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Old 10-29-11, 09:04 AM   #1
Ralph III
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Default Solar "Batch" Water Heater, help please....

Hello All,
I would appreciate a little input on constructing a solar "batch" water heater system. It will be a typical DIY with a 50gallon black water tank encased within a box with glass panel(probably glass door). I live in south Alabama, btw.

The batch tank will basically be used to preheat the water coming into my existing indoor electric Hot Water Heater. SEE THUMBNAIL SKETCH.

1) How hot can these batch tanks get and what do you do to protect against excessive heat/pressure buildup? Can you vent the box via an automotive type thermostat as it gets too hot? I assume a tempering valve will need to be installed on the batch water heater irrespective.

2) Can pex piping be used for the underground hot water run? My hot water line, between the batch tank and my indoor HW heater, will be about 50ft in length and approxiametly 18 inches underground(top soil). Copper tubing will be used within the box itself...

3) I can "supply" incoming water to the batch water heater by taping into either my cold or hot water lines at master bathroom faucette? If I tap into the hot water side that would create a loop and possible thermo-siphon setup? However, what if the water in the batch water heater gets cool/cold? I'm afraid I'd lose hot water at my master faucete? Can it be setup to draw hot water from the indoor HW heater automatically in that case?

4) How much lower does the batch tank need to be in comparison to the indoor HW heater for thermo-siphoning to work? Also, does the hot water line coming out of the batch tank have to always be above the batch tank or can it drop down(for underground run) and then come back up in feeding the indoor HW heater?

5) Lastly, how do I protect the batch tank in freezing weather or in retaining heat? Would building the batch housing somewhat below grade and using three pane glass help? I mean, how long would it take for 50 gallons of water to cool below 55 degree tap water or even freezing? We get very few winter days into the teens here......

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Thanks, Ralph

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Last edited by Ralph III; 10-29-11 at 09:29 AM..
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Old 10-30-11, 10:01 AM   #2
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I've used batch type heaters that were just a 50 gallon drum in an insulated box with a single pane of glass over it and it was connected right to a shower, no tempering valve or anything, it would get warm, 90 to 100F, nice for showering under, but because it had such a small collection area the heat input was small.
If you had more surface area you would get more heat, one batch heater I saw was two pieces of 4" copper pipe 8' long in a covered and insulated box, that made for a steamy bath but the cost of copper was higher.
Water heaters already come with a tempature pressure valve, use that common off the shelf part and it will thread right in to standard pipe thread.
Trouble with batch heaters is that they radiate heat almost as fast as they absorb it, unless you have a good way to concentrate the light with reflectors or something, it will cool off pretty quickly over night, that is why flat panel collectors are popular, they get hot and store that heat in a protected insulated tank.

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