Air heat exchanger for shop

[Shuswap Pat]

Has anyone built an air/air heat exchager for their shop? It gets a little brisk here in the winter (-20c). so when you open the windows/doors to get fresh air, it gets a bit cool. I would like to exhaust air, but capture to heat to warm the incomming air.

Patrick

[sch]

Are you referring to the heat exchanger Evan designed and posted about a year of so ago? IIRC it used soda/beer cans joined end to to end and paralleled as the heat exchange tubing.
It does not appear to be on his website, at least the public portions.

[jlevie]

Making a crude air-to-air heat exchanger would be no big deal. Making a good one would me more of a challenge. For good heat exchange the air passages need to be quite small and the air paths need to be quite long. A cross flow design is commonly used.

In a shop I would guess that the purpose would be to exhaust fumes/smoke. Which would be contamination problem for heat exchanger of decent performance. Contamination of the the outgoing passages would impact heat transfer.

[Shuswap Pat]

That is the trick - capture the heat, and get rid of the crud.

Patrick

Making a crude air-to-air heat exchanger would be no big deal. Making a good one would me more of a challenge. For good heat exchange the air passages need to be quite small and the air paths need to be quite long. A cross flow design is commonly used.

In a shop I would guess that the purpose would be to exhaust fumes/smoke. Which would be contamination problem for heat exchanger of decent performance. Contamination of the the outgoing passages would impact heat transfer.

[Toolguy]

Maybe you could use one of those woodworking shop air filters. They recirculate the same heated or air conditioned air but run it through a filter to clean it. You just clean or change the filter once in a while.

[Ironwoodsmith]

But they would not remove fumes. Dust yes, smoke no.

[Shuswap Pat]

The other thing I want to do is eliminate moisture. The place is so well sealed, when I bring something in that is wet, or with snow on it that melts, I get a lot of condensation on the windows. I want to get that moisture out also.

Patrick

[batt-man]

I have no idea if this would work but how about getting a few old car radiators and join them sequentially then stack them one in front of the other.

Build a box of some sort around them and use a ducted fan to extract the stale air from your shop going through the radiators and eventually vent outside.

Any fresh air is sucked in over the radiator fins thus getting extracting the heat from the old stale air passing through/warming the radiators.


I have no idea if or how well this would work but i've had it in the back of my mind for a few years now. maybe one day i'll actually get time to try it.

Cheers
Batt...

[EVguru]

First of all, do a search for 'single room heat recovery'. You may find the price reasonable compared to brewing your own.

For heat recovery you need a large exchange surface area and a conductive seperator. The commercial units tend to use a plastic membrane, that whilst the plastic itself is not a good conductor, performs well because the membrane is so thin.

The home brew unit I saw used long plywood ducts, about a foot square, with baking foil folded into a concertina shape diving the airflow. The ducts nearly filled a roof space, but seemed to work quite well acording to the datalogging the guy had set up.

[Duffy]

You know, Evan's design will be awful hard to beat for the time and money involved.
I have a commercially built whole-house unit that cost about $600.00 or so.It uses an exchanger made of layers of Coroplast and a double-drum fan sothat air flows are automatically balanced. When it is -20 or better, it probably earns its keep, but I would not recommend one. I doubt very much that i will recover my investment.

[bhowden]

I always thought that you could take some of that plastic sign board that is like plastic corrugated cardboard and cut it into square pieces. Stack them all up alternating 90 degrees apart from each other and then mount the stack diagonally in a box so you have incoming airflow running 90 degrees to the outgoing air. Election time would provide lots of free material. 12 - 16 inch squares stacked 6 or 8 inches high would let you use 5" HVAC plumbing.

Brian

[jlevie]

Plastic's thermal conductivity is pretty low. Couple that with the poor thermal conductivity of air and you'd wind up with little heat being transferred between the incoming and outgoing air streams. What you want a a very thin separator with high thermal conductivity (aluminum is good and copper is better), a high surface area to volume ratio for the air passages, and fairly long air passages.

[Duffy]

That corrugated plastic used for signs IS Corroplast, and is used in my commercial exchanger. My core is actually layers of Corroplast separated by strips of the same, built up into a cube and mounted as you describe. The strip side of the core handles unfiltered incoming air and therefore has to be capable of handling whatever. The exhaust side is discharging air from the heating system that has been through the furnace filter.
The argument for highly conductive separating membranes really does not apply.The limiting heat transfer barrier is the boundary layer of air on each side of the membrane. Since it has nearly zero velocity, it has very low turbulence and acts as an insulator. There would be no significant improvement in heat transfer using copper or aluminum, but it sure would cost more!