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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Aaron,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>It is a fact that infiltration or outside
air can dominate the heating loads in buildings with significant internal heat
gains, high mass, insulated shells and/or good or few windows. It is
always a high contributor per CFM in cold weather, and IAQ concerns can mandate
significant quantities of ventilation air. Also, bear in mind that
infiltration is always proportional to wind speed, but it can be reduced significantly
when the building is pressurized with outside air drawn in through air
handlers.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>If you really need to estimate heat losses
due to infiltration, you should apply a method that accounts for the wind
speed. A problem that you might encounter, however, is the somewhat
random nature of this variable in the TMY and TMY2 files. I have found
that very high wind speeds can occur during times of relatively mild
temperatures, and can set the peak heating loads. These wind speeds are
relatively random compared to the dry bulb temperatures in these files because
they were assigned a much lower weight in the statistical selection of the TMY
monthly data. You can check the wind speed whenever the peak heating load
is occurring at a strange time, and just disregard this peak, or you can alter
the wind speeds in the TMY file you are using.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Temperature data in the TMY files are
fairly well behaved because they typically vary much slower than wind speed.
In a truly average season, the heating loads will be strongly correlated to
temperature, but when you introduce high wind speeds with significant infiltration
effects into a model, a few high hourly wind speeds can dominate your heating
loads. This is counter-intuitive, and should not be occurring during an
average weather season (although it can truly occur in any single weather
season). More often than not, we intend to model typical (or even average)
conditions in a building energy and demand simulation. If you do not
somehow adjust (chop the extremes, average over time, etc.) the hourly wind
speeds in the “typical” weather file, you can obtain strange hourly
heating results due to infiltration. My personal preference is to
estimate average wind speeds and average peak speeds, and alter the TMY file to
reflect these averages throughout the typical year. This way, the average
seasonal energy effects of infiltration are not altered, and the peak wind
speeds are kept in place hourly but buffered (to reflect more typical values).
You can do this or something similar using the DOE2 weather utilities and a
spreadsheet.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>This might be more than you asked for, but
I hope it will help you or some other modelers on this list to answer some
questions you may still have regarding the effects of infiltration.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><st1:PersonName w:st="on"><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy'>Glenn
Haynes</span></font></st1:PersonName><font size=2 color=navy face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:navy'>, PE<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Senior Consulting Engineer<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>RLW Analytics, Inc.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>860-346-5001x202<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
bldg-sim@gard.com [mailto:bldg-sim@gard.com] <b><span style='font-weight:bold'>On
Behalf Of </span></b>Dahlstrom, Aaron<br>
<b><span style='font-weight:bold'>Sent:</span></b> Wednesday, January 31, 2007
9:29 PM<br>
<b><span style='font-weight:bold'>To:</span></b> bldg-sim@gard.com<br>
<b><span style='font-weight:bold'>Subject:</span></b> [bldg-sim] how much cold
air infiltration can I really expect?</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I have noticed that infiltration makes up most of the winter
heating load for several high-bay single-story commercial buildings I'm
modeling. (big-box retailer, light manufacturing facility)</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
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<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I've used a variety of methods - ACH estimates, CFM / so of
facade (per ASHRAE F27.10), and Area(crack) x Velocity(winter wind) - to
estimate infiltration.</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Have other people stuck with these methods? Or does anyone
know of better ways to estimate infiltration?</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><em><i><font size=3 face="Bookman Old Style"><span
style='font-size:12.0pt;font-family:"Bookman Old Style"'>Aaron Dahlstrom</span></font></i></em><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=2 face="Century Gothic"><span style='font-size:
10.0pt;font-family:"Century Gothic"'>AKF Engineers, LLP<br>
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Phone: (215) 282-2169<br>
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