A heat pump water heater can cut water heating energy costs by 50% or more, and save even more energy if the cool air it produces is used to supplement air conditioning needs.
How It Works
Heat pump water heaters heat water by transferring heat from the surrounding air to the water heater tank. They can be installed to draw heat from indoor air (if cooling is desired) or from outdoor air. Even at relatively cool outside air temperatures, a heat pump water heater can usually extract enough energy to meet water heating needs. It uses the same principle as refrigerators and air conditioners. The difference is that refrigerators and air conditioners are used to remove unwanted heat, while the heat pump water heater captures that heat and puts it to work.
Waste Cooling
Because the heat pump water heater works by removing heat from the surrounding air, it cools the air at the same time. This "free cooling" can be captured for use by installing ducts to transport the cooled air to places that need it. A heating and air conditioning contractor can help you evaluate the cost effectiveness of installing the necessary ductwork and controls, and a system for venting the cooled air outdoors during the heating season.
Applicability
The heat pump water heater provides the best energy savings when used in areas where temperatures are mild. When the air temperature drops below 40° F or rises above 100° F, the heat pump water heater will not operate as efficiently. If you provide a back-up heating source (such as a booster heater installed near the point of use) it may be able to meet the demand. However, remember that increased use of back-up water heating may result in lower savings.
Although heat pump water heaters are not widely used for residential domestic water heating, most likely due to their higher initial cost, they are an excellent option for heating swimming pools. In fact, the majority of water heaters using heat pump technology are designed and sold specifically as swimming pool or spa heaters.
Heat Pump Water Heater Types
Retrofit or Add-on Heat Pump Water Heater
There are two types of heat pump water heaters: a retrofit or add-on heat pump to work with your existing water heater, or an integral unit that includes the water storage tank and heat pump all in one. In general, if the existing water heater is in good condition, the retrofit or add-on unit is a good choice. If water heater replacement is necessary (or anticipated in the near future), an integral unit is the optimal solution.
Integral Heat Pump Water Heater
Installation Tips
Follow these guidelines when installing either a retrofit or integral unit:
- Follow the manufacturer's guidelines for minimum dimensions of the area in which the unit will be installed. If installed in smaller areas, extra ventilation must be provided. Refer to the manufacturer's literature for exact specifications.
- Install the unit in an area that won't be adversely affected by the waste cooling.
- If possible, install the unit near equipment that produces waste heat; such as dryers, boilers, or furnaces.
- Provide a drainage outlet for condensation. During humid weather, the heat pump water heater may produce as much as five pints of condensation every hour.
- Install a pressure relief valve and direct the discharge outdoors or into the condensation drain.
- Insulate exposed hot water pipes to reduce heat loss.
When installing a retrofit unit, follow these installation guidelines:
- Install a shut-off valve on each line between the heat pump and the water heater tank.
- Supply back-up heating, if necessary. In a retrofit situation, you can usually leave the electric heating elements and thermostats in the storage tank intact. When the heat pump alone can't satisfy the thermostat setting, the electric elements will turn on and make up the difference.
- If back-up heating is unnecessary, disconnect the heating elements in the storage tank (or turn off the circuit breaker).
