solar water heating temp question

[hrspwr]

Hello, I have been reading this board for some time and am very impressed. I am interested in building a super efficient home in 3 to 4 years and have been trying to do some homework.

My question is what are some of the temps delivered by your solar hot water systems designed for domestic hot water needs? Thanks

[tecker]

  Most waterheaters achieve 165 F and that's easy for a solar preheater . Area is directly proportional to energy absorbed ( I know you knew that ) mathmatically  

speaking.

[Chagrin]

If you're looking for a little more guesstimation:

The sun supplies approximately 1 kilowatt per square meter; 1 kilowatt/hr is equal to approximately 3400 BTUs. 1 BTU is the amount of heat require to raise the temperature of 1 pound of water by 1 degree. So you could potentially heat 34 pounds of water (approx. 4 gallons) from 65 to 165 in an hour with a 1 square meter panel.

[dudevato]

I'm in southern california and my batch heater, that supplies my 'garden shower' (which I just got out of) gets to 140*F after a day in the sun. I just got this going a few months ago, so I don't know about the fall temps.  Without closing the insulated panel at night I still have readings of 115* in the morning.  This is a 40 gal. waterheater tank inside an insulated plywood box, angled toward the sun, with a patio door covering the top.  

[tecker]

 very cool

[hrspwr]

Thank you for answering my question. My plans include collectors filled with poly glycol and running everything in closed loops. The domestic needs should be fine at 120 but the radiant floor will need the 165. I am going to use 2 seperate sytems on pumps tied into amtrol boiler mate heat exchangers.

[jacquesm]

I run a heat exchanger as a source of heat from our outdoor woodstove. It works, delivers hot water (but not enough) and requires us to keep the woodstove running in the summer. I plan on installing collectors next year. A combination system would be ideal here, drain the panels for the winter season, fill them back up in the spring and shut off the heater.  

165 f is a minimum, below that you get bacterial trouble (and not just annoying, possibly dangerous, it's called the legionella bacteria), this goes for any hot water storage medium.