Heating water takes a great deal of energy, due to its high heat capacity. In fact, domestic water heating accounts for 19% of total energy consumption in the average American home, according to the US Energy Information Administration. Therefore, increasing water heater efficiency results in a significant reduction of energy consumption whilst providing an opportunity for monetary savings.
One such high efficiency solution is the heat pump hot water heater (HPWH). HPWHs operate using the same thermodynamic cycle as a refrigerator or air conditioner. Like those devices, HPWHs siphon heat from an area of low temperature and transfer it to one at a higher temperature. Whereas air conditioners and refrigerators provide cold air and output heat as a byproduct, HPWHs produce hot water while generating cool, dry air.
In favorable environmental conditions, an HPWH offers a coefficient of performance (COP) of roughly three, meaning that the amount of heat energy transferred to the water is approximately three times the electrical input of the water heater. This is possible since the electrical input to the HPWH is not used to directly heat water; instead, it is used to force the transfer of heat energy from the surroundings to the water. Due to this fact, it is generally desirable to install an HPWH in an unheated space.
In use, an HPWH is very similar to a conventional electric hot water heater, despite operating on different principles. However, there are a few distinctions. HPWHs require access to a large body of air from which to remove heat. This can be achieved by placing the unit in a large room or by running ducting. An HPWH provides a degree of dehumidification and cooling to its surroundings during operation. This is particularly desirable when installed in a basement. Much like a refrigerator, these units make some noise because they contain a compressor and a fan. A drain for condensate is required, like a dehumidifier.
As with any device that operates on the refrigeration cycle, performance tends to decrease as the temperature difference between the hot and cold sides increases. In this case, the temperature difference is between the heated water and the surrounding air. For this reason, most HPWHs on the market are of the hybrid variety. Along with a heat pump, hybrid units contain conventional resistance heating elements that can be activated when ambient temperatures are too low, or when the heat pump cannot meet peak hot water demands.
The Solar Initiative is now offering a subsidy towards the purchase and installation of HPWHs on Block Island. Specifically, the Solar Initiative will contribute 50% of the installed cost up to a maximum of $1,000.
For more information, please contact Wade Ortel at wade@thesolarinitiative.com