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Posted by t38 on August 25, 2005, 6:32 am
It's been over 20 years since I've taken thermo in school. I'm looking
for a more idiot-proof way to avoid overheating. Is there any way of
installing a SIMPLE thermostat to close water flow from the collector
to the tank when a set temp is exceeded? What I've spent hours
unsuccessfully looking for is a backwards operating automotive coolant
thermostat. Instead of opening when a temp is exceeded, I want one that
closes. I wouldn't need a calculator to make my water heater way down
in Baja California.

Posted by Robert Morien on August 25, 2005, 8:08 am

If you  stop water flow when there is still viable energy to be
collected you run the risk of "stagnation". That could be terribly

What's so horrible about depending on a simple temperature/pressure
relief valve?

Posted by Kiwi John on August 25, 2005, 11:43 am
 or you could use a relay for the water  that they use in the back of a
washing machine

Posted by nicksanspam on August 25, 2005, 12:28 pm

Is this a pressurized fresh water tank above the collector with
a thermosyphoning antifreeze loop? You might just boil some
fresh water off with a P&T or pressure cooker valve...
An overhang for summer shading might help.

And explodes the collector? :-) You might limit the heat output with
an extra loop at the top, just above the normal collector fluid level,
which allows the collector fluid to flow back down to the collector via
some fin tube pipe when the fluid expands at a high temperature.

How about a solar pond with a flat PE pipe spiral under and EPDM rubber
over a polyiso board cover? See



Don't miss this opportunity to have every solar question you ever asked
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Join PE Drew Gillett and PhD Rich Komp and me for a workshop on Solar House
Heating and Natural Cooling Strategies at the first Pennsylvania Renewable
Energy Festival on Saturday September 24, 2005 near Allentown. See


Posted by t38 on August 25, 2005, 2:54 pm
I don't understand the "expensive" ramification.

The tank would probably be an old hot water heater with the outlet of
the collector going into the P&T opening and returning to the collector
via the drain valve at the bottom of the heater. I don't need to worry
about freezing.

It would be under pressure but I've heard that P&T valves start to leak
after a few cycles. Also, I have to truck my water in so water
conservation is very important to me. (I just don't have it in me to
tackle the desal project yet, I'm having to start from scratch).

Do you really think that 1/4" copper painted black would explode if
left out in the sun? I just assumed that it wouldn't. Also, I have a
pressure tank further upstream of the heater that I imagine would
prevent catastrophe.

I like that idea, I could use my auto thermostat to open up and create
a bypass loop. Still not as easy as just shutting off flow to the tank
but it doesn't sound like anyone is aware of such a valve that doesn't
need electricity. (I need to conserve electrons as well - being on

Thanks for all your help folks,

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