[Greenbuilding] Night Flushing Humidity Issues

elitalking elitalking at rockbridge.net
Fri May 4 11:30:38 CDT 2012


 

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.  

 

We are coming into the hot time of year again.  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.  We close the house off during the daytime to block out air delivered heat.  Last year after only the  ceilings were complete, we hit our record high of 103F with house at 79F without ac.  As part of the Thermal improvement project, I have installed an HRV.  We run the HRV during the day to deliver fresh air when windows are closed to block heat out.  The peak temperature outdoor air has much lower relative humidity than indoor air from night flushing.  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.  

 

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.  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.  

 

The outdoor air, even when entering with a high relative humidity is being warmed up by the warmer house, reducing the relative humidity.  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 redily dry up allowing more contagons.  Is this health risk mitigated by fresh air delivered by HRV?  The higher humidity reduces the evaporative cooling of our body at a given temperature.  However, the lower temperature is definitely more comfortable than the hot outdoor air.  

 

I know I am much more comfortable with the strategy of night flushing than I would be with leaving windows open all the time.  The greatest discomfort comes on the rare occasion where the outdoor temperature does not get down to 70F.  This greatly reduces the cooling of the house at night.  When this happens, I use a direct fan to keep my body comfortable. 

 

Insights on the impacts of high humidity in the house will be appreciated.  

 

Eli  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/greenbuilding_lists.bioenergylists.org/attachments/20120504/52864171/attachment.html>


More information about the Greenbuilding mailing list