Heat My Shop

[Semon]

This is what I would like to do.
Build a box 4' X 8' with with copper tubing and glass for the collector on the roof coming into the shop with 3/8" tube coiled around a 30 gal water tank to heat the tank.
Using the water in the tank to heat the shop going threw 2 heat exchangers with fans behind each.
Both will have a thermostat, one on the roof to shut off the pump when temp. gets low and the other in the shop to regulate the shop temp.
The shop is 24' X 40' the temp. here gets a low of about 30 degrees (in Tn.)
What I need to know is will this work?
Pump GPM?
Size of collector?
Size of shop heat exchangers to heat shop?

Thanks for any help
Semon

[Dana]

With low temp solar hydro-air coil heat exchangers and a tiny buffer tank you may end up using more pumping & fan power than the solar heat you'd collect. Active solar systems have to be designed carefully to really work. This is not something amenable to design-by-web-forum. With sloped glass on the roof you'd also be running a real risk of summertime steam explosions unless you provided for a heat-dump (== more pumping power wasted.)

Cheaper and more effective approach would be to build a thermal air panel on the side of the building, either thermosiphoning or using fans. See:

http://www.mofga.org/Default.aspx?tabid=488



http://www.builditsolar.com/Projects....htm#ActiveAir

The air-tightness and insulation values of the building will likely need to be upgraded if you hope to get a decent fraction of your space heating energy out of solar (any type.)

[Semon]

I don't have enough sun on the side of my shop. I think I can get around the summer problems.

[Dana]

And of the roof you'll have too much sun, exactly when you don't need it, and very little when you do. Seriously, if you're going to do active solar it needs to be more than hacked together, or you'll spend a whole lot of time & money for very little return.

Thirty gallons of water is nowhere near enough thermal mass to buffer a space heating load of any size, at 250-500gallons maybe you'll have something to work with, might even get you through the night with sufficient collector and a tight enough building, but there's no getting around doing the math on all of it. Solar-hacker central lives here, if you're committed. You can probably scale up some of the "$1000 water heater" designs and run flat-panel radiators or something as the heat emitters. As I stated previously, tepid-air fan coils would likely use more power than it's worth- you can move a lot more BTU per kilowatt-hour into the room with pumps & radiators than you can with fans.

If you take that approach don't use PEX anywhere, as the stagnation temps and even high end of the operating temp will likely be well over spec for PEX. The roof angle & orientation need to analyzed for solar gain too. Low angle roofs are terrible for winter gains, pretty good for summertime, so you may have to tip 'em up to make them useful. Latitude +10 degrees when oriented due south is the rule of thumb for space heating, but that's an extremely crude estimate.) In TN that would be about 35 degrees + 10- are your roofs pitched at ~45 degrees (a 12:12 roof) and facing due south?

[Semon]

Ya I guess you are right Well I guess I'll try solar air. Here's what I'm thinking To start bottom 4'X8' plywood and foam foiled insulation painted black, 2"X4" sides and baffles Plex for the top, 4" duck to transfer the heat with a fan to push the air. My shop roof faces south and angle not a problem. Would it make a difference if the 8' ran horizontal or vertical

[Dana]

Use polycarbonate rated for green house use, not plexi, or it'll get brittle and fratz on you in short years.

If you're using a blower/fan it doesn't matter what the orientation of the panel is.

Be sure to use foil faced polyiso and not foil-faced EPS (bead-board). EPS isn't rated for the higher temps that it will likely experience. Don't paint the foil, use some sheet metal siding instead leaving an inch or so between the foam and metal, and an inch between the metal and the glazing.

Fan control using a 110F on/90F off make-on-rise snap disc on the sheet metal works. You can also use a line-voltage room thermostat in series with the snap-disc to keep it from coming on if it's already too warm in the shop.

The amount of heat you'll get out of this will vary with climate & orientation, but a 4'x8' would be offset ~50-75 therms of gas (or 40-55 gallons of heating oil) per year in my neighborhood.

[Semon]

I have the polycarbonate Should have said that instead of Plex. I'll have to get metal siding and the thermostat.
Thanks

[Semon]

I can't pull the sight for the line-voltage thermostat could you re-post it?
Thanks Lee

[Dana]

http://www.grainger.com/Grainger/DAY...H07?Pid=search

http://www.*********.com/h_d1/N-5yc1...atalogId=10053

http://www.*********.com/h_d1/N-5yc1...atalogId=10053

http://www.lowes.com/pd_92197-74493-...tat&facetInfo=

[Semon]

What size holes for air flow with a fan should I put in the sides of the solar panel?

[Dana]

Hitting the exact most-efficient sizing depends on a whole bunch of design factors and the rated flow of the fan, but at a minimum design the cross section of the air passages to be at least that of the fan.

[Semon]

Thanks
Lee