Neon John wrote:
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.
Sounds like you have enough concrete, but few dry days... 500 pints
is only 10 days at 50 pints per day.
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.
Unsmart venting can *add* moisture to basements by condensation.
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.
This technique was quite useful in New Orleans after Katrina.
By law (US Code 102/103), the patent would not have been
issued if it were not novel.
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.
That's 67 pints per day with less than 1 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.
I wish they made a version like that, with a "season sensor" to change
the sense of the differential thermostat.
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...
Philadelphia? :-) As I mentioned above, that outdoor temp/RH sensor
was in partial sun. The outdoor temp was 76 in the shade, which made
the outdoor RH about 25%, rare but nice here in the spring.
This morning it's 64.6 F and 55% outdoors.
... We, OTOH, have many "95-95" days - 95 degrees and 95% humidity.
We have a few nights like that in August.
Your overpriced hair dryer blower won't touch that.
It works well in humider Arkansas, where it was developed.
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.
But then you have to do all those horrible calculations every day.
You want to remove more than 67 pints per day?
None of this addresses a moisture problem in a basement, of course.
Of course it does, precisely.
I don't understand your abnormal advocacy of that little fan. Do you
have a financial interest in the product?
No, but I've been trying to help get a product like this to market for
several years now, since Murray Milne and Pablo LaRoche from UCLA gave
a talk on a "smart whole house fan controller" at the ASU Cooling Frontiers
symposium. Their box (with an Onset Tattletale controller) automatically
cooled a massy test house by ventilation, but it didn't address humidity.
With RH sensors, we can efficiently dehumidify and also cool and warm
houses with outdoor air, with no danger of indoor condensation.
Nick
Berlin is a nice town and there were many opportunities for a student to
spend his time in an agreeable manner, for instance with the nice girls.
But instead of that we had to perform big and awful calculations.
Konrad Zuse, inventor of the 1936 Z1 computer