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Swimming pools are very energy hungry! They can represent an enormous heating demand and most conventional pool heaters are very inefficient. The costs of running a pool can be reduced enormously by proper design, sensible choices of heating methods, taking care in choosing pool covers and in managing how the pool is used.

Outdoor pools

An uncovered outdoor swimming pool will lose about 75% or more of its energy by evaporation from the surface of the water. A good swimming pool cover will go a long way to eliminating this source of energy loss and can also allow some of the sun's energy to go through the cover and heat up the water (when it is sunny).

The rate of evaporation in an exposed situation can be four or five times what it is in a sheltered location (think how much faster washing dries on a windy day than a calm one). So a well sheltered swimming pool will much lose less heat, be cheaper to run, and will be much more pleasant to use than an exposed one. Over time, providing shelter for your pool will reduce heating demand.

Once you have covered the pool properly, the heat loss to the ground is likely to be the next most significant factor in the running costs. For this reason current building standards require that the shell that the pool is made from is very highly insulated. It may not be possible to do much to change this with an existing pool, and it may be exacerbated if there are ground water flows past the site of the pool, but it is very important to design new build pools with as much insulation as possible.

It makes sense to turn down the temperature of the water if you know that the pool will not be used for an extended period of time, so long as you remember to turn it up in good time before wanting to use it again because pools take time to respond. Reducing the temperature by 1oC can reduce the energy demand by approximately 5%.

When everything possible has been done to reduce heat losses, you can reduce the costs of heating you pool by installing an energy-efficient pool heater such as an air source heat pump or by using solar thermal panels.

An air source heat pump is well-suited to heating an outdoor pool during the summer months. The air temperatures are warm and the efficiency of the heat pump will be high. While the outside air temperature is more than about 10oC, you could normally expect an air-source heat pump to deliver between three-times and seven-times more heat to the pool water than the electricity it consumes.

A solar thermal system, consisting of solar collectors on a suitable south-facing roof (or ground-mounted), a pump station and a heat exchanger, can make a significant contribution to heating your pool during the summer months. The running costs of a solar thermal system are very low, and whilst the sun is out it will make a valuable contribution to the heating of the pool. Of course, because of the variability of the weather it must be backed-up by a second heating system for pool water temperatures to be reasonable when the sun is weak and to provide sufficient heating to extend the swimming season in spring and autumn.

Indoor pools

You might have thought that an indoor pool would be cheaper to run than an outdoor pool. This is unlikely to be the case. Indoor pools are usually heated throughout the year, the pool room will need to be kept at a high temperature (around 32oC when the pool is in use), and the building is likely to have a large amount of glazing with the associated poor levels of thermal insulation. A significant proportion of the heat loss from an indoor pool arises from keeping a poorly insulated space at a high temperature when the outside temperature is low!

Indoor pools, unless they are in use all the time, just like outdoor pools need to be covered to minimise evaporation. To keep the humidity in a pool room at a reasonable level and to protect the fabric of the building, you need a good air-handling system that dehumidifies and recovers the heat in the moist air. To reduce the load on the dehumidifier you need to cover the pool when it is not in use to reduce evaporation. A modern, well designed system will also reduce the air temperature in the pool room when the pool is covered to reduce heat losses from the building. It will need to have sufficient power to bring the air temperature back up to the design conditions rapidly when the pool is brought into use.

All the same considerations about insulating the shell of the pool as much as possible apply to indoor pools just as they do to outdoor pools. It is also important that the pool room is as well insulated as it can be.

One of the significant differences between indoor and outdoor pools is that an air source heat pump is unlikely to be the ideal heating solution for an indoor pool hall. There are more efficient means of heating the pool during the winter months when the demand will be highest and the efficiency of an air source heat pump at its lowest. We often find that the combination of a ground source heat pump system for the base load, combined with a fossil fuel backup system to cover the winter peaks works well. Alternatively a biomass boiler can be a very effective heater for indoor pools.

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