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Condensation problem - Page 2

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Posted by nicksanspam on August 5, 2006, 10:43 am

Airseal it well, and use a small AC or ventilate it when the outdoor
vapor pressure is less than the indoor vapor pressure.


Posted by News on August 5, 2006, 7:01 pm

I would go along with that. The problem in Hong Kong was that venting it
meant the place was kept hot. You could experiment and have a variable speed
fan and see what the optimum speed was as you don't want to bring in too
much hot outside air. Just a little may be good enough.  This takes time to
determine, as it varies with usage.  More people and more inside humidity.
Many just slammed cheap Japanese a/c window units in. One in the house with
all the doors open in the rooms seemed to do the job. This was a concrete
building with high thermal mass too.

In a superinsulated house I would try and get it incorporated into a heat
recovery and vent unit, using proper controls.  In sort only bring in this
energy sucking a/c unit when conditions dictate it need be - high humidity.

Posted by nicksanspam on August 5, 2006, 8:42 pm
Then again, New York and Hong Kong are different :-)

A fixed speed works fine. In summertime, we want to bring in COOL dry air
if possible.


Posted by Greg on August 7, 2006, 6:29 pm
 There are 3 choices for cold slab condensation problems.  Dehumidify,
heat the slab or air movement.

Dehumidification will lower the dew point and pump heat into the space
taking the air mass near the cooler slab even further away from dew
point.  This is the easiest solution because it is a simple plug and
play solution.

A longer term solution is to run hydronic in floor tubing on the
existing floor and build a floor over the tubing.  With a solar home, a
small pump and a trickle of hot water will keep the floor well above
dew point.  The top floor will need some venting to allow moisture that
seeps up through the slab to evaporate.  This solution has the higher
capital cost but lowest energy cost in the long term.  You probably
only have to raise the air temperature in the space between the floors
to 75 F to eliminate the condensing on the slab.  You will also lose
about 3 inches of head clearance.

Fans blowing from the top of the room where the warmer air is down at
the slab will heat the floor (hopefully) above dew point.  Warmer air
can be ducted from uninsulated attic or other uncomfortably warm hot
spot in the house.  Again, you are shooting for a slab temp around 75

All of your pipes need to be insulated.  1/2" of closed cell insulation
is sufficient.  If you don't go with the dehumidifier route, your
toilet tank and bowl will sweat with every flush..  entering water
temps from wells or the water system will be below dew point.  Have a
plumber mix hot and cold water for about 75 F toilet water or, make
sure the flooring around the john is perfectly water proof and wash
area down once a weak with a mild bleach water solution.

nicksanspam@ece.villanova.edu wrote:

Posted by nicksanspam on August 7, 2006, 7:20 pm

Or put a $5 aquarium heater in the tank.


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