| By :
Francis Lowe
Swimming Pools lose heat in a variety of different ways such as convection and conduction, but evaporation through the water surface area is by far the greatest source of energy loss. The reason evaporation has such an impact on heat loss is because evaporating water uses up very large amounts of energy. According to information from the United States Department of Energy, it only takes 1 BTU of energy to raise 0.22 gallons of water by 1°F. However, each 0.22 gallons of 80 °F water that evaporates takes a very large 1048 BTU's of heat out of the pool. The metric equivalent means that it takes 0.001163 kilo watt hour of energy to raise one litre of water 1°C and each litre of water at 27°C that evaporates wastes 1.218 kWh of energy. Tests conducted on outdoor pools have revealed that evaporation has a huge influence on the total energy consumption. Heat Losses: Radiation to the air 20%, conduction lost to the ground 10%, evaporation 70%. The rate of evaporation from an outdoor pool varies depending on a variety of factors, including the temperature of the water, the temperature and humidity of the air, and the wind speed at the surface of the water. The higher the pool temperature and wind speed and the lower the humidity air temperature, the greater the evaporation rate. How can this energy problem be addressed? The only real answer is to make regular use of a pool cover. To gain the maximum benefit from your cover it should be placed over the water surface area at all times when the pool is not in use, and only taken off just before you would like to swim, and then replaced afterwards. Covers are available in a variety of different weights, materials, colours and designs. Any type of pool cover, whatever the fabric, will achieve: Reduced energy consumption by up to 50%. Reduce chemical consumption by up to 60%. Virtually eliminate evaporation by 98%. Potentially increase water temperature up to 8°C. Inhibit algae growth. Absorb the heat of the sun. Reduce filtration/pump time by up to 50%. Reduce debris contamination and subsequent cleaning costs. Suitable Covers. Bubble covers protect the water from evaporation by covering the surface of the water, but also give solar gain, raising the temperature of the pool. These are most commonly found on relatively small outdoor domestic pools. A solar cover will usually last for between 5 and 10 years. The initial cost of buying these covers is therefore more than recouped during the life of the cover. Heat Retention blankets are produced from 5mm thick foam fabrics. These covers are very durable and an excellent barrier to evaporation, but they provide no temperature rise through solar gain.
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