Pool heat pump – a waste of energy?
Now the holiday home has been built and the pool invites you to cool off: who wouldn’t think of extending the bathing season and heating up the pool water? In the past, pool heaters were often operated with fossil fuels (gas or oil burners), but this has no longer been permitted in Spain since 2013 (Real Decreto 238/2013, de 5 de Abril).
Now, as always, there are different ways to heat the pool water: A) using solar thermal energy (dark heating hoses on the roof are heated by the sun): here the solar heat obtained is fed to the pool water via a heat exchanger. Or B) with an electrically operated heat pump.
Solar thermal energy – an economical method
The idea of using heating coils and solar thermal energy is an obvious one, as there is plenty of sunshine in Andalusia. The problem is: what to do when the water in the pool gets too warm, where to put all the heat? Another problem with this technology is the control system: to ensure that the ideal water temperature of 28ºC is reached but not exceeded, a mechanical (or manual) flap control has to do the work of a thermostat. Especially in the height of summer in southern Spain, we tend to have the problem that our pools get too warm, which requires more intensive maintenance (algae growth, increased use of chemicals …).
And please don’t forget: solar thermal heating of the water only works when the sun is shining, so it reaches its limits in the transitional periods / in winter / when it is cloudy. The days are getting shorter and the few hours of sunshine in November are not enough to heat the pool water. Nevertheless, a very economical option.
A pool heat pump
is easier to control: The heat generated is transferred to the pool water via a heat exchanger, and the heat pump remains switched off in high summer. It is important to note that the heat exchangers must be made of stainless steel, or titanium zinc in the case of salt water pools. The pool is mainly heated when the sun is shining and the electricity is produced by the PV system itself. Particularly in the transitional periods (April / May and September / October), electricity is produced in large quantities but not consumed. The surplus and free electricity is therefore ideal for operating the pool heating with a heat pump. What is left over is fed into the grid.
What do we need to consider during installation? Good thermal insulation of the pool water is important to limit energy loss overnight. Electrically controlled pool covers, made of PVC or polycarbonate, are ideal. They cover the pool water like a roller shutter and also provide good protection for children falling into the water. These covers are available in various colours, including solar (black energy-absorbing underside). They can be installed in different ways, lying in the water, rolling out of the ground, as a ‘rucksack’ attached to the pool or as a roll above the water. With a pool cover we achieve approx. 4-6ºC higher water temperatures, with a solar cover even more.
When the swimming fun ends, the pool cover is closed to minimise the temperature loss overnight. As soon as the sun comes out again, our pool heat pump starts up and heats the water almost free of charge with the electricity it produces.
COP of a pool heat pump?
This is where the wheat is separated from the chaff: the better the product, the higher the efficiency or COP (coefficient of performance). It is important to identify the outside temperature at which this COP was measured. Inexpensive devices like to determine this at an outside temperature of around 30ºC – which of course falsifies the result, because at 30ºC we no longer need pool heating. As a rule of thumb, a power of 200 W per m2 of pool water surface area is used. The standard pool of 4x8m therefore requires 6.5 KW. With a COP of 5, we have an energy consumption of less than 1.5 KW, which is roughly equivalent to the power of your hairdryer. Pools with overflow (‘infinity’) require a significantly higher heat output, as the infinity effect promotes evaporation, which draws energy from the water (outdoor pool, evaporation, temperatures around 10ºC in autumn, pools without a cover …) the power requirement increases.
How much energy does the pool heat pump need?
The rule is: to raise 1000 litres of water by one ºC at a room temperature of 20ºC, we need approx. 1.2 KWh of energy. If we take into account the circumstances (outdoor pool, evaporation, temperatures around 10ºC in autumn, pools without a cover …), the power requirement increases. In other words, if we want to heat a 100,000 litre pool with a cover from 20ºC to 25ºC we need approx. 600 KWh, from 15ºC to 25ºC we need 1,200 KWh to reach the desired temperature. We also need energy to maintain the temperature reached. This calculation applies to ideal conditions, with a cover, no evaporation energy, not much colder at night, etc…
As you can see, it is advisable to maintain the temperature once it has been reached. Bringing cold pool water to bathing temperature requires a lot of energy. It is highly recommended to control the consumption with a suitable home manager and to programme the system accordingly: heat with solar power during the day, maintain the temperature with inexpensive night-time electricity from 0:00 and leave the pool covered. From mid-December to the beginning of March, pool heating makes almost no sense (> high consumption)
Good appliances advertise low noise levels, an important criterion: we prefer not to hear anything from the heat pump when we are swimming. Low noise levels combined with the right position of the appliance allow us to enjoy the heated pool water without restrictions.
Ideally, the air conditioning of the pool should be planned right from the start if it is a new build or renovation of an old house. This allows you to plan the ideal location, the best COP, the best dimensions and also the combination with the pool cover.
Please contact us for further details!
Tip!
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