Heat Pump Water Heater-Residential Integrated Units
Electric Water Heater: Heat Pump vs. Electric Resistance
Heat pump water heaters (HPWHs) use a heat pump refrigeration cycle to remove heat from the surrounding air and transfer that heat at a higher temperature into the integral hot water storage tank. “Integrated Units” means that the heat pump and water heater tank are pre-manufactured as a single piece of equipment.
Item ID: 172
Water Heating--Water Heaters
Technical Advisory Group: 2010 HVAC TAG (#3)
Average TAG Rating: 3 out of 5
TAG Ranking Date: 06/29/2010
Heat pump water heaters (HPWHs) use electricity to transfer heat from the ambient air to stored water, as opposed to using electric resistance heat or natural gas for water heating. This enables them to be two to three times more energy efficient than conventional electric resistance water heaters (FEMP Promising Technologies List).
To move the heat, heat pumps work like a refrigerator in reverse. While a refrigerator pulls heat from inside a box and dumps it into the surrounding room, a stand-alone air-source heat pump water heater pulls heat from the surrounding air and dumps it — at a higher temperature — into a tank to heat water.
Water heating accounts for 3,030 kWh annually or 15%–20% percent of electric energy use in homes with electric water heat ( Ecotope, 04/28/2014). New HPWHs offer an energy-savings potential of 50% or more. The cost of this product is approximately $600–$1,300 above the installed cost of a conventional 50-gallon electric water heater, so the simple payback of a HPWH is expected to be in the range of 5–16 years.
HPWHs work best in locations that remain between 40⁰ to 90⁰F year-round and provide at least 1,000 cubic feet of air volume around the water heater. Cool exhaust air can be exhausted to the room or outdoors. Locating the HPWH in an attached garage is ideal, but when installed in an unconditioned space, the reduced temperature in the winter will reduce performance. Heat extracted by the HPWH from a conditioned space in the heating season will require more heat input from the existing space heating system. In an electric resistance heated house, heating the water with heat from the conditioned space provides no energy savings as it results in a water heating COP less than 1.0.
Baseline Description: Electric resistance water heater
Baseline Energy Use: 3030 kWh per year per unit
The 2014 Ecotope "Residential Building Stock Assessment: Metering Study" provides the annual average electric water heating energy by site. The average annual energy use for electric water heaters in the Northwest region is 3,030 kWh/year ( Ecotope, 04/28/2014 Pg Table 31).
Manufacturer's Energy Savings Claims:
BPA's "Heat Pump Water Heater Laboratory Testing Results" studied HPWH's from three different manufacturers. They examined use in various climate zones, with HPWHs from three different manufacturers located in garages, unheated basements, and in conditioned space. COPs for the various HPWHs varied from 0.8 to 2.3. They noted that the system is highly interactive as heat extracted from conditioned space in the heating season will require more heat input from the heating system. In an electric resistance heated house, heating the water with heat from the conditioned space requires additional space heat and results in a COP of 1---the heat pump provides no benefit as it is equivalent to heating the water with resistance heat. Lab testing also found that some energy to heat water always comes from the resistance heating elements and the compressor. Use of a HPWH in a gas-heated house results in increased therm usage. Homes with heat pumps have a reduced interaction relative to electric resistance heated houses (Bedney, 2011).
Best Estimate of Energy Savings:
"Typical" Savings: 50%
Energy Savings Reliability: 6 - Approved Measure
The 50% savings is based on comparison to electric resistance heaters. While the operative term in this Emerging Technology is "integrated," and is a comparison with split systems, this does not show the potential of savings in typical examples. The Building Technologies Office of the U.S. Department of Energy assumes a 55% savings in the "Buildings Prioritization Tool".
Note: This is a deemed measure under the October 1, 2014 BPA "Energy Efficiency Implementation Manual". The deemed amount is $300 to $500 per water heater.
Energy Use of Emerging Technology:
1,515 kWh per unit per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
According to the 2011 Residential Building Stock Assessment (RBSA), there are a total of 6,190,672 living units in the Northwest. It also states that 18.7% of the multifamily units have central hot water systems. Taking that into account, and using the percentages of electric water heaters in the RBSA gives a total of 3,369,102 electric water heaters in the Northwest in all locations. The derivation of this total is given in the table below.
| ||Living Units ||% Elect. |
|% Homes |
|# Elect. |
| Single Family Homes || 4,023,937 || 55.2% || 100 || 2,221,213 |
| Manufactured Homes || 543,730 || 88.9% || 100 || 483,375 |
| Multifamily Units || 863,104 || 94.7% || 81.3 || 664,513 |
| Total || 5,430,771 || || || 3,369,102 |
If heat pump water heaters are only installed in unconditioned spaces, e.g., the basement, crawlspace or garage, that reduces the total technical potential to 1,422,646, or about a third of the total potential (David Baylon, 2012-09-18 Pg Table 105). Finding a way to use heat pump water heaters effectively in conditioned spaced (e.g., with ducting or with split systems) more than doubles the technical potential indicated by this analysis. According to the Sixth Northwest Conservation and Electric Power Plan (NWPCC, 2010 Pg 4-7), the achievable potential of heat pump water heaters in the Northwest is 490 MWa, assuming a 50% penetration.
Regional Technical Potential:
| ||# Elect. |
|% in |
|% in |
|% in |
| Single Family Homes || 2,221,213 || 28.8% || 3.6% || 31.3% || 1,414,912 |
| Manufactured Homes || 483,375 || 0.8% || 0.2% || 0.6% || 7734 |
| Multifamily Units || 1,249,569 || || || || |
| Total || 3,369,102 || || || || 1,422,646 |
2.16 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: unit
Emerging Technology Unit Cost (Equipment Only): $1600.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $100.00
Baseline Technology Unit Cost (Equipment Only): $1000.00
The GE and Rheem units retail at approximately $1500–$1,600, which is $600–$1,300 above the installed cost of a conventional 50-gallon electric water heater, assuming that installation costs are similar.
Simple payback, new construction (years): 4.4
Simple payback, retrofit (years): 12.5
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
Water heating accounts for 15%–20% percent of electric energy use in homes with an electric water heater. New HPWHs have an energy-savings potential of 50% or more. Based on the figures above:
• 1,000–1,500 kWh annual savings per home,
• Marginal cost of $600–$1,300, and
• Electricity cost of $0.08/kWh,
The simple payback for a HPWH ranges from 5–16 years.
Heat pump water heaters (HPWHs) use a heat pump refrigeration cycle to remove heat from the surrounding air and transfer that heat at a higher temperature into the integral storage tank. An “Integrated Unit” means that the heat pump and water heater tank are pre-manufactured as a single piece of equipment. These are also sometimes called “drop-in” or stand-alone units, as opposed to add-on units that work in conjunction with your existing water heater. All drop-in units now available have a backup electric resistance heating element that is used for supplemental heat when the ambient temperature gets too low for the heat pump to work effectively.
The standard practice for residential domestic water heating where natural gas is not available is to use electric water heaters with electric resistance heating elements. If natural gas is available and natural gas water heating is an option, then heat pump water heaters are not as desirable an option from a first cost and electric energy savings standpoint.
HPWHs have been in use in warm climates for over 20 years—starting as early as the 1970s—but have not taken root in the Pacific Northwest because they perform poorly in climates with cold winters. However, manufacturers are beginning to develop HPWH equipment that performs well in colder conditions, which will help facilitate this technology’s adoption in the Pacific Northwest. The Northwest Energy Efficiency Alliance (NEEA) has recently spearheaded an effort to create a specification for residential HPWH's installed in northern climates. This should help manufacturers know what changes to make in order to perform well in this market, and a few of the manufacturers are already making some of the changes required in the specification.
Early HPWHs were unreliable. Since the 1970s, several attempts have been made to commercialize HPWHs. Typically, they have rushed to market and failed, then been taken off the market. Commercial equipment has had more success than residential, with increasingly more solid offerings. With improved technology and the help of the NEAA specification, HPWHs should enjoy more success in the market this time around.
BPA is conducting a field test of integrated heat pump water heaters. They were installed in 40 homes in the Northwest (in all climate zones) with 13 control group homes also being monitored. This effort is part of a larger U.S. study being conducted by the Electric Power Research Institute (EPRI) of 160 installations.
End User Drawbacks:
There are questions about the effectiveness of HPWHs in cold climates and their savings potential in the Pacific Northwest. They cost approximately $600-$1300 above the installed cost of a conventional 50-gallon electric water heater. A good location is in an unfinished interior space, like a garage, but even there, adequate ventilation must be assured for best performance. The best location is actually outside, protected from the weather. However, the user needs to be aware that the HPWH can lower the temperature of the space it is in significantly if the space is closed and inadequately vented. This may be an advantage in the summer, but a detriment in the winter. If the HPWH cools the space enough, it will cause the auxiliary electric resistance heat to come on more frequently than it would in a fully vented space. NREL estimates that net energy savings due to this HVAC interaction will result in a decrease in HPWH net energy savings of 14% to 63% (depending on climate zone) when the home is electrically resistance heated and from 11% to 35% when the home is heated and cooled by an air source heat pump (Widder, Page 2.3). HPWHs also make more noise than traditional water heaters, and they are more complex equipment so maintenance costs may be higher.
PNNL evaluated the impact of providing exhaust ducts or both supply air and exhaust ducts for an interior HPWH. The exhaust duct alone resulted in an increase in energy use due to increased infiltration resulting from depressurizing the interior space. The fully-ducted comparison showed benefits in terms of reduced HVAC interaction, but results in a higher installation cost (Widder, 2014).
Lastly, the heat pump water heaters currently available are equipped with single speed compressors with a rated Coefficient of Performance (COP) of 2.0 to 2.5. Studies are underway to develop a split-system Carbon-Dioxide heat pump water heater with a dedicated, variable-speed outdoor compressor. This unit would have a COP of 3.0 and would not add to or capture the space heat load of the home to which it supplies hot water (BPA Technology Innovation Project, 2014). Current technology may be a bridge to the availability of more efficient equipment in the near future.
Operations and Maintenance Costs:
No information available.
Fifteen years is a reasonable expectation for the effective life of this product, which is somewhat longer than a standard gas or electric water heater.
Increasingly, ground source heat pumps (GSHP) have been used in the region in custom residential projects for space heating as well as domestic hot water heating. However, the cost implications of GSHP technology make it unlikely that GSHPs will ever take a significant portion of the single family residential market. As a result, there are no other currently viable competing technology options for domestic water heating in the residential sector.
Reference and Citations:
Energy Savings and Breakeven Cost for Residential Heat Pump Water Heaters in the United States
National Renewable Energy Laboratory
Some of the findings in this report are somewhat surprising. Most interesting and relevant is that in the PNW (and other heating dominated climates) in an all-electric home with an efficient heating system (i.e., heat pump), it turns out to be more efficient and cost-effective to locate the HPWH in the conditioned space.
Baylon, et. al.,
2011 Residential Building Stock Assessment: Single-Family Characteristics and Energy Use
Northwest Energy Efficiency Alliance & Ecotope
Heat Pump Water Heaters
Bonneville Power Administration
Northern Climate Heat Pump Water Heater Specification
Northwest Energy Efficiency Alliance
BPA makes strides with utility partners on heat pump water heater demonstration
Bonneville Power Administration
Heat Pump Water Heaters
U.S. Department of Energy
Heat Pump Water Heater Technology
Building America Residential Buildings Energy Efficiency Meeting
Case Study: Heat Pump Water Heater Retrofit
Energy Efficiency & Renewable Energy
In this project, the Pacific Northwest National Laboratory studied heat pump water heaters, an efficient, cost-effective alternative to traditional electric resistance water heaters that can improve energy efficiency by up to 62%.
Buildings Prioritization Tool
U.S. DOE, EERE, Building Technologies Office (Click on View Required Application Documents, then RFI Attachments.)
Sixth Northwest Conservation and Electric Power Plan
Northwest Power and Conservation Council
"Melting" Drywall Keeps Rooms Cool
MIT - Technology Review
Northwest Heat Pump Water Heater Market Test Assessment
Northwest Energy Efficiency Alliance
Residential Building Stock Assessment: Metering Study
Northwest Energy Efficiency Alliance
Heat Pump Water Heater Laboratory Testing Results
Presentation to: BPA HPWH Advisory Committee
TIP 292: Advanced Heat Pump Water Heater Research
Bonneville Power Administration Technology Innovation Project
Impact of Ducting on Heat Pump Water Heater Space Conditioning Energy Use and Comfort
Pacific Northwest National Laboratory