Heat pumps transfer heat from one space to another using a compressor and refrigeration circuit. For heat pump water heaters, this is the transfer of heat from the environment into the water. They operate in reverse to the refrigeration cycle that cools the food in a refrigerator. This diagram shows how a heat pump water heater works. Typically, 3 kilowatts of heat from the outside is transferred to the water for every 1 kW of electricity supplied to the compressor.
By CHARLES CHAVES/ecoRI News contributor
"We rely on having sufficient hot water for showering, washing clothes and dishes, among other needs. About 14 percent of a typical household’s energy bill goes to water heating, which is the biggest energy expense apart from heating and cooling, according to the U.S. Department of Energy.
In particular, the cost of heating water is significantly higher for homes using electric water heaters. A heat pump, however, heats water more efficiently than an electric one — thus saving energy and reducing electricity costs.
A heat pump works by absorbing heat from ambient air and transferring it to the water in the storage tank, and hence there must be an appropriate volume of air surrounding it for optimal operation. A heat pump water heater (HPWH) is much like a refrigerator or air conditioner in that a refrigerator moves heat from one’s fridge to the kitchen. For an HPWH to operate efficiently, surrounding space should generally remain above 50 degrees.
Heat pump water heaters remove moisture from the air and as such condensed water must be drained or a condensate pump must be installed. Many HPWHs have air filters that should be cleaned regularly for optimal performance. It’s also generally suggested to install heat pump systems away from bedrooms, given that they make a noise similar to that of an air compressor on an air conditioner. As a beneficial upside, a heat pump keeps basements cooler and drier in the summer, making it possible to pipe cool basement air upstairs.
Heat pump water heaters have been widely utilized in Japan for years, where energy efficiency has long been a focal concern. However, such technology is relatively new to the U.S. market. HPWHs nevertheless resonate with those who are trying to find viable energy technologies that save money and help mitigate vexing environmental issues such as pollution and climate change.
A new 50-gallon heat pump water heater costs about a $1,000, excluding installation, which is similar to a standard electric water heater. To help offset the initial cost, National Grid offers a rebate of $750 to replace an existing electric hot water heating system."
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