Enough collector area for domestic HW and hot tub + heat exchanger questions

3 Posts
Sep 22, 2008 01:21 am
Enough collector area for domestic HW and hot tub + heat exchanger questions

Folks

I've been reading, drawing, and thinking. Last one is the scary part.

What I want to do it heat my hot water, and supplement the electric heater in my hot tub (approx 300 gallons), with solar. I am in Jacksonville Fl

What I was thinking of was an AET drainback retrofit kit, 2 4*10 AET MSC collectors, and a bunch of copper pipe. What I was hoping I could do was run the collectors, pipe down to the drainback tank (heat exchanger 1), bury a 30 foot run to the hot tub, hit hot tub (heat exchanger 2), come back through existing trench, and back into the drainback tank to begin the cycle over again.

I figured by doing it this way, I'll have my DHW first, and then I'll have a hot tub, hopefully heated with thermal energy that the drainback system didn't absorb. I'm trying to avoid having to put in two independent systems.

Anybody see anything glaring wrong in my plans?

I appreciate your help.
 
Sep 22, 2008 05:13 am
Re: Enough collector area for domestic HW and hot tub + heat exchanger questions

I am not really focused on looking for anything "wrong" with your ideas but, I am curious to know, what the benefits are and what the payback is. Is there a circulating pump motor? If so, what is the kWh cost over 30 days? Cost of materials, labor? I guess what I am really asking is, do you think it is more cost effective when compared to having two separate systems?
 
Sep 22, 2008 05:33 am
Re: Enough collector area for domestic HW and hot tub + heat exchanger questions

As if you didn't already have enough on your "plate."
http://www.toad.net/~jsmeenen/recovery.html
Here are other ideas to mull over.
http://climatewell.com
 
3 Posts
Sep 22, 2008 09:11 am
Re: Enough collector area for domestic HW and hot tub + heat exchanger questions

Benefits, or at least benefits I'm hoping.... Maintain hot tub as close to 100 degrees as possible, and heat the DHW, without firing off 15Kw of electric heating elements...

Yes, I'm looking at a high head Taco circulating pump, to run the heat exchanger fluid through both heat exchangers and the collectors.

The cost of running the circ pump is $3 a month, or 10 cents a day, if my math was correct.

Labor I'm not too worried about, I've got me.. Materials I am. I am in a freeze zone, so if I were to put to independent systems in, thats two drainback tanks, 4 circ pumps etc etc.... I could buy each drainback system for about 1000, or, hopefully, just one will do and run piping to both heat exchangers....
 
462 Posts
Sep 22, 2008 10:45 am
Re: Enough collector area for domestic HW and hot tub + heat exchanger questions

Elbie, does the hot tub have a heat exchanger or does it heat the water in the tub directly? If it is indeed a heat exchanger then your idea will work. If it does not have a heat exchanger then you may have to rethink.
 You said you are in a freezing zone so I would think that you would use an antifreeze loop. If the tub has a heat exchanger, then do as you said. Send the heated antifreeze into the domestic hot water heat exchanger tank and then send the return water into the hot tub, then back to the panels. Install bypass valves for those times you do not wish to heat one or the other.
 If the tub does not have a heat exchanger then you may have to draw the water directly from the tub to be heated. It should have a drain somewhere. Pump the water from the drain into the panels and back into the tub using a hose so you have an air gap to prevent syphoning. Modifying components may void warranties.
 Using this scenario, you could skip the domestic hot water and only purchase the panels, pump and piping.
 If you do not use the tub year round, add a tank, flush out the piping and panels and switch over to solar hot water the rest of the year.
 
3 Posts
Sep 22, 2008 04:38 pm
Re: Enough collector area for domestic HW and hot tub + heat exchanger questions

Thanks everybody for the replys so far...

The hot tub does not have a heat exchanger per say. But then again, it doesn't really have much of anything until UPS delivers all the stuff..

I'm torn between trying to make my own heat exchanger, or buying one, but either way I go, I'll use the hot tubs internal circulation pump to feed one side of the exchanger, and the solar pump would run the other... I'm thinking that if I bury the pipe 12 inches, it should be protected from what we get as a "freeze", the hot tub has a freeze protect mode, which would keep warm water through the heat exchanger....

All the thinking about the amount of valves required is making my head hurt..

Elbie
 

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