Swimming Pool Heat Pumps: Why honesty is our policy

Automated Environmental Systems Blog

There are many claims made about the heating abilities of swimming pool heat pumps and the savings that can be made to your energy bill.

While there is no doubt that an air source heat pump is the most cost effective and efficient way to heat a swimming pool in the UK, it is worth taking a moment to look at why choosing a heat pump based purely on the manufacturer’s specifications is not always the right choice.

Most manufacturers base the sizing and heating capacity of a heat pump on average air and water temperatures, there are usually two sets of figures, a lower figure based on an air temperature of around 15°C and a water temperature of 26°C, and a higher figure based on both air and water temperature of around 27°C.

The actual heating performance of a heat pump is referred to as C.O.P., the co-efficient of performance, put simply if a heat pump has a C.O.P. of 5.0 at air temperature of 15°C and water temperature of 26°C, then for every 1kW of energy consumed by the heat pump 5kW of energy is returned to your pool as heat.

Assuming that these average temperatures are maintained on a well insulated pool then a heat pump could be selected purely on the manufacturer’s specifications.

If for example your pool is 30m³ you could reasonably select a heat pump based purely on the manufacturer’s pool sizing of up to 30m³ – but you need to remember the average air and water temperatures would need to be met to achieve the stated heating capacity – the reality is that the British weather does not maintain these averages and therein lies the first problem.

The second problem that cannot easily be factored into a manufacturer’s calculations is heat loss, up to 80% of heat is lost through the surface of your pool – assuming that the rest of the pool is properly insulated – heat loss on above ground pools is further exaggerated as the sides of the pool are not usually insulated (unless a separate insulating frame has been constructed).

The third unknown is usage, the manufacturer cannot factor in how a pool is used, some pools may stay covered most of the day or week and only get occasional use, other pools could be uncovered all day and have high usage. You may only be a ‘fair weather’ swimmer and use your pool for a couple of months a year, you might open your pool in early spring and close it in late autumn or you may want to heat your pool all year round.

Any of these variables will have an impact on the ability of a heat pump to achieve the manufacturer’s stated heating capacity, restricting the temperature that can be achieved and reducing the period of use.

This is why we only ever take the manufacturer’s specifications as a guide, if you purchase a heat pump from us you can expect us to ask about the size and shape of your pool, whether the pool is insulated and covered when not in use, when and how you intend to use the pool and what your desired temperature is.

Talking of desired temperature, let’s take a moment to address one particular issue.

The speedometer on your car probably has a top speed that, in all likelihood, you would not achieve under normal driving conditions (even if it was legal to do so). In the same way while the temperature selector on most heat pumps will go up to 40°C, given our climate it would be unrealistic to expect that a heat pump on an outdoor pool in the UK could achieve this temperature, manufacturer guidelines are normally based on expectations of achieving a water temperature of 27-28°C.

Heating above this point is perfectly possible but the energy required to achieve each additional degree increases exponentially as does your heat loss, leading to a requirement for higher energy capacity (the compressor has to work much harder to create the differential of heat at higher temperatures, in the same way a kettle requires more much energy to actually boil water than to achieve 90°C). Therefore it maybe that you require a larger heat pump selection if you want a higher water temperature.

A heat pump has the potential to save you between 50% and 80% on traditional heating methods, such as oil or gas boilers, inline electric heaters etc., however the actual saving will depend on the weather, your desired temperature and the heat loss that needs to be overcome. The lower the ambient temperature the lower the heating capacity and the greater the heat loss.

It is for this reason that we usually look to the start and end of your pool season when recommending a heat pump, the points at which you are most likely to struggle to achieve your desired temperature. In most cases recommending a larger model provides additional heating capacity to overcome heat loss, increasing the achievable water temperature.

A common misconception is that putting a larger heat pump on your pool will cost you more to run, while it is true that a larger heat pump will consume more energy, it will run for a shorter time to achieve the same heat output as a smaller unit.

For example, if your pool required 100kW of energy to maintain your temperature at X (under ideal air temperatures). An 18kW heat pump with a power input of 2.51kW would run for 5.6 hours to heat your pool (100/18kW). This means you would consume approximately 14kW of energy (5.6 hrs x 2.51kW). A smaller 13kW heat pump with a power input of 1.86kW would run for 7.7 hours to heat your pool (100/13kW). This means you would consume approximately 14.3kW of energy (7.7 hrs x 1.86kW).

It is for this reason that more and more of our customers are choosing to over specify their heat pump, the higher initial purchase cost is more than offset by the flexibility provided by the additional heating capacity, if we don’t think a particular heat pump is right for your pool given the details you have provided, we will always explain why and make an alternative recommendation.

Nobody wants to make a purchase more than once, which is why honesty is always our policy.

If you would like to speak to us about a heat pump for your swimming pool, you can call us on 01842 819130 Monday to Friday 9am to 5pm or you can email sales@automatedenvironmentalsystems.co.uk