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re: diy dehumidifier
18 may 2005
songofruth  wrote:

>my house suffers from too much humidity.  the wood floors my dh
>installed (his trade) are beginning to buckle.  so the situation has
>now become somewhat critical.
>as i understand it i should build able to build basically an exhaust
>fan that is controlled by humidity.

sure, if it's less humid outdoors, in the absolute sense, ie if wo < wi,
ie ln(ro/ri) < 9621(1/(460+to)-1/(460+ti)).  for example, if it's 70 f with
80% rh indoors and 80 f outdoors, ventilate when ro < 0.8e^-0.336 = 0.57,
ie the outdoor rh is less than 57%. this could use 100x less energy than
a dehumidifier with a compressor. for efficient house heating and cooling,
you'd want to ventilate at night in summertime and during the day in
wintertime, every few days, when outdoor air happens to be dry.

>but i have no clue exactly how to go about it.  i intend initially to
>fit it into a window (similar to the way a window air conditioner is
>installed in a window).  i don't know where to obtain the fan (get a
>bathroom exhaust fan and rip the guts out?) and i definitely don't know
>where to get the humidity control.

you might put lasko's 2155a reversible window fan (2470 cfm, 90 w, $53
from ace hardware stores) in a partition wall that divides the house into
two "airtight" spaces and run it whenever the house rh exceeds 50%, along
with the calc above, and reverse from time to time to turn all the exterior
house wall cracks and crevices into efficient bidirectional heat exchangers.
you can do this automatically with a repeat cycle timer like grainger's
$83.90 2a179 (with its $4.26 5x582 socket), with adjustable off and cycle
times from 1.2 seconds to 300 hours.

herbach and rademan (800) 848-8001 sell a nice
$4.95 navy surplus humidistat, their item number tm89hvc5203, with a
20-80% range, a 3-6% differential, and a 7.5a 125v switch that can be
wired to open or close on humidity rise.

we may see a wireless home automation controller that can do all this
and more automatically at the u mass doe decathlon contest house on
the washington dc mall in october :-)


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