SIMPLE BATCH HEATER
This simple batch heater is popular in many southern states where freezing is not a problem. It's used to preheat well water for a domestic hot water system, however it's not very efficient because of night heat loss. The nice thing about this "Bread Box" is that it's inexpensive and easy to build. If you can find a small water tank like the one in the picture you might like to build this batch collector.
If you don't have access to a small tank you can still make a very simple bread box out of cardboard, crinkled newspaper, aluminum foil, a piece of plastic and a jug of water.
1. First stuff the insides of a box (2'x2'x2) with crinkled, damp, newspaper. Make the sides about an inch thick. This should take you less than an hour, although you might have to wait a week for the newspaper to dry out. To speed the process up. Place the box with the wet newspaper in your attic. As a matter of fact you should install the wet newspaper into the box while your in the attic. I know it sounds messy, but if you're on a budget this is a great way to make an insulated box.
2. After the wet newspaper dries out glue aluminum foil onto it. Now take a bowl and place it upside down in the center of the box. Place a one gallon jug of water, painted black, on top of the bowl.
3. Take a temperature reading of the jug of water before putting a glass or plastic lid on your Bread Box. Now place it in direct, bright sunlight for three hours and then measure the temperature of the jug of water.
4. To measure the amount of solar heat you
collected in three hours multiply the temperature of the water by 8. One gallons
has a weight of 8 pounds.
A British Thermal Unit or BTU is the amount of heat energy required to raise one pound of water one degree Fahrenheit. So if the starting temperature of the water is 70 F and the ending temperature is 150 F the temperature difference is 80.
80x8 = 640 BTU. 640 BTU's worth of heat energy has a street value of about $.005.
If you achieved a temperature difference of 80 degrees I'd say you did a good job. That's about all that can be expected from a crude "Bread Box" like this even though there's about 4,000 BTU's available to a surface area of 4 sq ft over a period of 3 hours in bright sunlight.
thermo siphoning BATCH HEATER
This thermo siphoning batch collector is a great improvement over the simple batch heater above because the heat storage area is separated from the heat collection area and the tank is insulated. The only complaints I have about this direct water heating system have to do with the small capacity of the storage tank and the possibility of freezing in a cold climate.
This kind of collector might be too difficult for you to build, but you can still demonstrate the thermo siphoning phenomena.
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