[Greenbuilding] clothes dryer vents

[Corwyn]

On Mar 08, 2007, at 17:46, I wrote:
>
> 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.

I forgot the energy taken up by the evaporating water, in the inside 
air scenario.

Heating the air plus evaporating the water take 15 BTU/lb of air. or 
8790 BTUs.

for a total of 14470 BTUs.

so it saves you 3610 BTU minus whatever the difference in non-heating 
energy used by your dryer for the difference in time between the two.

Hopefully, that's right.

Thank You Kindly,

Corwyn

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