It’s often repeated that a heat pump works like a refrigerator, and it heats your home like a refrigerator in reverse. But how many people know how a refrigerator works?
This is how Dana Fischer, the residential program manager at Efficiency Maine, explains what’s going on.
The basis for both devices is to move heat energy from one place to another by circulating refrigerant gas between two radiator coils, with the help of an electric compressor pump.
In this cycle, a special refrigerant that’s contained in copper lines is pumped in a loop between an outdoor radiator coil and an indoor radiator coil. As the refrigerant travels through the loop, it’s placed under high pressure by a compressor at one radiator coil, then under lower pressure, just before entering the other radiator coil.
This cycle alternately absorbs and gives off heat, as long as circulation continues. The refrigerant itself is never lost, because it’s contained in a closed-loop system.
In some ways, heat pumps act like sponges. They absorb heat from outside air, then squeeze it out into your living room, repeating the cycle continuously to heat your home. A dry sponge can absorb and hold moisture from a wet countertop. When you squeeze the sponge, the water pours out, and the sponge can be used again to absorb moisture.
Here’s how that process heats your home: a heat pump can absorb heat energy from outdoor air, even when it is very cold outside. That’s because the refrigerant has a boiling point of -55F. So even when it is -10F outside, the air traveling through the outdoor radiator will get colder as it warms the refrigerant in the coil.
When the slightly-warmer refrigerant enters the compressor pump, both the refrigerant and the absorbed heat energy are compressed to the point where they are more concentrated than the heat energy in your living room. In other words, the refrigerant is hot, not because heat energy was added by the compressor, but because the absorbed heat was concentrated by the compressor.
In the indoor air unit, a fan draws air across the radiator coil flowing with hot refrigerant, pouring the concentrated, absorbed heat into your living room. The refrigerant, now room temperature, returns to the outside radiator coil through a special low pressure valve. That allows the refrigerant gas to expand, returning to -55F and absorbing heat
once again.
In the summer, a heat pump can reverse its cycle, absorbing heat from indoor air, then squeezing it out through the outdoor radiator coil to provide cooling.
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