How it works
A heat pump moves heat from one place to another. The parts of a heat pump system sit in two places, an outdoor unit and an air handler indoors, joined by two refrigerant lines.
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The heating cycle, outdoors
Liquid refrigerant passes through the expansion device into the outdoor coil, where it takes heat from the outdoor air and boils. The vapor crosses the reversing valve to the accumulator, which catches any liquid, and on to the compressor. The compressor squeezes it, and that makes it hot.
Indoors
The reversing valve sends the hot gas along a refrigerant line to the indoor coil in the air handler. The blower pushes air over the coil, the gas gives up its heat and turns back to liquid, and the liquid returns outdoors. The thermostat tells the system when to run.
- Switch the reversing valve and the refrigerant runs the other way: the same parts then cool the house.
Questions and answers
What are the main parts of a heat pump?
A compressor, two coils (one outdoors and one indoors), an expansion device and a reversing valve, joined by refrigerant lines. A fan moves air over the outdoor coil and a blower moves air over the indoor coil.
What does the reversing valve do in a heat pump?
It controls the direction the refrigerant flows, which switches the heat pump between heating and cooling.
What is the difference between a heat pump and an air conditioner?
An air conditioner made for cooling only moves heat out of the house. A heat pump has a reversing valve, so it can also run the cycle the other way and bring heat in from the outdoor air.
What does the accumulator do in a heat pump?
It sits between the reversing valve and the compressor and collects liquid refrigerant that did not turn to vapor, before the vapor enters the compressor. Not all heat pumps have one.
Why does a heat pump have a strip heater?
For supplementary heat. As the outdoor air gets colder, a heat pump can take less heat from it, and electric resistance strips make up the rest.