Hot-water use in restaurants, laboratories, dormitories, hospitals, and other institutions can be a generous percentage of the utility costs. Many such facilities have a commercial-grade heat pump to provide space conditioning, or several heat pumps serving different areas of the facility. Heat pumps reject heat to the air at the condenser by way of a refrigerant circuit from the inside air handler. An inexpensive add-on device called a desuperheater can transfer a portion of this heat to the domestic hot water. All it takes is a shell-in-tube heat exchanger with a few controls and a thermostat to circulate water (when the compressors are operating) from the hot-water tank through the desuperheater. Once the water is at the setpoint temperature, the flow halts, and the system
goes off-line.
This arrangement accomplishes three tasks:
1. The heat pump operates much more effectively since the fluid-to-water heat-transfer rate is much more efficient than the fluid-to-air process;
2. The condenser fan does not have to run when heat is being absorbed by the water; and
3. The water heater does not have to use purchased energy to supply the demand, thus saving use as well as demand costs on the utility bills.
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Excerpted from Going Green, available as an eBook at this list of eBook retailers online.