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They can be divided roughly into 3 main groupings:

1. Ground-source heat pumps - these draw the heat energy from the ground via a system of pipes laid in trenches. Plus points for this type include the fact that they tend to be more efficient than other types of heat pump (for reasons I will go into later.) Negative points are that they tend to be the more expensive option up front, due to higher installation costs.

2. Air-source heat pumps - these take energy from the air by means of a heat exchanger mechanism. They tend to be much cheaper and easier to set up, so installation costs are significantly lower. They also take up much less physical space than other types of heat pump. The biggest problem is that they are inherently less efficient than the other systems. Also, as air temperature drops very low in some climates in winter, the heat exchange can ice up, requiring periodic melting by the system.

3. Water-source heat pumps. These systems rely on a water supply (such as a stream) to source the required heat energy (are you getting the hang of this now?) Their advantages and disadvantages are essentially a middle path between the other two main systems outlined above ie they are somewhat cheaper to install than ground-source but less efficient. Conversely they are more expensive than air-source systems but significantly more efficient.

The above is one means of classifying the different heating systems. Other ways of dividing them up exist, such as categorising them as either "compression driven" or "absorption" systems. The heating systems described above are all examples of compression driven systems, as they operate on mechanical energy.

Now we must also differentiate from other types of geothermal energy. Heat pumps rely on gas compression by a mechanical pump. By contrast, geothermal systems rely on using energy from the the earths interior to turn water (pumped through pipes into fissures in the earth in areas of high seismic activity) into steam which turn turbines to generate electricity. These types of generating plants tend to be large scale, and are more common in countries such as Iceland, which has huge geothermal energy resources.

My name is Malcolm Rutledge, and I have a strong interest in energy efficient methods of home living. I will be self-building my own home (in due course) in which I hope to incorporate as many of these principles as possible. Thank you for reading, look out for further similar articles in the future.