Once the hot water tank is full of hot water, one limitation of this type of solar system is that you must contend with unwanted heat. If the propylene glycol/water mixture is left in the panels, it will overheat. This can breakdown the propylene glycol and blow open the pressure release valve. To avoid these problems, I am using a heat dump.
From some dude on Craig's list, I purchased about 70 feet of baseboard radiators for $120. These pieces are new and left over from plumbing jobs the gentleman had worked on. I decided to run the radiators in parallel to reduce the flow restriction. The heat dump consists of 10 parallel sections each 7 feet long. This really should be overkill for this job. But I wanted to make sure that I could shed the energy from a midday summer sun.
I built the heat dump in two halves. In the image below, you can see the front half. The radiators are spaced at 5" from each other. This plumbing is done with 3/4" copper sweat joints. I created a wooden fixture to make sure the spacing and angle of the header pieces were just right. Otherwise I might not have been able to assemble the finished halves together.
The front and back halves were jointed together at the top with a 3/4"x1"x3/4" tee. In this way the fluid can flow into a large 1" opening and then split into two 3/4" sections. This should minimize flow restriction. In the image below, you can see a "baseboard tee" which is really an elbow with a 1/8" npt female thread at the corner. I am planning to put an air trap at that location. There is a similar fitting at the bottom that will be used as a drain.
The completed assembly consists of about 60 solder joints and weighs 40 pounds (dry). I need to pressure test it and then mount it on the wall.
Any guesses on how hot my basement will get when this thing is turned on?
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