[BLDG-SIM] Infiltration: Standard versus Proposed Design

Varkie Thomas Varkie.Thomas at som.com
Wed May 19 07:33:57 PDT 2004


Can infiltration be considered in comparing standard versus proposed
design models using the ECB method and for LEED credits under "Optimize
Energy Performance"?  Typically we use the same criteria in both models,
but this is a particular case of a proposed double-wall building.
"10CFR435 Table 402.2.1. - Air Leakage for Fenestration & Doors Maximum
Allowable Infiltration Rate" provides standard model information for
federal buildings.  For example, the infiltration rate is 0.15 cfm/ft2
for fixed aluminum windows.  Can this be used for LEED standard design
and can a lower rate be used for double wall buildings?

 

The CFR table does not account for Heating & Cooling Degree Days as with
Table-B Building Envelope Requirements of STD90.  In my opinion, the
peak design infiltration rate should be varied from maximum in winter to
minimum in summer (typically zero for pressurized buildings) using a
schedule.  The maximum, of say 0.15 cfm/ft2, would apply to a cold
climate such as Chicago and it should be scaled down for warmer
climates.  Since DOE2 does not allow infiltration rates on the basis of
cfm/ft2 of wall or window area or cfm per lineal foot of window
perimeter, we create a typical perimeter space and convert the window
based infiltration rate to cfm/ft2 of space area or space air changes.
We then look at the results in "REPORT- LS-C BUILDING PEAK LOAD
COMPONENTS" of the DOE2 output to see if the infiltration load looks
reasonable (relative to the other loads) for the location and type of
building and make adjustments by trial and error.  Judgment and
experience is considered more reliable than theoretical mathematical
models.  The BEPS and BEPU reports in DOE2 should separate out the
infiltration loads from the heating & cooling loads.  Any comments?

 

Thanks for the comments and suggestions to using different utilities in
standard versus proposed design.  They were very helpful in making some
decisions here.  Most of the responses seem to go directly to the person
asking the question.

 

Varkie Thomas

Skidmore, Owings & Merrill LLP

 

 

 



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