[Greenbuilding] Central vs window AC

[nick pine]

 John Straube writes:

>... consider the humidity. At night, since it cools down, the RH rises. 
>Flooding a house with 68F/80-90%RH air loads the house up with vapor in all 
>the drywall, wood, furnishings.  The next morning even if the temperature 
>stays low (say 76 or 78) the RH in the house will be uncomfortably high. 
>If you have more mass (lots of exposed concrete ceilings for example) the 
>concrete stays cool enough that you can get condensation on the ceiling. I 
>have seen this happen in old masonry warehouses .

To me, smart ventilation considers absolute humidity, with ventilation only 
on cool dry nights when the result would be comfortable. Flooding a house 
with dry air can store dryness in the same way that thermal mass can store 
coolth. Concrete absorbs 1% of its weight by moisture as the RH rises from 
40 to 60%.

Nick