re: a superinsulated cat house SOLAR.KnowledgePublications.com

re: a superinsulated cat house
15 dec 2000
dave smith wrote:

>this one is too much fun to pass up.  what about some natural hygroscopic
>material (hair, wood "bimetal") to reposition the door magnet. as the
>humidity rises the door would be held slightly ajar. something like this
>simple hygrometer.
>http://www.apluschilddev.com/pages/projects/hygrometer/hygrometer.htm

but why waste the latent heat, vs condensing water vapor in a fresh-to-room
air heat exchanger? on further reflection, the 0.21 cfm requirement seems
too low. thinking about a furnace requiring combustion air, it seems more
appropriate to scale the human requirement by relative heat production
vs weight, so a 6.61 lb ashrae-standard 68 btu/h cat would need 5cfmx68/300
= 1 cfm, compared to an ashrae-standard 154 lb 300 btu/h human.

nrel says the average december humidity ratio is 0.0032 pounds of water
vapor per pound of dry air where i live, near phila. an ashrae-standard
cat generates 22.5 btu/h of water vapor, ie 0.024 pounds of water per hour.
it takes about 40 btu/h to heat 1 cfm of 30 f air to 70 f. why not condense
the water from the moist outgoing air to heat incoming air? 

moving 1 cfm of air moves about 60ft^3/h/13.5ft^3/lb = 4.52 lb/hour of air
into the box, which makes w = (0.0032+0.024)/4.52 = 0.00841 and pw = 0.399
"hg and r = 0.399/0.747 = 0.53, ie 53% rh at 70 f, vs "177% with 0.21 cfm.

nick