What are the Pros & Cons of Air / Ground Source Heat Pumps for heating the pool water?

I. Air Source Heat Pumps

Air to water heat pumps have been successfully installed for many years, especially for providing very efficient pool water heating.

They absorb energy directly from the external air rather then from the earths strata and this eliminates the need for heat collector pipework in the ground.

Coefficient of Performance (COP)

The efficiency of both air and ground source heat pumps is expressed as a number - normally between 2 and 6. This number provides the energy output of the heat pump as a multiple of the energy required to run the electric motors that power the compressor and fans etc within the heat pump.

So a heat pump with a COP of 4 will provide 4kW of energy for every 1kW that is needed to make it work.

Air Source Heat Pump Disadvantages

The disadvantage of air source heat pumps is that the heat pump's COP reduces when the air temperature is low.

At colder periods, the outside air temperature is often less than the ground temperature (at a depth at which heat is extracted by a ground-source heat pump). This lower temperature has the effect of reducing the COP of an air source heat pump.

Ground Source Heat Pumps Cost a Lot More

But Ground Source Heat Pumps are a lot more costly to install because of the installation of underground pipework.

There are many types of air source heat pump being sold today and the cheap ones will work on a small outside pool for the summer months and may even last 2 or 3 years and you can rarely get spare parts for them.

Better quality Air Source Heat Pumps provide the Best Value for Money

Better quality Air Source Heat Pumps will provide a lot more heating power and last much longer - and spare parts will always be available.

II. Ground Source Heat Pumps

Collect the Sunlight Energy that Falls on the Earths Surface

These machines provide the means to collect the sunlight energy that falls on the earth's surface and is then transferred deep underground by the thermal conductance of the surface layers and rock below.

The transfer of heat down into the deep layers is quite slow and as a result the temperature of the ground about 20m below the surface is constant all year round no matter how much the temperature of the surface layer varies between summer and winter.

The Heat Collector pipework can be installed in shallow excavations or in deep boreholes

The Heat Collector pipework can be installed in shallow excavations where the heat energy available will be high in the summer and low in the winter or in deep boreholes where the heat energy availability is constant throughout the year.

The deep boreholes are a lot more complicated to design and install - get it wrong and the ground will freeze up!

The deep borehole options are much more expensive than the shallow borehole option and are a lot more complicated to design and install.

If the borehole is not deep enough and the ground around cannot provide enough energy to sustain the the transfer rate of the Ground Source Heat Pump the rocks around the borehole will get colder and colder until the ground freezes and the heat pump stops working!