How Do I Switch a Heat Pump From Heating to Cooling?

Heat pumps are becoming increasingly popular for year-round climate control for homes and office buildings in moderate climate zones. While supplying ultra high-efficiency cooling during summer months, they can also provide heat during winter more efficiently than resistance heating provided that the outside temperature is above about 30 degrees Fahrenheit. Switching a heat pump from heating to cooling in a residential system is a simple procedure with the heat-cool mode selector switch on the wall thermostat.

Air Conditioning Operation

Standard residential air conditioners, window units and central systems, are types of heat pumps that are intended to provide only interior cooling. Heat pumps are a type of sealed continuous refrigeration system that absorbs heat in one location by evaporating a refrigerant such as Freon, and then discharging the heat by condensing the refrigerant in another location. In hot weather, heat pumps used in air conditioning mode provide comfort by absorbing heat inside the building at a lower temperature and releasing it outside the building at a higher temperature. They also reduce relative humidity by condensing water out of the warmer air merely by cooling it.

Cooling to Heating Switch

Switching a heat pump from cooling to heating is functionally equivalent to turning a window air conditioner around in the window so that the heat is absorbed outside and discharged inside the room instead of outdoors. A heat pump accomplishes this changeover by crossing the condenser and evaporator using an X-type exchange valve. In the heating mode, hot high pressure refrigerant from the compressor is routed to the heat exchanger inside the house instead of to the heat exchanger outside the house, as is the case with cooling mode. Then cold-expanded refrigerant is sent to the heat exchanger outside the house to absorb more heat from a cooler environment.

Heating to Cooling Switch

Sometime during the spring thaw, the homeowner will want to switch the climate control to cooling mode using the operation mode switch on the wall thermostat. This procedure will again cross exchange the refrigerant routing within the heat pump system by sending hot compressed liquefied refrigerant to the outside heat exchange unit, making it a condenser, and sending the cold expanded gaseous refrigerant to the inside heat exchanger, again making it an evaporator.

Summarizing a Simple Exchange

Heat pumps in cooling mode absorb heat inside the building and expel it outside the building. Heat pumps in heating mode absorb heat outside the building and expel it inside. A heat-cool mode switch on the thermostat accomplishes this exchange.

References

• Carrier; Heat Pumps
• Ask the Builder; Heat Pumps--How Well Do They Work?; Tom Carter

Resources

• Energy Savers; Heat Pump Systems