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Re: dehumidifiers

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Posted by nicksanspam on June 19, 2007, 10:01 am
 


And they use lots of electrical energy. A Smart Vent (40 watts max)
would probably last longer. It has an electronic circuit that turns
on 2 small fans whenever the dew point of outdoor air is less than
the dew point of indoor air, ie the absolute humidity of the outdoor
air is lower. The Zomeworks H2 ventilator for battery boxes seems
to do the same thing, something like this, viewed in a fixed font:

                
outdoors       up           indoors

          ---------------
      <-- moist air
   ----------------------
  |                       --> dry air
  |   -------------------
  |  |
  |  |    ---------------
  |  |    heat exchanger
  |  |    
  |  |        down
  |  |
  |  | dip tube

as described in Steve Baer's ASES 2004 Humidity Chimneys paper. Moist air
is less dense than dry air, at the same temperature (hence the heat
exchanger.) Steve says a 1% moisture difference with a 2.5 foot height
difference (hence the dip tube) can make 75 feet per minute of air flow,
so a 6" pipe with an 8' height might make Pi(3/12)^2sqrt(8/2.5)75 = 26 cfm
flow and remove about 26x60x0.075x0.01x24h = 28 pints per day of water
from a basement, in dry weather, with a concentric pipe heat exchange
chimney inside the house, from the first floor ceiling to the basement.

The external "dip tube" might be a box with a transparent south side
and 150 Tyvek bags filled with desiccant clay, which can absorb 28%
of their weight in water, ie 53 pints:

http://www.uline.com/ProductDetail.asp?model=S-1606&ref 06

The Florida Solar Energy Center puts clay bags on wire racks in an attic
with a tin roof which heats up and dries them out during the day. After
they cool, at night, they remove moisture from house air that circulates
up through the attic. Here's some Desi-Pak (tm) tech info:

http://www.agmcontainer.com/desiccantcity/pdfs/Desiccant%20performance.pdf  

Graph 4 shows Desi-Paks can absorb 12% of their weight in 10 hours
at 30C and 60% RH, ie 2.3 pints per hour for the 189 pound collection
above. This rises with more airflow or thinner bags. Graph 3 says
they can absorb 8% in 100 hours at 25C and 10% RH, ie 0.15 pints
per hour for 189 pounds.

Nick


Posted by carneyke on June 20, 2007, 12:11 am
 
I have a Sears dehumifier that is 20 years old, it had the fan go once
($00 fan). The problem I see with drawing hot dry air from an attic
is, it would make the basement hot. I enjoy my cool / semi dry
basement because of the dehumifier. I can't see desicant doing the job
a dehumifier does..... It may work but I doubt it would be an easy
install.

On Jun 19, 6:01 am, nicksans...@ece.villanova.edu wrote:


Posted by Neon John on June 20, 2007, 1:19 am
 Nick has a "thing" for this gadget and is rehashing a "discussion" we had last
winter.  He exaggerates the "badness" of dehumidifiers and IMO, exaggerates the
goodness of his pet gadget.

I've measured my mid-quality GE dehumidifier using the equipment and techniques
described here:

http://www.neon-john.com/Misc/Energy_Audit.htm

Feel free to download and use my spreadsheet.  Bottom line, measuring long term
from
11/04/06 to 04/23/07, my dehumidifier used 2.03 KWH per day or about 15 cents'
worth
of power at our rate.  The watt-hour meter is still connected and come November,
I'll
have a year's worth of data.  I suspect that Nick's gadget will operate in the
same
ballpark of energy consumption.  Meanwhile, my basement is both cool AND
precisely
controlled to 50% humidity.  Me and my fairly large library love it.

There are more efficient dehumidifers available but as I correctly anticipated,
the
savings would take a lifetime to make up the difference in costs of the machines.

John



John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com  <-- best little blog on the net!
Cleveland, Occupied TN
Remember, amateurs made the Ark, professionals made the Titanic.


Posted by on June 20, 2007, 1:48 am
 Are you all distinguishing between an indoor dehumidifier and an A/C?
An indoor dehumidifier provides *net heat* to the space while dehumidifying,
and an A/C cools, while providing the same (I think)dehumidification.

I use both in my shop.
Summer:  A crappy Amana portable A/C, venting out of a hole in the wall,
about 850 watts, and
Winter: a brandX dehumidifier from Sam's/Costco, about 600 watts.
Both produce prodigious amounts of water--the Amana, about 7,000 btu at a
miserable 8.5 EER, cranks out about 5 gals/day, moderately humid weather.

I wonder if a 40 W system could do that.

An indoor dehumidifier is basically window A/C brought inside, and rigged in
such a way that it doesn't freeze up.  I've tried a regular window A/C as an
indoor dehumidifer, and it worked, but froze.
Also, A/C's cycle on temp, dehumidifiers cycle on, well, humidity.  I have a
broke dehumidifier, and I'm thinking of scavenging the humidity sensor and
wiring it to the A/C--if that makes sense.
--
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Posted by carneyke on June 20, 2007, 7:47 am
 On Jun 19, 9:48 pm, "Proctologically Violated"

My dehumidifier does "throw" heat while running. It is in my basement
and there are no windows that would support an AC unit. I believe if I
had to do it again, a window unit would be the best of both worlds. I
would have to modify a casemount window to accomodate an AC unit.


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