Heat Pumps
A heat pump leverages the heat/cool in an external heat source. External heat sources can be air, water and ground.
Regardless of the heat source, the source will provide heat for an evaporator to gasify a refrigerant. A compressor will then send the gas to a condenser where it cools and condenses back to a liquid releasing the heat energy. A heat exchanger captures this heat and sends it to the facility.
A heat pump can work in reverse, using the external heat source to provide cooling for the facility.
Heat pumps essentially translate electricity into heat. Simple baseboard heaters have a “coefficient of performance (COP)” of one. This means that for one unit of input electricity energy, we get one unit of output thermal energy.
Heat pumps improve the COP depending on the temperature of the heat source as shown in the COP performance curve. As the temperature of the heat source increase, so does the COP performance for heating. For example, if the heat source is -30C, then the COP is close to 1. If the heat source is 20C, then the COP is 5.
For cooling mode, the COP performance curve changes. In this case, as the heat source temperature increase, the COP performance for cooling decreases.
Air source heat pumps
Air source heat pumps are the simplest and most popular. The evaporator is a unit that sits outside the facility and leverages the ambient outdoor temperature to provide heat or cooling. The advantage of these systems is that they are simple, cheaper and easy to install. However, their performance (COP) varies dramatically given the season swings in outdoor temperatures.
Water source heat pumps
Water source heat pumps leverage the seasonally consistent temperature from a water source such as the ocean or a deep lake. Most often, the water source provides a consistent 5-10C thermal source regardless of time of day or season. This makes water source heat pumps much more predictable in terms of their coefficient of performance. However, these systems are more expensive to install and require access to a water source.
Ground source heat pumps
Ground source heat pumps are often referred to as “geothermal” as they leverage the consistent temperatures from shallow buried pipes. Most often, the ground source provides a consistent 10-15C thermal source regardless of the time of day or season. This makes water source heat pumps much more predictable in terms of their coefficient of performance. However, these systems are very expensive to install.
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For a video on heat pumps and how they work, see here.