Two students of Hanzehogeschool Groningen have investigated the use of the product Heatsavr to reduce the energy consumption of indoor swimming pools. The product has been found to lead to effective energy savings both in laboratory tests and in a practical test in an indoor swimming pool.
Swimming pools use a lot of energy. After all, the water must be kept warm. The high energy consumption is due to losses through the pool building and to the evaporation of water, which consequently cools this water. Moreover, this evaporation leads to excessive levels of humidity. With this comes the need to refresh the pool space with relatively dry, but cold, outside air.
Heatsavr is used in desert areas to reduce the evaporation of water from drinking water reservoirs. It has been sold to swimming pools in the Netherlands for some time to reduce the evaporation of the pool water. The aim is to save energy. However, the precise effect of Heatsavr is difficult to measure. The energy management of a swimming pool is strongly influenced by external factors such as the outside temperature, the wind speed, and the humidity.
Our students built a test set-up to test Heatsavr under controlled conditions at the Entrance Innovation Center of Hanzehogeschool Groningen. The set-up consisted of an insulated aquarium tank with 30 oC water. The energy loss by water evaporation was then determined by the water cooling in the aquarium tank. The result of a series of experiments was that by adding Heatsavr to the water, a saving of approximately 100 Watt per square meter can be achieved. This corresponds to a saving of 100 m3 natural gas per square meter water surface per year.
The experiment was then repeated in the subtropical swimming pool Aqualaren in Zuidlaren. Under practical pool conditions, the laboratory results were confirmed, although the savings were slightly less: 80 watts per square meter. This lower saving is explained by the fact that air in a swimming pool is relatively warm and humid, limiting the evaporation of water.
Less evaporation of the pool water results in a lower humidity. As a result, less air needs to be refreshed in the pool. This provides additional savings, because the replacement of warm indoor air by relatively cold outdoor air is accompanied by additional energy losses; especially in case there is a system of heat recovery, such as in Aqualaren.
When using HeatSavr in the practical situation of an indoor swimming pool, it is important that the air circulation is adapted to the reduced humidity. Without that adjustment, the humidity above the water would drop to low values due to Heatsavr. As a result, the evaporation increases sharply, which largely negates the effect of Heatsavr.
This does not alter the fact that the effect of Heatsavr in the practical situation of a swimming pool is less than in laboratory conditions. First of all, Heatsavr ideally floats on the pool water like an (invisible) film. During the day, with many swimming activities, this is not the case. The effect is optimal at night. Secondly, Heatsavr is broken down naturally by the (chlorinated) swimming pool water. Experiments with Aqualaren’s pool water showed that HeatSavr’s activity was reduced by about half after about 12 hours. Heatsavr should therefore be added to the pool water daily, preferably immediately after the swimming activities.
Taking into account that the air circulation is set in such a way that the humidity above the pool remains the same, it can be concluded from the experiments that Heatsavr amounts to a saving of 20% on evaporation. For an average pool in total, so including the heat losses through the building, this amounts to a saving of about 10%.
The results with the Aquarium tank are confirmed by the results of the use of Heatsavr in the Aqualaren swimming pool itself. Despite the fact that it was relatively cold in the first half of 2013, Aqualaren’s gas consumption was 10% lower than in 2012. This is equivalent to an energy saving of approximately 60 m3 natural gas per square meter of swimming surface per year.