For some reason, cheaper solar collectors designed specifically for swimming pools are called "heating panels" rather than "collectors" — even though they work on the same principle. Regular collectors — the type we’ve been discussing throughout this book — can be used. But it’s a little like taking a Ferrari to pick up a load of 2 x 4’s at the lumber yard.
Figure 95. Using a little imagination, designers at Parallax in Hinesburg, Vermont, have built a concrete pool deck that doubles as a flat plate collector. There are several features you should notice:
1. The concrete slab sits on at least a foot of well – compacted gravel or sand.
2. The slab is "floating," which means that it’s not firmly anchored to the ground anywhere. This is why the edges of the concrete "turn down," or get thicker. The turn-downs keep the deck from shifting.
3. The insulation on the bottom of the slab is 1-1/2 inch styrofoam.
4. Between the insulation and the slab, there is a vapor barrier. This is no more than a sheet of polyethylene.
5. The slab is held together and reinforced with steel bars running in both directions — as well as #10 steel mesh.
6. The water channels — 1 inch plastic pipes — sit about 4 inches below the surface of the deck, which is painted dark green. Filtered water is pumped through these channels before it returns to the pool.
This type of solar pool heater is about 45% efficient — more than adequate to keep pool water warm.
Large-capacity pool panels, unlike high – performance collectors for domestic hot water, operate in the low-temperature range. Obviously there’s a big difference between heating a fluid to 160 degrees or higher on a winter day, and simply warming it to 82 degrees on an already-warm day. You don’t need anything very fancy to make pool water tepid (Figure 96).
Today the market is loaded with swimming pool panels. Some of them are good, and some not so good. Sometimes they’re made of plastic, sometimes of rubber, and sometimes of metal. Most have no glazing because they work when the ambient air temperature is high and because water circulating through them doesn’t need to get that hot.
There are some problems with some of them: (Ultraviolet rays, for instance, can raise the dickens with certain types of plastics that contain no ultraviolet inhibitors. And ozone will eventually break down certain components in rubber. After some of these cheaper panels have been used
for a while, they end up looking like a blackened potato chip — curled, warped, chipped and cracked.
Watch out for aluminum panels, too. Chlorinated water corrodes aluminum very quickly. Again, copper is much safer. Some of the better panels have copper tubing covered by an aluminum absorber plate. They work fine for heating pool water, but, like all other pool panels, they’ll never be suitable for domestic hot water applications (Figure 97).
Be careful what you choose. There are too many questionable manufacturers in this new and lucrative field. In some parts of the country the Better Business Bureau is actually warning prospective buyers against fly-by-night installers and distributors of solar pool heaters — all of whom claim their products are made with the "right" materials.
Check out the reputation of any company you’re thinking of dealing with. Find out how long they’ve been in business, and see what kind of warranty they offer. And don’t swallow any extrav
agant claims like, "Our system will give you comfortable year-round swimming in any climate." That’s an open invitation to a shady deal.
One of the oldest and most respected names in pool heating systems is Fafco, located at 235 Constitution Drive, Menlo Park, California 94025. Fafco has dealerships in many parts of the country. But Fafco is not the only one; there are plenty of other superior pool panel makers around, too (see appendix).
A complete solar pool heating system — with panels — shouldn’t cost more than $1000 to $1500, fully installed. (It could be less, of course, if you do your own plumbing.) So what can you expect from all this? In Florida, where it’s sunny and warm most of the year, an extensive solar heating system for a 10,000 gallon pool — costing as much as $2500 —might keep the water at 75 degrees even between October and April. Even there, some auxiliary heating might be needed to keep the water very warm. In short, if you live in Atlanta or points north, don’t rely on the sun to keep your pool warm all winter.
