Attic cooling and heating hot water.

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On 19 Jul 2005 00:13:43 GMT, snipped-for-privacy@ipal.net wrote:

That is how the solar panels work.
Kevin
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If you want to cool the attic then you will need to have quite an ample supply of cold water.
Otherwise, ( at best ) the attic can only be brought to the same temperature as the air that is entering into it.
--
SVL







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Hello everyone!
Thanks for all your emails they were great!

Just what I was concern with I don't think I am going to use one, though it's a excellent heat exchanger. As well I am also concerned with minerals building up in the rad.
What I might try is a simple 1/2" 50 to 75 ft coil of cu tubing with a fan blowing through it. Cheap and simple I like that no lead problem with drip pan.
Next problem:
Since I will have a preheat water tank in series with the main hot water tank. How do I circulate the water in the preheat tank up to the attic HE and down while still connected to the city water supply?
I am thinking of some valves to isolate the loop and maybe a DC water pump. It will only come on when the attic temp is higher then the preheat water temperature.
When the water is drawn from the main hot water heater a valve has to open drawing the warmer water from the preheat water tank and city water to goes up to the attic HE.
Hmm???

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With about 0.625/12xPix50 = 8.2 ft^2 of surface. If the fan moves air at 6 mph, you might have 8.2(2+6/2) = 41 Btu/h-F of air-water conductance, vs 800 for a radiator or 100 for 16' of fin-tube pipe, with no fan.

Omit the preheat tank and pump water from the tank drain or cold water input back to the hot water outlet.

You might control the pump with a differential thermostat, which could also pump cold water up through the copper coil to keep it from freezing.
Nick
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There a lot of refinements in these posts that will bust your budget and give you only marginal increases in efficientcy. I suggest keeping it simple.-Jitney
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J Poy wrote:

You could simply treat the tubing /as/ the pre-heat tank. Use valves to bypass it when the air temperature isn't high enough.
Otherwise:
1) If the pre-heat tank is open-topped, float-valve level controlled: Use a drinking-water quality submersible pump in the tank and a thermosatat to switch it on when the air/ water temperature difference is enough. The end of the loop can simply pour back into the tank.
2)If the pre-heat tank is under mains water pressure: Here, as there is a possibility of water syphoning back into the mains, you may need building control approval. Practically any drinking-water rated pump should do - but don't forget to allow for expansion. Be aware that, during the night/winter, the loop may easily be at a lower temperature than the supply and thus you can get water circulation that you /don't want. So as well as powerering off the pump, you may need to cut off the supply or return of the loop. The loop isn't in series with the tank - but in parallel to it.
--

Sue




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You have made some very good suggestions thanks!
Please note as I am in Ontario Canada I will not be using the system and will drain the heat recovery loop before winter.
I would like to keep it as simple as possible I would prefer to have it run under city mains pressure. What I meant was that the preheat water tank would be in series with the main water heating tank and like you said the heat recovery loop in parallel with the preheat water tank.
I also considered using the copper loop as the preheat tank, but it would be to small and would not make the project worth while. Getting back to my main objectives is to provide a little cooling in the attic and reclaim some of heat in the attic to off set the cost of water heating.
I like option 2. using a couple check valves (one way valves) should prevent water circulating backwards.
.... I need some way to isolate the heat recovery loop and preheat water tank, a pump to circulate the water in the loop when the temperature conditions are met. .... When hot water is demanded from the main hot water tank, the water from the preheat tank should open up and supply water to the inlet of the main hot water tank. As well the make up water should now enter into the input of the heat exchanger in the attic. I would use a manual bypass valve during the winter to supply water direct to the hot water tank.
Other objectives:
Make the overall system efficient as possible, what I mean is, if possible no pumps, no fans, electric valves etc. Not sure I can do it but I will try. The overall system could be built totally automatic, semi automatic and manual. At this point I am looking at a manual system to keep the cost down. Try to keep the system as simple as possible yet reliable which usually results in a fast payback time.
All the best, thanks again.

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J Poy wrote:

It isn't so much circulating backwards - but upwards. The loft heat exchanger loop will presumably be above the preheat tank (it should be as it should be as near the hottest part of the roof as is practical). At night, the loop can easily be cooler than the water in the preheat tank and so the (lighter) water in the tank will like to rise up /one/ of the uprisers to the loop and displace the denser colder water down the other - but it may not be the direction you expect. All other things being equal - it could circulate one way or the opposite direction. Hence an isolating valve which will stop circulation in /either/ direction. Of course you could set the system up, see which way it circulates and then fit a check valve - but if you later changed anything, the circulation could reverse and the check valve achieve nothing.

As the hot water will be above the cold water - you can't use gravity. So you either have to use a pump or have to direct the mains water flow via the loop - in which case it won't circulate, but just displace. Sorry, I reckon that you will need a pump if you want circulation. Unless you stick the tank /on/ the roof - as has been suggested, IIRC.
A manual system will be a pita. For efficent operation the system needs to be designed by a control engineer. Who would totally shudder at my idea of simply having an electronic differential thermostat with hysteresis that opens the valve and starts the pump when the loop temperature is significantly higher than the tank temperature. By arranging the pipework properly, the outlet to the main heating tank would automatically preferentially take almost all its water from the (pumped) loop when the loop temperature is higher than the preheat tank and there is demand.

Totally agree - but. You will need a pump, I think. Which will use electrickery - unless you fancy sticking a Stirling Engine up there that would automatically run and pump whenever its "hot end" got enough sunshine. Otherwise, the pump needs switching off and the loop isolated whenever the temperature difference doesn't make it worthwhile - So, unless you fancy sitting there watching thermometers all day...
--

Sue

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Very true, but two heat traps in the water loop would solve this problem or you could simply design the piping and create heat traps. I will add heat traps for both water tanks.
Another thing that you mention earlier.

What expansion? Oh yes hot water, any suggestions what I need here?
What type of pump would you recommend to put into the heat recovery loop? I think a low flow would be fine, something readily available, low cost but reliable and requires only small amount of power would be great. (drinking-water rated pump) Any suggestions where to purchase one?
With one manual bypass valve to supply city water directly to the hot water tank (winter) or directly to the heat exchanger via on/off solenoid (Normally OFF) water valve and another one (Normally OFF) to totally isolate the main hot water tank and divert the water via a pump through a check valve into the heat recovery loop. I think I will need a flow switch (signal) to turn on and off the solenoid valves and use the temperature differential signal to control the water pump in the loop. I am not sure what will happen when I open the hot water tap as both solenoid valves will be closed for that instant in time. Will the flow switch react fast enough to open solenoid water valves. When you turn on the hot water tap both solenoid valves will be open there will be no water pressure. Flow switch may not be the best way to control the valves?
I am looking for some control signals, I'll have to think little more on this one.
Thanks for your comments!

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I've seen engineering mags where they staple plastic tubing under floorboards for heating and I wonder how reliable that is.. can't possibly last more than five years without bursting a leak, right?
I mean, I don't anyone who had water flowing through the fridge door where the tubing didn't break during the first ten years..
then again, it's really cool where they use this to de-ice driveways
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I wouldn't use a auto radiator if the water pressure will be above about 15 psi. it will probably blow out and flood your home.
Maybe you could use a refrigeration coil of a suitable size, I think you can order them custom made from a HVAC supply business.
Mr. Who
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