Air Source Heat Pump

Air Source Heat Pumps (ASHP)

These have been around for a number of years but peoples interest in these have increased dramatically in recent years due to rising fuel prices.  We have therefore created this page to explain how these work and the advantages and disadvantages to using one to heat your swimming pool. They work by extracting heat from the air and putting this into the pool and are essentially a fridge working in reverse.

One of the main selling points about these is that they give you free heat from the air. This is true, but a portion of the heat input has to be paid for in terms of electricity purchased.  Here in lies one of the biggest misconceptions about heat pumps which we will explain below.

A gas heater that is for example rated at 35kW will output 35kW, day in day out, no matter what the air or water temperature is.

The output of an ASHP will vary depending on what the current air temperature is.  Manufacturers and specifically sellers of ASHP’s will say that for every kW of electricity paid for, 5 kW of heat will be put into the pool.  Some sellers quote even larger figures but this is just marketing hype or misreading of the manufacturers efficiencies which can easily be manipulated in their favour.  This 5kW of heat into the pool is made of of 1kW of purchased electricity to power the ASHP, the fan and compressor.  The ‘free’ 4kW of heat comes from the warm air that is sucked into the ASHP.  This 5:1 ratio is called the Co-efficiency Of Performance (COP).  This COP does vary depending on the air temperature at any one time and the COP of 5:1 only occurs when the air temperature is above 25ºC.  At air temperatures this high, which is not common in the UK, the pool will naturally be around 29 – 30ºC due to a well performing solar cover.

In reality, the average 24hr air temperature in the UK during the summer season is around 15ºC so if we look at the table below which is produced by Calorex who are one of the largest manufacturers of ASHP’s in the UK, we see that with an air temperature of 15ºC, the COP is 4:1.  Therefore burning, or paying for 1kW of electricity, puts 4kW of heat into the pool.  This might seem to be a good result as you’re getting 3 free units of heat into the pool but what promoters of ASHP’s don’t point out is that 1kW of electricity costs you at least three times more than 1kW of gas.

In summary, and in using average fuel prices from the table below, to put in 4kW of heat into your pool using an ASHP will cost you 18.7pence per hour but to put in 4kW of heat into your pool using a high efficiency gas pool heater such as the Certikin Genie will cost you 4×3.9p=15.6 pence per hour.  If you had an oil heater, the corresponding cost would be 4×4.4p=17.6 pence per hour and finally, if you used bulk storage LPG, the cost would be 4x7p=28 pence per hour.

There is therefore not a major saving, even one at all, using an ASHP over more conventional fossil fuel types of heaters.  

Sources of ASHP

As a company that prides itself in only supplying high quality equipment that as far as possible is British or American made, we will only supply ASHP’s made by Heatstar or Dantherm (used to be called Calorex until being taken over recently).  These units are well built, of high quality with a good warranty and parts are easy to obtain with the UK.  There are a myriad of cheaper units on the market which are Chinese or French but generally speaking these are of much poorer build quality and spares are hard, if not impossible to obtain and as such, Calypso will not supply, install or repair any of these units.

Noise

Another consideration of fitting an ASHP is that there is a continual noise coming from the fan assembly, even on the newer invertor type, albeit but to a lessor extent.  This noise must be considered as a potential nuisance either to your neighbours or yourselves as you trying to relax, lying around your pool.

Installation Cost 

The cost to supply and fit a quality ASHP, as detailed above, will typically cost around twice that of a comparable gas or oil heater, partly due to them having a higher purchase price but also their need to have an uprated electrical supply and concrete base that would typically need to be laid just outside the plant room.  ASHP’s can be installed inside the plant room and the exhaust air ducted to the outside in order the make use of the heat that builds up within the plant room but in reality, this heat is evacuated and used up within a few minutes of the heat pump running.  

If you also have an old style pool heater in the plant room such as a Jandy, Laar’s, Purex, Certikin MB etc., you are not allowed to install an ASHP in the same room as one of these as the ASHP would pull the spent flue gases from the heater down into the plant room and cause dangerous levels of carbon monoxide to accrue in the room.

Guarantee of Performance.

We said earlier that the output of a heat pump varies with the air temperature whereas the output of a gas or oil heater is guaranteed.  If during summer we have a cooler period, the heat pump may not be able to maintain the pool at your required temperature so the pool temperature will drop until the weather warms up.  At the start of the pool season, a gas or oil heater will typically take 2 days to heat the pool up to its target temperature (typically 29-30ºC) but an ASHP will generally take a couple of weeks due to its lower output.  If a cold snap should then occur during summer, the temperature of the pool may drop below your target temperature and not recover that heat until the weather warms up.

All of the above might make you think that we won’t fit or support an ASHP, which is not true.  We have supplied and fitted numerous units over the years but we just want to clearly layout some of the issues with them and make sure that you, our valued customer, have a good understanding of how these work, what they do and the Pro’s and Con’s of having one.  If we haven’t managed to answer any of your questions here or you would like to discuss further, please do not hesitate to contact us.