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<DIV><FONT face=Courier>"elitalking" <elitalking@rockbridge.net>
writes:<BR><BR>> I feel fortunate to live in a location where during the
summer, the night time cools about 30F from the highs. I have made a
commitment to live without air conditioning here in the mountains of
Virginia. I have incrementally been upgrading the tightness of my house,
having installed new continuous thermal barriers of 3" iso foam over most but
not all of the exteriors walls and below cathedral ceiling. Piece by
piece, I am covering all the holes that remain. <BR><BR>Have you
done a blower door test?<BR><BR>> We have been in the practice of
opening windows at night and aggressively changing the air in the house with
window fans to cool the mass inside the house. Most days, we can get the
house to below 70F.<BR><BR>NREL says July is the warmest and most humid month in
Sterling, VA... 1910 Btu/ft^2 of sun falls on the ground and 1040 falls on a
south wall on an average 75.6 F day with a 64.1 low and a 0.0136 humidity
ratio... 580 falls on the ground and 950 falls on a south wall on an average
35.4 F December day with a 45.0 high. You might dehumidify with an
equilateral A-frame on the lawn full of solar-regenerated clumping
kitty litter in summertime and solar-heated water in wintertime. The deep ground
temp is 53.8. Earth tubes could cool on humid nights. </FONT></DIV><FONT
face="Courier New"></FONT><FONT face=Courier>
<DIV><BR>> We close the house off during the daytime to block out air
delivered heat.</DIV>
<DIV> </DIV>
<DIV>Do you ventilate every night by the clock, or only when outdoor air is
cooler than indoor air, using a differential thermostat or passive plastic film
dampers?</DIV>
<DIV> </DIV>
<DIV>>I have installed an HRV. We run the HRV during the day to deliver
fresh air when windows are closed to block heat out. <BR><BR>Do you need to do
that, or is the house natural air leakage sufficient for fresh air? You might
only run the HRV when the house CO2 level is above 1000 ppm. <BR><BR>> The
peak temperature outdoor air has much lower relative humidity than indoor air
from night flushing.<BR><BR>How about the absolute humidity, ie the humidity
ratio in pounds of water per pound of dry air?<BR><BR>> I can observe
the condensate drain. Under normal fair weather days, there is negligible
if any condensation. My hunch is that the interior and exterior absolute
humidity is about the same, so cooling the outdoor air closer to the indoor
night flushed temperature never reaches dew point. <BR><BR>If you can cool
the outdoor air all the way to the indoor air temp with no condensation, the
outdoor air may have lower absolute humidity. You might add a sensor to the
condensate drain and only enable night ventilation if there is no condensation.
Or use a smart ventilation controller that only night-flushes when outdoor air
is more comfortable in an ASHRAE-55 comfort calculation or when it has less
absolute humidity. IIRC, the ASHRAE comfort zone has an upper right corner at 80
F and w = 0.0120, at 66% RH.<BR><BR>> However, night flushing does result in
high humidity in the house. I have now been observing humidity for the
past year more closely. The result of night flushing is to seasonally
build up humidity in the house. This time of year, the house has some
residual dryness from the heating season. I think the material of the
house is a humidity flywheel as well as a thermal flywheel. <BR><BR>In an
airtight house, hygroscopic materials can beneficially store dryness, with
the house closed up on humid nights. Like thermal mass for solar heat storage.
You might fill up your house with books and papers and clothing... <A
title="http://www.ornl.gov/sci/buildings/2010/Session%20PDFs/129_New.pdf
CTRL + Click to follow link"
href="http://www.ornl.gov/sci/buildings/2010/Session%20PDFs/129_New.pdf">http://www.ornl.gov/sci/buildings/2010/Session%20PDFs/129_New.pdf</A> Tim
Padfield has lots of humidity insights... <A
title="http://www.conservationphysics.org/
CTRL + Click to follow link"
href="http://www.conservationphysics.org/">http://www.conservationphysics.org/</A> <A
title="http://www.conservationphysics.org/isothrm/isothrm.php
CTRL + Click to follow link"
href="http://www.conservationphysics.org/isothrm/isothrm.php">http://www.conservationphysics.org/isothrm/isothrm.php</A><BR><BR>>
However, this material is gradually wetted with increasingly high indoor
humidity. Late summer, wood work swells and there is some mold. This
goes away when it dries out again as heating begins in the fall.
<BR><BR>Sounds like your house can store dryness well. You might add
humidity to your night ventilation decision criteria.</DIV>
<DIV><BR>>However, late summer the house can be in 70% range. This
slows down the rate of drying for anything in the house. How much is our
health at risk? I presume there is some dust that becomes air born from
mold. I learned from this list that floating pathogens do not readily dry
up allowing more contagions.</DIV>
<DIV> </DIV>
<DIV>You might enjoy a 2-watt 7KV DC electrostatic media filter, eg
http://www.nsaw.com/enviro2.htm "After only twenty minutes, the equivalent of
two air exchanges, "EnviroSept" removed over 45% of particles in the 0.09 to 0.5
micron range and over 77% of the particles in the 0.5 to 1.0 micron range."
<BR><BR>http://www.engineeringtoolbox.com/particle-sizes-d_934.html
gives:<BR> <BR>Dust
Mites
100 - 300<BR>Mold
Spores
10 -
30<BR>Mold
3 - 12<BR>Spider
web
2 -
3<BR>Spores
3 - 40<BR>Talcum
Dust
0.7 -
90<BR>Clay
0.1 - 50<BR>Copier
Toner
0.5 - 15<BR>Liquid
Droplets
0.5 -
5<BR>Anthrax
1 - 5<BR>Yeast
Cells
1 - 50<BR>Atmospheric
Dust
0.001 -
40<BR>Bacteria
0.3 - 60<BR>Radioactive
Fallout 0.1 -
10<BR>Smoke from Natural Materials 0.01 - 0.1<BR>Burning
Wood
0.2 - 3<BR>Tobacco
Smoke
0.01 -
4<BR>Viruses
0.005 - 0.3<BR>Typical Atmospheric Dust 0.001 to
30<BR><BR>Nick</DIV></FONT></BODY></HTML>