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Information on Solar Pool Heating

Overview

So you are thinking about using the Sun to help heat your pool water ? Great idea ! In fact many satisfied people have come before you and used Solar Energy in this way. Keeping your pool warm is the best way of ensuring maximum use of your pool; making it enjoyable for more people and extending the months of pool use. Solar Energy is particulaly well suited for use as an energy source to heat your pool water. Not only is the Sun's Energy available freely and environmentally friendly, the months that you need the energy is when the sun's rays are the strongest. They are a perfect match.

The other alternative to Pool Heating is to use an auxillary heater that uses natural gas, propane, oil or electricity. These are expensive to operate and are prone to breakdowns and tank issues. Solar Pool Heating on the otherhand is virtually maintenance free and should provide many years of enjoyment. The following table taken from this Natural Resources Canada document gives a Year 2000 comparison of heating options for a pool in Ontario, 16ft x 32ft.

What Will a Solar Pool Heater Do For My Pool ?

The more heating ability you apply to your pool, the longer your swimming season will be. For most people, July is the peak of their swimming pool season. The further away in time you are from July, the more heat you will need for your pool to be enjoyable. It may even be necessary to add heat at the peak of your season, in certain locations. The below diagram helps give you an idea of the potential for Solar Energy to heat your pool.

You can easily see that with Solar Pool Heating, you can easily make your pool more comfortable and extend your pool season at the same time. While the graph was based on data from California, the principle is the same anywhere in the world. The area in the graph above the Setpoint line is used to indicate the potential of Solar to heat your pool. In reality, the Solar Pool Controller would limit the pool temperature to what temperature you have set.

Basics of Solar Pool Heating

The fundamental principle of heating a pool is to provide at least as much energy that the pool would lose to the environment, at the desired temperature. Temperature is very important because it has a significant impact on the energy losses of a pool. In certain cases, raising the temperature of the pool by 4 degrees can almost double the energy required. The pool can also gain Solar Energy directly into the water. The pool can maintain its desired temperature when the Solar Pool Heating System provides at least as much energy as the projected net losses from the pool.

Solar Pool Heating System Energy > Losses (Evaporation, Convection, Conduction, Radiative, Makeup) - Direct Solar Gain.

These terms will now be explained:

Evaporation Losses:

Typically, evaporation accounts for 30 to 50 percent of all heat lost from a swimming pool. In midsummer, most average-sized pools lose about 50 mm (2 inches) of water per week by evaporation, the equivalent of 150 kilowatt-hours or 500 000 BTU. These losses are higher in dry or windy weather. Evaporation also removes substantial amounts of expensive pool chemicals. Using a pool cover frequently will significantly decrease these evaporative losses.

Radiation Losses:

Radiation transfers heat through air from warmer objects to cooler objects. Radiation typically accounts for 25 to 35 percent of pool heat loss. Most radiative heat loss occurs on clear nights.

Convection Losses:

Convection is the transfer of heat from the pool to the air by fluid flow. When the pump is not operating, mixing warm and cool water, the warm water rises to the top of the pool. Then, through convection, the heat of the warm water escapes to the cooler air. If the wind is blowing, convective heat loss increases. Convection typically accounts for about 15 to 25 percent of total heat loss.

Conduction Losses:

Conduction is heat transfer by physical contact through materials. A swimming pool loses heat by conduction through the pools walls and bottom. A high water table or flowing ground water will carry away an in-ground pools heat through conduction.

Makeup Losses:

Through normal pool activity, some water is removed from the pool by clothing, splashes and other activity. In addition to this water, the water that is evaporated into the air must also be replaced back into the pool. Otherwise, the pool's water level would fall below the skimmer line and cause problems. The water that is replaced into the pool must also be heated to the same level as the pool water. Since most replacement water comes from normal household taps and hoses, it always is at a colder temperature than the pool. Upon entering the pool, this water must also be heated with energy. Therefore, the making-up of water that is lost, removes heat energy from the pool.

Direct Solar Gain:

Any swimming pool in a sunny location is also naturally heated by solar energy. Sunlight is absorbed by the water, adding heat to the pool. This "passive" solar energy is a valuable commodity to a pool owner. An unshaded swimming pool costs significantly less to heat than one that is shaded. Solar pool covers permit some of this passive solar heating while also reducing heat losses. Many outdoor pools require no auxiliary heating during the peak of the summer (in July and August) when heat losses are low and sunshine is abundant.

Efficiency of Solar Pool Panels

Pool Panels work with the best energy output when they feel the coldest. This doesn't seem right, but let me explain. The amount of solar energy that falls on the panel depends on its location, angle and the amount of surface area exposed to the sun. So, for a given panel beside your pool, the solar energy that can be absorbed is pretty much constant. There are some efficiency differences between panel manufacturers, which is shown below (Techno-Sollis is among the leaders in solar efficiency). The other very important factor is the heat that is lost from the panel to the outside air. These heat losses increase with wind and with panel temperatures that are greater than the air around them.

What does this all mean ? Well, to maximize the heat delivered to the pool (by reducing panel heat losses), the panels should have enough pool water flowing through them that their output temperature is only a few degrees above the pool temperature. This minimizes panel heat losses. The concept is simple; there is so much water in your pool that you can efficiently heat a large volume of water; a few degrees at a time. The alternative is heating a smaller amount of water to a higher temperature before it enters your pool, but the net result will be a cooler pool because of the extra heat losses. So, if the return water temperature from your Solar Panels feels quite warm compared with your pool then you are not getting the full value of your solar panels. Read on to find out how to properly setup your Solar Pool System. For special applications or for extended pool seasons in demanding conditions, Sonideft Solar can also provide Solar Pool Heating Systems with glazed (covered with glass) Solar Collectors.

Collector>			Rated Annual Output (GJ/m2)
Manufacturer	Model	Size (m2)	Toronto, Ontario
Aquatherm	Ecosun 4 x 10	3.607	1.3
Fafco	Sunsaver 4 x 10	3.631	1.3
Heliocol	Heliocol - 40	3.768	1.1
Hot Sun Industries	Powermat 4 x 10	3.630	1.2
Techno Sollis	Techno-Solis 4 x 10	3.672	1.3

Full details of these results can be found in this report.

Design of Solar Pool Heating Systems

You can shop around for a while looking for the best looking Solar Pool Panels at the best price. But it won't mean much if you can't heat your pool, or if you need to purchase a lot more panels than you really need. At Sonideft Solar we pay attention to many of the design details that can make the difference in your system. In this section we will explain how we recommend systems are put together, and why they work well.

The first most important aspect of pool system design is to mount the solar panels with a slight slope (1/4" per panel) towards the side with the output port. This ensures that air will not be trapped in your panels. This can easily happen and rob you of half of your energy output. Use a level when mounting the panels. You don't want level or wrongly sloped panels ! The slope is barely noticable from a distance, so you don't need to worry about aesthetics.

The next, not always obvious point to note is that the hot/warm return to the pool needs to come from the top of the panel array, diagonally opposite the lower input port. Two reasons for this. One is that warmed water rises, so why not work with it and not against it ? This is also the reason that the panel temperature sensor is mounted on the top output port. If the input and output port were on the same end (left/right) or both on the top or the bottom, the pool water would not flow evenly through each panel; resulting in reduced energy output overall. Each panel should handle an equal amount of pool water; to the maximum extent possible.

We design all of our pool heating systems using a "drain back" design. When the pump is off or there is insufficient solar energy to collect, the water in the solar panels will drain back into the pool very slowly. This is possible because of the vaccum break mounted at the panels and a diverter valve that does not make a positive seal. This is desirable in all locations because you never need to worry about frost conditions late at night or draining your solar panels for winter. You will still need to worry about the rest of your pool equipment, but the solar panels will be safe all winter or any point in between. By locating the vaccum break in the location shown, the panels will be able to drain easily without drawing air into the system under normal flow conditions. There will normally be a short spurt of air when the pool water is first diverted through the panels, but not after 5 minutes unless there is an air leak in the system.

The diverter valve is used to divert the water flow from flowing into the pool (as it would without solar panels) and send it through the solar panels for heating. The diverter's flow position is controlled by the Solar Pool Controller. When the controller senses that there is a higher temperature in the solar panels than in the pool water (notice the second temperature sensor near the pool), the controller will activate a motorized actuator that will turn the handle of the diverter valve and divert the flow through the solar panels. The check valves are also very important as they prevent your pool filter from backwashing into the pool under a variety of conditions.

The last important design feature of our systems is the bypass valve plumbed across the diverter valve. It is very important not to divert 100% of your pool water (unless your pool pump is under-powered) through the solar panels. It will only serve to make your pool pump work harder (harder means more electricity consumed) and to place unneeded stresses on your solar panels. More information on setup is included in the Installation section below.

Pool Heating Controls

There are three main areas of a pool that can be controlled :

1. Pool Temperature. Controls the flow of water through the Solar Panels in order to raise or lower the temperature of the pool. When the pool needs heating and there is sufficient Solar Energy, the controller will divert the pumped pool water through the Solar Panels. In some locations, the controller's ability to lower the pool water temperature at night is useful. If your pool is getting too hot, circulating pool water through the solar panels at night (which radiates heat) is an effective method.
2. Pool Water Chlorination. Modern chlorinators can easily be controlled with an electronic controller. These chlorinators use a salt mixture and a chlorination sensor to do their job.
3. Pool Pump Timing. Usually this is an add-on to a Solar Pool Temperature Controller. Most installations do not need the pool pump operating 24 hours/day and users want some way of reducing their pump's electricity consumption in a way that does not effect their pool. This timer allows you to set the hours that the pool pump is operating.

All of these types of Pool Controllers are available here.

Installing Solar Pool Heating Systems

The most important thing to remember when installing your system is that the solar panels will need to expand and contract as they go through their thermal cycles of heating and cooling down. So think about this important point as you install the panels, leaving flexibility for the panels to move about 1/4" per panel in a row. This applies to the piping as well, so don't clamp pipes to roof structures too close to the panels themselves. The pipe can handle a little bending if given some distance to do it in.

The diagram above shows a bank of 3 solar panels in a row. Manufacturer's recommendation state that you can place up to 10 in one row. Follow the Solar Pool Controller Installation Manual, and also the manufacturer's installation instructions for all aspects except for the diverter valve area described above.

Winterizing Your Pool

If you have followed the Installation Instructions properly, your Solar Panels should drain out easily for winter. The piping going to the panels should be drained by opening a clean-out valve near the pool filter, or otherwise letting the water out of the piping to the roof. As part of your winterizing, in accordance with your pool manufacturer's instructions, you should drain the remaining water from your pipes in areas that could be exposed to frost. In some cases this will require a drain valve to be installed at the lowest point of your piping so that these can be drained of water. As each pool system is a little different, we do not provide drawings on how to do this. We will gladly discuss the winterizing of your pool system with you though.

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