PEX Under Metal Roof Solar Hot Water System

[pexuniverse]

I live in Texas and I am planning to install PEX tubing (OxyPEX or Everhot) under my existing metal roof on the south side of my house and directly connect it to a Solar Hot Water Heater. Does anyone have any information on a do-it-yourself system like this. It seems to me it would work great and of course look great because one would not see it. It would also be low on maintenance. Any info would be appreciated. Thank you in advance.

solarcollector.jpg

Max

[russ]

Look at www.builditsolar.com - they have a few designs of this nature as I remember.

[pexuniverse]

thanks for link but I can have time for reading all this uncategorized information

[russ]

You are planning to do something out of the usual - that requires far more time in researching, studying and planning than the actual doing normally.

[Naptown]

An immediate downside I can think of is what happens if you are on a well and ground water is 60 degrees and the dew point is at 70 degrees as in a humid area. It's gong to rain in your attic.

[fafcosolar]

PEX Water Heating

I live in Texas and I am planning to install PEX tubing (OxyPEX or Everhot) under my existing metal roof on the south side of my house and directly connect it to a Solar Hot Water Heater. Does anyone have any information on a do-it-yourself system like this. It seems to me it would work great and of course look great because one would not see it. It would also be low on maintenance. Any info would be appreciated. Thank you in advance.

Max

What you are describing won't work... or at least it won't work very well. The tubing will absorb the ambient heat from the hot attic, but once you start water flowing through it, the heat gain through air will be essentially nil. If you want it to absorb heat from the roof surface, you will need to thermally bond the tubing to the underside of the roof sheathing. This will be cumbersome and relatively inefficient. If you want to absorb heat from the sun, your "collector," in this case, the tubing, really needs to absorb the solar radiation directly. In addition, with all that plumbing in the attic, you are increasing your risk of leaks. You want to keep the amount of plumbing in your attic to a minimum. While I like your concept and spirit, I just don't think you're heading down the right path.

You should consider a Fafco Revolution 500 Series water heating system if you want a polymer solution to water heating. This uses crosslinked polyethylene to carry a heat transfer fluid through the attic to a polymer water heating collector on the roof. This isn't exactly what you are talking about, but similar.
If you are really serious about pursuing your idea, it would make more sense to have the poly tubing on the top of the roof surface rather than underneath. Take note that PEX is not UV stabilized. The Fafco crosslinked poly tubing is. That being said, you would need a control to bypass the "solar loop" when the temperature on the roof is less than that in the tank.

Respectfully,

Jason Szumlanski
Operations Manager
Fafco Solar

[russ]

Sorry but I am not a fan of this type of collector (all plastic) though they should be real cheap - which I doubt they are.

The link I removed went to a page where it was pointed out that during power failures this home would have hot water where others would not. With no power available hot water is the least of one's worries.

[fafcosolar]

The panels are quite inexpensive, but because it is an indirect closed loop system, there is a heat exchanger and circulation module involved.

Is utility electric cheap? Not relative to a solar water heater in the medium to long run! It's pretty easy to make a financial case in almost every household.

[fafcosolar]

With no power available hot water is the least of one's worries.

I guess you have never lived wiithout a hot shower in the aftermath of a storm. Millions would disagree with you.

[russ]

I guess you have never lived wiithout a hot shower in the aftermath of a storm. Millions would disagree with you.

Sure have and in many places around the world - one was after hurricane Hugo in North Carolina in 1989 - as we were at the end of the line out in the country it took nearly 3 weeks to get power back.

I did have a generator that was still in the box so we had minimal power and that helped greatly for the fridge, TV and a couple of lights. Hot water we did not have.

Yesterday we installed a 73 kVA generator here - that will be a problem of the past I suppose.

[Designer_Mike]

As was mentioned earlier, if the pex isn't touching the roof, you'll get virtually zero production. Yep, the air is hot but air is an awesome insulator. The fiberglass in insulation doesn't restrict the movement of heat, it's all the trapped air between the fibers. Take a 6" batt and crush it to 1/2" and see how well it insulates!

It will be difficult at best to try and get any thermal conduction from the tin roof into the pex without melting it.

You could put 100 feet of pex up there within 3" of the roof and I would be willing to bet you that you could heat more water with an 8' length of copper tubing thermally bonded to the roof with some thermal conductive putty.

Measure the air temp up there...seems hot but doubt it's over 145 deg. Now touch the tin. On a good day you should get a little sizzle and an OUCH
You need the water to sizzle not just warm up a bit. That's only going to happen if the water it touching the tin.

BUT I get the feeling your gonna try it anyway