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nightime cooling

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Posted by j on March 16, 2012, 3:26 am
 
  I can reroute my central solar collector to blow in air from a shady
and cool part of the yard into the house. This would be distributed
through the heating vents. So, blowing cool pre morning air instead of
what a whole house fan does: sucking it out into the attic from open
windows.

   That would seem to be useful cooling, at least for some days.
However, morning air has a high relative humidity and since comfort is
related to both temperature and humidity that would argue against
changing out air that has been air conditioned (lower humidity).

   Is it worth the effort?

Jeff

Posted by Rod Speed on March 16, 2012, 6:36 am
 
j wrote:


to both temperature and humidity that

Really depends on how cool that air is.

My gut feeling is that it wouldnt be worth doing but when
you dont supply the actual figures for temperature and
humidity, its hard to so for sure.



Posted by Jim Wilkins on March 16, 2012, 11:38 am
 

I've been venting the house when the outdoor air comfort factor is
better than the indoor one. Here in New England the range where I need
to figure in the humidity is outdoor temperatures around 65-70F and
humidity over 70%.

I take around 3% of humidity as equal to 1 degree F, so 75F and 70%
humidity inside is equivalent to 70F and 85% outside, by adding 1/3 of
the humidity difference to the lower temperature.
http://en.wikipedia.org/wiki/Heat_index
http://en.wikipedia.org/wiki/Humidex

The sensing could be automated, but opening and closing my tightly
sealed windows and attic hatch will likely remain a manual operation,
so I just read the instruments and do the mental math.

This is the actual water content of air vs temperature:
http://en.wikipedia.org/wiki/File:Relative_Humidity.png
The relationship is non-linear and barometric pressure affects the RH,
but for the restricted temperature range where the decision to vent
isn't obvious my linear relationship seems adequate.

jsw



Posted by j on March 16, 2012, 12:24 pm
 On 3/16/2012 7:38 AM, Jim Wilkins wrote:

It's tough to open and close windows automatically!

I've just started looking into the Arduino:

http://arduino.cc/playground/

Humidity/temp sensors are readily available. As is wifi. It would seem
doable to vent the house with consideration for what the weather will be
like later in the day. Ie, no reason to cool the house when it will be a
cold day.

   Thanks for the rough guidelines for heat index, they would seem to
suffice. I'll set up a full manual operation and dream about the
automation until I find time!

We are into May/June weather here (80's), so it has me thinking...

   Jeff



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