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Q & A: clearing smoky hot air

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Most recent answer: 01/04/2015
Q:
Warm/cold air transfer?Warm air in kitchen. External brick wall with single small window to outside winter air. The window is open to release cigarette smoke and smell. I understand molecular kinetic energy, but with hot air rising, and cold air falling. 1) Is an air flowing cycle a result. I imagine that at some stage of the process at the point of the window that the greater number of outside molecules would enter at the lower part of the window and visa versa for the internal molecules. If so, 2) a cycle in which direction(s), and 3) will less smoky and cleaner air result (albeit colder)? My thanks in advance for your help. ph
- p (age 53)
Italy
A:

You raise an important practical problem. How can we get rid of smoke or other air pollutants without losing heat in the winter (or gaining unwanted heat in the summer)?

If your house were completely sealed off except for the little window, you're right that in winter hot air would flow out the top of the window and cold air would flow in at the bottom. The flow rate might be rather small. It's not a great way to clear smoke because you also lose heat. In a typical house air might just go out through the small window, replaced by cold air leaking in at various points around the house.

It is more efficient to use a heat-recovery air exchanger () whenever there's a big temperature difference between inside and outside. These systems exchange heat between the air going out and the air coming in, so that your heater or air conditioner has much less work to do for a given amount of air exchange.

Mike W.


(published on 01/04/2015)

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