What is a water source heat pump?
A water source heat pump is a fully packaged, ready to run, device which cools or heats a space. It rejects the heat from the room (in cooling mode) or collects the heat to warm the room up (in heating) using a water loop. This water loop can be heated by a remote boiler or cooled by a dry cooler or cooling tower. It is not limited by needing a remote outdoor unit to operate.
How it works
It is a typical refrigeration circuit.
In cooling heat - a lot of heat - is taken out of the room by evaporating the refrigerant in the air coil which is then compressed. This compressed refrigerant is rapidly cooled by the water in the water loop which condenses it into a liquid again. This liquid is squirted into the air coil by an expansion valve where it is boiled off again and the process begins all over again.
In heating the process is reversed. Heat is collected from the water loop which boils off the refrigerant. The air coil heats up the air in the room and in the process the refrigerant gas condenses into a liquid.
An optional device called a desuperheater can be fitted to produce hot water locally to the unit for washing or other purposes.
The reason that this process is so efficient is that in order to change the state of the refrigerant from liquid to gas and then from gas to liquid again takes a lot of energy. If you have a cold liquid in a heat exchanger and pass air through it then it cools it a little bit but when we have liquid refrigerant which boils off, as in our system, then the air is cooled a whole lot more.
Typically if we take 1KW of energy to run a compressor then we can take another 3 or 4 KW from the heat source (in our case water) and introduce 4 or 5KW of heat into the room. Compare that with a boiler that needs 1KW of gas energy to produce around 0.9KW of heat into the room.
The beauty of a water source heat pump is its ability to match numerous units from the same water loop where some are cooling and some are heating. This allows us to pump heat from one part of the building where it is not needed to other parts where it is.
It also means that we can use the ground as a heat source for geothermal heating.