Home built solar collector (shop heat) - build thread. (1 Viewer)

[MrMoMo]

Anyone here messed around building one before? (Don't seem to be any threads as far as I can find)

So.... Here is what I am doing. I live in Canada, and for the past few years I have been suffering through the winters in my well insulated, but un-heated workshop. When I built it I planned ahead, and ran pex tube all through the 1500 sq ft concrete floor, but with no heat source. So now I am working on step 2.... The heat source.

First some rough calculations I have been through.

Rough numbers
Suns energy = 320btu/sqft/hr.

Based on one online calculator To heat my shop I need about 15W/sqft
Watts x 3.4 = BTU

Thus, 1500 x 15 = 22,500W
= 76,500BTU

If collector is 50% efficient I can absorb half the suns energy @
160BTU/hr / sqft

76,500 / 160 = 478sqft of panel needed

478/8' high = 59' long panel... Seems big

Method 2 (Internet)
Divide square footage by 200 and multiply by 600 to get BTU required for insulated garage.

1500/200 = 7.5 x 6000 = 45,000BTU
(Seems small)

Method 3 (greenhousemegastore.com)
Calculator
1500 sqft x 15' ceiling
20 degree F rise, well insulated
= 39,000 BTU
Average insulation
= 78,000 BTU

Method 4... I don't feel like building that much, so let's look at some reality. I have reasonably quickly heated my shop to comfortable temp using my salamander propane heater which is 35K BTU. Generally if I run it for an hour, I'm good for an hour. I generally only do this a few times a month over the winter. So, let's say I got 35K BTU a day, but every day, that would keep my shop much warmer.

Based on the above numbers of getting 160BTU per square foot of collector, I decided to start a little smaller and be able to scale up. An 8' high by 12' long panel would be simple size to build, and would give me nearly 100 square feet. 100 square feet should get me about 16,000BTU. Sounds like a decent number to start with. I'm not looking for a sauna, is be happy to keep the shop above freezing.


So, I am building one panel, with 3 sections in it. Each section is a 4x8 sheet, so roughly my collector will be 8' high and 12' wide (slightly larger due to lumber in framing)

I have started building, using 2x8 lumber for the outer frame, with 1/4" OSB for the outer skin on the back. The same OSB will be used to mount the PEX tubing, which is then covered in Aluminum heat sink material.

Here is the basic framing, face down (for painting) on my shop floor:

After a coat of Rustoleum (not the metal stuff):

Once this dried I moved it out of the way (to work on my 40'), but next is to put it face up, put a layer of insulation in it, then drop in the 3 4x8 panels with tubing attached.

So far I have made 100 aluminum heat sink fins to fit the pex tube. When installed over the tube and staples to the OSB they are flat, not V shaped.

These fins are 2' long by approximately 6" wide. Made by cutting a 50' x 14" roll into 2' sections, then in half to 7" sections, then pressing them in my customized form on my pipe bender to get the shape seen above.

Air over hydraulic bender with wood and steel forms: (can see the edge of a sheet in it)

Flat sheet partially compressed:

(More to follow momentarily)

 

[MrMoMo]

Fully compressed...

(The wood split the first test piece so I backed it with another layer)

Fresh out of the press:

And into the stack! (Half way there!)

That's as far as I am for now, hopefully by the end of the month I have it up and running...

Any thoughts or experiences would be appreciated! I will post up as I progress for anyone else who would like to build one. I figure my panel cost will be about $500 all said and done... (Excluding fluid!)

 

[rc10]

Can't wait to see how this turns out.

 

[pillguy]

I need to build one. THat looks great!!

 

[ff347]

Very cool, will follow.

 

[MrMoMo]

Well due to the fact that it's not the most exciting thing to build, it's going kinda slow.... Temps in my shop are not too cold as we seem to be having a mild winter so far this year.... But needless to say, that's exactly why I should be getting my ass in gear. So today I started building the actual collector portion. I think the end radius is slightly too tight for the pex and I'm having to be very careful to not have it collapse, but so far I think it's working out OK. Lots of stapling!!!

Kind of a secondary project as my 40 frame is back from galvanizing so I kind of have the bug to work on it most of my spare time, but I figure if I do a few runs of this at a time, eventually it will be done!

Progress today.... Not much! Every dent you see in the aluminum is a staple or two.
Each horizontal run is slightly up hill, hopefully to improve the thermal syphon.

 

[MrMoMo]

Ok, so passing along a little "learning" this far for anyone deciding to make one of these...

1) use a hair drier to hear the pex for the corners, much easier and the corners come out much better. It's also possible to improve the corners by heating after, but do NOT heat the very center of the radius, as it may kink. (Don't ask how I know). However, it is also possible to push kinks back out again by heating and pressing down on the kink, while at the same time pushing in towards the center point (widen the radius).

2)Use a rigid bar to make everything line up, and after trapping the pex pipe in the heat sink, push as hard as you can against the pex with the bar, while you staple.

3)It seems to be easier to work towards yourself (so you can push on the bar) as opposed to away from yourself (having to pull the bar)

4)Make smaller panels! If I had made 3 individual panels instead of 1 big one, I could install the first and get it working while working in the second and third!

5)Always keep your staples in reach - you WILL run out when you can't quite reach them!

I'm using a 46" piece of 1"x1" aluminum round corner box tube (part of the future roof rack for my 80) as my pusher bar in the pic below. The last U towards my hand was made by heating the pex, the previous two were "cold" bends (now fixed)

 

[rustybucket]

You have the right idea. But BY far the BEST way to heat water is evactuated tube. Evacuated tub is amazing how well it heats water even in the coldest of days.

 

[MrMoMo]

Yeah, I thought about going that route, but the idea with this project was to try to keep it simple to build and cheap. Even if these panels are only 50% efficient I should get decent heat out of them. Maybe not enough to make it 21c in my shop all day every day, but I can always add more of the same build in parallel. I figure if I can get 16,000BTU for a few hours a day, for a $500 investment I'll be happy!

 

[tlin]

Awesome project, I love seeing these DIY efforts.

No idea if this is of possible interest to you but an additional heating project to consider......seems to be aligned with your interest in capturing solar energy to help heat the space, might be one to add after you get the floor heating up and running?

5)Always keep your staples in reach - you WILL run out when you can't quite reach them!View attachment 1010633

YUP!!!

Good luck man!

 

[MrMoMo]

Awesome project, I love seeing these DIY efforts.

No idea if this is of possible interest to you but an additional heating project to consider......seems to be aligned with your interest in capturing solar energy to help heat the space, might be one to add after you get the floor heating up and running?



YUP!!!

Good luck man!

Funny, I actually have one of those half built as well. Takes an insane amount of cans and a lot of drilling and glue!

Unfortunately both of these projects have kind of stalled. Too cold to work on heating!

 

[mdsims]

Following along. Really interested to see how all this turns out. Keep up the motivation.