Heat-exchanging venntilators | <– Date –> <– Thread –> |
From: DanR510 (DanR510aol.com) | |
Date: Fri, 4 Nov 94 08:48 CST |
Several years ago I gave considerable thought to wood stove design. I thought about doubled-walled stovepipes, not for fire safety purposes, but to bring cold outside air in and recover the heat going up the stovepipe, rather than pulling warm air in from the room, and cold air into the room from outside. One problem here is that you'd need a very clean burning fire to prevent chimney condensation of creosotes and tars, much of which would normaly be carried away as smoke. You'd also need maybe a stainless steel stovepipe to keep water condensation and other chemicals from rusting it away very quickly. You might also need a blower to replace thermal convection draft. While on that tack, I also thought of this type of ventilator. (Perhaps unfortunately, I went on to other things.) Frosting up is one problem I hadn't considered, living in western Oregon at the time. Getting dirty is one I did consider. Either one reduces heat exchange. To be efficient, it must must have a lot of heat- exchanging surface, which would be hard to keep clean. Do present versions do anything about this? Another important factor, which I assume commercial versions incorporate, partly since it would be more complicated not to, is the counter-current effect. Two bodies of still air, or air currents moving in the same direction, of different temperatures, with a heat conducting surface between them, will both approach a medium temperature. 0 degree air and 70 degree air will both approach 35 degrees. Two air currents moving in opposite directions will each approach the original temperature of the other. The 70 degree air will approach 0 degrees, and vica versa. Just how much heat is exchanged depends on how long they share the heat-conducting surface. To Roger Diggle: I've always assumed that carbon dioxide is a major pollutant in a "tight house", but you don't mention it. Not so? >Air-to-air heat exchangers, or, as the industry seems to want to call them these daze, heat recovery ventilators,... "Air-to-air heat exchangers" says nothing about the fact that they are venilators, which seems rather important here. >They also offer an impermeable heat exchanger core (polyethylene, I think) that would not be appropriate for Northern winter weather. Is aluminum (a very good heat conductor) or other metal a problem because it corrodes too fast? I like the idea of the "heat wheel", but preferably with flat surfaces instead of honeycombs. Then brushes could isolate the two air streams, and also keep the surfaces clean. Now that I've said my piece, and hopefully impressed you all, I must also say that it seems like this subject would be more appropriate under something like "building environmental design". Dan Robinson
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Heat-exchanging venntilators DanR510, November 4 1994
- Re: Heat-exchanging venntilators Roger Diggle, November 7 1994
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