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.
If you live in an area where it regularly drops below freezing, these units may not be right for you.
If you do live in these areas, you can use these units. But, it is usually a good idea to have a control installed so the unit does not run when it is freezing. This is called an outdoor thermostat. When the outdoor temperature drops below its' setpoint, it can shut off the outdoor unit and use the furnace to provide the required heat.
The latest thing on the market is called a hybrid heat system. This system combines a heat pump with a gas furnace. This control senses which type is more cost effective and switches back and forth as conditions change.
Because these units provide both heating and cooling, it is even more important that you have the proper size. The wrong size unit will steal money from your pocket the whole year long. That can add up in a hurry!