The Heat Pump
Does your HVAC system lack electric-resistance or gas heating? Does it have a reversing valve? Then that is a heat pump! Technically speaking, all AC units are heat pumps. But when we say ‘heat pump’ what we mean is a device capable of using the refrigerant cycle to extract usable heat from one area and transfer it to another area where it is desired.
Obtaining Heat From Cold Air
The heat pump cycle is able to extract usable heat energy from places that are ordinarily considered cold to us. Even in winter, an HVAC system with reversing valve, or a dedicated heat pump, is able to extract heat from the winter air. Sounds counter-intuitive, doesn’t it? Any substance above absolute zero has heat energy in it. So the winter air in a good portion of the continental United States has a lot of heat energy in it, even if it feels cold to us.
A good way to understand how a heat pump works is the refrigerator-door analogy. Suppose that to cool your house all you have is a refrigerator and a door frame that fits it perfectly. During the summer you’re going to turn the refrigerator so that the inside faces in and blows cool air inside, and puts the hot air from the coils on the back, outside. During the winter you’re going to turn the refrigerator around and use the coil on the back to heat your house. The heat pump and heating cycle on a modern split system or package unit, functions very much like that.
Other Style Heat Pumps
The heat pump above is an air sourced heat pump, or ASHP. There is another type of heat pump that is very similar, but instead of using the outside air, it uses an antifreeze solution that has been circulated through the ground known as a ground source heat pump, or GSHP. The ground maintains a more steady temperature throughout the year than the air does and is better at absorbing or dissipating heat, and makes for a much higher-efficiency unit. Some of them are even able to obtain above 100% efficiency ratings!
Heat pumps aren’t a terribly complex issue but they can be a little confusing as most people are familiar with them working one way – bringing cool air inside and moving hot air outside. If you can imagine the reverse of that then you have a good working understanding of what a heat pump is and how it works.
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