market
Presence NATIONAL RENEWABLE ENERGY LABORATORY
Five Integrated HPWHs Tested All integrated HPWHs currently on the market were tested Experiment Objectives
- Map performance over wide range of operating conditions - Evaluate operability and usability
GE GeoSpring HPWH
50 Gallons
Rheem HPWH AO Smith Stiebel Eltron Air Generate Airtap 50 Gallons Voltex HPWH Accelera 300 HPWH Integrated HPWH
80 Gallons 80 Gallons 66 Gallons
NATIONAL RENEWABLE ENERGY LABORATORY 3
Experimental Set-up amp Test Plan Testing took place at NRELrsquos Advanced Thermal Conversion Laboratory
- Established HVAC Laboratory (accurate wide range best-inshyclass speed of testing)
- Allowed for precise control of air and water conditions
Air-sealed insulated plenum for testing two units side-by-side
Test Plan Summary Test Name Dry bulb (F) RH Inlet Water (F) Outlet Water Airflow Operating Mode
(F) 1 OPERATING MODE TESTS
OM‐67 675 50 58 135 100 All Factory Modes OM‐95 95 40 58 135 100 Hybrid Modes Test Plan Included OM‐47 47 73 58 135 100 Hybrid Modes
2 DOE STANDARD RATING POINT TESTS
DOE‐1hr 675 50 58 135 100 Factory Default - DOE Standard Tests DOE‐130‐1hr 675 50 58 130 100 Factory Default DOE‐140‐1hr 675 50 58 140 100 Factory Default - Operating Mode Tests DOE‐24hr 675 50 58 135 100 Factory Default
3 DRAW PROFILES - Performance Mapping DP‐2 675 50 45 120 100 Factory Default DP‐3 675 50 45 120 100 Factory Default - Draw Profiles 4 COP CURVE DEVELOPMENT - PERFORMANCE MAPPING
COP‐47 47 73 35 135 100 Compressor Only COP‐57 57 61 35 135 100 Compressor Only - Reduced Airflow COP‐67 675 50 35 135 100 Compressor Only COP‐77 77 40 35 135 100 Compressor Only COP‐85 85 42 35 135 100 Compressor Only COP‐95 95 40 35 135 100 Compressor Only Each unit was in the test stand for
COP‐95 dry 95 20 35 135 100 Compressor Only COP‐105 105 42 35 135 100 Compressor Only
COP‐105 dry 105 16 35 135 100 Compressor Only ~5 weeks 5 REDUCED AIRFLOW
AF‐13 675 50 35 135 66 Compressor Only AF‐23 675 50 35 135 33 Compressor Only
4NATIONAL RENEWABLE ENERGY LABORATORY
DOE Standard Test Results
Purpose - Verify that Manufacturerrsquos Ratings for
First Hour Rating (FHR) and Energy Factor (EF) are reasonable
- Determine if set point has an effect on First Hour Rating
Procedure - DOE 1 hour test and 24
hour test were followed per Federal Register 10 CFR Part 430 Subpart B Appendix E
Results - Results were similar to
manufacturerrsquos ratings - Set point temperature
had effect on FHR for some units but not all Control logic could be responsible Note NRELrsquos Advanced Thermal Conversion Laboratory is NOT A RATINGS LABORATORY Results
from the DOE standard tests presented here are ESTIMATES and should not be used as ratings
5NATIONAL RENEWABLE ENERGY LABORATORY
Operating Mode Test Results
Purpose Operating Mode Test Summary Table Determine control logic for each HPWH in each mode of operation
Procedure - Starting with a tank of hot water
draw water until heat pump turns on - Allow unit to recover to set point
temperature - Draw water until electric resistance
elements turn on - Repeat for each mode of operation
Results Unique control logic for each HPWH
- Upper lower or combination of both thermistors used to control heating
- Temperature drops ranged from 05degC to 10degC before heating is initiated
GE Rheem A O Smith Stiebel Eltron Air Generate Most efficient Mode eHeat EnergySaver Efficiency On Econ Heat pump Yes Yes Yes Yes Yes Control logic to turn on heat pump
ΔTupper = -05degC
Tlower = 22degC ΔTtank = -5degC ΔTupper = -2degC ΔTlower = -10degC
Resistance elements No Yes No Yes No
Control logic to turn on heating elements
- Tlower = 22degC - ΔTupper = -10degC -
Hybrid Mode Hybrid Normal Hybrid NA Auto Heat pump Yes Yes Yes - Yes Control logic to turn on heat pump
ΔTupper
= -05degC Tlower
= 22degC ΔTtank
= -5degC - ΔTlower = -10degC
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper
= -10degC Tlower = 22degC
ΔTtank
= -10degC - ΔTupper = -10degC
Additional Mode High
Demand NA NA NA NA
Heat pump Yes - - - -Control logic to turn on heat pump
ΔTupper
= -05degC - - - -
Resistance elements Yes - - - -
Control logic to turn on heating elements
ΔTupper
= -3degC - - - -
Resistance-only Mode Electric Only Electric Only Electric Only NA Heater
Heat pump No No No - No Control logic to turn on heat pump
- - - - -
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper = shy05degC
Tlower = 20degC ΔTtank
= -2degC - ΔTupper = -10degC
- Various control strategies for electric resistance elements
NATIONAL RENEWABLE ENERGY LABORATORY 6
Coefficient of Performance (COP) Test Results
NATIONAL RENEWABLE ENERGY LABORATORY
COP Curves for All HPWHs at Twb = 14degC (67degF)
7
Purpose Map heat pump performance over a wide range of inlet air conditions
Procedure - Set HPWH to operate using only
the heat pump - Fill tank with cold (~3degC) water - Heat water until highest set point
temperature is reached - Calculate ten-minute running
average COP
Results - COP increases with increasing air
temperature - COP decreases with increasing
water temperature - Icing limits heat pump operating
range for some HPWHs for low air and water conditions
Typical Operating Range
Beyond Typical Operating Range
COP Curves for AOSmith HPWH
Coefficient of Performance (COP) Test Results
Typical Operating Range
Beyond Typical Operating Range
COP Curves for Rheem HPWH COP Curves for GE HPWH
COP Curves for Stiebel Eltron HPWH COP Curves for Air Generate HPWH
8NATIONAL RENEWABLE ENERGY LABORATORY
Draw Profile Test Results Purpose DP1 Results for the Air Generate HPWH Determine realistic HPWH performance using two Draw Profiles DP1 ndash Morning and Evening Draws DP2 ndash Series of Short Draws
Procedure Run draw profile with air and water conditions held constant
Results for DP1 Outlet water temperature fell below lsquohotrsquo value of 405degC depending on storage tank size and control logic Draw Profile COP
- HPWHs with 80 gallon tanks did not have issues maintaining outlet temperature using the heat pump
- HPWHs with smaller tanks dropped below lsquohotrsquo outlet temperature and relied on electric resistance elements thus reducing performance
HPWH COP
(DP1 ndash Morning) COP
(DP1 ndash Evening) COP (DP2)
GE 12 18 35 Rheem 14 26 25
AO Smith 36 34 26 Stiebel Eltron 39 54 31
Air Generate 17 28 NA
9NATIONAL RENEWABLE ENERGY LABORATORY
Preliminary TRNSYS Model Results - HPWH model developed in TRNSYS - Annual simulations run in 6 climate regions in conditioned and
unconditioned space bull Effect on space conditioned was included bull Simulations ran for new homes Existing homes is next step
- Initial results show HPWH technology is applicable in any climate region for electric resistance water heater replacements
- TRNSYS modeling has some limitations including bull Performance map based on data Extrapolation used for conditions not tested bull Home models include simple foundation and infiltration models
- Future modeling efforts will develop an Energy Plus HPWH model for use in NRELrsquos Building Energy Optimization software BEopt
Water Heater Annual Source Energy Consumption in Conditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐53 54 Chicago IL ‐30 42 Houston TX 36 63 Los Angeles CA 70 54 Phoenix AZ 33 58 Seattle WA ‐32 40
Water Heater Annual Source Energy Consumption in Unconditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐025 50 Chicago IL ‐37 37 Houston TX ‐23 35 Los Angeles CA ‐24 35 Phoenix AZ ‐20 35 Seattle WA ‐21 42
These homes have the HPWH located in the basement In all other homes the HPWH is in the garage
NATIONAL RENEWABLE ENERGY LABORATORY 10
Homeowner Concerns Recovery Rate Installation
- Installation location must be large enough to accommodate
1 Size of a HPWH 2 Air flow rate of heat pump
Cost - Units currently range from $1300 to $2600 - Installation costs are expected to be in-line
with conventional water heaters HPWH Cooling Capacity vs Average Tank Temperature
Performance - Cold Climate Performance A HPWH will
perform best in warmer climates but significant energy savings can be achieved in cold climates as well
- Recovery Rate Significantly reduced relative to an electric resistance water heater A larger storage tank will help mitigate this issue
- Cooling Effect Between 02 and 07 tons of refrigeration in typical operating range
11NATIONAL RENEWABLE ENERGY LABORATORY
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Five Integrated HPWHs Tested All integrated HPWHs currently on the market were tested Experiment Objectives
- Map performance over wide range of operating conditions - Evaluate operability and usability
GE GeoSpring HPWH
50 Gallons
Rheem HPWH AO Smith Stiebel Eltron Air Generate Airtap 50 Gallons Voltex HPWH Accelera 300 HPWH Integrated HPWH
80 Gallons 80 Gallons 66 Gallons
NATIONAL RENEWABLE ENERGY LABORATORY 3
Experimental Set-up amp Test Plan Testing took place at NRELrsquos Advanced Thermal Conversion Laboratory
- Established HVAC Laboratory (accurate wide range best-inshyclass speed of testing)
- Allowed for precise control of air and water conditions
Air-sealed insulated plenum for testing two units side-by-side
Test Plan Summary Test Name Dry bulb (F) RH Inlet Water (F) Outlet Water Airflow Operating Mode
(F) 1 OPERATING MODE TESTS
OM‐67 675 50 58 135 100 All Factory Modes OM‐95 95 40 58 135 100 Hybrid Modes Test Plan Included OM‐47 47 73 58 135 100 Hybrid Modes
2 DOE STANDARD RATING POINT TESTS
DOE‐1hr 675 50 58 135 100 Factory Default - DOE Standard Tests DOE‐130‐1hr 675 50 58 130 100 Factory Default DOE‐140‐1hr 675 50 58 140 100 Factory Default - Operating Mode Tests DOE‐24hr 675 50 58 135 100 Factory Default
3 DRAW PROFILES - Performance Mapping DP‐2 675 50 45 120 100 Factory Default DP‐3 675 50 45 120 100 Factory Default - Draw Profiles 4 COP CURVE DEVELOPMENT - PERFORMANCE MAPPING
COP‐47 47 73 35 135 100 Compressor Only COP‐57 57 61 35 135 100 Compressor Only - Reduced Airflow COP‐67 675 50 35 135 100 Compressor Only COP‐77 77 40 35 135 100 Compressor Only COP‐85 85 42 35 135 100 Compressor Only COP‐95 95 40 35 135 100 Compressor Only Each unit was in the test stand for
COP‐95 dry 95 20 35 135 100 Compressor Only COP‐105 105 42 35 135 100 Compressor Only
COP‐105 dry 105 16 35 135 100 Compressor Only ~5 weeks 5 REDUCED AIRFLOW
AF‐13 675 50 35 135 66 Compressor Only AF‐23 675 50 35 135 33 Compressor Only
4NATIONAL RENEWABLE ENERGY LABORATORY
DOE Standard Test Results
Purpose - Verify that Manufacturerrsquos Ratings for
First Hour Rating (FHR) and Energy Factor (EF) are reasonable
- Determine if set point has an effect on First Hour Rating
Procedure - DOE 1 hour test and 24
hour test were followed per Federal Register 10 CFR Part 430 Subpart B Appendix E
Results - Results were similar to
manufacturerrsquos ratings - Set point temperature
had effect on FHR for some units but not all Control logic could be responsible Note NRELrsquos Advanced Thermal Conversion Laboratory is NOT A RATINGS LABORATORY Results
from the DOE standard tests presented here are ESTIMATES and should not be used as ratings
5NATIONAL RENEWABLE ENERGY LABORATORY
Operating Mode Test Results
Purpose Operating Mode Test Summary Table Determine control logic for each HPWH in each mode of operation
Procedure - Starting with a tank of hot water
draw water until heat pump turns on - Allow unit to recover to set point
temperature - Draw water until electric resistance
elements turn on - Repeat for each mode of operation
Results Unique control logic for each HPWH
- Upper lower or combination of both thermistors used to control heating
- Temperature drops ranged from 05degC to 10degC before heating is initiated
GE Rheem A O Smith Stiebel Eltron Air Generate Most efficient Mode eHeat EnergySaver Efficiency On Econ Heat pump Yes Yes Yes Yes Yes Control logic to turn on heat pump
ΔTupper = -05degC
Tlower = 22degC ΔTtank = -5degC ΔTupper = -2degC ΔTlower = -10degC
Resistance elements No Yes No Yes No
Control logic to turn on heating elements
- Tlower = 22degC - ΔTupper = -10degC -
Hybrid Mode Hybrid Normal Hybrid NA Auto Heat pump Yes Yes Yes - Yes Control logic to turn on heat pump
ΔTupper
= -05degC Tlower
= 22degC ΔTtank
= -5degC - ΔTlower = -10degC
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper
= -10degC Tlower = 22degC
ΔTtank
= -10degC - ΔTupper = -10degC
Additional Mode High
Demand NA NA NA NA
Heat pump Yes - - - -Control logic to turn on heat pump
ΔTupper
= -05degC - - - -
Resistance elements Yes - - - -
Control logic to turn on heating elements
ΔTupper
= -3degC - - - -
Resistance-only Mode Electric Only Electric Only Electric Only NA Heater
Heat pump No No No - No Control logic to turn on heat pump
- - - - -
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper = shy05degC
Tlower = 20degC ΔTtank
= -2degC - ΔTupper = -10degC
- Various control strategies for electric resistance elements
NATIONAL RENEWABLE ENERGY LABORATORY 6
Coefficient of Performance (COP) Test Results
NATIONAL RENEWABLE ENERGY LABORATORY
COP Curves for All HPWHs at Twb = 14degC (67degF)
7
Purpose Map heat pump performance over a wide range of inlet air conditions
Procedure - Set HPWH to operate using only
the heat pump - Fill tank with cold (~3degC) water - Heat water until highest set point
temperature is reached - Calculate ten-minute running
average COP
Results - COP increases with increasing air
temperature - COP decreases with increasing
water temperature - Icing limits heat pump operating
range for some HPWHs for low air and water conditions
Typical Operating Range
Beyond Typical Operating Range
COP Curves for AOSmith HPWH
Coefficient of Performance (COP) Test Results
Typical Operating Range
Beyond Typical Operating Range
COP Curves for Rheem HPWH COP Curves for GE HPWH
COP Curves for Stiebel Eltron HPWH COP Curves for Air Generate HPWH
8NATIONAL RENEWABLE ENERGY LABORATORY
Draw Profile Test Results Purpose DP1 Results for the Air Generate HPWH Determine realistic HPWH performance using two Draw Profiles DP1 ndash Morning and Evening Draws DP2 ndash Series of Short Draws
Procedure Run draw profile with air and water conditions held constant
Results for DP1 Outlet water temperature fell below lsquohotrsquo value of 405degC depending on storage tank size and control logic Draw Profile COP
- HPWHs with 80 gallon tanks did not have issues maintaining outlet temperature using the heat pump
- HPWHs with smaller tanks dropped below lsquohotrsquo outlet temperature and relied on electric resistance elements thus reducing performance
HPWH COP
(DP1 ndash Morning) COP
(DP1 ndash Evening) COP (DP2)
GE 12 18 35 Rheem 14 26 25
AO Smith 36 34 26 Stiebel Eltron 39 54 31
Air Generate 17 28 NA
9NATIONAL RENEWABLE ENERGY LABORATORY
Preliminary TRNSYS Model Results - HPWH model developed in TRNSYS - Annual simulations run in 6 climate regions in conditioned and
unconditioned space bull Effect on space conditioned was included bull Simulations ran for new homes Existing homes is next step
- Initial results show HPWH technology is applicable in any climate region for electric resistance water heater replacements
- TRNSYS modeling has some limitations including bull Performance map based on data Extrapolation used for conditions not tested bull Home models include simple foundation and infiltration models
- Future modeling efforts will develop an Energy Plus HPWH model for use in NRELrsquos Building Energy Optimization software BEopt
Water Heater Annual Source Energy Consumption in Conditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐53 54 Chicago IL ‐30 42 Houston TX 36 63 Los Angeles CA 70 54 Phoenix AZ 33 58 Seattle WA ‐32 40
Water Heater Annual Source Energy Consumption in Unconditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐025 50 Chicago IL ‐37 37 Houston TX ‐23 35 Los Angeles CA ‐24 35 Phoenix AZ ‐20 35 Seattle WA ‐21 42
These homes have the HPWH located in the basement In all other homes the HPWH is in the garage
NATIONAL RENEWABLE ENERGY LABORATORY 10
Homeowner Concerns Recovery Rate Installation
- Installation location must be large enough to accommodate
1 Size of a HPWH 2 Air flow rate of heat pump
Cost - Units currently range from $1300 to $2600 - Installation costs are expected to be in-line
with conventional water heaters HPWH Cooling Capacity vs Average Tank Temperature
Performance - Cold Climate Performance A HPWH will
perform best in warmer climates but significant energy savings can be achieved in cold climates as well
- Recovery Rate Significantly reduced relative to an electric resistance water heater A larger storage tank will help mitigate this issue
- Cooling Effect Between 02 and 07 tons of refrigeration in typical operating range
11NATIONAL RENEWABLE ENERGY LABORATORY
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Experimental Set-up amp Test Plan Testing took place at NRELrsquos Advanced Thermal Conversion Laboratory
- Established HVAC Laboratory (accurate wide range best-inshyclass speed of testing)
- Allowed for precise control of air and water conditions
Air-sealed insulated plenum for testing two units side-by-side
Test Plan Summary Test Name Dry bulb (F) RH Inlet Water (F) Outlet Water Airflow Operating Mode
(F) 1 OPERATING MODE TESTS
OM‐67 675 50 58 135 100 All Factory Modes OM‐95 95 40 58 135 100 Hybrid Modes Test Plan Included OM‐47 47 73 58 135 100 Hybrid Modes
2 DOE STANDARD RATING POINT TESTS
DOE‐1hr 675 50 58 135 100 Factory Default - DOE Standard Tests DOE‐130‐1hr 675 50 58 130 100 Factory Default DOE‐140‐1hr 675 50 58 140 100 Factory Default - Operating Mode Tests DOE‐24hr 675 50 58 135 100 Factory Default
3 DRAW PROFILES - Performance Mapping DP‐2 675 50 45 120 100 Factory Default DP‐3 675 50 45 120 100 Factory Default - Draw Profiles 4 COP CURVE DEVELOPMENT - PERFORMANCE MAPPING
COP‐47 47 73 35 135 100 Compressor Only COP‐57 57 61 35 135 100 Compressor Only - Reduced Airflow COP‐67 675 50 35 135 100 Compressor Only COP‐77 77 40 35 135 100 Compressor Only COP‐85 85 42 35 135 100 Compressor Only COP‐95 95 40 35 135 100 Compressor Only Each unit was in the test stand for
COP‐95 dry 95 20 35 135 100 Compressor Only COP‐105 105 42 35 135 100 Compressor Only
COP‐105 dry 105 16 35 135 100 Compressor Only ~5 weeks 5 REDUCED AIRFLOW
AF‐13 675 50 35 135 66 Compressor Only AF‐23 675 50 35 135 33 Compressor Only
4NATIONAL RENEWABLE ENERGY LABORATORY
DOE Standard Test Results
Purpose - Verify that Manufacturerrsquos Ratings for
First Hour Rating (FHR) and Energy Factor (EF) are reasonable
- Determine if set point has an effect on First Hour Rating
Procedure - DOE 1 hour test and 24
hour test were followed per Federal Register 10 CFR Part 430 Subpart B Appendix E
Results - Results were similar to
manufacturerrsquos ratings - Set point temperature
had effect on FHR for some units but not all Control logic could be responsible Note NRELrsquos Advanced Thermal Conversion Laboratory is NOT A RATINGS LABORATORY Results
from the DOE standard tests presented here are ESTIMATES and should not be used as ratings
5NATIONAL RENEWABLE ENERGY LABORATORY
Operating Mode Test Results
Purpose Operating Mode Test Summary Table Determine control logic for each HPWH in each mode of operation
Procedure - Starting with a tank of hot water
draw water until heat pump turns on - Allow unit to recover to set point
temperature - Draw water until electric resistance
elements turn on - Repeat for each mode of operation
Results Unique control logic for each HPWH
- Upper lower or combination of both thermistors used to control heating
- Temperature drops ranged from 05degC to 10degC before heating is initiated
GE Rheem A O Smith Stiebel Eltron Air Generate Most efficient Mode eHeat EnergySaver Efficiency On Econ Heat pump Yes Yes Yes Yes Yes Control logic to turn on heat pump
ΔTupper = -05degC
Tlower = 22degC ΔTtank = -5degC ΔTupper = -2degC ΔTlower = -10degC
Resistance elements No Yes No Yes No
Control logic to turn on heating elements
- Tlower = 22degC - ΔTupper = -10degC -
Hybrid Mode Hybrid Normal Hybrid NA Auto Heat pump Yes Yes Yes - Yes Control logic to turn on heat pump
ΔTupper
= -05degC Tlower
= 22degC ΔTtank
= -5degC - ΔTlower = -10degC
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper
= -10degC Tlower = 22degC
ΔTtank
= -10degC - ΔTupper = -10degC
Additional Mode High
Demand NA NA NA NA
Heat pump Yes - - - -Control logic to turn on heat pump
ΔTupper
= -05degC - - - -
Resistance elements Yes - - - -
Control logic to turn on heating elements
ΔTupper
= -3degC - - - -
Resistance-only Mode Electric Only Electric Only Electric Only NA Heater
Heat pump No No No - No Control logic to turn on heat pump
- - - - -
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper = shy05degC
Tlower = 20degC ΔTtank
= -2degC - ΔTupper = -10degC
- Various control strategies for electric resistance elements
NATIONAL RENEWABLE ENERGY LABORATORY 6
Coefficient of Performance (COP) Test Results
NATIONAL RENEWABLE ENERGY LABORATORY
COP Curves for All HPWHs at Twb = 14degC (67degF)
7
Purpose Map heat pump performance over a wide range of inlet air conditions
Procedure - Set HPWH to operate using only
the heat pump - Fill tank with cold (~3degC) water - Heat water until highest set point
temperature is reached - Calculate ten-minute running
average COP
Results - COP increases with increasing air
temperature - COP decreases with increasing
water temperature - Icing limits heat pump operating
range for some HPWHs for low air and water conditions
Typical Operating Range
Beyond Typical Operating Range
COP Curves for AOSmith HPWH
Coefficient of Performance (COP) Test Results
Typical Operating Range
Beyond Typical Operating Range
COP Curves for Rheem HPWH COP Curves for GE HPWH
COP Curves for Stiebel Eltron HPWH COP Curves for Air Generate HPWH
8NATIONAL RENEWABLE ENERGY LABORATORY
Draw Profile Test Results Purpose DP1 Results for the Air Generate HPWH Determine realistic HPWH performance using two Draw Profiles DP1 ndash Morning and Evening Draws DP2 ndash Series of Short Draws
Procedure Run draw profile with air and water conditions held constant
Results for DP1 Outlet water temperature fell below lsquohotrsquo value of 405degC depending on storage tank size and control logic Draw Profile COP
- HPWHs with 80 gallon tanks did not have issues maintaining outlet temperature using the heat pump
- HPWHs with smaller tanks dropped below lsquohotrsquo outlet temperature and relied on electric resistance elements thus reducing performance
HPWH COP
(DP1 ndash Morning) COP
(DP1 ndash Evening) COP (DP2)
GE 12 18 35 Rheem 14 26 25
AO Smith 36 34 26 Stiebel Eltron 39 54 31
Air Generate 17 28 NA
9NATIONAL RENEWABLE ENERGY LABORATORY
Preliminary TRNSYS Model Results - HPWH model developed in TRNSYS - Annual simulations run in 6 climate regions in conditioned and
unconditioned space bull Effect on space conditioned was included bull Simulations ran for new homes Existing homes is next step
- Initial results show HPWH technology is applicable in any climate region for electric resistance water heater replacements
- TRNSYS modeling has some limitations including bull Performance map based on data Extrapolation used for conditions not tested bull Home models include simple foundation and infiltration models
- Future modeling efforts will develop an Energy Plus HPWH model for use in NRELrsquos Building Energy Optimization software BEopt
Water Heater Annual Source Energy Consumption in Conditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐53 54 Chicago IL ‐30 42 Houston TX 36 63 Los Angeles CA 70 54 Phoenix AZ 33 58 Seattle WA ‐32 40
Water Heater Annual Source Energy Consumption in Unconditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐025 50 Chicago IL ‐37 37 Houston TX ‐23 35 Los Angeles CA ‐24 35 Phoenix AZ ‐20 35 Seattle WA ‐21 42
These homes have the HPWH located in the basement In all other homes the HPWH is in the garage
NATIONAL RENEWABLE ENERGY LABORATORY 10
Homeowner Concerns Recovery Rate Installation
- Installation location must be large enough to accommodate
1 Size of a HPWH 2 Air flow rate of heat pump
Cost - Units currently range from $1300 to $2600 - Installation costs are expected to be in-line
with conventional water heaters HPWH Cooling Capacity vs Average Tank Temperature
Performance - Cold Climate Performance A HPWH will
perform best in warmer climates but significant energy savings can be achieved in cold climates as well
- Recovery Rate Significantly reduced relative to an electric resistance water heater A larger storage tank will help mitigate this issue
- Cooling Effect Between 02 and 07 tons of refrigeration in typical operating range
11NATIONAL RENEWABLE ENERGY LABORATORY
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
DOE Standard Test Results
Purpose - Verify that Manufacturerrsquos Ratings for
First Hour Rating (FHR) and Energy Factor (EF) are reasonable
- Determine if set point has an effect on First Hour Rating
Procedure - DOE 1 hour test and 24
hour test were followed per Federal Register 10 CFR Part 430 Subpart B Appendix E
Results - Results were similar to
manufacturerrsquos ratings - Set point temperature
had effect on FHR for some units but not all Control logic could be responsible Note NRELrsquos Advanced Thermal Conversion Laboratory is NOT A RATINGS LABORATORY Results
from the DOE standard tests presented here are ESTIMATES and should not be used as ratings
5NATIONAL RENEWABLE ENERGY LABORATORY
Operating Mode Test Results
Purpose Operating Mode Test Summary Table Determine control logic for each HPWH in each mode of operation
Procedure - Starting with a tank of hot water
draw water until heat pump turns on - Allow unit to recover to set point
temperature - Draw water until electric resistance
elements turn on - Repeat for each mode of operation
Results Unique control logic for each HPWH
- Upper lower or combination of both thermistors used to control heating
- Temperature drops ranged from 05degC to 10degC before heating is initiated
GE Rheem A O Smith Stiebel Eltron Air Generate Most efficient Mode eHeat EnergySaver Efficiency On Econ Heat pump Yes Yes Yes Yes Yes Control logic to turn on heat pump
ΔTupper = -05degC
Tlower = 22degC ΔTtank = -5degC ΔTupper = -2degC ΔTlower = -10degC
Resistance elements No Yes No Yes No
Control logic to turn on heating elements
- Tlower = 22degC - ΔTupper = -10degC -
Hybrid Mode Hybrid Normal Hybrid NA Auto Heat pump Yes Yes Yes - Yes Control logic to turn on heat pump
ΔTupper
= -05degC Tlower
= 22degC ΔTtank
= -5degC - ΔTlower = -10degC
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper
= -10degC Tlower = 22degC
ΔTtank
= -10degC - ΔTupper = -10degC
Additional Mode High
Demand NA NA NA NA
Heat pump Yes - - - -Control logic to turn on heat pump
ΔTupper
= -05degC - - - -
Resistance elements Yes - - - -
Control logic to turn on heating elements
ΔTupper
= -3degC - - - -
Resistance-only Mode Electric Only Electric Only Electric Only NA Heater
Heat pump No No No - No Control logic to turn on heat pump
- - - - -
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper = shy05degC
Tlower = 20degC ΔTtank
= -2degC - ΔTupper = -10degC
- Various control strategies for electric resistance elements
NATIONAL RENEWABLE ENERGY LABORATORY 6
Coefficient of Performance (COP) Test Results
NATIONAL RENEWABLE ENERGY LABORATORY
COP Curves for All HPWHs at Twb = 14degC (67degF)
7
Purpose Map heat pump performance over a wide range of inlet air conditions
Procedure - Set HPWH to operate using only
the heat pump - Fill tank with cold (~3degC) water - Heat water until highest set point
temperature is reached - Calculate ten-minute running
average COP
Results - COP increases with increasing air
temperature - COP decreases with increasing
water temperature - Icing limits heat pump operating
range for some HPWHs for low air and water conditions
Typical Operating Range
Beyond Typical Operating Range
COP Curves for AOSmith HPWH
Coefficient of Performance (COP) Test Results
Typical Operating Range
Beyond Typical Operating Range
COP Curves for Rheem HPWH COP Curves for GE HPWH
COP Curves for Stiebel Eltron HPWH COP Curves for Air Generate HPWH
8NATIONAL RENEWABLE ENERGY LABORATORY
Draw Profile Test Results Purpose DP1 Results for the Air Generate HPWH Determine realistic HPWH performance using two Draw Profiles DP1 ndash Morning and Evening Draws DP2 ndash Series of Short Draws
Procedure Run draw profile with air and water conditions held constant
Results for DP1 Outlet water temperature fell below lsquohotrsquo value of 405degC depending on storage tank size and control logic Draw Profile COP
- HPWHs with 80 gallon tanks did not have issues maintaining outlet temperature using the heat pump
- HPWHs with smaller tanks dropped below lsquohotrsquo outlet temperature and relied on electric resistance elements thus reducing performance
HPWH COP
(DP1 ndash Morning) COP
(DP1 ndash Evening) COP (DP2)
GE 12 18 35 Rheem 14 26 25
AO Smith 36 34 26 Stiebel Eltron 39 54 31
Air Generate 17 28 NA
9NATIONAL RENEWABLE ENERGY LABORATORY
Preliminary TRNSYS Model Results - HPWH model developed in TRNSYS - Annual simulations run in 6 climate regions in conditioned and
unconditioned space bull Effect on space conditioned was included bull Simulations ran for new homes Existing homes is next step
- Initial results show HPWH technology is applicable in any climate region for electric resistance water heater replacements
- TRNSYS modeling has some limitations including bull Performance map based on data Extrapolation used for conditions not tested bull Home models include simple foundation and infiltration models
- Future modeling efforts will develop an Energy Plus HPWH model for use in NRELrsquos Building Energy Optimization software BEopt
Water Heater Annual Source Energy Consumption in Conditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐53 54 Chicago IL ‐30 42 Houston TX 36 63 Los Angeles CA 70 54 Phoenix AZ 33 58 Seattle WA ‐32 40
Water Heater Annual Source Energy Consumption in Unconditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐025 50 Chicago IL ‐37 37 Houston TX ‐23 35 Los Angeles CA ‐24 35 Phoenix AZ ‐20 35 Seattle WA ‐21 42
These homes have the HPWH located in the basement In all other homes the HPWH is in the garage
NATIONAL RENEWABLE ENERGY LABORATORY 10
Homeowner Concerns Recovery Rate Installation
- Installation location must be large enough to accommodate
1 Size of a HPWH 2 Air flow rate of heat pump
Cost - Units currently range from $1300 to $2600 - Installation costs are expected to be in-line
with conventional water heaters HPWH Cooling Capacity vs Average Tank Temperature
Performance - Cold Climate Performance A HPWH will
perform best in warmer climates but significant energy savings can be achieved in cold climates as well
- Recovery Rate Significantly reduced relative to an electric resistance water heater A larger storage tank will help mitigate this issue
- Cooling Effect Between 02 and 07 tons of refrigeration in typical operating range
11NATIONAL RENEWABLE ENERGY LABORATORY
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Operating Mode Test Results
Purpose Operating Mode Test Summary Table Determine control logic for each HPWH in each mode of operation
Procedure - Starting with a tank of hot water
draw water until heat pump turns on - Allow unit to recover to set point
temperature - Draw water until electric resistance
elements turn on - Repeat for each mode of operation
Results Unique control logic for each HPWH
- Upper lower or combination of both thermistors used to control heating
- Temperature drops ranged from 05degC to 10degC before heating is initiated
GE Rheem A O Smith Stiebel Eltron Air Generate Most efficient Mode eHeat EnergySaver Efficiency On Econ Heat pump Yes Yes Yes Yes Yes Control logic to turn on heat pump
ΔTupper = -05degC
Tlower = 22degC ΔTtank = -5degC ΔTupper = -2degC ΔTlower = -10degC
Resistance elements No Yes No Yes No
Control logic to turn on heating elements
- Tlower = 22degC - ΔTupper = -10degC -
Hybrid Mode Hybrid Normal Hybrid NA Auto Heat pump Yes Yes Yes - Yes Control logic to turn on heat pump
ΔTupper
= -05degC Tlower
= 22degC ΔTtank
= -5degC - ΔTlower = -10degC
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper
= -10degC Tlower = 22degC
ΔTtank
= -10degC - ΔTupper = -10degC
Additional Mode High
Demand NA NA NA NA
Heat pump Yes - - - -Control logic to turn on heat pump
ΔTupper
= -05degC - - - -
Resistance elements Yes - - - -
Control logic to turn on heating elements
ΔTupper
= -3degC - - - -
Resistance-only Mode Electric Only Electric Only Electric Only NA Heater
Heat pump No No No - No Control logic to turn on heat pump
- - - - -
Resistance elements Yes Yes Yes - Yes
Control logic to turn on heating elements
ΔTupper = shy05degC
Tlower = 20degC ΔTtank
= -2degC - ΔTupper = -10degC
- Various control strategies for electric resistance elements
NATIONAL RENEWABLE ENERGY LABORATORY 6
Coefficient of Performance (COP) Test Results
NATIONAL RENEWABLE ENERGY LABORATORY
COP Curves for All HPWHs at Twb = 14degC (67degF)
7
Purpose Map heat pump performance over a wide range of inlet air conditions
Procedure - Set HPWH to operate using only
the heat pump - Fill tank with cold (~3degC) water - Heat water until highest set point
temperature is reached - Calculate ten-minute running
average COP
Results - COP increases with increasing air
temperature - COP decreases with increasing
water temperature - Icing limits heat pump operating
range for some HPWHs for low air and water conditions
Typical Operating Range
Beyond Typical Operating Range
COP Curves for AOSmith HPWH
Coefficient of Performance (COP) Test Results
Typical Operating Range
Beyond Typical Operating Range
COP Curves for Rheem HPWH COP Curves for GE HPWH
COP Curves for Stiebel Eltron HPWH COP Curves for Air Generate HPWH
8NATIONAL RENEWABLE ENERGY LABORATORY
Draw Profile Test Results Purpose DP1 Results for the Air Generate HPWH Determine realistic HPWH performance using two Draw Profiles DP1 ndash Morning and Evening Draws DP2 ndash Series of Short Draws
Procedure Run draw profile with air and water conditions held constant
Results for DP1 Outlet water temperature fell below lsquohotrsquo value of 405degC depending on storage tank size and control logic Draw Profile COP
- HPWHs with 80 gallon tanks did not have issues maintaining outlet temperature using the heat pump
- HPWHs with smaller tanks dropped below lsquohotrsquo outlet temperature and relied on electric resistance elements thus reducing performance
HPWH COP
(DP1 ndash Morning) COP
(DP1 ndash Evening) COP (DP2)
GE 12 18 35 Rheem 14 26 25
AO Smith 36 34 26 Stiebel Eltron 39 54 31
Air Generate 17 28 NA
9NATIONAL RENEWABLE ENERGY LABORATORY
Preliminary TRNSYS Model Results - HPWH model developed in TRNSYS - Annual simulations run in 6 climate regions in conditioned and
unconditioned space bull Effect on space conditioned was included bull Simulations ran for new homes Existing homes is next step
- Initial results show HPWH technology is applicable in any climate region for electric resistance water heater replacements
- TRNSYS modeling has some limitations including bull Performance map based on data Extrapolation used for conditions not tested bull Home models include simple foundation and infiltration models
- Future modeling efforts will develop an Energy Plus HPWH model for use in NRELrsquos Building Energy Optimization software BEopt
Water Heater Annual Source Energy Consumption in Conditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐53 54 Chicago IL ‐30 42 Houston TX 36 63 Los Angeles CA 70 54 Phoenix AZ 33 58 Seattle WA ‐32 40
Water Heater Annual Source Energy Consumption in Unconditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐025 50 Chicago IL ‐37 37 Houston TX ‐23 35 Los Angeles CA ‐24 35 Phoenix AZ ‐20 35 Seattle WA ‐21 42
These homes have the HPWH located in the basement In all other homes the HPWH is in the garage
NATIONAL RENEWABLE ENERGY LABORATORY 10
Homeowner Concerns Recovery Rate Installation
- Installation location must be large enough to accommodate
1 Size of a HPWH 2 Air flow rate of heat pump
Cost - Units currently range from $1300 to $2600 - Installation costs are expected to be in-line
with conventional water heaters HPWH Cooling Capacity vs Average Tank Temperature
Performance - Cold Climate Performance A HPWH will
perform best in warmer climates but significant energy savings can be achieved in cold climates as well
- Recovery Rate Significantly reduced relative to an electric resistance water heater A larger storage tank will help mitigate this issue
- Cooling Effect Between 02 and 07 tons of refrigeration in typical operating range
11NATIONAL RENEWABLE ENERGY LABORATORY
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Coefficient of Performance (COP) Test Results
NATIONAL RENEWABLE ENERGY LABORATORY
COP Curves for All HPWHs at Twb = 14degC (67degF)
7
Purpose Map heat pump performance over a wide range of inlet air conditions
Procedure - Set HPWH to operate using only
the heat pump - Fill tank with cold (~3degC) water - Heat water until highest set point
temperature is reached - Calculate ten-minute running
average COP
Results - COP increases with increasing air
temperature - COP decreases with increasing
water temperature - Icing limits heat pump operating
range for some HPWHs for low air and water conditions
Typical Operating Range
Beyond Typical Operating Range
COP Curves for AOSmith HPWH
Coefficient of Performance (COP) Test Results
Typical Operating Range
Beyond Typical Operating Range
COP Curves for Rheem HPWH COP Curves for GE HPWH
COP Curves for Stiebel Eltron HPWH COP Curves for Air Generate HPWH
8NATIONAL RENEWABLE ENERGY LABORATORY
Draw Profile Test Results Purpose DP1 Results for the Air Generate HPWH Determine realistic HPWH performance using two Draw Profiles DP1 ndash Morning and Evening Draws DP2 ndash Series of Short Draws
Procedure Run draw profile with air and water conditions held constant
Results for DP1 Outlet water temperature fell below lsquohotrsquo value of 405degC depending on storage tank size and control logic Draw Profile COP
- HPWHs with 80 gallon tanks did not have issues maintaining outlet temperature using the heat pump
- HPWHs with smaller tanks dropped below lsquohotrsquo outlet temperature and relied on electric resistance elements thus reducing performance
HPWH COP
(DP1 ndash Morning) COP
(DP1 ndash Evening) COP (DP2)
GE 12 18 35 Rheem 14 26 25
AO Smith 36 34 26 Stiebel Eltron 39 54 31
Air Generate 17 28 NA
9NATIONAL RENEWABLE ENERGY LABORATORY
Preliminary TRNSYS Model Results - HPWH model developed in TRNSYS - Annual simulations run in 6 climate regions in conditioned and
unconditioned space bull Effect on space conditioned was included bull Simulations ran for new homes Existing homes is next step
- Initial results show HPWH technology is applicable in any climate region for electric resistance water heater replacements
- TRNSYS modeling has some limitations including bull Performance map based on data Extrapolation used for conditions not tested bull Home models include simple foundation and infiltration models
- Future modeling efforts will develop an Energy Plus HPWH model for use in NRELrsquos Building Energy Optimization software BEopt
Water Heater Annual Source Energy Consumption in Conditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐53 54 Chicago IL ‐30 42 Houston TX 36 63 Los Angeles CA 70 54 Phoenix AZ 33 58 Seattle WA ‐32 40
Water Heater Annual Source Energy Consumption in Unconditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐025 50 Chicago IL ‐37 37 Houston TX ‐23 35 Los Angeles CA ‐24 35 Phoenix AZ ‐20 35 Seattle WA ‐21 42
These homes have the HPWH located in the basement In all other homes the HPWH is in the garage
NATIONAL RENEWABLE ENERGY LABORATORY 10
Homeowner Concerns Recovery Rate Installation
- Installation location must be large enough to accommodate
1 Size of a HPWH 2 Air flow rate of heat pump
Cost - Units currently range from $1300 to $2600 - Installation costs are expected to be in-line
with conventional water heaters HPWH Cooling Capacity vs Average Tank Temperature
Performance - Cold Climate Performance A HPWH will
perform best in warmer climates but significant energy savings can be achieved in cold climates as well
- Recovery Rate Significantly reduced relative to an electric resistance water heater A larger storage tank will help mitigate this issue
- Cooling Effect Between 02 and 07 tons of refrigeration in typical operating range
11NATIONAL RENEWABLE ENERGY LABORATORY
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Coefficient of Performance (COP) Test Results
Typical Operating Range
Beyond Typical Operating Range
COP Curves for Rheem HPWH COP Curves for GE HPWH
COP Curves for Stiebel Eltron HPWH COP Curves for Air Generate HPWH
8NATIONAL RENEWABLE ENERGY LABORATORY
Draw Profile Test Results Purpose DP1 Results for the Air Generate HPWH Determine realistic HPWH performance using two Draw Profiles DP1 ndash Morning and Evening Draws DP2 ndash Series of Short Draws
Procedure Run draw profile with air and water conditions held constant
Results for DP1 Outlet water temperature fell below lsquohotrsquo value of 405degC depending on storage tank size and control logic Draw Profile COP
- HPWHs with 80 gallon tanks did not have issues maintaining outlet temperature using the heat pump
- HPWHs with smaller tanks dropped below lsquohotrsquo outlet temperature and relied on electric resistance elements thus reducing performance
HPWH COP
(DP1 ndash Morning) COP
(DP1 ndash Evening) COP (DP2)
GE 12 18 35 Rheem 14 26 25
AO Smith 36 34 26 Stiebel Eltron 39 54 31
Air Generate 17 28 NA
9NATIONAL RENEWABLE ENERGY LABORATORY
Preliminary TRNSYS Model Results - HPWH model developed in TRNSYS - Annual simulations run in 6 climate regions in conditioned and
unconditioned space bull Effect on space conditioned was included bull Simulations ran for new homes Existing homes is next step
- Initial results show HPWH technology is applicable in any climate region for electric resistance water heater replacements
- TRNSYS modeling has some limitations including bull Performance map based on data Extrapolation used for conditions not tested bull Home models include simple foundation and infiltration models
- Future modeling efforts will develop an Energy Plus HPWH model for use in NRELrsquos Building Energy Optimization software BEopt
Water Heater Annual Source Energy Consumption in Conditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐53 54 Chicago IL ‐30 42 Houston TX 36 63 Los Angeles CA 70 54 Phoenix AZ 33 58 Seattle WA ‐32 40
Water Heater Annual Source Energy Consumption in Unconditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐025 50 Chicago IL ‐37 37 Houston TX ‐23 35 Los Angeles CA ‐24 35 Phoenix AZ ‐20 35 Seattle WA ‐21 42
These homes have the HPWH located in the basement In all other homes the HPWH is in the garage
NATIONAL RENEWABLE ENERGY LABORATORY 10
Homeowner Concerns Recovery Rate Installation
- Installation location must be large enough to accommodate
1 Size of a HPWH 2 Air flow rate of heat pump
Cost - Units currently range from $1300 to $2600 - Installation costs are expected to be in-line
with conventional water heaters HPWH Cooling Capacity vs Average Tank Temperature
Performance - Cold Climate Performance A HPWH will
perform best in warmer climates but significant energy savings can be achieved in cold climates as well
- Recovery Rate Significantly reduced relative to an electric resistance water heater A larger storage tank will help mitigate this issue
- Cooling Effect Between 02 and 07 tons of refrigeration in typical operating range
11NATIONAL RENEWABLE ENERGY LABORATORY
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Draw Profile Test Results Purpose DP1 Results for the Air Generate HPWH Determine realistic HPWH performance using two Draw Profiles DP1 ndash Morning and Evening Draws DP2 ndash Series of Short Draws
Procedure Run draw profile with air and water conditions held constant
Results for DP1 Outlet water temperature fell below lsquohotrsquo value of 405degC depending on storage tank size and control logic Draw Profile COP
- HPWHs with 80 gallon tanks did not have issues maintaining outlet temperature using the heat pump
- HPWHs with smaller tanks dropped below lsquohotrsquo outlet temperature and relied on electric resistance elements thus reducing performance
HPWH COP
(DP1 ndash Morning) COP
(DP1 ndash Evening) COP (DP2)
GE 12 18 35 Rheem 14 26 25
AO Smith 36 34 26 Stiebel Eltron 39 54 31
Air Generate 17 28 NA
9NATIONAL RENEWABLE ENERGY LABORATORY
Preliminary TRNSYS Model Results - HPWH model developed in TRNSYS - Annual simulations run in 6 climate regions in conditioned and
unconditioned space bull Effect on space conditioned was included bull Simulations ran for new homes Existing homes is next step
- Initial results show HPWH technology is applicable in any climate region for electric resistance water heater replacements
- TRNSYS modeling has some limitations including bull Performance map based on data Extrapolation used for conditions not tested bull Home models include simple foundation and infiltration models
- Future modeling efforts will develop an Energy Plus HPWH model for use in NRELrsquos Building Energy Optimization software BEopt
Water Heater Annual Source Energy Consumption in Conditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐53 54 Chicago IL ‐30 42 Houston TX 36 63 Los Angeles CA 70 54 Phoenix AZ 33 58 Seattle WA ‐32 40
Water Heater Annual Source Energy Consumption in Unconditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐025 50 Chicago IL ‐37 37 Houston TX ‐23 35 Los Angeles CA ‐24 35 Phoenix AZ ‐20 35 Seattle WA ‐21 42
These homes have the HPWH located in the basement In all other homes the HPWH is in the garage
NATIONAL RENEWABLE ENERGY LABORATORY 10
Homeowner Concerns Recovery Rate Installation
- Installation location must be large enough to accommodate
1 Size of a HPWH 2 Air flow rate of heat pump
Cost - Units currently range from $1300 to $2600 - Installation costs are expected to be in-line
with conventional water heaters HPWH Cooling Capacity vs Average Tank Temperature
Performance - Cold Climate Performance A HPWH will
perform best in warmer climates but significant energy savings can be achieved in cold climates as well
- Recovery Rate Significantly reduced relative to an electric resistance water heater A larger storage tank will help mitigate this issue
- Cooling Effect Between 02 and 07 tons of refrigeration in typical operating range
11NATIONAL RENEWABLE ENERGY LABORATORY
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Preliminary TRNSYS Model Results - HPWH model developed in TRNSYS - Annual simulations run in 6 climate regions in conditioned and
unconditioned space bull Effect on space conditioned was included bull Simulations ran for new homes Existing homes is next step
- Initial results show HPWH technology is applicable in any climate region for electric resistance water heater replacements
- TRNSYS modeling has some limitations including bull Performance map based on data Extrapolation used for conditions not tested bull Home models include simple foundation and infiltration models
- Future modeling efforts will develop an Energy Plus HPWH model for use in NRELrsquos Building Energy Optimization software BEopt
Water Heater Annual Source Energy Consumption in Conditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐53 54 Chicago IL ‐30 42 Houston TX 36 63 Los Angeles CA 70 54 Phoenix AZ 33 58 Seattle WA ‐32 40
Water Heater Annual Source Energy Consumption in Unconditioned Space
Location HPWH Savings
vs Gas HPWH Savings vs Electric
Atlanta GA ‐025 50 Chicago IL ‐37 37 Houston TX ‐23 35 Los Angeles CA ‐24 35 Phoenix AZ ‐20 35 Seattle WA ‐21 42
These homes have the HPWH located in the basement In all other homes the HPWH is in the garage
NATIONAL RENEWABLE ENERGY LABORATORY 10
Homeowner Concerns Recovery Rate Installation
- Installation location must be large enough to accommodate
1 Size of a HPWH 2 Air flow rate of heat pump
Cost - Units currently range from $1300 to $2600 - Installation costs are expected to be in-line
with conventional water heaters HPWH Cooling Capacity vs Average Tank Temperature
Performance - Cold Climate Performance A HPWH will
perform best in warmer climates but significant energy savings can be achieved in cold climates as well
- Recovery Rate Significantly reduced relative to an electric resistance water heater A larger storage tank will help mitigate this issue
- Cooling Effect Between 02 and 07 tons of refrigeration in typical operating range
11NATIONAL RENEWABLE ENERGY LABORATORY
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Homeowner Concerns Recovery Rate Installation
- Installation location must be large enough to accommodate
1 Size of a HPWH 2 Air flow rate of heat pump
Cost - Units currently range from $1300 to $2600 - Installation costs are expected to be in-line
with conventional water heaters HPWH Cooling Capacity vs Average Tank Temperature
Performance - Cold Climate Performance A HPWH will
perform best in warmer climates but significant energy savings can be achieved in cold climates as well
- Recovery Rate Significantly reduced relative to an electric resistance water heater A larger storage tank will help mitigate this issue
- Cooling Effect Between 02 and 07 tons of refrigeration in typical operating range
11NATIONAL RENEWABLE ENERGY LABORATORY
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Conclusions
- In general the HPWHs performed well over the operating range tested and are consistent with manufacturer ratings
- Initial modeling results show that HPWH technology can be used in any climate to replace an electric resistance water heater
bull Performance decreases with decreased air temperatures but energy savings of at least 35 can be realized in cold climates
bull HPWHs are not a cost-effective option for replacing gas water heaters in most climates
- Results will be used to improve future HPWH designs bull Control logic changes may be easy to implement with large effect on
performance
NATIONAL RENEWABLE ENERGY LABORATORY 12
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Back-up
HPWH Comparisons
Unit Capacity (Gallons)
Compressor Power (W)
Electric Element Sizes (kW)
Refrigerant Type
Condenser Type
Circulation Pump
Water Lines
GE 50 700 45 Upper 45 Lower
R‐134a Wrap‐Around
Tank No
Top Vertical
Rheem 50 1000 20 Upper 20 Lower
R‐410a Coaxial Heat Exchanger
Yes Side
Horizontal A O Smith
80 960 45 Upper 20 Lower
R‐134a Wrap‐Around
Tank No
Side Horizontal
Stiebel Eltron
80 500 17 Upper R‐134a Wrap‐Around
Tank No
Side Horizontal
Air Generate
66 800 40 Upper R‐410a Immersed
Coils No
Side Horizontal
NATIONAL RENEWABLE ENERGY LABORATORY 13
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Water-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 14
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
Air-Side Schematic
NATIONAL RENEWABLE ENERGY LABORATORY 15
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