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One of the most logical uses of solar energy is to heat a home swimming pool, since sunshine and swimming weather are so closely linked. The simplest and least expensive way to warm an unheated pool with sunrays, or to ease the load on a gas or electric pool heater, is to cover the water with a transparent plastic blanket, commonly made of heavy, double- thickness polyethylene. By preventing evaporation (which can account for up to 55 percent of a pool’s heat loss) while still permitting sunlight to warm the water, a plastic cover can raise the temperature of a pool by as much as 100 F. on a sunny day. Used in conjunction with a conventional heater, a pool blanket can pay for itself over a single season in reduced energy bills. But full-fledged solar systems, available from solar equipment-dealers and from some pool-supply stores, are even more effective. Most pools are heated to around 80 F.; in warm weather, a solar system can do the job unaided by a standard gas or electric heater. In cooler weather it can save considerable energy by preheating the water before it passes into the conventional heater. Because the basic plumbing necessary to circulate the water through the solar collector panels is already included in the pool’s filter system, a solar heating loop need only tap into the existing pipes— usually at a point just beyond the filter but before the conventional heater, if any. A one-way check valve prevents water from draining back into the filter from the elevated collectors, and a manual or thermostatically-control led gate valve al lows pool water to bypass the solar heater on cloudy days, or whenever the pool has heated up sufficiently. The existing swimming-pool pump will often be powerful enough to circulate water through the panels, but the panel manufacturer or dealer may recommend that you retro fit a larger pump. Solar collector panels for pool heating are simpler and lighter than the ones that are designed for hot-water systems, requiring no insulation or glazing. Many are copper; others are merely 3-by- 8-foot sheets of molded plastic, honey combed with channels through which the water circulates. The panels must be mounted on a roof and oriented toward the sun in the same manner as other solar collectors. If near by south-facing roof surfaces don’t provide the proper angle, you can secure the panels to an inclined roof rack, similar to the one shown, but covered with 3 plywood (the lightweight pool panels will sag in the middle if they are not supported). In many cases, however, the simplest way to mount the collectors is to build a nearby cabana-style shelter with its roof oriented due south and pitched at an angle equaling your latitude. To heat the water adequately, you will need collector panels with a total surface area equal to half the area of your pool. To ease installation, use schedule-40 PVC pipe and, whenever possible, PVC valves and fittings to make the plumbing connections. Buy the type of pipe that is specifically labeled for outdoor use; the plastic is formulated with a stabilizer that enables it to withstand prolonged expo sure to sunlight. The PVC pipe ordinarily used for indoor plumbing degrades rapidly in the sun and must be painted if it’s used outside the house. You can buy pipe, fittings, and any other hardware not included with the panels, at plumbing and home-improvement stores. Installing Panels and Pipes 1 Mounting the collector panels. Mark the position of each panel and the locations of the rafters on the roof (-- 81, Step 1). Along the top and bottom guidelines, drill a ¼-inch hole into each rafter. Fill the holes with butyl rubber caulking. Haul the first panel to the roof (-- 82) and position it between the guidelines. Anchor the bottom header pipe to each rafter by hooking a 1-inch one-hole pipe strap over the pipe and securing it with a 2-inch galvanized lag bolt, driven into the filled hole. Secure the top header pipe in the same way. Mount the subsequent panels, connecting the abutting headers with 3-inch lengths of 1½-inch-diameter rubber hose slipped over the ends of the pipes and secured with hose clamps. At each end of the row of panels, spread a ½-inch band of PVC solvent cement around the end of the pipe that won’t be used as a water inlet or outlet, and twist on a plastic pipe cap. Secure the midsection of each panel with three flexible nylon or rubber retaining straps, stretched horizontally across the panel, 2 feet apart. Fasten the straps with 2-inch lag bolts, screwed into caulked holes in the rafters. 94 Rerouting the filter system. Before tapping into the existing system, assemble the valves and fittings that will divert water to the collectors. Attach a 2-inch length of 1½-inch-diameter PVC pipe to each end of a PVC gate valve with PVC pipe cement. (If you are installing a thermostatically-controlled automatic valve, use plastic-to-steel adapters between the valve and the adjoining PVC fittings.) Bond a 1 1/2-inch PVC T fitting to each end of the assembly. Then connect a check valve to the end of one T with a plastic-to-steel adapter. On the opposite side of the check valve, install a second plastic-to-steel adapter if the existing pool pipe is plastic. If it’s copper, attach a copper-to-steel adapter in stead, and add a plastic-to-copper adapter at the opposite end of the assembly. If the run of pipe carrying pool water from filter to conventional heater or back to the pool is long enough, splice the valve-and-fitting assembly into the existing line, using reducers, if necessary, to match pipe diameters. Shut down the filter system, then use a hacksaw or tubing cutter to remove the necessary length of pipe, and bond the assembly in place with solvent cement. If you cannot fit the assembly into the existing pipe run, use elbows and pipe to construct a loop that is wide enough to accommodate the new valves and fittings. Linking the panels to the filter circuit. Run 1½- inch PVC pipe from the T fitting farthest from the pool filter to the water outlet of the collector panels. Secure vertical runs longer than 8 feet, using plastic pipe supports spaced every 6 feet. Connect the pipe to the panel outlet with a T fitting. Attach a 2-inch length of pipe to the open leg of the T, then add a reducer of the appropriate size and an air vent. Complete the loop by running pipe from the second T on the filter line to the panel inlet. To activate the system, close the gate valve; with an automatic valve, connect the temperature sensor leads to the points on the circuit recommended by the valve manufacturer. Turn on the pump to send water up to the collectors. 95 |