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re: powered vs bypass humidifier?
10 nov 2004
zypher  wrote:

>as for energy use, when the moisture level is kept around 50% - 60% during
>the winter, the we use less energy (less cycling)

you seem confused. "cycling" has little to do with energy use.

>...we feel more comfortable at lower temperatures than if the air
>was warmer and dry.

not much lower... the ashrae 55-2004 comfort standard says a 48x48x8'
house with r20 walls and ceiling would be equally comfy at 69.4 f and
20% rh or 68 f and 50% rh. if it's very tight, with 0.5 air changes
per hour, would humidification to 50% save energy? 

g = 48'x48'/r20 + 48x4x8/r20 = 192 btu/h-f, so dropping the room temp
from 69.4 to 68 f saves 1.4x192 = 269 btu/h. at 69.4 f and 20% rh, pd
= 0.2e^(17.863-9621/(460+69.4)) = 0.1466 "hg, approximately, with wd
= 0.62198/(29.921/0.1466-1) = 0.003063. air at 68 f and 50% rh has wh
= 0.007347. with 0.5x48x48x8/60 = 154 cfm of air leakage, humidifying
from wd to wh requires evaporating 154x60x0.075(wh-wd) = 2.96 pounds of
water per hour, which requires about 1000x2.96 = 2960 btu/h of energy,
so the net "savings" is 2960-269 = -2691 btu/h, or minus 64.6k btu/day,
costing about $1/day more with oil heat or $2 per day with electric heat.

people tend to forget that evaporating water takes heat energy, even if
the "humidifier" uses little energy by itself, and that heat energy has
to come from somewhere. and we often get into discussions about health
and furniture, vs energy, and forget that caulking (vs humidification)
can raise the indoor rh while saving vs wasting more heating fuel.

>if the air is dryer, we feel the need for more heat.

heat and temperature are different. 

>also, the air is more receptive to heating when moisture is present.

you have an unusual grasp of physics :-)

nick




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