Pool Heating
Solar heating of swimming pools is a very effective application for solar energy. Solcan has supplied and installed many pool heating system throughout the years and has experience with a variety of swimming pool panels made by different manufacturers. Most of the products for solar pool heating are extremely durable and many have 15 year warranties. Generally, they work the same way whereby pool water is diverted to the solar panels from the pipe returning water from the filter back to the pool. As the water flows through the panels it is heated by the sun and then flows back to the pool.
The panels are fastened to the roof using straps and clamps. Solcan Ltd is an authorized distributor of Techno-Solis swimming pool panels. The Techno-Solis pool panels are made from a black plastic co-polymer which combines polyethylene and polypropylene. The system can be automated so you can set the automatic controller to a comfortable water temperature. When the water temperature drops below the desired level, the system activates a flow control valve which diverts the water so it is pumped from the pool through the filter to the solar collectors and back to the pool.
Sizing the System
Sizing a solar system for a pool is relatively simple and straightforward. Assuming the pool is in the sun, it receives passive solar heat gain. Most of the heat loss from the pool is by convection from the surface and evaporation so the system is sized in terms of the area of the surface of the pool. On a roof facing south, if the pool is covered at night with a solar blanket to reduce heat loss, use a panel area 50% of the pool surface area. The pool warms up when the sun shines on it (passive heating) so the pool temperature rises every sunny day.
Evaluating the site for solar panels for pool heating is similar to the siting of collectors for hot water systems. Solar pool heating is used in the summer when the sun goes from northeast to northwest and the days are longer, so the panels can be placed on east and west-facing roofs. However, the system may have to be enlarged to compensate for the loss of sunshine hours in the morning and the evening.
A solar blanket on the pool surface keeps the heat in and reduces evaporation. When water evaporates from the pool, heat is lost because the energy to evaporate the water comes from the water itself. A solar blanket on the pool reduces evaporation, and the resulting heat loss from the pool. With a pool blanket the solar system can be smaller because there is less heat to replace. If a solar blanket is not used, there is more heat lost at night, and the size of the solar system should be increased to about 75% of the pool's surface area. If the pool is shaded, add 5% for each hour the pool is shaded between the peak sunshine hours of 10 am to 4 pm. A panel area approaching 100% of the pool surface may be required if you do not use a pool blanket and have a shaded pool. A solar pool heating system may require a very large area.
Expected Performance
The solar pool panels usually heat the water to between 3C (5F) and 5C (8F) warmer than the pool would otherwise be. It is possible to get this temperature rise in one day depending on the initial temperature and assuming the pool is also getting the natural heating of the sun. It For example, when the solar system is activated on a warm day in the springtime (air temperature at 20 to 24C), and the pool is at 13C (55F), the pool temperature would rise about 5C each day for the first several days, and slip back about 2C each night. As the pool gets warmer than the air temperature, the amount of heat delivered by the solar system becomes less. The efficiency of the solar panels goes down as the temperature difference between the air and the solar panel increases. Eventually the pool is so warm that the collectors operate at very low efficiency.
A solar pool heating system will pay for itself in between two and three years compared to a gas-fired pool heater. Typical costs for an installed solar system for a 16 x 32 pool range between $2,700 and $4,000 depending on site factors. An average 16 x 32 pool, opening on 24th May and closing on Labour Day weekend, using a pool blanket and maintaining 27C (82 F) with natural gas will cost between $400 and $800 per season for natural gas plus $1600 to $2000 for the heater whereas a solar pool heater will cost about $3,000. Many customers who purchase a pool with a gas heater use it for the first year and then turn the thermostat down and shorten the pool season to reduce the cost of the gas.
Installing an automatic control on a solar pool heating system will produce additional energy because the system is on when the sun's energy is available. The homeowner does not have to switch the system on and off as the sun appears and disappears. If the pool gets too hot the solar system can be switched off or you can also use the system to cool the water by running the solar system at night.
There is no build-up of minerals in the solar pool panels as in the bottom of a kettle. The pool panels heat the water to between 3C (5F) and 5C (8F) warmer than the pool. At that temperature difference, there is no liming or calcium precipitation from the water, a problem which occurs in gas heaters and heat pumps because they have larger temperature differences, typically 50C difference. Most solar panels run at a pressure of 10 to 12 psi but can take higher pressures, typically 30 to 40 psi.
Investing in Solar Energy
Below is a five year cost comparison between a solar heating system and a gas heating system, on an average 16 x 32 foot pool.
Solar Heater Gas Heater
System Costs $3,500 - $5000 $1,500 - $2,000
Cost of Energy Per Year $0 $800 to 1,000
Total After Five Year Period $3,500 $6,000 +
Indoor Pools
Many indoor pools are seasonally heated and not used in the wintertime. Plastic pool panels can be used for indoor pools although glazed metal panels are generally recommended because they are more efficient at lower outside air temperatures. However, if the panels do not have to operate year-round they do not have to be glazed. Indoor pools have an extended season and more privacy; but when the outside temperature is cold, most people just shut it down because it costs too much to heat the space above the pool as well as the water. It is not comfortable swimming in a pool if the air above the pool is too cool. Solar heated pools are warmer and warm pools are used more frequently than cold pools.
Although the convection loss is not as great, indoor pools require more heat than outdoor pools because they do not receive direct sunlight so it makes sense to put a solar system on an indoor pool. Plastic pool panels can be used for indoor pools although glazed metal panels are often recommended. It is possible to circulate the pool water through an all-copper panel but the water quality may affect the copper. A panel used in a direct circulation system may be subject to wide swings in pH and chlorine content. It is best to use a stainless steel heat exchanger and an intermediate heat transfer fluid.
A solar pool heating system can be combined with a solar domestic water heating system. A typical installation has several solar collectors mounted on the roof facing south. Solar fluid (a 50:50 mixture of propylene glycol and water) is circulated between the solar panels and the pool mechanical room, at a location which provides easy access for plumbing between the solar lines and the heat exchangers. The solar system is controlled by a differential thermostat (model GL30). The solar fluid from the solar panels continuously passes through two heat exchangers, one to heat the domestic water, and the other of stainless steel to heat the pool water.
The pool water is diverted by a three-way valve controlled by a differential thermostat (model GL35) either through the pool heat exchanger and then back to the pool, or directly back to the pool. The solar fluid then passes through the other heat exchanger, giving up any heat remaining. A control on the differential thermostat allows setting a maximum (high limit) temperature at which point the system shuts off. The simplest strategy and the most dependable one is to add heat to the pool until the pool is up to temperature, then add heat to the domestic hot water until the storage tank is up to temperature. Any energy remaining goes to the other application. The priority can be reversed to heat the domestic hot water first and then the pool.
A common question is whether the plastic panel can be used for a hot tub. Many people install a hot tub so that they can jump into the tub after a cold swim, especially in the evening. If the water has been maintained warm all day and then the jets are turned on, whoosh, it cools off. There is no additional heat unless there is a backup heater.
Pool Heating Gallery
