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Air infiltration heat losses - Page 4

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Posted by Jeff on December 24, 2007, 4:00 pm
 
nicksanspam@ece.villanova.edu wrote:

   My fault. I thought the "v" was a velocity in mph, but I see that I
misread that.

   Jeff


Posted by daestrom on December 24, 2007, 6:43 pm
 


<snip>

Yes, infiltration/exfiltration can be a significant part of your total
heating losses.  I know I'll sound like a broken record here, but don't
forget the simple weatherstripping, wall-outlets, windows and doors.  And if
you have a conventional attic, take some time and peek around up there.
Especially over bathrooms and ceiling light fixtures.  But if it's like
mine, take a can of 'Great Stuff' and some caulking before you head up
there, you'll be using it.  :-)


Well, I did some calculations off-line using a nice fluid-flow text called
Crane TP-410.  It's takes a bit more work than Nick's ASHRAE formula but can
be a bit more accurate with some things.  Used the ideal gas law for air and
assumed a 20 foot high column for a two-story house to find the different
densities inside/out to come up with the psf.  And for wind pressure used
formula for dynamic head.  To convert from pressure to volume used D'Arcy's
formula.  Have to find the viscosity and density of the air at the
temperature interested (70F is about 0.018 cP).  I *assumed* a round 'pipe'
about 1 ft long reaching up through the ceiling.  Since the leakage probably
isn't one single 'hole' that is circular, the cross-section is not going to
be exact.  But this gives you a pretty good idea how little an area can be a
problem.  (p.s.  If you did have a single hole, you'd notice a pretty nice
draft :-) )


I've been tracking my heating needs versus the NWS calculations for number
of degree-days.  Each year I do some project and then see how the heating
season goes.  By comparing Therm/degree-day, variations due to mild winters
and such are pretty well eliminated.  Over the past seven years, I've
knocked it down from a high of about 0.14 Therm/DD to a low last year of
only 0.045 Therm/DD.  And so far, my wife and family aren't threatening to
mutiny :-) The biggest single year drop was 2005/2006 after doing all the
work I mentioned in the attic (also added about R-19 more insulation up
there while I was at it).

From what I understand, your cellulose insulation in the attic can do a
pretty fair job of settling/ceiling around things to seal off air leakage up
there..  Mine was fiber-glass.  So you may want to concentrate on the
basement (all the way around).

It's sort of a hobby with me, my wife says I should watch more football
instead :-)

Now, if I can just convince her to let me drill a couple of holes in the
upstairs south-facing wall for a solar air heater....

daestrom


Posted by Ralph Doncaster on January 19, 2008, 9:41 pm
 On Dec 24 2007, 2:43 pm, "daestrom"


Congratulations; that's an impressive improvement in energy
efficiency.

I'm looking at ~2.7kWh/DD(Farenheit) for my house (5400sqft of
floorspace, 54,000cf of volume) for my first heating season.

-Ralph

Posted by Ralph Doncaster on January 19, 2008, 8:57 pm
 On Dec 22 2007, 8:53 am, nicksans...@ece.villanova.edu wrote:

I'm going by EC climate data:
http://climate.weatheroffice.ec.gc.ca/climate_normals/results_e.html?Province=ALL&StationName=truro&SearchType=BeginsWith&LocateBy=Province&Proximity%&ProximityFrom=City&StationNumber=&IDType=MSC&CityName=&ParkName=&LatitudeDegrees=&LatitudeMinutes=&LongitudeDegrees=&LongitudeMinutes=&NormalsClass=A&SelNormals=&StnIdd91&&autofwd=1
I'm using a SHGC of 46% for my windows:
http://www.peterkohler.com/index.php?option=com_content&task=view&id 6&ItemidA5
I'm assuming ~600W/m^2 insolation for a south-facing window in January
(from a NRCan paper I read a couple years ago).
I'm also being a bit conservative as in this case I am trying not to
over-estimate solar gains.

-Ralph

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