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Old 02-05-15, 08:37 AM   #1
gtojohn
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Default Hot Water panel sizing 63sqft

I'm building a currently off grid week end cabin. Currently there's nothing there, no water, no power, no structure. Sturcture will be
about 600 sqft living with rain water collection before I go all in with a well.
I'm meeting a guy today with (3) used 7'x3' hot water panels, $80 each. He's been heating his water with 2 similiar panels in a tanked system without issue for 15 yrs. I will definatley buy 2 for my cabin. I will most likely use a solar powered pump to circulate to an 80 gallon electric hot water tank.

The 3rd panel...I will most likely buy, but what would be the best use for it?
I could tie it in with the other 3 for lots of hot water and possible make enough heat for floor or a radiant coil. We have mild and mostly sunny winters. Other heating options will be wood stove and generator powered minisplits. Since the cabin will only be occupied on weekends I can probably average enough heat through the week to keep it comfortable from October through March.

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Old 02-05-15, 10:22 AM   #2
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The 3rd panel...I will most likely buy, but what would be the best use for it?
Outdoor shower?
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Old 02-05-15, 12:39 PM   #3
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For the shower I suggest a propane on demand shower , they make them for places that do not have electricity , remote getaways etc.

I have some family that have one set up at their ocean front fish camp . easy as pie to install. You can choose from various models, from basic to home quality. They use one of the more basic models that cost a few hundred , mounted over a bathtub.

Then you could use all the panels for the in floor heating , which will save you heating costs and labor.
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Old 02-06-15, 08:51 AM   #4
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Original plan was on mini on demand propane, but now I have 3 solar water panels. With the solar I hope be able to set it up and let it run automatically without any additional fuel cost. Pumps and fans will be dc solar. For storage I'm thinking 1-2 electric hot water heaters. If we were desperate I can hook one into my generator. Truly its a 50 minute drive from my front door and I won't be out there if its super cold. From other experiences I've found its more fun to arrive and not have to worry about heating up a cold cabin. Before I go outdoor shower I plan on indoor shower, but we'll see.

I'll study up on floor heating. Its not common here, mostly concerned about cooling. Floor insulation isn't even common. A fan coil unit would be easy for me to set up and might be all I need.
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Old 02-07-15, 06:56 AM   #5
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Default Solar hot water heated weekend place

Gtojohn

Solar hot water heating is quite viable however it must be applied properly. The low energy space heating will work but it has to be distributed well or a level of comfort will not be reached. You hadn't mentioned how far your construction has proceeded but the best method to distribute the heat is in-floor heated concrete. This is indeed the holy grail.
If your only thinking hot water for domestic uses you have enough panel but for space heating you will require more panel area. It is recommended 10-30%of floor area but I would strongly suggest the higher end of 30%

I would also suggest for space heating with a concrete floor to install a dedicated in-floor loop which will carry the heated fluid directly from the panels to the floor this way you will have no losses from heat exchangers.

Your thoughts of care free heating of your cottage is a reality. Yes a PV driven pump with solar hot water panels heating your floor and ultimately your space will work and very well but the manner of collection and distribution needs to be done properly.

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Old 02-07-15, 09:59 AM   #6
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Quote:
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I would also suggest for space heating with a concrete floor to install a dedicated in-floor loop which will carry the heated fluid directly from the panels to the floor this way you will have no losses from heat exchangers.
I am not sure that, in a small cabin, losses from heat exchangers need be much concern. Assuming the heat exchangers are in the living space any losses from them will be heat put into the living space which is the goal anyway.

I have a solar contribution to my space heating and I really don't worry about heat losses from my heat exchangers heating the house directly rather than feeding into the heating system.

I think a direct in-floor loop is probably a good idea because it is the simplest & cheapest approach, not because it avoids heat exchanger losses.
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Old 02-07-15, 03:51 PM   #7
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SDMCF

I would agree heat losses to the interior is no problem but if the heated water is returned to the panel is not a good situation.
A simple solar hot water system would provide an excellent space heating solution for a weekend home. PV to power the pumps and be totally autonomic. Imagine your weekend retreat being warmed all week to be cozy warm on your arrival. FREE!!!!! Nirvana!

For a back-up source maybe wood or propane.
Tubing is quite inexpensive compared to a heat exchanger. A dedicated loop is the simplest, lowest cost and most effective. Drain-back system would also simplify and improve the efficiency. Glycol isn't cheap.
The insulated concrete is a huge heat battery that can be charged and stay relatively warm for a few days.
In our large installation I have noted a good amount of heat is returning to the solar panel. As with any system there is no heat-exchanger 100% efficient. This situation returns heated glycol solution to the panels and heat that could have been sent to the in-floor heating loop isn't harvested. Especially on a clear high energy day.

If I were to build again I would put two loops in the floor. One dedicated for the solar hot water collection and another for back-up heat.

Randen
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Old 02-08-15, 04:16 AM   #8
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For cost and my semi remote location my foundation will be pier and beam 2x12 on 24" centers. Overall design is open floor plan with loft. Maybe a radiant wall? Perhaps 1-2 radiators will be all I need to take the chill out. I've found some 16x20 heat exchangers for less than $100. Average winter temps are low 40s with highs in low 60s.
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Old 02-08-15, 07:25 AM   #9
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Gtojohn

Ok your thinking costs. I'm going to take a wild guess concrete in you area $120/cubic yard. and the area of your building 600 sq ft or 20 x 30

A slab of concrete 20 x 30 x 6" is approx. $1333.00 less foam insulation and tube.

Lumber 2 x 12 x 20 pressure treated are $54.00 ea. (Menards)you will require 16 pcs @24" centers plus rims joists so 20 total Minimum $1080.00 you will need plywood 20 sheets @$35.00 so thats another $700.00 for the decking Total so far is $1780.00 additionally you will require insulation underneath not to mention the added cost for piers and saddles. I'm sorry I don't see any cost savings going old school lumber.???

level ground, run perimeter forming boards, put foam on ground, lay steel mesh(or not) put tubing down, pour concrete. First floor completed!! AND half your heating system completed.!

That $100 you were going to spend on those used heat exchangers save it and put it towards the PE tubing. Not to mention those heat exchangers will not work with low temp solar hot water.

I wouldn't steer you wrong concrete slab is the way to go. Ran the numbers, built more than one, enjoyed the FREE heat on my feet.!!

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Old 02-09-15, 06:28 PM   #10
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Nothing has been built yet. Im not using pressure treated wood for my floor deck. my piers will be pt posts on top of concrete. I do already have 2 truck loads of pt 4 x 4 posts gratis. Non pt 2 x 12 on 24" centers come out to about $ 500 locally. I also have 30 sheets Recycled 3/4" cdx. And personally i prefer a crawlspace for plumbing, wiring, and maintenance. I could pour a thin concrete floor with tubing on top of my subfloor if the gains are there. Being in a mostly cooling environment id hate to go crazy with the heating if a less involved heating solution will suffice.

At what water temp are you heating yout floors with? Is any ony solar wayer heating their floor?

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