Solar water heating

zickOctober 8, 2008

Went on the solar tour last weekend and saw a really neat design.

A guy had active water roof mounted solar panels that were run through PEX tubing into a bed of sand under the foundation slab. He had 2ft of sand that the PEX was turning it into a large thermal mass.

My question is this;

We are building a new home on a concrete slab that will already have PEX tubing in the concrete for radiate heat that will run off a Geothermal unit.

Will I be able to connect the solar unit into the same PEX tubing that will be used by the Geo unit so that the Geo unit only runs when the solar can't keep up?

I was also thinking about running PEX under the garage to use strictly w/ the solar unit to help warm the garage in the winter.

Which would work better, having the large 2ft sand bed or just running the PEX in the concrete like the rest of the house?

Thanks

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greif

yes, you will need a large water tank store the heat from the panels.

where did you see the sand bed?

    Bookmark   October 8, 2008 at 9:31PM
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zick

Sorry greif, I'm confused by your answer. I never asked about a large water tank for storage. Not sure what your referring to.

I did not personally see the sand bed, I saw pictures of it and that is what the owner told me.

I'm just wondering if I would need to run two separate PEX tubing lines (one for the Geo unit and one for the Solar unit) or if both units can use the same lines together.

    Bookmark   October 8, 2008 at 10:41PM
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zl700

I would think if you are attempting to design a heat sink out of a sand bed, and once it's solar potential is recovered, you would want automated changeover valves to redirect flow and kick in the geo system. Thus the solar tubes and sand bed tubes are separate, much like a heat exchanger in a solar storage tank.

    Bookmark   October 9, 2008 at 10:02AM
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chris8796

How did they recapture the heat from the heat sink? There are similar systems for greenhouses that circulate air through the mass (2 ft of soil) to warm the greenhouse in the winter.

What climate is this in?

    Bookmark   October 9, 2008 at 1:19PM
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zick

Good thought zl700.

Chris,
This guys particular setup did have a water tank to storage the excess heat. It was a insulated 600 gallon tank.
I was going to go with some kind of water tank heat storage but probably not to that extreme since his house is larger than what ours is going to be.
I'm just wondering if I need to keep the two systems independent of each other.
This is in Southern WI.

Here is the link to the guy place we looked at;

Here is a link that might be useful: http://www.the-mrea.org/solartour.php?id=1221043223

    Bookmark   October 10, 2008 at 2:53PM
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chris8796

It sounds like he has a pretty complicated system. Anyhow, I would keep the systems separate.

"Which would work better, having the large 2ft sand bed or just running the PEX in the concrete like the rest of the house?"

The sand bed (heat sink) and the floor should be thermal insulated from each other. Your storing heat from the high solar months(summer) and recapturing it in the cooler months. You don't want to heat the slab in the summer, otherwise your fighting the AC. They also usually have a thermal break on the sides of a large soil heat sink. They are not usually needed on the bottom.

    Bookmark   October 10, 2008 at 4:46PM
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greif

if you are talking about the pex in the slab, same pex for both. you will need a control to tell it which source to use.
the water tank is to storage the heat from the solar colectors as they only heat during the day, also they can generate heat in the 170-180 degree range on some nice winter days and that is way to hot to put into the floor.
if corectly design the system will pull only the heat from the tank as needed.

if you want to do this system, hire this guy as an consultant, I have learned a lot from him

Here is a link that might be useful: solar consultant

    Bookmark   October 10, 2008 at 9:59PM
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zick

Chris,
I think I may have confused you, I'm not trying to use the sand bed as a storage unit like a water tank. I'm trying to use it as a larger thermal mass like the concrete slab and use it to heat the house. Putting a thermal break between the two will defeat what I'm trying to accomplish.

Greif,
That you for that info, I will definately consider contacting that solar consultant.

Thanks for the info guys!

    Bookmark   October 11, 2008 at 1:33PM
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greif

gary, thanks for the solar today link, that's bob ramlow who is the consultant I said zick should hire if he is serious, he's got 30 years in solar hot water and air and now works for wisconsin's focus on energy and does consulting and teaching

gary

    Bookmark   October 11, 2008 at 11:39PM
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