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psnow

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Posts: 2
Reply with quote  #1 
I love you site and videos and have the perfect garage space for this project. I think I can do this since I am a novice but need some guidance. So I want to standardize this as much as possible for build so my thoughts are this - a  4 foot x 8 foot downspout style collector using the Home Depot available SunTurf 26in x 8ft clear polycarbonate corregated panel and using the SunTurf plastic closure strips. I would also use the box type plenum approach. Given what I have said, what would be the correct number of downspouts for "maximum efficiency" and size of each end for plenums for airflow? Also what size fan (output) - either radon or other - using 4 inch pvc tubes for airflow for a collector this size?  Please lt me know if there are any other things to consider or tips with this build. Thank you

gbwillson

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Reply with quote  #2 
Welcome psnow!

You asked a lot of good questions. But I have a few questions...

What is your location? 
What is the size of the garage?
Is the garage insulated?

I ask because building a 4x8 collector in a large uninsulated location is not going to do much for you want to work in a warm garage. So I want to have some idea as to your goal and expectations for a solar heater. 

I personally know members who have built 4x16 collectors for their large, insulated garages in Minnesota and Wisconsin that can work in their t-shirts all winter long! So it is very possible, if that is your goal. If your needs are different, let us know and we can help you build a collector for your needs.

Greg in Minneapolis



psnow

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Reply with quote  #3 
It is an insulated garage in southern Vermont. It is approx. 1200 sq ft and does have a wood stove but really want to warm it up using a solar air downspout collector and want to get dimensions. Thanks
Rick H Parker

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Reply with quote  #4 
I ask because building a 4x8 collector in a large uninsulated location is not going to do much for you want to work in a warm garage.

I'll second that, conservation of energy is more cost effective then the Tim Taylor solution.

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
gbwillson

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Reply with quote  #5 
1,200sf for a garage? VERY nice! The workshops/garages that use solar heat are roughly half that size and have about 64sf of solar heater, so a 1,200 sf garage you would likely need roughly 128sf of collector. Now if your garage is attached to the house, has living space above it, or is protected by the prevailing winter winds you may get by with a bit less. But every time you open the garage door to pull a vehicle in or out you lose all of the stored heat. 

Keep in mind that a larger collector is no harder to build than a smaller collector. And while you do have the wood stove, you would have to keep it running almost constantly to make up the difference from having a collector that is too small. So if you have the space I would suggest one of two options:

First, build a 4x8 collector as a proof of concept. You could either keep the unit in place, re-task the unit to a different location on the house such as a room or two, or sell the unit to recoup your material costs. This would allow you to learn and understand solar heaters. Then, build a much larger unit as needed that better fits the needs of the space. Once you have built your first solar heater, any future builds go much faster due to your experience.

OR

Second, build a unit sized to better fit the size of the space in question. While any heat added is good, a 32sf unit is enough to heat a room or two, not a very large space, like your garage.

Greg in MN
Fearless

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Posts: 6
Reply with quote  #6 
Not trying to steal the thread, but I'm in the same position as psnow in that I'm building my first, have about 1000sf garage, and need the same answers relating to plenum size and airflow/fans. I've read quite a bit from the wealth of information on this forum, but cant seem to nail down what I need before actually building it and getting numbers for formulas....

I'm in Georgia and dont need to heat the garage per se, just keep it above freezing, and I'm limited on my panel size. My current design is like psnow's, 4x8 facing due south using 2.5" alum tubes w/ two 4" computer fans working in series (~25cfm ea., one @ intake side one @ output) controlled by snap disk.... one 90/130 and one 110/160.

Am I on the right track here, or am I too optimistic on the heat output?
gbwillson

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Reply with quote  #7 
Welcome Fearless!

I'm sure we can get this switched over to a new thread if needed.

A 4x8 heater will give you about the same heat output as an electric space heater while the sun is shining on it. Assuming the garage is insulated, try an electric space heater in your garage for a couple of hours and see if the temperature changes. And while your climate is far less demanding than psnow's, a small space heater will likely be unable to add enough heat to the space to your satisfaction. So as I mentioned to psnow, a large heater is no more difficult to build than a small one. 

As far as the fans needed, you may want to lower the snap switch settings. I use one set to go on at 100˚, off at 85˚ to capture more BTU's. Settings as high as 130 or 160 are far too high and may damage the fans, especially at the exhaust end. Settings that high also tends waste BTUs out through the glazing. The goal is to have LOTS of lukewarm air as opposed to small amounts of hot air as this maximizes the BTU's captured. 

Greg in Minneapolis[wave]
Fearless

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Posts: 6
Reply with quote  #8 
Thank you, Greg. Exactly the type info I am looking for. And hopefully it'll help psnow along, too.

I have marginal 1950's insulation. I did run a 1500w heater over our coldest nights last week (around 17° lows). According to Killawatt It ran all night but it was able to reach around 35° by the mornings. Keep in mind, I start it when it hits ~28° and I don't run it during the daylight hours. That still equates to about $50~75 a month over the winter, which is the reason for this venture. I feel that if I can supply heat during the day and just use a heater to maintain it overnight I can cut that cost at in half... perhaps better.

I would love to cover the entire south wall with heaters and do away with space heaters altogether, but with overhead doors and shading, I have only one area of wall that receives full sun and it measures 4.5' x 7.75', so that's what I'm building. If I get good results with it, I may look at a roof mounted system to supplement it, but that's down the road.

And I was hoping to use the 12v fans w/an old motorcycle battery and a PV panel charger for zero operating cost, but if I need more volume I'll probably have to go AC. The snap switches just happen to be what I have in the toolbox, salvaged from dead microwaves... picking up a couple of lower temps wouldn't be an issue.

My overall thinking on fans was:
Natural convection till it starts getting warm, fan kicks in @ 130 which would bring it back down to that 90~100° butter zone. The second fan was kind of like a fail safe idea.... if it starts to get up to that 160 mark, it needs to be evacuated and the second fan kicks in. Thats why I was looking for air movement numbers.... is the one 25 cfm fan enough, too much, or just right to dissipate the heat from a 16 cubic foot box? (4x8x0.5) Does the second fan in series double the flow, or am I better off running them in parallel (ie: side by side at the intake point) and push the air through?

I'm really enjoying the project so far and really appreciate your input on what I'm doing.
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