How a Ground Source Heat Pump Works
What Is the Purpose of a Ground Source Heat Pump?
The basic purpose of a ground source heat pump system is to transfer heat from the soil (or a pond or lake) to the inside of a building. Notice that a heat pump can also work the other way round, that is, extracting heat form the building and releasing it in the ground. In this post the first functioning mode is taken as a frame of reference. Next you will find a technical explanation of the operation of a ground source heat pump.
The video below explains how a ground source heat pump works:
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Components of a Ground Source Heat Pump System
The basic elements of a ground source heat pump system are the heat pump itself, the ground loop and the distribution system. Each one of them is a separate closed circuit (the ground loop can be established as an open loop, although this is not its most common configuration), but this doesn’t mean they work independently.
Both the ground loop and the distribution system are connected to the heat pump, with which they exchange heat. Depending on the type you opt for, ground source heat pump prices can vary. Next we are going to see what role each of the components plays.
- It is the basic component of the whole ground source heat pump system. It receives heat from the ground loop, adds some more energy thanks to the compressor and delivers it to the distribution system.
- The ground loop is the component of the ground source heat pump system that distinguishes ground source heat pumps from any other kind of heat pump systems. It basically draws heat from either soil or water (this last case is the cheapest option when there’s a pond or lake nearby), by means of a fluid circulating through a network of pipes, and carries it to the heat pump (specifically, to the evaporator).
- That network can be laid out in different configurations depending on various factors such as the heating and cooling load required, soil conditions and available land. The fluid flows thanks to a pump (it demands the use of external energy).
- The distribution system transports the heat collected by the heat pump (in particular, in the condenser) to the building and distributes it by a network of pipes. That heat is finally released using underfloor heating systems, radiators, forced-air system, etc. The distribution system includes a pump that keeps the fluid that runs through the building flowing.
Components of the Heat Pump
The heat pump is the core element of the ground source heat pump system. It consists of four parts, each of them with a very specific task. Let’s get to know them.
- The evaporator is the component of the heat pump where the working fluid absorbs heat pumped from the ground by the ground loop. This working fluid is a cold and low pressure mix of liquid and vapour. This heat causes the working fluid to evaporate, that is, to become pure vapour.
- This vapour has the same pressure than the previous mix, but its temperature is slightly higher. The function of the evaporator is critical, as it is extremely important that the working fluid is, at this point, only in vapour form. This is due to the fact that its next step is to go through the compressor.
- The compressor is the element responsible for raising dramatically the temperature of the working fluid. It achieves this by increasing its pressure. The mechanics of the compressor entail that all the fluid that enters it needs to be vapour, since even the smallest drops of liquid could damage it (the rotation speed of the compressor is considerably high).
- The reason why the compressor is a necessary element of the heat pump is that the working fluid temperature needs to be high enough for heat to be transferred from it to the building. And also that it acts as a pump, allowing the circulation of the working fluid at any moment. The compressor is the only element of the heat pump that requires the use of external energy in order to work.
- The condenser transfers the heat collected by the working fluid at the evaporator and the compressor to the building’s distribution system. This heat exchange process constitutes the ultimate purpose of the heat pump. It also implies that the hot and high pressure vapour that comes from the compressor becomes a medium temperature and not so high pressure liquid.
- The liquid that exits the condenser has to cool down so that it is cold enough to absorb the heat coming from the ground at the evaporator. This cooling takes place at the expansion valve, where the working fluid expands, that is to say, it reduces its pressure, becoming a cold mix of liquid and vapour. From the expansion valve, the working fluid goes to the evaporator, closing the heat pump circuit.