Neon John wrote:

wrote:

Joe wrote:

I've been looking for a good dehumidifier and I notice that each big
box store only really carries one brand and there really isn't much
online as far as reviews. I know some dehumidifiers are energy hogs...

How about a Crawlspace Smart Vent?

http://www.smartvent.net

They cost $365, but they only use 40 watts when moving 290 cfm of air
out of a basement when the absolute moisture content of basement air
is greater than the absolute moisture content of outdoor air.

But that isn't what he asked about. If he has a serious humidity
problem as I did then venting won't do a thing.

Au contraire. It will, with suitable weather conditions and controls
and building materials that can store moisture and dryness, eg paper
and wood and clothing and concrete with suitable sorption isotherms.

Concrete stores about 1% moisture by weight as the RH of the surrounding
air increases from 40 to 60%, and it weighs about 150 lb/ft^3, so
a 4"x1000ft^2 50K pound floorslab might store 500 pints of water as
a basement RH increases from 40 to 60%.

Smart Vent's 12/19/2000 US patent no. 6,161,763 "Module-controlled building
drying system and process" at http://www.freepatentsonline.com describes

"...drying air circulation between inside and outside the building based
on absolute humidity and temperature sensor measurements... the input ports
are connected to... outside absolute humidity sensors... [and] inside
absolute humidity sensors [and] the output ports are connected to...
[a fan system.] ...if the outside air has a lower absolute humidity than
the inside air... the fan system output will be activated... if the outside
air has a higher absolute humidity than the inside air... the fan system
will be shut down."

Last year when I turned my vacation home into my residence and moved a
lot of possessions into my basement, I bought this dehumidifier:

http://www.samsclub.com/shopping/nav...95&prDeTab=2#A

The way to evaluate the efficiency of a dehumidifier is its rating in
pints removed per KWH consumed. Using the spec sheet of 580 watts
draw and 40 pints/day, that works out to 2.9 Pts/KWH.

It turns out that this is worst-case, for I just checked my unit with
a Kill-A-Watt and measured 450 watts. That makes the Pts/KWH a much
better 3.7...

Yesterday it was 67.8F with 41% RH in my house with some windows open,
so the vapor pressure Pi = 0.41e^(17.863-9621/(460+67.8)) = 0.284 "Hg.
The indoor humidity ratio wi = 0.62198/(29.921/Pi-1) = 0.00597 pounds
of water per pound of dry air. The outdoor sensor in partial sun read
84.0 at 19%, so Po = 0.181 "Hg and wo = 0.00379, so every pound of air
that flowed through the house removed wi-wo pounds of water.

A Smart Vent could have removed 290x60x0.075(wi-wo) = 2.8 pints of water
per hour, at 70 vs 3.7 pints per kWh.

To also heat (cool) a house in a cool (warm) season, we might power up
a Smart Vent with a differential thermostat only when outdoor air is
warmer (cooler) than house air.

And we could hook a relay in parallel with the Smart Vent fan to power
a whole house fan, and add house room air thermostats to shut off the fan
if the house becomes too warm or too cool.

Nick