Getting into Hot Water Therese Peffer c.1992 Therese Peffer I first learned about thermosiphon solar hot water system several months ago, and the whole concept really piqued my interest. What a simple and clever system! I found a simple plan to build such a system in Renewables are Ready, a pamphlet with Renewable Energy projects for Junior and Senior High Schools, and I decided to try it. I learned in grammar school that hot air rises. Hot water rises, too. In a tank full of water, the warmest water will be at the top, while the cold water sinks to the bottom. In a thermosiphon solar hot water system, the solar collector sits below the storage tank, so as the water warms, it rises and enters the tank. Since it is a siphon system, this pulls cold water at the bottom of the tank down to the collector. Materials and Tools The materials are quite simple: a shallow rectangular cardboard box (I noted that photovoltaic module boxes would work quite nicely!). The booklet says "at least 45 x 30 cm (18 x 12 inches), no higher than 10 cm (4 inches)." approximately 3 meters of plastic tubing, approximately 2 mm thick and 1.2 cm (0.5 inch) in diameter black paint and a brush (I used spray paint) a bucket that holds at least 2 gallons of water thermometer plastic wrap, glass, or Plexiglas the same size or larger than the box aluminum foil extra cardboard tape a sunny day Tools: knife or razor blade to cut cardboard Making the Collector Amanda Potter, a new member of the HP crew, and I found a shallow corrugated cardboard box, approximately 20 x 30 x 4 inches. Luckily we had a piece of glass (1/8 inch thick plate glass) that was just a couple inches too big in one dimension. We cut the glass to the proper size. We had enough corrugated cardboard around that we decided to insulate the box. We used my Swiss army knife to cut cardboard and taped 3 layers of double thickness cardboard to the bottom and sides. The next step was to glue aluminum foil on the inside of the box and paint the box black inside. At first I just painted the box black inside, but after talking with Richard, I realized that the aluminum foil acts as a radiant barrier to prevent heat escape. I mixed Elmer's white glue with water (the 1:1 mixture is easier to spread and doesn't dry as fast) and glued aluminum foil to the bottom of the box, and then spray painted the box black. The tubing caused the most problems. I had a 16 foot piece of 1/2 inch black plastic tubing that I had bought for irrigating the garden, but never used. It turned out to be too stiff. We cut a small hole through the side of the box towards the bottom and snaked one end of the tube through. Amanda and I tried to loop the tubing back and forth. It kinked in a couple places. We let the plastic tubing warm up in the sun, and used 2 inch pieces of wire to hold the curves into place. I cut a hole in the opposite side of the box near the top and put the other end of the tubing through. Eventually we gave up on this tubing and tried flexible rubber tubing. We placed the glass on top of the box. I cut a cardboard frame for the glass and taped this to the sides of the box. The Storage Tank We wrapped newspaper and bubblewrap around the sides and bottom of a 5 gallon white plastic bucket. Since it did not have a cover, we cut a circle of cardboard for a lid. The directions recommend cutting two holes in the cardboard for the two ends of tubing. I tried that, but found it easier to tape the tubing to the sides of the bucket, and cut the edges of the lid to fit around them. We set the collector at a slant (about 45ø); the top of the box was supported by a shelf. As per directions we put the bucket on the shelf "completely above the level of the collector." We filled the bucket about three-quarters full of water. We stuck the two ends of tubing into the bucket. The end that goes down to the bottom of the box goes down to the bottom of the bucket. The end that comes off the top of the collector sticks just under the surface of the water (see diagram). The other problem we had was filling the tubing with water. The directions recommend sucking on the higher end of the tubing. "Make sure there is no air in the pipe when you insert it back in the water." This was the hard part. I tried but couldn't get all the air out the tubing. The thermosiphon did not work very well, at first, although the tube coming from the top of the collector was much warmer than the tube going to the bottom of the collector. I finally took the garden hose and filled the tubing under water in the bucket. Then it worked great! The temperature of the water went from 65øF to 85øF in two hours, and climbed to 105øF when checked about two hours later. So What Next? I'm already thinking about changes. I don't recommend rubber tubing. When I mouth-siphoned the water through the rubber tubing, it tasted absolutely horrible! I imagine there are other types of plastic or vinyl tubing that I could paint black. I'd like to try making a larger collector with more tubing to increase the water temperature. I wonder if reflectors, like those on a solar cooker, would help increase the temperature. I could try using thicker glass or use two layers of glass. This project is not meant to serve all my hot water needs, but to learn about thermosiphoning solar water heaters. I use the hot water for dishes, and it supplements our 5 gallon solar shower. But I learned a lot. I'm anxious to see how it works in the winter time! On the Home Front Part of the work going on at HP Central includes redoing the kitchen. We needed to replace the 1960 propane range that had served Karen and Richard for 12 years, but was showing its age. We looked around for propane ranges (we'd like to convert to hydrogen eventually). Sealed burners are so much easier to clean, but these come with the fancy models with clocks and buzzers. We didn't want any phantom loadsÄour term for appliances, such as my radio/ cassette player, which draw a small amount of electricity when plugged into an outlet, though not being used. We brought home a Magic Chef range with sealed burners, piezoelectric ignition, and a clock/timer. We figured that we could save electricity by connecting it to a plugstrip (a multi-outlet strip with an on/off switch). That way the range would not draw electricity all the time, but could be turned on when we needed to heat or cook food. Then someone used the oven while Richard was in the battery roomÄhe measured 600 watts! We discovered a 600 watt glow bar ignition that lights the burner. Then we thought that the glow bar was just used to start the oven, but actually 600 watts is drawn the whole time the oven burner is on! After several phone calls, we discovered that in the state of Oregon, gas appliance dealers cannot sell pilot light ignition systems for gas appliancesÄthe new models are all electronic ignition. The rationale? Because they are more energy efficient!! So we ended up with a commercial propane range with pilot lightÄno sealed burners, but no electricity required. This was a real lesson for us. If you are looking to buy propane appliances, watch out for those with electric power needs! Access Author: Therese Peffer c/o Home Power, POB 520, Ashland, OR 97520 ù 916-475-3179 Renewables are Ready: A Guide to Teaching Renewable Energy in Junior and Senior High School Classrooms, available for $10 from the Union of Concerned Scientists, 26 Church Street, Cambridge, MA 02238 ù 617-547-5552