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A thermosiphoning air panel, commonly called a TAP, is a single-room space heater that uses convection to waft warm air into a room. A TAP draws cool air near the floor of the room into the bottom of a glass-faced box. There, the air is warmed by a metal absorber plate that itself is heated by the sun; the air then circulates back into the room. On a sun- fly day, the air inside a TAP reaches temperatures of between 90° and 120° F. Un like a Trombe wall (-- 40), however, a TAP has no storage capacity for nighttime heating. Vents must be closed at night to keep cold air out of the house. Because a TAP can heat only a single room and function only while the sun is out, it’s best situated on a room that is used during the day. This may be a child’s playroom, a study or a family room. The TAP’s peak production will be between the hours of 10 a.m. and 3 p.m. The TAP design shown opposite can be retrofitted onto a wood-frame house. Like a Trombe wall, it must be installed on a wall that faces within 20° of true south ( 8-9) and has exposure to the sun unobstructed by buildings or trees. Depending upon the amount of such wall space available, the TAP can be constructed one, two, or three panels wide; the example opposite is a double panel. In all cases, the TAP surface area should be no more than one third the floor area of the room you plan to heat. The panels can be mounted on a first- or second-story wall. One variation on the installation shown here is to build 8- foot-high panels that draw cool air from a room downstairs and vent warm air just above the floor on the second story. All of the materials used to build a TAP are readily available at lumberyards and building-supply outlets. As on a Trombe wall, it’s the size of the glazing material used on the face of the TAP that deter mines the dimensions of the panels. Although you can use plastic materials made for solar glazing, many experts prefer the double-glazed panes sold as re placement glass for sliding patio doors. Since the edges of such panes are hermetically sealed, they cannot be trimmed to size; rather, the frames of the panels are built to fit around the glass. To keep the heat that a TAP collects from being absorbed by the wall of the house, the panels are backed by sheets of 1 foil-faced sheathing made of rigid laminated cardboard. This kind of sheathing is sold in several grades; you will need the most rigid grade. The absorber plate can be made from corrugated aluminum of the type used for roofs and siding. It’s sold in sheets of various lengths and widths, so you should order pieces close in size to the glass panels. Cut the sheets to the length you need by trimming across the ribs with tin snips; to cut along the ribs, score the cutting line with a utility knife and then bend the metal repeatedly until it breaks. A carbide-tipped blade in a circular saw will make the cuts in either direction. Wear eye and ear protectors when you work with a saw. After the absorber panels have been trimmed to size, use a solution of tn sodium phosphate and warm water to wash off the greasy film that coats the aluminum. Rinse the panels, then paint the sides that will face the sun with a flat black heat-resistant paint. The perimeter frame for the TAP panels can be made with any 2-by-4 lumber. But the stops inside the frame that brace the absorber plates and glass are subject to very high heat. Avoid pine in making those pieces—the fumes that pine emits when it gets hot can fog the glass face of the TAP, making it less efficient. Fir and spruce are good alternatives. The lumber depicted in the drawings that follow is 5 stock. The 1-inch actual thickness of such stock provides adequate surface area along its edges for seating the glass and aluminum securely. Five 8-foot-long 5 boards can be rip-cut to provide all the stops you need for a double-panel TAP. These include eight 1 absorber stops; six 2¾-inch-wide glazing stops for the sides, top and bottom of the TAP; a center glazing strip 2 1/2 inches wide; and a 1¾-inch-wide center mullion. If you have a table saw, you can make these rip cuts yourself; otherwise, have the cuts made for you at the lumberyard. You will also need a supply of 1-by-3s and 1-by-6s for battens that hold the glass in place on the face of the TAP and for trim around the vent openings inside the house. Among the other materials that you will need is lightweight .020-inch aluminum flashing, both for weatherproofing the top of the TAP frame and for fabricating vent sleeves that ease the flow of air through the panels. For the vent opening inside the house, buy a sheet of the plastic egg-crate grating used to cover ceiling light fixtures. And for the lower vents, buy sheets of 2-mil polyethylene to serve as back-draft dampers when the air in the panel cools. For installing the glass, buy 103 feet of butyl glazing tape ½ inch wide by /32 inch thick and four neoprene set ting blocks 1/4 inch thick, /3 inch wide and 2 inches long. And finally, buy rubber filler strips to seal off the tops and bottoms of the absorber plates. These are available where you purchase the corrugated aluminum. Although a TAP is a valuable supplement to your winter heating plant, you will need to shut it down during the warm months by shading it. On some houses, a wide roof overhang may shade the TAP in summer, when the angle of the sun’s rays is high. If there is no adequate overhang, you may have to install an awning or rig up a tarpaulin. 48 Anatomy of a TAP. The passive solar collector at left has been installed on the south-facing wall of a wood-frame house. Sunlight passes through double-wall panels of glass and is absorbed by dark-colored aluminum plates. Heat that is conducted through the metal plates is held inside the TAP by a reflective backing that is flush against the sheathing of the house and by rubber filler strips shaped to match the profile of the corrugated aluminum. Cool air near the floor of the room inside flows into the TAP through vent openings at the bottom of the collector. The vent openings have been cut between the wall studs and through the reflective backing. As the air inside the TAP warms, it rises and reenters the house through vents at the top. During daylight hours, a steady flow of air through the TAP is established by natural convection, which draws a constant Supply of cooler air from inside the house. The siding of the house has been removed around the collector. The 2-by-4 frame is supported by a shelflike wooden wall brace at the bottom and fastened at the top with angle brackets. Inside the frame are wooden stops and a center mullion to hold the metal and glass in position. Stiffener blocks at the centers of the panels keep the metal absorber plates rigid. The front of the glass is held by battens screwed to the edges of the frame. Flashing at the top protects the TAP from runoff rain; drainage kerfs at the bottom of the frame allow accumulated moisture to escape. Thin plastic sheets on the lower vents serve as dampers to prevent reverse drafts. Making Thermosiphoning Air Panels 1 Joining the frame. Working on a flat surface, assemble a framework that consists of 2-by-4-inch stiles 31/2 inches longer than the height of the glass; 2-by-4-inch rails 1½ inches longer than the combined widths of the two gloss panels; and a 1-by-1 mullion cut to fit between the rolls. Join the pieces with yellow glue and 3½-inch common nails, fitting the rails between the ends of the stiles. Install the mullion with a narrow edge facing up, between center points on the rails and flush with the bottom edge. Make seven evenly spaced pencil marks along the outside edge of one rail. At each mark, make a ¼-inch-deep cut with a circular sow. The kerfs will serve to drain moisture from the TAP. -GLAZING STOP; ABSORBER FILLER STRIPS STOP 49 2. Attaching the reflective backing. Turn the frame over so that the saw kerfs face down, then measure diagonally between the corners to be sure that the frame pieces are joined at right angles. The measurements should be equal. Make adjustments, if necessary, by pushing on opposite corners. Spread glue, construction adhesive or caulk on the edges of the frame, then lay sheets of the reflective backing on the adhesive; align the edges of the backing with the edges of the frame. For a double panel, as shown here, you will need to use two sheets of the backing material with their edges adjoining along the center of the mullion. Drive 1-inch roofing nails through the backing at 3-inch intervals around the perimeter of the frame and along the center mullion. Again, flop the entire frame so that the saw kerfs are facing upward. 3. Adding the stops. Line the inside of the frame rails and stiles with 1-by-2 glazing stops, seated flush with the backing and secured with yellow glue and 2½-inch common nails. In side the glazing stops, attach 1-by-1 absorber stops with their wider edges flush against the glazing stops. A cross section shows the relative positions of the stops, the frame and the backing. Nail the absorber stops to each side of the center mullion with the wide side flush against the mullion. 50 5. Marking the bottom. To determine how far down to remove the siding, establish marks out side the house that show the level of the baseboard inside. Begin inside the house by measuring from the top of a window frame to the top of the baseboard. Outside the house, mark the siding at that level after measuring down from the same window. Hold a carpenter’s level at the baseboard mark, and place a second mark where the level crosses a vertical chalk line. From this second mark, measure down 8 1/2 inches (the combined thicknesses of the bottom of the TAP frame and its supports) and use the carpenter’s level to mark a horizontal line between the two vertical lines. If there is a slab foundation, position the TAP supports at the baseboard line or above to cross the studs. Measure 86½ inches up from the bottom line to accommodate the top and bottom of the frame, the supports and the 76-inch-high glass panels used in this example. Make a final mark at that point: this is where the top of the TAP frame will be attached to the wall. 4. Plotting the panel location. On the siding of the house, snap two vertical chalk lines as far apart as the TAP frame is wide. To maximize the number of vents you can build into the pan el, situate the chalk lines so that they will be 3½ inches outside the studs at each side. Nail heads in the siding will reveal the stud locations; they will be either 16 or 24 inches apart. After snapping the first chalk line, measure from that line to position the second chalk line. 51 6. Removing the siding. With the blade of a circular saw set to the maximum depth of the siding, cut along the lines marked in Step 5. Guide the blade carefully along the outside edges of the lines. If the mark indicating the top of the TAP frame is 3 inches or more from the bottom of the next piece of siding above, cut to the top of the marked siding piece. If the mark is closer than 3 inches, cut through to the top of the next piece of siding as well. This will give you room to install fasteners and flashing above the TAP. Pry off the siding between the cut lines, and set aside the top pieces for later use. If the siding is aluminum, cut it with a carbide blade. On the exposed sheathing of the house, mark cut ting lines for the vent openings. Mark the bottom edge of the lower vents 10 1/2 inches up from the top of the siding still in place. From that line, measure up 72½ inches and mark the top edge of the upper vents. Use a framing square to complete outlines for the vents. Make the vents 6 inches high and as wide as the space between the studs in your wall. 7. Cutting the exterior vent openings. Set the circular saw to the depth of the sheathing—usually ½ to 3/4 inch. After turning off the power to any wires that may be hidden in the wall, cut out the vents outlined in Step 6. To do this, you will have to repeatedly plunge the saw blade into the surface of the sheathing—a procedure that requires some care. Holding the blade guard open, tilt the saw onto the front of its base until the blade is clear of the wood. Position the blade over the cutting line, then turn on the power and slowly lower the saw until its base rests flat. Grasp the saw firmly as the blade bites into the wood. If you prefer to use a keyhole saw or a saber saw, drill a starter hole at each corner to get the saw blade started. 8. Marking the interior vents. After cutting away the insulation exposed by the exterior vent openings, hammer an awl through the back of the wallboard at the bottom right corner of the right lower vent. Pull out the awl, and punch a second hole at the bottom left corner of the left lower vent. In the same way, mark the wallboard at the top right corner of the right upper vent and the top left corner of the left upper vent. Inside the house, draw a line connecting the bottom holes and a line between the top holes. With a framing square, mark 3½-inch-high rectangles above the bottom line and below the top line, then cut away the entire length of wallboard within the marked lines. Remove more wallboard at the sides of each hole to expose ¾ inch of the stud on each side of the vent. 52 9. Building the supports. To install a sup porting ledger, cut a 2-by-6 to the width of the TAP frame and rest it on the siding at the bottom of the opening. Tack the board temporarily in place with 3-inch nails driven partway in. Mark the ledger where it crosses the studs or the band joist, and at 16-inch intervals drill pilot holes for a pair of 3½-inch- long ¼-inch lag bolts, Insert the lag bolts and their washers, and tighten them with a socket wrench. Pull Out the nails. Cut triangular braces from 2-by-6 stock to extend 2 inches out from the top edge of the ledger --. Mark positions for these braces at each end of the ledger and between the lag bolt locations. To attach the braces, drill a pilot hole through the front edge of each piece for a 2½-inch No. 10 wood screw. Drive a Countersink bit into the pilot holes so that the heads of the wood screws can be seated under the surface of the wood, Lay a 2-by-4 shelf on the ledger, and screw it to the tops of the braces and into the ledger, again using 2½-inch No. 10 wood screws and countersinking the heads. 10. Attaching the frame. Working with a helper, lift the TAP frame into place atop its shelf, and tack it to the wall with galvanized roofing nails driven through the reflective backing. Secure the top of the frame with 3-inch angle brackets at every stud location. At the bottom of the frame, drive a 3¼-inch nail every 12 inches through the glazing stop into the support shelf. Apply caulk around the frame where it meets the edges of the siding. If the gap is bigger than ½ inch, fill it with fiberglass insulation and then caulk it. From inside, use an awl to poke holes through the backing of the TAP at the bottom corners of the lower vent openings and the top corners of the upper vents. Go outside and use the holes as guides to mark 6-inch-high vent openings on the backing (Step 8). Cut the vent openings with a utility knife. 11. Fabricating vent sleeves. For each flared vent between the TAP and the room inside, you will need to cut and shape four pieces of aluminum flashing. To make 900 bends in the metal for flanges that will hold the flashing in place, scribe a line with an awl and fold the aluminum over a 2-by-4 nailed to the top of a workbench. Wear gloves to protect your hands as you shape the metal. Begin by covering the studs at the sides of each vent. For these pieces, cut the aluminum 5 inches wide by 6 inches high, and shape ½- inch flanges on the longer edges to wrap around the 2-by-4 studs. Nail one flange to the stud inside the house; nail the other flange to the stud through the reflective backing, using 1-inch galvanized roofing nails. For the vent sides next to the center stud, make one flange to be nailed to the stud inside the house. Bend the flashing around the center absorber stop, and nail it to the side of the stop. Next, make a flat bottom for the lower vents and a flat top for the upper vents. Cut these pieces as wide as the vent openings and 6 inches deep, with a ½-inch flange predrilled at each end for drywall screws that at tach the piece to the wallboard inside the house. Nail the outside edges of these pieces to the absorber stops. For the vents next to the center stud, notch the flashing to go around the center absorber stops. The final pieces of the vent sleeves—the tops of the lower vents and the bottoms of the upper vents—must be curved to ease the flow of air through the TAP. Cut sections of aluminum as wide as the vent openings, and shape a ½- inch flange at the end of each piece. From outside the house, reach through the vent opening and hold the flange against the face of the wall board inside. With your other hand, bend the flashing in a gentle curve to the rim of the exterior vent opening (bottom right). Mark with a felt- tipped pen where the flashing meets the rim; then remove the piece, cut it, and shape a ½-inch flange at that point. For the vents next to the center stud, trim the flashing first so that it can be pulled past the mullion and stops. Put the flashing back in place, and attach it to the wallboard and the backing of the TAP --. When the sleeves are completed, seal all of the seams in the aluminum with beads of silicone caulk. 54 12. Installing the absorber plates. Cut corrugated aluminum plates to dimensions ½ inch smaller than the spaces between the glazing stops, and with a 3/4 to 1-inch flange for nailing on each vertical edge. Clean and paint the plates --- 48. On the unpainted sides of the plates, run ‘/4-inch beads of silicone caulk along the top and bottom edges. Cut rubber filler strips with a utility knife, and press them into the caulk to cement them to the aluminum. Nail a stiffener block—a scrap of wood 1 inch thick and 6 inches long—to the backing of the TAP on each side of the center mullion. Position the blocks so that they will hold the ribbed surfaces of the absorber plates 1 inch away from the backing. Drill pilot holes at 3-inch intervals around the perimeter of the plates, then apply beads of caulk along those same edges on the unpainted side. Press the plates into place on the absorber stops. Drive 1-inch galvanized roofing nails through the pilot holes into the stops, then caulk the edges of the plates to make them airtight. Cut the 3 center glazing stop to fit between the glazing stops that are already in place on the frame, and nail it to the center mullion. Paint the glazing stops and the nailheads with flat black paint, and touch up scratches in the paint on the absorber plate if necessary. 55 13. Setting in the glazing. Apply butyl glazing tape to the face of the glazing stops; keep the tape flush with the inner edges of the stops. Lay four ¼-inch-thick, %-inch-wide neoprene blocks on the bottom rail of the TAP frame to cushion the bottom edges of the glass panel Position two beneath each panel, 16 inches apart. After cleaning the inside of the glass and removing the protective paper from the tape, have a helper assist you in lifting the glass onto the neoprene blocks, then press the glass into the tape. Nail temporary cleats to the edges of the frame to hold the glass until you are ready to install the battens. Cut three 1-by-3-inch battens as long as the stiles on the TAP frame. Line the front edges of the glass with butyl tape, then attach the vertical bat tens to the front of the frame, overlapping the tape. Use 1½-inch wood screws to fasten the bars. Screw the center batten to the center glazing stop, overlapping both panels of glass. After removing the cleats, fasten 1-by-3 battens across the top between the vertical battens. For the bottom battens, use 1-by-6s; rip-cut them to 4 inches in width, and bevel the top edges for drainage --. Caulk between the glass and the inside edges of all the battens. 14. Weatherproofing the panel. Cut a piece of flashing 9 inches wide and 3 inches longer than the top of the frame. Scribe a line along the length of the piece, 3 inches in from one of the long edges. Use tin snips to make a 1 1/2-iflch cut along the line at each end, then cut diagonally from the corners to make angled notches in the flashing material (above, left). Make a 90-dgr. bend on the line. Scribe a line, and make a second 900 bend in the opposite direction, 1½ inches from the other edge of the metal. Center the flashing along the top of the TAP frame so that it overhangs the sides of the panel by 1½ inches. Press in the front corners, and use pliers to make sharp creases on the flaps that result (above, right). Fold the flaps down against the sides of the TAP frame, and secure them with ¾-inch galvanized nails --. Drive nails every 10 inches across the front edge of the frame to secure the front of the flashing. Nail the back of the flashing to the sheathing of the house, and then cover it over with the top piece of siding removed in Step 6. 56 Grilles and Doors for the Vent Openings 1. Installing the grilles. Cut sections of plastic grating to fit the openings in the wallboard. Cover the edges of the grating with %-inch J molding of the kind used with gypsum wallboard. Set the top vents in place with the wide edge of the molding facing into the room. For the lower vents, set the grating into the opening and mark the plastic at the edges of the studs it crosses, as well as at the end studs --. Pull the grating back out and cut pieces of aluminum flashing 2 1/2 and 1½ inches wide. Fasten the flashing with duct tape to the thin edge of the J molding so that it will over lap the marks by ½ inch. Then cut sheets of 2- mil polyethylene to cover the grating between the studs. Use duct tape to fasten it to the J molding. Set in the bottom vents with the dampers facing into the TAP. 2. Adding wood trim and doors. Cut a pair of 1-by-3s 1 1/2 inches longer than the vent openings. Attach these trim pieces just above and below the vents, using 2-inch finishing nails driven into the studs. The trim should overlap the vent grilles 1/2 inch to create a vent 2½ inches high. Cut vertical trim pieces to cover the studs. Sink all of the nails with a nail set, and cover the nailheads with wood putty. Use more 1-by-3s to make a door to cover each vent opening. Plane the top edges of the doors to a slight bevel to allow them to close. Hang the doors, using butt hinges, to the edges of the bottom wood trim; install a butterfly latch on the trim above each door --. Paint or finish the doors and wood trim to match the other moldings in the room. |