Our "Hot Box" Solar Collector

This instructable will document and explain the construction of a solar collector designed and built by the Convection and Solar Energy class at Creighton University. This was built over a three-week time period with a cost of 250$.

        The first activity to prepare us to make a solar collector, was to see a few of the past collectors. We looked at them from both sides, and looked at them with a thermal camera. The best of the solar collectors was pumping out 95 degree air, and the worst was at 80 degrees; these were small successes in 75 degree weather in full summer sunlight for 3 hours. A wooden support next to the collectors reached 115 degrees, and a black trailer parked nearby was at a blistering 125 degrees.

           Next, to get a better idea of how solar collectors work in general, our class installed a commercial collector in a building on campus. The collector was designed to attach to a standard house wall, so naturally the ductwork was to short to run through our buildings cinderblock walls. The first order of business was to extend the ducts to attach to the panel that we had a construction team attach to the wall. To accomplish this, we cut some HVAC tube to make up for the thicker walls. The extensions were attached to the original ducts using two HVAC couplers, and sealed with foil tape.

          We took the fan and thermostat back to our workshop to solder the leads to allow the panel to be " turned off " if the room inside got too hot. After testing the system with a DC power supply, we headed back to the installation site. Using the plastic flanges and foam padding that came with the panel, we attached the extended pipes to their proper places on the back of the panel. Finally, we turned the project back over to the construction team to patch the hole in the wall and mount the thermostat on the wall.

        After experiencing a professionally made solar collector, we brainstormed ideas for our very own solar heater. We decided to use a coiled dryer hose in an insulated plywood box, with a double " glaizing " of Lexan polycarbonate separated by an inch or so of air space. A 120mm computer fan, powered by a photovoltaic panel, would blow into the building from the output to pull air into the box through the filtered input. After talking to the Creighton machinist, we drew up a more precise blueprint (shown bellow). With the dimensions solidified, it was time to build.

          After purchasing most of our materials at Menards, we measured out and cut the back of the panel. The hose was traced onto the back and cut out using a jigsaw. Next, we cut the 2x4 supports to the necissary lengths. While the back most 2x4s where being screwed into place, another part of the team measured and cut the walls of our box. As the end of class drew near, we screwed the walls onto the box at the bottom.

         The inner 2x4s where screwed into place, and our foam insulation was cut to fit into the space between them. At this point, we split into two groups: a painting group and a construction group. On the painting side, the foil backed insulation was sprayed with a self-etching spray primer, and allowed to dry. We used an etching primer, because paint usually doesn't adhere to aluminum well. Next, we stretched out the dryer hose, and two of us held it above the ground, as a third person sprayed on the etcher. Once the etcher was dry, we covered the insulation and dryer hose (as much as we could) with extra flat black enamel spray. On the construction side, we screwed the walls together at the top, and began working on the risers for the Lexan sheets. These were screwed into place, after the black-painted insulation was dropped into place; the screws' points protruded into the box, so they were trimmed off using heavy duty snips.

          On the final day, the entire box was completely sprayed with the black enamal paint, while construction soldered the fan, thermostat, and PV panel together. The dryer hose was secured to the back of the box using extra large outdoor zip-ties. The hose was connected to the holes using 6in 90 degree HVAC elbows, and then all the corners and joints were caulked using a black silicon caulk. The fan was caulked into place, in the output duct. As the final step in building our collector, we put in the Lexan. To do this, we laid down a line of caulk around the bottom riser, and carefully lowered the first sheet of polycarbonate into place, followed by another riser. The second panel was secured in the same way as the first, and the collector was finished!

Net R value = .56
EnergyIn =  3,000BTU
Effeciency = 32%
LostConduction = 727 BTU
LostRadiation = 1,487BTU
UsefulEnergy = 796BTU

Over all, this proved to be a successful design.