On 24 Apr 2007 01:00:42 -0400, wrote:

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%.

yeah, that's all well and good if you're starting from scratch. But
neither he nor I are. We both have existing buildings with moisture
problems and not amount of math will solve the problem.

In addition to using the best available construction techniques back
in the early 70s when we built the place, over the years I've had the
foundation dug out, French drains installed, the block walls tarred
and polyethylene sheathed and gravel backfill placed next to the
house. Plus painting the inside walls with water-stop paint. The
walls and slab are STILL moist to the touch. There's simply too much
water in the ground, too much flora to hold it in place and almost no
sun to drive it off.

I ventilated the basement with far more air flow than your $360 gadget
provides and it made no difference in either the mold growth or the
measured RH.


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."

Another worthless rubber-stamp patent issued in spite of vast amount
of prior art. Disgusting.



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.

You don't have anything nearly approximating a moisture problem. You
live in an arid environment as evidenced by those outdoor readings and
only need a little humidity management, something that throwing open
the windows will probably accomplish. We, OTOH, have many "95-95"
days - 95 degrees and 95% humidity. Your overpriced hair dryer blower
won't touch that.

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.

For about 2/3rds the cost of that so-called smart vent, one can
install a whole house attic fan and actually move some air. Which is
precisely what I did years ago. In my case, equipped with a PMDC
motor and variable voltage drive. I can spin it at ceiling fan
velocity and generate a gentle draft-free air exchange or I can crank
it up and sail the drapes. And still have much money left over
compared to that gadget.

None of this addresses a moisture problem in a basement, of course. In
my case, in the 30 years this cabin has been in existence, this is the
first year the basement has been dry enough to store valuable goods
such as electronic gear and books. That's thanks to a dehumidifier
that costs less than half your fan and uses only slightly more power.

I don't understand your abnormal advocacy of that little fan. Do you
have a financial interest in the product?

John
---
John De Armond
See my website for my current email address
http://www.neon-john.com
Cleveland, Occupied TN
All great things are simple and many can be expressed in single words:
Freedom, Justice, Honor, Duty, Mercy, Hope. -Churchill