Solar Tank Water Heater

Q: I have started to build a solar tank water heater and have a few questions now that I have started. I have removed the tank from an old gas water and am going to paint it black. I have inspected the anode and it still looks ok. In this setup, does it even need the anode? I am also curious as to how far away from ones house this will work as in my current situation, to get the most sun (without putting it on the roof), I would have to place it farther away from the in house water heater or lose all the west sun. Any and all info appreciated. Thanks in advance,

A: You didn't say what kind of solar hot water heater it is, but it sounds like a batch heater -- i.e. the tank is the collector? Anode Rod: Since your collector tank sees pretty much the same environment as a hot water tank,I would think it would be good to retain the anode rod. Heat loss from pipe: For 3/4 inch copper pipe with the 3/8 inch thick hardware store type foam insulation on it, you will lose about half the heat you added to the water in the pipe in an hour(1), and about 3/4's of the heat in two hours. If (for example) you moved the collector enough to add 30 ft of extra pipe between the collector and your hot water tank, and you have (say) 5 hot water draws a day that are spaced a couple hours apart, you will lose the heat you put into (30/43) (5) (3/4)= 2.6 gallons/day (43ft of 3/4 pipe holds 1 gal) of the water. If your system is working pretty well, this might be around 5% of what your daily production. Maybe not too big a deal? You could reduce this by: 1) Using more insulation. If you doubled the thickness of the insulation to 3/4inch, you would cut the heat loss by about 25%. 2) If you lump your heavy hot water draws together, you will lessen the effect of pipe heat losses. In addition, if you time your major water draws for late afternoon to early evening, you will use the water before it starts the night time cool down -- this is probably more important than the pipe losses. Losing Western exposure Problem: If you are trying to locate your collector such that it has enough sun to work well, and you have obstacles to contend with, I would suggest this approach: Get the CAM 417 "Sun Chart: Orientation" writeup from this site in Seattle: www.cityofseattle.net/dclu/camlist/camlist.asp Go through the procedure it recommends for each of your candidate collector locations. This procedure is for locating windows for good gain, but the process is the same for your collector. To use this method, you will need a sun chart for your location, you can get one here: http://solardat.uoregon.edu/SunChartProgram.html Look for a location you can place the collector such that it gets at least 6 hrs of continuous sun (ideally centered around noon). Aim the collector such that the sun is perpendicular to the collector glazing in the middle of the daily collection period. Some additional rules of thumb for solar batch hot water heaters: Glazing should point roughly South (+- 20 deg) Glazing tilt should be roughly equal to latitude (+- 20 deg) Use about 1 ft^2 of glazing per 2.5 gal of collector water tank capacity. Ideally, provide 20 to 30 gals of collector tank capacity per person. The inside surfaces of the box that encloses the tank should be designed to reflect sunlight onto tank. Cold water should enter at bottom of tank, and hot water should be taken off at top of tank. This takes advantage of stratification. (vertical tanks encourage stratification, which is good) Use copper pipe for plumbing. Water weighs 8lb/gal -- tanks full of water need good support. If you live in a climate where it gets below freezing: Freezing of the supply lines is a common problem. If you can integrate the solar water heater with the south wall of the house, this eliminates freeze problems. If you can work out some form of insulated cover that is manually or automatically placed over the tank or the glazing at night, this is a major gain, since it greatly reduces night time heat loss.

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