Pool heat pumps are an increasing popular way for heating a pool. They are cheap to run and environmentally friendly but do have some disadvantages.
What is a Heat Pump?
A heat pump is a device for moving heat from one location to another. In the case of pool heat pumps heat is taken from the surrounding air and transferred to the pool water. The efficiency of air source heat pumps, like pool heaters, declines with the air temperature and ice formation is a problem at low temperatures.
A heat pump providing heating for a house is likely to be a ground source heat pump where the heat is taken from the ground using a length of well buried pipes. These have the advantage of being able to work at low temperatures but are expensive to install.
There are also water source heat pumps which take heat from one body of water and transfer it to another. These are rarely suitable as pool heaters but there are models available designed to take heat from a swimming pool to heat a spa.
How do Heat Pumps work?
We are all used to refrigerators and air conditioning units which work in the same way except they are used for cooling rather than heating. In fact the top of the range pool heat pumps usually have a reverse mode in which they cool the pool.
Heat pumps transfer heat by circulating a refrigerant through a cycle of evaporation and condensation. An electrically powered compressor pumps the refrigerant between the two heat exchanger coils. In one coil, the refrigerant is evaporated at low pressure and absorbs heat from its surroundings. The refrigerant is then compressed en route to the other coil, where it condenses at high pressure. At this point, it releases the heat it absorbed earlier in the cycle.
With any other type of heater it is impossible to have an efficiency in excess of 100% because energy output cannot exceed energy input. In practice, for example, most gas pool heaters are 80-90% efficient. The key point about a heat pump is that because it does not actually generate heat, the amount of energy (heat) produced is much greater than the energy (electricity) used. So even though a pool heat pump is powered by electricity is still much cheaper to run than a gas heater.
How efficient are Pool Heat Pumps?
The efficiency of pool heat pumps is measured by their COP (Coefficient of Performance). This is a measure of how many units of heat energy are produced for every unit of electricity used. For a residential pool heat pump a value in excess of 5 is good. However a word of warning, the COP varies depending on the air and pool water temperature and relative humidity. It is normally measured at 80 degrees for air/water and 80% RH but this is not a defined standard.
Pros and Cons of Pool Heat Pumps
- Cheap to run
- Eco Friendly
- No emissions
- More expensive to buy
- Less powerful than gas heaters
- Not so good in cold conditions
Should you buy one?
If you want to extend the season during which your pool is usable and you heat the pool most of the time then a heat pump will be your best option. If you only want to heat your pool occasionally then you might be better with a gas heater because it will be able to heat the pool faster and its lower purchase cost will offset the higher running cost.
Click this link for information on Pool Heat Pumps that are available.