A heat pump is a mechanical refrigeration system. It is arranged and controlled to utilize the condenser heat. The condenser heat is wasted or dissipated into the air when a condenser-compressor are mounted outside a building being air conditioned. By utilizing the heat generated by the condenser can be used for some useful purpose. This useful purpose is in most instances, space heating. Heat-pump systems may be classified as:
• Package, or built-up
Earth coupled systems are also used as a variation of the water-to-water concept. Keep in mind that the heat pump is primarily a central air conditioner. It can also act as a heating system. During the cooling season the heat pump performs exactly like a central air conditioner. It removes heat from the indoor air and discharges it outside. See Fig. 17-17.
During the heating season, the heat pump reverses its function. It changes from a cooling system to a heating system. It then removes the available heat from the outdoor air and discharges it inside the house. See Fig. 17-18.
There is heat in outdoor air, even at 0°F (−17.8°C). In fact, heat is available in outdoor air down to −460°F (−273°C).
Since the heat pump is a refrigeration machine, it needs only enough electrical power to run a compressor, an outdoor fan, and an indoor blower. The result is a heating system with a seasonal efficiency of better than 150 percent. This means that for every kilowatt of electric power used, the heat pump will produce more than 1.5 kW of heat energy. Only the heat pump can give this level of efficiency.
Heat pumps are available in all sizes for apartments, homes, and commercial applications. Heat pumps are not new. General Electric has been selling them since 1952. There are now various types of units on the market.
One unit, the Fuel master, works with a heat pump. It can be used with gas, oil, and electric furnaces. See Fig. 17-19. As can be seen from the illustration, the heat pump resembles a compressor-condenser unit. However, the control box is different. See Fig. 17-20. The control box has relays and terminal strips factory installed and wired. The heat pump delay and defrost limit control are included in the unit.