[Greenbuilding] [BULK] clothes dryer vents

[Corwyn]

On Mar 08, 2007, at 14:16, Lawrence Lile wrote:

> I am considering hacking a dryer so that it has an outside air
> combustion intake, so that at least it doesn't suck up expensive heated
> indoor air to blow outside. That would involve adding a second hole in
> the back of the unit, plugging up any vent holes, and running the sair
> intake pipe outside through a screen.

Let me see if I can do these calculations, I have been trying to 
understand the psychrometric chart, hopefully someone will check me 
work.

Assumptions:
• Dryers don't check incoming or outgoing temperature or humidity (they 
just pumped heat in and air out) 10 BTU/lb of air
• Air coming in is at 40% relative humidity and 40º; no humidity is 
added in house.
• Clothes contain 10 lbs of moisture to be removed.
• Dryer is maximally efficient.

Inside Air:
	Dryer gets air at 65º, heats it to 76º increases the humidity ratio by 
0.0176 lb of water / lb of dry air.
	Drying takes 568 lbs of air, or alternatively 5680 BTUs.
	Heating that air takes 5 BTU/lb of air, or 2840 BTUs.
	Total = 8520 BTUs.

Outside Air:
	Dryer gets air at 40º heats it to 58º, increase the humidity ration by 
0.0092 lb of water / lb of dry air.
	Drying takes 1086 lbs of dry air, or alternatively 10860 BTUs.

So, from this, using outside air _costs_ you 2350 BTU per load, plus 
any leakage in your system.

Thank You Kindly,

Corwyn

-- 
Corwyn
Kermit didn't know the half of it...
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corwyn at greenfret.com