The roof of a pool house or cabana makes an ideal location for solar heating panels — especially if the roof faces south. If there’s a flat roof, or if you decide to mount panels on the ground, they will have to be tilted a few degrees to give you reasonable heating efficiency. You may want to build a rack that raises the tops of the panels so they face the sun at a better angle for your latitude — even though finding the exact angle is not critical. Any structure that supports the panels should be super-strong and anchored to the roof or ground so the wind can’t budge it There should be no need to insulate either the water lines or the backs of the panels, but any nails, screws, bolts or lags that fasten the panels should be caulked to keep the roof from leaking. (A flat tar and gravel roof may have to be re – fiinished in spots with hot tar.) It’s particularly important to have the panels secure where the feed
line and return line to the pool attach, so no joints can be broken.
How many panels will you need? That depends mostly on how big the pool is. The normal rule of thumb is to have a total panel surface equivalent to at least 1/2 the surface of the pool (that’s if the panels face south or slightly southwest, and assuming that they’re more or less properly tilted). If the panels face east or west, or if the panels are lying flat, you may need a panel array equal to 70 to 75 percent of the pool surface.
But experience has shown that this formula provides more heating capacity than you really need in most cases. Remember: Once you get your pool water to a comfortable temperature, the panels won’t do much except balance off your nighttime heat losses. Less than 50 percent is usually enough panel area, although with fewer panels it may take as long as 4 or 5 days to heat the pool 10 degrees above the ambient air. But once you get there, this 10-degree gain should be easy to maintain during the summer, spring, and fall, especially if you have a pool cover.
Pool heating panels, like all flat plate collectors, work best when there’s lots of water running through them. If you keep the temperature differential between the pool and the water in the panels as small as possible — by running the system a lot — it will be most efficient. Water should return to the pool from the panels no more than 6 degrees warmer than the pool itself. If it’s a lot hotter than this, you’re not operating at maximum efficiency.
Because a pool system must have a large circulation capacity, and because pool panels operate at such high efficiency (70 to 80%), you may want to use 1-1/2- to 2-inch water mains. And be sure your pool pump is strong enough to keep a large supply of water going through the panels to keep them cool. Most pool pumps are more than adequate.
As you plan your system, try to keep the lines between the pump and panels as short as possible. You don’t need to worry that much about heat loss, the way you would with a domestic hot water system, but you are concerned with keeping head loss at a minimum. The shorter the lines, the less resistance in the pipes. Here are some other hints to keep in the back of your mind:
1. Make sure your unglazed panels are selfdraining. This is not so much to prevent freezing, as it’s a fail-safe mechanism. If for some reason the pump should fail, water must automatically run out of the panels, eliminating any possibility of pressure build-up and damage to the system. Because there’s no glazing, there’s no danger of damage to the panel when there’s no water in it Remember too that any self-draining system must have an air vent near its top or it will not drain.
2. Keep your pool filter clean. Don’t forget that you don’t have a closed-circuit collector loop like the one in a domestic hot water heater. There’s plenty of opportunity for debris to fall into the pool and work its way into the panels. Once there, it could destroy them. A fouled strainer and clogged filter can bog down the whole system, put unnecessary strain on the pump, and slow the progress of water through the panels.
3. Use plastic plumbing. Polyvinyl chloride (PVC) or chlorinated polyvinyl chloride (CPVC) is much cheaper than comparable copper plumbing. It can be cut in an ordinary carpenter’s miter box, and be glued together with regular CPVC cement. Plastic pipe looses some of its strength at temperatures above 180 degrees Fahrenheit, and this is why it’s not recommended for regular domestic hot water. But for a solar heater that operates well below 100 degrees most of the
Figure 98. Special adapters will be needed if you use plastic plumbing in your solar pool heating system. Ells and tees will be no problem, but certain valves are only made in metal, and these cannot be connected to plastic directly.
time, plastic will hold up fine. Valves and special fittings may have to be metal. When you put these in, you’ll need special (but cheap) metal – to-plastic and plastic-to-metal adapters (Figure 98).