The best way to describe a heat pump to somebody who is unfamiliar with them is to explain that a heat pump is similar to an air conditioner—with the important difference that a heat pump can switch the direction it works so that it will also heat the interior of a house. An air conditioner operates by evaporating refrigerant indoors to absorb heat and then condensing the refrigerant outdoors to release heat. A heat pump can do that, but it can also reverse the process so it releases heat inside.
That’s the difference in how the two operate. But what is the difference in the actual systems? What allows a heat pump to be able to change the direction it runs with only a single adjustment on the thermostat? We’ll go into those details below.
The reversing valve
Heat pumps and air conditioners share most of the same components because they run according to an identical principle: a compressor places refrigerant under pressure so that it circulates between two sets of coils. The refrigerant goes through a process of condensation (heat release) and evaporation (heat absorption). But a heat pump has a few additional components that allow it to toggle between heating and cooling. The most important of these components is the reversing valve.
This is a four-way valve that is able to switch the direction the refrigerant flows. As refrigerant leaves the compressor, it enters this valve. If the heat pump is set for cooling mode, the valve sends the heated refrigerant toward the outdoor coils first, where heat is released. If the heat pump is set for heating mode, a slider in the valve will send the refrigerant toward the indoor coils first, releasing heat indoors.
Liquid refrigerant entering the suction line of a heat pump can cause damage to the compressor. This is a potential danger with a heat pump because of the change in direction of the refrigerant. The suction line accumulator is designed to prevent this from happening.
The Defrost Cycle
Because heat pumps run during cold weather as well as hot weather, the outdoor coils can freeze over because of the moisture that develops on them as they pull heat from the air. This will eventually cause the heat pump to be unable to heat the home. To keep this from happening, a heat pump will occasionally switch into a defrost cycle. Devices called thermistors, temperature sensitive resistors, detect when a defrost cycle is necessary. During the defrost cycle, the heat pump will briefly switch back to cooling mode so that heat is released through the coils. This melts the ice so the heat pump can get back to normal heating operation.
If you need assistance with either an air conditioner or a heat pump in Bellevue, WA or the surrounding areas, we’re the local HVAC contractor to call! You can reach our technicians any time of the day or night when you have a home comfort emergency—they’re standing by to help!
S&L Mechanical Heating and Cooling serves the Greater Bellevue Area. Quality Service for Quality Living!