Have fun being green

Swimming pools can be part of the great and all-too-short prairie summer.They are a good way to cool down, get exercise and help little people become comfortable in the water.However, pools use a lot of conventional energy if they are heated with electricity or natural gas. It can cost as much to heat a pool in the summer as it takes to heat a house all winter. Solar pool heating can reduce costs and make a pool usable for a longer period of time. As well, it can significantly cut the annual operating costs of a community swimming pool and make it more affordable. Solar pool heating on a seasonal basis is probably the most cost-effective active renewable energy technology available.There are two types of solar collectors: solar electric and solar thermal. Solar thermal collectors are used to heat hot water and for swimming pools.There are different types of solar thermal collectors: evacuated tube, flat plate, and unglazed, which is usually plastic. The first two types are used for all-season pools because they are capable of producing heat in cold and windy conditions. They cannot directly heat chlorinated pool water because they typically use copper as an internal component, which means a heat exchanger is required with additional cost and lost efficiency. Evacuated tube or flat plate collectors are most suitable when they can be used for pool heating in the summer and heating hot water for another facility in the winter.The most efficient solar collector for summer pool heating is the unglazed collector made of a black material, usually a plastic polymer. Ordinary black plastic pipe can work, but a solar collector has a larger surface area heating smaller volumes of water. The temperature can rise two or more degrees C with every pass of water through the collector. Chlorinated water does not harm the plastic, and cool water circulates directly through the collectors, which means a heat exchanger is not needed. This is more efficient and cost effective.The unglazed collector with its dark surface can be as high as 80 percent efficient. It is well suited for summer because ambient temperatures are moderate in summer and heat loss from the collector is minimized.Don’t expect solar collectors to work miracles. Although some solar collection occurs on cloudy days, depending on the intensity of the clouds, the solar contribution will be reduced and the boiler will do the lion’s share of the work.If the pool is heated only by solar, the temperature can be expected to drop.A pool cover is critical because the greatest heat loss is from evaporation. A solar collector system would need to be at least 50 percent larger to compensate for the lack of an overnight pool cover.Temperature is another factor. Some homeowners and communities have developed an affection for water temperature as high as 30 C, which means boiler operating costs are high. There is also a case of diminishing returns. It is harder for solar to provide the extra heat as pool operating temperatures rise.Collectors are typically four feet wide and are generally eight, 10 or 12 feet long for residential purposes, although 20 foot units are available. A pool heated at a moderate temperature of 27 C that isn’t covered with a pool cover at night will need collectors equivalent to at least 50 percent of the pool area if 50 percent savings in heating are to be accomplished. A 16 by 32 foot pool will need at least eight, four by eight foot collectors. An 18 foot round pool will need about half that number. The ratio of collector area-to-pool area rises considerably with higher pool temperatures.Collectors need to have backing. They can lay directly on the ground but must be thoroughly drained if freezing is expected. As well, nothing will grow underneath because they are solid. Collectors are usually mounted on a roof – maybe a pool shed if it is large enough but often the roof of the house. They must be secured so they do not blow away in the wind. That requires roof penetration but there should be no problem if properly installed. It makes no sense to install collectors on a roof that is due for a shingle replacement in a few years. Most plastic panels come with warranties of at least 10 years and can be expected to last at least double that time, which is longer than the lifespan of cheap shingles.Small pools don’t need a separate pump. It is just a matter of cutting into the plumbing after the filter and before the heater with a diverter valve to direct the water through the collectors. If you opt for the manual valve, you will need to turn it on every sunny morning and off again at night because if you don’t, the collectors can act as great radiators at night, effectively chilling the pool. Like the rest of the system, the collectors need to be drained when temperatures fall below zero. Other than that, maintenance is minimal. Rain keeps dust off the units.It is possible to recoup the cost in as little as six years.Will Oddie is a renewable energy, sustainable building consultant with a lifetime interest in energy conservation. To contact Oddie, send e-mail to energyfield@producer.com.