An add-on heat pump water heater (HPWH) is only one of several technologies to cool and dehumidify a house as it provides your hot water. Others use heat exchangers, combination fresh air ventilators/dehumidifiers or the earth itself for low-cost water heating and better comfort.
A super-efficient HPWH can cut water heating costs by 60% - a savings of more than $200 per year. As it heats the water, it produces up to 7,000 Btu per hour (Btuh) of free cooling and dehumidification.
A typical HPWH is somewhat like a mini-air conditioner; however, instead of transferring the waste heat outdoors through the condenser coils, it transfers this heat to your hot water tank. HPWH's are usually located in a utility room or basement. They are only about 18 to 24 inches square. If your space is limited, several round HPWH's are designed to mount on top of an existing electric water heater.
A small HPWH is usually adequate for much of a family's hot water needs in the summer. It can turn a musty old basement into comfortable dry living space or the cool dried air can be ducted to another area of your house. Microprocessors control the operation and they have simple digital readouts.
One new model, Aqua Plus, is designed with one heat exchanger in the main central air return duct. It draws extra heat out of the return air reducing the load on your central air conditioner. Another heat exchanger transfers this heat to the hot water tank. This extra cooling helps on extremely hot days.
Another option is a ground source heat pump to use the earth's natural heat. When the central air-conditioner runs, heat from your house is transferred to the ground. When it stops, the HPWH runs and pulls this extra free heat back out of the ground. Overall, both systems run more efficiently.
Therma-Vent is a HPWH designed to continuously bring in fresh outdoor air for a healthy indoor environment. A small heat pump cools and dehumidifies the incoming fresh air and transfers this waste heat to the water heater. In the winter, it draws the heat from the outgoing warm stale air.
Several desuperheater devices capture the heat from the air conditioner's freon before it goes outdoors and direct it to the water heater. One design, Heat Harvester, uses a freon-to-water heat exchanger and small pump. Another space-saver model, Hot Plate, is located beneath the existing water heater.