This simple batch heater is popular in many southern states where freezing is not a problem. It's used to preheat well water or town water for a domestic hot water system, however it's not very efficient because of night time heat losses. 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 you might like to build it.
Batch heaters can be made from a wood frame, some polyisocyanurate insulation, aluminum flashing and an old, electric 40 gallon hot water tank.
Mounting batch heaters safely on a roofs, though, can be a challenge. This is why many people prefer mounting them on the ground where they can keep an eye on them.
GROUND MOUNTED BATCH HEATER
Ground mounted batch heaters are popular because they are easy and safe to install. If a leaks do occur on ground mounted systems they are easy to repair. As long as the batch heater tank receives adequate sunlight they harvest heat, but some ground mounted locations are shrouded shadows so a practical heat harvest may not be a possibility.
Of course heat losses through the glazing will be great but in the right climate heat losses are minimal.
Batch heating systems can be improved by isolating the glazing with insulation. This would minimize heat loss to the atmosphere. Let's take a quick look at how this may be accomplished.
thermo siphoning BATCH HEATER
A 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 connect 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 may also be difficult for you to build, but they are commercially available.
Another variation on the batch heater involves the installation of a tank in the attic space connected to the collector. If you decide to install a water tank in your attic be sure the tank is well supported and positioned under a bearing wall.
The illustration on the right demonstrates a Thermosyphoning system that depends on gravity to separate hot water from cold water. Unfortunately, the thermosyphoning convection currents may be sufficient insufficient to circulate water through the collector... In this case a circulator pump could be installed to augment the heat harveste.
WARNING: All thermosyphoning systems are connected directly to the potable water supply so if a pipe freezes anyplace in the system the leak will be continuous and serious. This attic batch heater is extremely vulnerable to the freezing problem.
Evacuated Tube batch heaters tanks are less prone to freezing than other, less insulated tanks, but pipes to and from the evacuated tube tank are exposed to the elements.
Freezing will never occur inside an evacuated tube but the volume of water inside a pipe is small and the temperature within a pipe could easily drop below the freezing in a short time unless the pipe is protected.
In conclusion I have to say that I would not recommend batch heater systems in any area where freezing could be a problem.
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