A look at traditional methods
The use of a properly maintained pool cover can significantly reduce evaporation and water wastage by as much as 95 per cent. Solar bubble covers are especially great at the beginning of the season to help the water heat up more quickly. There are, however, some downfalls to using a solar blanket, which some pool owners may not realize at first until they have to wrestle with it to put it back on. They can be bulky, tough to move, and in some cases can introduce additional dirt and debris to the pool after being dragged through the yard.
Further, leaving a solar blanket on the pool too long—especially during a string of hot days—can overheat the pool water. As a result, chlorine is consumed more rapidly, which can lead to the water turning green. Automatic pool covers are also available; however, due to their cost, they may not be an option for every pool owner. For these reasons, some pool owners may want to consider the use of a liquid solar product.
These products also help to retain heat in the water for those pools equipped with a heater, which can extend the swim season. It takes one British thermal unit (Btu) to raise 0.45 kg (1 lb) of water by one degree. However, each pound of 26-C (80-F) water that evaporates takes 1048 Btu’s of heat out of the pool.
Types of liquid covers
There are different types of liquid solar evaporation suppressants used in the pool industry, including cetyl alcohol, stearyl alcohol, and ethyl alcohol (ethanol). The technology of evaporation suppression uses monomolecular films. The films are a single molecule in thickness and create additional surface tension. All of these are fatty alcohols so they readily float on the water surface.
Dispersants are also used in the formulas to spread the material across the water surface, which is a technology from the drinking water reservoir industry. Numerous studies on evaporation suppression go back to the ’50s and ’60s, and many ingredients have been tested, but the studies concluded the use of cetyl or stearyl alcohols were found to be effective. In some cases, combining the two alcohols proved to be the most effective at reducing evaporation.
All three types of liquid solar products are tested and proven non-toxic. In fact, cetyl and stearyl alcohol can be found in numerous cosmetics and detergents, and are used for food preservation, as well. The levels of ethanol-based liquids have been tested and shown to be relatively benign in pool use; however, it can be flammable.
How liquid covers work
Liquid evaporation suppressants create an invisible barrier on the surface of the water to help trap heat and reduce evaporation. The product is added to the skimmer, with the circulation system running, to disperse the monomolecular layer on the surface. This can be likened to putting a lid on a pot of boiling water.
Some pool professionals have expressed concern about the formation of chloramines and the inability of oxidation gases escaping the pool due to the surface tension caused by these products. That said, despite its ability to move with the motion of the water surface, these films are disrupted when the surface tension is broken (e.g. during swimming, high winds, or rainfall, etc.). When this happens, there is plenty of opportunity for gases to escape to the atmosphere. Further, these films have some natural permeability, as well.
The purpose of liquid solar technology is to reduce heat loss and evaporation, and it even works when bathers are in the pool. While the surface tension can be broken when swimmers are present, the tight molecular arrangement of the film allows it to reform quickly. The typical evaporation reduction rate of liquid covers is between 15 to 40 per cent. Considering the 56,781-L (15,000-gal) pool that loses 5678 L (1500 gal) a month in the summer, a liquid solar cover can save between 852 and 2271 L (225 and 600 gal) of water per month. Over the course of the summer, it can save between 2555 and 6814 L (675 and 1800 gal) of water.
The biggest difference between a physical solar cover and a liquid product is the former does nothing if it is sitting bunched up in the homeowner’s backyard. If someone forgets to put the solar blanket on the pool when the temperature drops on a cool night, considerable water and heat loss will occur. When liquid solar products are used in conjunction with a physical pool cover, it increases the coverage and provides added protection.
