Heat Pump Basics, A Homeowner's Guide
With these heat pump basics, you will be able to make more informed HVAC decisions. The units work like a normal central air conditioning system. The main difference is that instead of taking the colder months off, the unit must work all year long.
When your thermostat senses a need for cooling, the fan in the furnace or air handler comes to life.
This fan blows air over a coil containing refrigerant. The outdoor unit contains a pump which is called a compressor.
This compressor pumps the refrigerant to the air handler where heat from the air is transferred to the refrigerant. Then the refrigerant is returned to the outdoor unit.
Here another fan pulls air over another coil and the heat is transferred to the outdoor air. This process is repeated over and over until the home is cool.
To provide heat to the home a few components are added to the basic air conditioner. A reversing valve is added to change the direction of refrigerant flow. In the heating mode, this makes the refrigerant temperature higher then the indoor temperature. Therefore, when the refrigerant flows to the indoor unit, heat is transferred to the homes' air.
When it gets below freezing outside, ice can build up on the outdoor coil. This reduces the units' ability to provide the required heat. Therefore, a process is required to melt this ice.
That process is called a defrost cycle. Most units use a timer, a thermostat, or a combination of the two to control this process. When the control senses the need, the outside fan is stopped and the reversing valve directs the hot refrigerant to the outdoor coil. This causes the ice to melt and the process is stopped by another thermostat in the outdoor unit.
To keep from blowing cold air into the home, during this process, backup heat is provided by the furnace.