Giving Your Water Heater a Sun-powered Start

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A solar water-heating system saves energy and reduces bills by cutting the work load of a conventional water heater, thus slowing its fuel consumption.

In warm climates, such systems can supply virtually all of a household’s hot water needs during daylight hours. How ever, in most instances they work primarily as pre-heaters.

Solar collector panels trap the sun’s heat, which is then transferred to a solar storage tank. City or well-supplied domestic water passes through the tank and is warmed by the stored heat. The warmed water is then drawn into a conventional water heater, which finishes the job, further raising the temperature. An electrical control panel regulates the temperature and the flow of water between the panels and the solar tank.

There are two basic designs for solar water heaters. In what is known as an open-loop system—the batch heater pictured is an example—the domestic water supply flows outdoors in to a combination solar collector and tank for preheating, then back into the tank of the conventional water heater. Although open-loop systems are efficient—the water is heated directly by the sun, and no energy is lost through heat transfer—the water in them may freeze in cold weather, so they must be drained and shut down during cold months.

The more elaborate closed-loop system (opposite) offers year-round use because the domestic water supply never leaves the house; it’s warmed by heat transferred from a second, separate liquid— usually plain water or a mixture of water, antifreeze and anticorrosion chemicals— that circulates in a closed loop between the outdoor collectors and the solar tank. Some closed-loop systems are designed with a drain-back feature, which returns the liquid to the solar tank when the pump is off or when the temperature out side drops below 36° F.

Any solar water-heating system will save some energy. You can make a rough estimation of the cost efficiency of a pro nosed solar system by following the steps outlined in the box opposite. To obtain all of the information you will need to make the calculations, contact your utility company to find out the average temperature of your community water supply and ask your local weather service for the average annual number of BTUs of solar energy per square foot in your geo graphical area.

You will also have to consult a solar- equipment manufacturer or supplier to get a preliminary estimate of the number of collectors you will need—most domes tic water systems use between two and four. You will also need to know the square footage of the collectors and their ASHRAE efficiency rating—a standard industry evaluation of collector capacity set by the American Society of Heating, Refrigeration and Air-Conditioning Engineers. The rating—expressed in BTUs—is an average of the amount of hot water an individual collector is capable of producing at various outside temperatures.

In addition to computing cost efficiency, you must study your house to deter mine whether it can easily accommodate a solar water-heating system. To work efficiently, the collectors—which generally are installed on a roof for better exposure to the sun—must face within 10° of true south and be positioned nearly perpendicular to the sun’s rays.

The wooden mounting racks shown --- 80 are designed so that collectors can be fixed at the correct angle on virtually any slope.

The location of the existing water-heater tank is an additional factor to consider when planning an installation. The new solar tank should be located beside the existing water tank, and both should be placed as close as possible to the collectors to minimize the heat loss that is inevitable with long runs of pipe.

If pipes must pass through one or more stories, try to route most of them vertically and keep horizontal runs short. Vertical pipes usually can be threaded through interior partition walls or closets. Running horizontal lines usually entails removing part of the ceiling and cutting holes through joists.

Solar tanks, collectors and control panels designed specifically for domestic water-heating systems are all standard components available through solar- equipment dealers. Collectors vary in size and design. The interior tubes that circulate the heating solution through the collector are made of copper, plastic or galvanized steel; copper is the most common and the most durable material. The glazed portions of the panels are made of glass or plastic.

The number of solar panels that you will need for your system will be deter mined primarily by the amount of hot water your household requires, taking in to consideration such factors as the climate and the latitude where you live and the orientation of your roof. Using calculations similar to those made to compute cost efficiency, a solar-equipment dealer should be able to help you pin down your needs accurately.

All of the additional equipment you will need for the installation is available at plumbing and home-improvement stores. The wooden support racks for the collectors are constructed of 2-by-4, 2-by-2 and 1-by-4 lumber. The plastic spacers used in fastening the racks to the rafters are made from ¼-inch-thick polyurethane— which is commonly available in sheet form—cut into 2-inch squares easily with a circular saw.

For the plumbing system, purchase Type K copper tubing, following the solar- equipment manufacturer’s recommendations to determine the pipe size. You will need enough 90° elbows to run the pipes between the tanks and the collectors, enough pipe strapping to anchor the pipes to a flat surface every 6 feet, and the valves and fittings described opposite. Buy a standard 1/20-horsepower pump for a system with one or two collector panels; for a system with three or more panels or for a two-story house, use a 1/12-horsepower pump.

Buy split-type pipe jackets of fiberglass, elastomer, urethane or isocyanurate to insulate the pipes once they are installed. For outdoor runs use plastic or metal jackets as well, to protect the insulation from moisture and ultraviolet light. Finally, buy a neoprene boot and collar to cover the opening where the pipes pass through the roof and butyl rubber caulk ing to seal the seam.

Connecting solar components into an existing hot-water system is a straight for ward plumbing job. You can readily accomplish the task with standard tools and techniques (-- 83).

A Closed-Loop System with Rooftop Collectors

A solar water-heating system. The solar water-heating system below has three main components: a solar loop filled with liquid that transports heat from the rooftop solar collectors to a solar storage tank; a domestic hot-water loop that circulates potable water through piping inside the solar tank to be heated and then passes it into the conventional water heater; an electrical circuit that controls the solar loop.

In the solar loop, sunlight passes into the collector panels to warm a network of narrow tubes soldered to a flat, black collector plate. Liquid passing through the tubes absorbs heat from the metal and carries it through a return line to the solar storage tank in the house. A second pipe, called the feed line, returns the liquid from the tank to the collectors.

In the domestic loop, cold tap water flows into a long coil of tubing inside the solar tank. The sun-warmed liquid surrounding the coil heats the water within. The heated water is fed into the water heater and then flows through hot-water pipes to the rest of the house.

An electrical control panel and two tempera ture sensors direct circulation in the solar loop. Whenever the first sensor (mounted near the collector) records temperatures higher than the second sensor (mounted at the solar tank), the control panel starts the pump, which circulates the liquid to the collector for heating. The temperature in the conventional water heater is monitored in the normal way by a regular thermostat, which switches on the gas or electric heating system as needed.

Besides the piping and pumps needed to operate the solar water heater, additional plumbing fit tings are included to simplify maintenance and repairs. On either side of the pump are gate valves that can be closed to allow the pump and strainer to be cleaned or replaced. Boiler drain valves above and below the solar tank are used to fill and empty the solar loop. On the roof an air vent lets air escape from the loop as it fills with water; a vacuum breaker performs the opposite function, letting air back into the loop when the liquid drains back to the solar tank. Between these fittings is a pressure-relief valve, which will open should excessive pressure build up in the solar loop. There are two gate valves in the domestic loop that can be closed if it be comes necessary to make repairs to the house plumbing or the solar tank.

COLLECTOR PANEL— FEED; BOILER DRAIN VALVE

Computing Cost Efficiency

To estimate the cost efficiency of a solar water-heating system, you must compute both your BTU requirement and the BTU capacity of the system you are considering. First subtract the tempera ture of the local water supply from the temperature of the hot water in your present system. Multiply the result by 165-the average amount of hot water, in pounds, used by one person per day.

Multiply this figure by the number of people living in the house and then by 365 to obtain the household's annual BTU requirement.

Next multiply the average annual BTUs of solar heat per square foot in your area by the number of square feet in the collectors you intend to install.

Multiply the result by the collectors' efficiency rating to get the annual BTUs the system will provide, if this figure is at least 40 percent of the BTU requirement, the system will reduce water heating bills substantially.

Making Panel Support Racks

1 Calculating the pitch of the rack. Using a ruler and a carpenters level, measure the pitch of the roof. First mark the level with a piece of tape 12 inches from one end, and set that end just under the roof’s rake board. Hold the level horizontal and set the ruler vertical against the taped mark. Read the distance in inches from the top of the level to the underside of the rake board; convert the number to degrees --.

Consult an atlas for the degrees of latitude in your area, and compare this figure with the pitch of the roof. If the difference between the two figures is greater than 100, you will have to prop up one end of the collector panels, which ideally should face south within 10° of latitude. This additional pitch, angle A, will be used when you are constructing the support rack.

2 Constructing the support rack. To determine the mitered cuts for the two 2-by-4s that form the slanting top of the rack, draw a right angle on graph paper and extend one side of the angle to represent the base of the rack --. Inter sect the sides of the angle with a line representing the length of the collector panel plus 1 1/2 inches, positioning the line so that angle A equals the pitch calculated as: Step 1. Add angle A to angle B (90°), and subtract the total from 180°; the result is angle C.

Mark off the height of the collector on two 2- by-4s, and use a T bevel to mark off angle A and angle C on both boards; miter the boards with a circular saw. Cut two 2-by-4s for the base of the rack and two for the uprights, using the graph- paper drawing to determine their lengths. Bevel the top of the uprights to match angle C. Cut a 2-by-2 front brace equal to the width of the collector panel. Then cut two 1-by-4 back braces equal to the width of the collector panel. Glue and screw all of the pieces together as shown be low with 3-inch, flat-head wood screws.

1 Marking the panel locations. Snap a chalk line on the roof to mark the front of the support rack, extending the line 2 to 3 feet beyond the width of the panel. To keep the tine parallel to the eave, measure up from the eave at 3- foot intervals, and make guide marks. Snap a second line at an angle to the first: Make this line slope upward from the planned position of the cold-water inlet at a rate of 1/4 inch per foot of total combined collector-panel width. Inside the house, mark off the distance from the first line to the eave, minus the length of the overhang, on the bottom edge of a rafter; drive a 3½-inch nail up through the roof directly beside the rafter. Outside the house, mea sure ¾ inch from the tip of the nail to mark the center of the rafter. Using this mark as a starting point, mark the center of each rafter along the lower chalk line, spacing the marks 16 or 24 inches apart, depending on the rafter spacing inside the house.

Working Safely on the Roof

Working on a pitched roof presents problems of logistics and safety. The most significant logistical problem— balancing yourself, your tools and your supplies—is easily solved with the aid of two rooftop devices.

A pair of ladder hooks -- converts an ordinary extension ladder into a convenient and movable toe hold—a necessity on any roof with a pitch greater than 4 inches in 12. The hooks, clamped to the two top rungs of the ladder with wing nuts, fit over the roof ridge. A wood block under the ends of the hooks spreads the weight to prevent damage to shingles.

A pair of adjustable metal brackets supports a level platform for supplies and tools on a roof of asphalt shingles. Each bracket has a shelf that supports a 2-by-10 plank; the shelf is hinged to an upright support. The base of the upright locks into one of a series of slots, so the shelf stays level on a roof of any pitch. The bracket is held to the roof by a steel strap with slots or holes for nails.

To mount the bracket, bend back the bottom edge of a shingle, insert a 2½ “ nail in a slot or hole, and drive the nail through the shingle below. Remove the bracket by knocking it toward the ridge with a hammer and slipping the strap off the nail. Then pound the nail flush and cover it with roofing cement.

A few simple safety rules apply any time you work on a roof: Always wear rubber-soled shoes to keep from slip ping and from damaging roofing material. Try to use cordless electric tools to minimize the danger of tripping over long extension cords. And never work on the roof in rainy weather.

Mounting Collector Panels

2 Mounting the racks on the roof. Position the support rack with one of the boards cut for the base centered over a rafter, and the front brace aligned with the sloped chalk line; set a ‘/ inch-thick plastic spacer beneath the base 8 inches from each end, and drill 5 holes through the board and spacers, 1 inch into the rafter. Inject butyl rubber caulking into the holes, and then screw in 6-inch galvanized-steel lag bolts with washers. Drill holes and fasten intermediate bolts at 2-foot intervals along the board, adding a spacer at each hole.

Fasten the opposite base in the same way. If the board does not fall over a rafter, drill from the roof through the board and the plastic spacers, insert a stove bolt through the hole, then cut a 2-by-4 spacer block with a hole drilled through its face and fit the hole over the end of the bolt. Anchor the bolt with a nut and a washer, and nail the spacer to adjacent rafter edges --.

Mount additional support racks in the same way, leaving a space of at least 6 inches and no more than 8 inches between racks.

3 Hauling the panels onto the roof. Wrap each panel with a protective covering of heavy brown paper, then loop and tie sturdy rope around each end of the panel, leaving rope ends long enough to reach from the eaves to the ground; knot the rope ends to form a handle. Lean two ladders against the eave, slanting them out from the house a distance equal to one fourth the wall’s height. While you stand on the roof and pull the rope handle, have two helpers slowly climb the ladders, pushing the panel up from below.

Rest the panel on the support rack, front edge against the front brace; remove enough of the brown paper wrapping to expose the pipe ends used to p the panels into the system, but leave the glazing covered. In the installation shown here, the plumbing is done with cop per tubing, as shown opposite.

Brush a light coat of flux over the cleaned surfaces, assemble the joint and give the tube a twist to distribute the flux evenly.

Joinery Techniques for Copper Plumbing

1 Cutting copper tubing. To cut lengths of copper tubing for plumbing the panels, slide a tube cutter onto the tubing at the desired cutting position; at each cut, leave an extra length of tubing equal to the depth of the fit ting socket that will slip over the tubing --. Turn the cutter knob clockwise until the cutter wheel barely bites into the tubing wall, then rotate the cutter once around the tube. Tighten the cutter wheel slightly and rotate it in the opposite direction around the tubing; continue tightening and turning until the tubing is severed. Use the triangular blade attached to the cutter to ream out the burr inside the cut, and file down the ridge left by the cutter on the tubing’s outer surface.

3 Sweating the Joint. Lay the fluxed joint on the work surface, protected with a heatproof pad. Light the propane torch, allow it to heat up for a few seconds, then play the flame evenly all around the joint between the pipe and the fit ting. Test the heat of the pieces by touching them with a piece of solder; when the solder melts on contact, the joint is ready for sweating. Continue to heat the metal, at the same time touching the solder tip to the joint; but don’t allow the flame to touch the solder. Feed solder into the Joint until a bead of metal forms around the rim and begins to drip. Then remove the torch and allow the joint to cool.

2 Cleaning and fluxing the copper. Clean the copper surfaces to be joined by abrading them lightly until they are shiny—rub pipe ends with emery cloth; scour the inside of fitting sockets with a cylindrical wire brush. Don’t touch the surfaces once they are cleaned; greasy finger prints will prevent the solder from adhering.

Putting Together a Closed-Loop System

1 Connecting pairs of panels. Join the pipe ends that protrude from the inner edges of the adjacent collector panels. Use a coupler to make the connection, following the techniques illustrated. If necessary, push the panels closer together or farther apart to get an exact fit.

Sweat copper caps on two of the four pipe ends along the two outer panel edges, leaving two ends open for hooking up the system—one lower pipe for an inlet and, on the opposite panel edge, one upper pipe for an outlet.

Attach the panels to the mounting racks with angle brackets at the top and bottom ends.

ASBESTOS

2 Beginning the feed and return lines. Mark the point where the feed and return lines will pass through the roof (-- 79), locating this opening about 1 inch from a rafter. Then, using copper tubing and 90-degree elbow fittings, lay out and join the first part of the feed line, sloping ¼ inch per foot from the collector inlet to the mark for the opening in the roof. Join the first section of tubing to the collector’s inlet pipe with a reducer (inset, above, left) that narrows the collector’s 1½- inch pipe to a diameter of 3/4 inch.

Next, assemble the line leading from the collector outlet to the air vent at the top of the panel (inset, above, right). To start this line, sweat a reducer onto the collector’s outlet pipe, and connect a T fitting with a short length of pipe to the reducer. Add enough tubing to the T fitting to clear the top of the panel. Then join, in order:

T fitting with a vacuum breaker, a 2-inch length of tubing, a pressure-relief valve, another 2- inch length of tubing, and finally an air vent.

At the other opening on the outlet’s T fitting, add a length of tubing long enough to lead from the outlet to the mark for the roof opening. This is the first section of the collector’s return line.

Cut two 18-inch lengths of tubing and insulate them with foam. Slide the neoprene boot collar over the tubing and slip the tubing down through the boot, fitting the collar snugly over the boot. Join the top ends of the tubing to the feed and return lines, using elbow fittings. Then, inside the house, anchor both of these pieces of tubing to the nearest rafter, using copper pipe straps.

4 Plumbing the lines into the solar tank. Run the return line from the roof down to a point 12 inches above the solar-tank inlet. Join a T fit ting to the line, then run tubing the rest of the way down to the tank inlet; there, use a reducer to join it to the inlet. Attach a boiler drain valve to the open leg of the T fitting.

Start the feed line by attaching a reducer to the solar-tank outlet, at the bottom of the tank. Then add, in order: a 10-inch length of tubing, a T fitting with a boiler drain valve, a piece of tubing 3 inches long, a gate valve, another 3-inch length of tubing, a strainer, a third 3-inch length of tubing, and finally the female flange of an electric pump of the appropriate size. As you work away from the tank, support the pipe and fittings on wood blocks.

5 Completing the feed line. Set the electric pump so that the arrow on its casing points away from the solar tank, and bolt the pump flange with its fitted washer to the female flange on the feed line. Sweat a second female flange to a 3-inch length of tubing with a gate valve, then bolt this onto the other side of the pump. Add enough tubing and elbows to carry the line up to meet the feed line ex tending down through the roof.

3 Running the lines through the roof. Drill a %-inch pilot hole through the roof at the point you have marked. Using the hole as a starting point for a saber saw, cut a circular opening, 4½ inches in diameter, through the roof; work from the pilot hole away from the nearby rafter. Position neoprene flashing over the opening; center the boot of the flashing over the opening, and push the upper half of the flashing up under the roof shingles by removing any interfering nails with a pry bar. Fasten the lower half of the flashing over the shingles with a layer of asphalt roofing cement.

6 Connecting the tanks. Turn off the cold water that runs to the existing tank and remove the cold- water pipe leading to the tank inlet by breaking the line at the final union above the water heater; use a pipe wrench to twist off the reducer, the pipe and the final elbow that carries the pipe downward. Then, starting with a reducer at the cold-water-feed inlet atop the solar tank, run copper tubing to meet the open end of the cold-water lead; install a gate valve in the horizontal section of new tubing and—if the existing house plumbing is galvanized steel, as shown here—join the new copper line to the old steel line with a dielectric union (left inset). Slip the hex nut and plastic insert of the union over the copper tubing, then sweat the bronze female portion onto the end. Wrap plastic joint tape around the galvanized pipe threads. Twist on the galvanized coupler, the rubber washer, then the hex nut, tightening with a wrench. If the house plumbing is copper, make the connection with a coupler.

Connect the inlet atop the existing tank to the upper outlet on the side of the solar tank with another run of copper tubing (right inset). Install a gate valve on the horizontal pipe and use reducers to make connections at the inlets.

7 Wiring the controls. Mount the control panel for the system on a wall close to the pump. Fasten one of the two sensor probes to the outlet line at the bottom of the solar storage tank, using a hose clamp to anchor the probe. Tighten the hose clamp until the probe is held firmly against the pipe. Then extend the probe’s bell wire to the control panel, and slip the wire’s spade connectors under the terminal screws labeled TANK SENSOR; tighten the screws.

On the roof, clamp the second sensor probe to the collector’s return line, as close to the collector outlet as possible. Run the bell wire down through the roof-vent boot beside the insulated tubing, and seal the top of the roof vent with butyl rubber caulking compound. Then run the bell wire from the roof down to the control panels, and fasten the spade connectors to the terminals labeled PLATE SENSOR or COLLECTOR. Anchor the collector’s bell wire to the return-line tubing with duct tape; anchor the solar tank’s bell wire to the wall with cable straps. Plug the power cord for the pump into its socket in the control panel and, with the control panel’s power switched off, plug the panel cord into a 120-volt outlet.

8 Filling the solar loop with water. Fasten a garden hose to the boiler drain at the top of the solar tank, and open the valve. Close the lower boiler drain valve at the bottom of the solar tank. Open the gate valves on either side of the pump. Run water into the solar loop, stopping when the air vent ceases to hiss. Have a helper check the roof lines for leaks; drain the loop and re-solder imperfect joints. When the sys tem is leak-free, let the water drain through the upper boiler drain valve and the hose out of the collectors; close the drain valve. To activate the system, switch on the control panel, starting the pump. Remove the protective paper wrap ping from the collector panels.

9 Insulating the pipes. Encase all the tubing in the solar loop and the line connecting the solar tank to the existing tank in sections of R-4 foam insulation. Notch the foam with scissors at the corners; tape together the ends of adjacent sections with duct tape. On outdoor lines, be sure the slit in the foam casing faces downward.

To protect outdoor lines further, jacket the foam insulation with sections of split plastic sheathing, again with the slit facing downward. On sloping lines, install the sheathing from the lowest point on the line to the highest, lapping the upper ends over the lower ones. This will keep water from seeping through the joints.

The Batch Collector: A Simple Solar Water Heater

A solar batch heater is basically just a detour built into the plumbing of the house water-heating system. Cold water headed for the conventional water heater inside the house is routed out through an exterior wall, into a solar collector tank that reclines on a small concrete slab be side the house, and then back through the wall to the water heater. During this jog in its journey, the water is warmed by thermal energy trapped in the solar collector, reducing the amount of work the indoor tank has to do.

Because of its size and shape, the tank- style batch collector absorbs heat less efficiently than the narrow network of thin-walled tubes in the flatplate panel-type collectors of the closed-loop system shown. And since the batch heater works as part of an open- loop system, where domestic tap water travels directly through the solar collector outside the house, there is a danger that the water may freeze in cold weather. In almost any climate, however, a batch heater works efficiently for enough of the year to substantially cut the cost of water-heating fuel bills; during the coldest months you can simply shut down and drain the system and rely on the existing water heater.

The batch heater is far simpler to build than a closed-loop system, because the collector generally stands on the ground rather than on the roof. And it’s a relatively inexpensive system, because you can make the collector yourself and in stall it with fewer plumbing fixtures and less copper tubing.

The main component of the system— the solar tank—is made of galvanized steel and generally holds 30 to 40 gallons of water. You can buy a tank designed especially for use as a batch collector from a plumbing-equipment dealer, but often a discarded water-heater tank will serve just as well; it needs only a few simple plumbing alterations to accommodate a cold-water inlet that may be located either on the side of the tank near the bottom or on the bottom end, as shown opposite.

If you find a used tank at a junk or scrap-metal dealer, you will have to cut away the outer sheet-metal housing and check the inner tank to be sure there are no cracks, holes, split seams or rusted spots; check for leaks by blocking all but one of the tank openings and filling the tank with water. Then clean the tank thoroughly. First, sand rough spots on the surface with medium-grit sandpaper, and then wash the entire tank with soap and water; use denatured alcohol on grease spots that soap won’t remove. Finally, cap off all but the inlet and outlet openings on the tank.

To turn the tank into a solar collector, you must increase its capacity for heat absorption by darkening its surface. You can paint the tank with an exterior flat black paint or apply a highly absorptive and nonreflective black coating made of nickel chromium; the latter comes in rolls with an adhesive backing that makes it quick and easy to apply. The cylindrical surface of the tank shown is covered with such an adhesive coating; the top and bottom of the tank—difficult to fit exactly—are painted black. The paint is available from any paint dealer, and the rolls of adhesive tank coating can be bought from solar- equipment dealers.

A thin plastic film called Mylar, aluminized to make it reflective, is used to cover the walls of the wood cradle that supports the tank, further increasing its heat absorption. Other types of plastic film are used to make the three layers of glazing that cover the collector and trap the sun’s rays inside the tank compartment. The two inner layers of glazing are made from a Teflon film 1 mil thick or, if Teflon film is unavailable, from any of the clear plastic films sold in rolls in hard ware stores. The single exterior layer is made of a 7-mil acrylic-polyester laminate called Flexigard but any of the rigid plastics listed in the chart are suitable, as is tempered glass.

The framework that supports the solar tank and its various reflective and trans parent surfaces is made from pressure- treated 2-by-4s and 2-by-2s along with several sheets of ¼-inch hardboard and /8-inch exterior-grade plywood. Insulation is provided by 3½-inch-thick glass-fiber batts with plastic or aluminum vapor barriers. The glazed panels are anchored on top of the frame with silicone caulk and wood screws; the edges of the panels are protected from moisture by strips of aluminum flashing.

The plumbing system consists of Type K ¾-inch copper tubing with T fittings and 90° elbows; three gate valves; a boiler drain valve; a vacuum breaker and a pressure-relief valve. The interior hot- water line is insulated with split foam jackets, all exterior lines with foam and plastic jackets (-- 87). The openings in the house wall for the cold- and hot- water lines are caulked with butyl rubber compound. All of this equipment is avail able at a plumbing-supply store, but be fore you buy it, plan the location of the collector so that you can determine how much copper tubing to purchase.

It’s best to build the collector as close as possible to the inside water heater, in order to reduce the heat loss that is inevitable when water must travel through long pipe runs. But like any solar collector, the batch heater must face within 10° of true south to work effectively. A south-facing wall is the logical location, but if you must choose a wall that faces in another direction in order to keep the collector close to the existing water heater, position the collector far enough from the house wall so that it can face south and remain unshaded for most of the day.

In calculating the correct angle of inclination for the tank, use the instructions Step 1. Plan to set the tank tilted on end as shown opposite, rather than on its side. This creates a more distinct separation between the cold water entering at the bottom of the tank and the heated water leaving at the top, allowing the system to work better.

The construction of the batch heater requires basic carpentry skills and the plumbing techniques illustrated --- 83. You must also pour a small concrete slab to support the weight—up to 500 pounds—of the water-filled solar tank.

Anatomy of a solar batch heater. Fashioned from a discarded water-heater tank, this solar collector rests in a wood cradle supported by a rack of 2-by-4s. The structure is sheathed in plywood and stands on a 4-inch concrete slab, which bears its considerable weight.

During operation of the system, the sun’s rays are trapped in the cradle compartment by three layers of transparent plastic film. They bounce off the reflective backing that coats the cradle and penetrate the tank. Domestic cold water, entering the tank through the in let at the bottom, is heated by the trapped thermal energy and then routed through the out let at the top to the conventional water heater.

2 Cutting diagonal supports. Mark center points on the faces of each crosspiece, then set a 2-by-4 diagonally on edge, its lower end aligned with a center mark and its upper end against both the edge of a side support and the bottom of a side rail. Mark the upper end of the 2-by-4 with a vertical line along its face; use the outer edge of the side support as a guide (above, left). Cut the board, then trim the corner off the other end to make the ends parallel. Cut seven more 2-by-4s to match, using the first board as a template.

Supporting the Solar Tank

1 Constructing the tank-frame exterior. Nail

2-by-4s together to form a rectangular frame.

The distance between the rails on opposite sides of the frame should be 12 inches greater than the diameter of the tank; the distance between the upper and lower side rails on the same side of the frame should be 12 inches greater than the tank’s diameter. The distance between the top and bottom rails should be 12 inches greater than the height of the tank.

Install supports to divide the top, the bottom and each side into thirds; divide the underside of the frame into thirds with two crosspieces. Cut the pieces and join them as shown.

Cut rectangles of ‘4-inch hardboard to match the outer dimensions of the top and bottom of the frame. Then cut notches 1½ inches deep and 3½ inches long at the four corners of each rectangle, and nail the pieces to the inside edges of the top and bottom rails.

OILER DRAIN VALVE

3 Installing the diagonal supports. Position pairs of diagonal supports end to end to form Vs extending from the center of each crosspiece to the edges of opposite side supports; nail the 2- by-4s to the crosspieces and to the side sup ports. At the top and bottom of the frame, nail through the diagonal supports and the hard- board into the frame pieces. Then, along the top edges of both side rails, mark the location of each diagonal support.

Cut two panels of ¼-inch hardboard to form a V shaped tank cradle that will rest atop the diagonal supports; nail the panels to the top edges of the supports. Then cut two 2-by-6 boards 12 inches long, and lay them in a V inside the tank cradle, flat against the sides, their edges butted against the planned bottom end of the frame --. Anchor the boards by driving wood screws through their faces and the hardboard, into the diagonal supports below.

4 Insulating the frame. With the frame face down, trim fiberglass insulation to fit over the hardboard cradle between the diagonal supports. Lay the batts over the cradle, vapor barrier up, and push the fiberglass in between the hardboard and the side rails; staple the vapor-barrier edges at 6-inch intervals to the edges of the diagonals. Fit rectangular pieces of insulation between the supports at the top and bottom of the frame, vapor barriers facing out, and staple. Cut ¾-inch exterior-grade plywood to fit over the ends and underside of the frame; nail the plywood to the frame.

5 Installing the reflective backing. Cut sheets of reflective backing to fit the sloped sides of the tank cradle, the triangular sections of hardboard at the top and bottom of the cradle and the 2-by-6 supports at the bottom end of the cradle. Lay each sheet in place and, while a helper holds the edge, roll the sheet back and spray adhesive over the wood with long, even strokes. Lay the sheet back down and wipe the surface with a soft, clean rag, working from the center outward, to stick the backing down and smooth out wrinkles and air pockets.

6 Building a support rack for the frame. Determine the correct angle of inclination for the collector according to your Iatiti (Step 1) and construct an angled support rack for the tank frame, as described, Step 2. Set the rack on its concrete slab, then anchor the tank frame to the rack, using steel truss plates and nails.

While a helper holds a large sheet of %-inch exterior-grade plywood against the side of the assembly, trace the outline of the structure’s side on the plywood. Cut around the outline, and nail the resulting plywood panel to the rack and frame to enclose the side of the structure. Mark and cut a similar panel for the other side, and nail it in place --.

7 Coating the tank. Paint the ends of the tank with flat black exterior paint and let the paint dry. Then, working on a clean, flat surface, cut a strip of black tank coating 1 inch longer than the circumference of the tank, peel back one edge of the adhesive backing and press the exposed edge against the tank, aligning the end of the coating strip with one end of the tank. Then peel the backing off slowly and evenly as a helper rolls the tank away from you and presses the coating against the tank with a soft rag, rubbing gently from the middle of the strip outward to smooth away wrinkles and air pockets.

After the first strip of coating has been applied, peel away 1 inch of protective covering from its inner edge and cut off the strip of covering with a utility knife; don’t damage the coating underneath. Then cut and apply a second strip of coating, overlapping the exposed edge of the first strip. Continue until the tank is completely covered, trimming the last strip of coating as necessary for an exact fit. Pull all of the protective covering off the coating.

8 Installing the tank. With a helper, set the tank in the cradle with its lower end against the 2-by-6 boards at the bottom; be careful not to slide the tank over the easily torn reflective backing in the cradle. Anchor the tank in place with pipe straps screwed to the diagonal supports below the cradle; use the marks on the frame side rails to locate the supports.

Hooking Up to the Existing Water Heater

1 Running copper tubing from the tank. At each end of the tank frame and in line with the tank inlet and outlet, drill a 1-inch hole through the layers of plywood, hardboard and insulation. At the bottom end, screw a 3 reducer into the cold-water inlet and then, protecting the wood of the frame with asbestos, use the pipe-sweating techniques illustrated to extend a length of pipe 4 or 5 inches beyond the bottom of the frame; sweat a T fitting onto the end of the pipe. Sweat a boiler drain valve onto one leg of the T; to the other leg sweat a run of pipe leading to the spot where the pipe will enter the house.

2. Connecting at the water heater. Switch off the water heater, shut off the cold water, then remove the final elbow and the attached vertical run of pipe leading to the tank’s cold-water inlet. Sweat a T fitting onto the line; to the vertical leg of the T sweat a short length of pipe with a gate valve, another I fitting and a pipe with a ¾-inch reducer to connect at the tank inlet. To the free leg of the upper T sweat a run of pipe, with a gate valve, leading to the collector’s cold-water line. To the lower T sweat a run of pipe, with a gate valve, that leads to the collector’s hot-water line. Insulate the lines.

To the hot-water outlet at the top of the tank add a reducer, a short length of pipe and a T fit ting. Sweat a pressure-relief valve to one leg of the T and to the other leg a short length of pipe, a T with a vacuum breaker and then a run of pipe to the planned opening in the house wall.

Drill holes through the house wall at least 2 feet above grade. Insulate the pipes with foam and plastic jackets, and run them into the house; caulk around the holes with butyl rubber caulking compound.

Glazing the Solar Collector

1. Making the panel frames. Construct two frames of unwarped 2-by-2 lumber; their outer dimensions should match the outer dimensions of the front face of the tank-support assembly, including the edges of the plywood that covers the ends and sides of the structure. Cut lap joints -- for the corners of each frame, and fasten the joints with 1-inch flat-head wood screws, countersinking the screwheads. Screw angle irons to all of the inside corners; then paint the frames and the outside of the support structure if desired. Allow the paint to dry completely; the 2-by-2 frames should be laid flat while drying so that they won’t warp.

Lay the second 2-by-2 frame atop a sheet of acrylic-polyester laminate, acrylic side up. Cut and fasten it as before; leave the opposite face of the frame uncovered.

helper, lay the double-glazed panel on the frame with the exposed edge of overlapped film facing down. Press the panel firmly into the caulk, then drill 1/4-inch holes at 12-inch intervals through the panel frame, counter-boring for the heads of 2½-inch wood screws. Screw the frame to the wood below. Apply a bead of caulk around the edges of the panel and lay the second panel, glazed side up, atop the first panel, anchoring it with screws as before. Then caulk all exposed seams and screw-heads.

3 Flashing the glazed panels. Cut a strip of aluminum flashing 6 inches wide and the same length as the lower end of the tank frame; bend so that 2 inches of aluminum will extend across the top surface of the glazed panel and 4 inches will extend down the side. Anchor both aluminum surfaces to the wood frame with 3 aluminum screws at 1-foot intervals. Cut flashing for both sides of the frame and attach it in the same way; then fashion a strip for the top. Use silicone caulk to cover all edges where the aluminum overlaps the acrylic-polyester film.

To fill the system, close the boiler drain valve at the bottom of the tank frame; open the gate valves on the hot-water and cold-water lines inside the house, and close the gate valve on the vertical line between them.

2. Stapling film to the panel frames.

Working on a clean, flat surface, lay a 2-by-2 frame atop a sheet of Teflon film, and cut a rectangle of film 3 inches longer and wider than the frame. Make a V-shaped cut from each corner of the film into the corner of the frame; then, working on the longer sides first, fold the edge of the film up over one side of the frame, and staple the film to the wood at 3-inch intervals.

Pull the film taut at the opposite side of the frame, and staple it in the same way. Staple the film over the shorter ends of the frame. Then flip the frame over, lay it atop a second sheet of film and repeat the same procedure.

Lay the second 2-by-2 frame atop a sheet of acrylic-polyester laminate, acrylic side up. Cut and fasten it as before; leave the opposite face of the frame uncovered.

Apply a continuous bead of silicone caulk around the top edge of the tank frame. Then, with a helper, lay the double-glazed panel on the frame with the exposed edge of overlapped film facing down. Press the panel firmly into the caulk, then drill 1/4-inch holes at 12-inch intervals through the panel frame, counter-boring for the heads of 2½-inch wood screws. Screw the frame to the wood below. Apply a bead of caulk around the edges of the panel and lay the second panel, glazed side up, atop the first panel, anchoring it with screws as before. Then caulk all exposed seams and screw-heads.

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