[Equest-users] Airflow

Nick Caton ncaton at smithboucher.com
Tue Jun 29 09:24:36 PDT 2010

Hi Katie,


I'm no expert, but unless otherwise noted,  I assume CFM's in eQuest are
not entered at 50 pascals, but are simply airflow rates without a
reference pressure.


There are a few methods (5) to calculate hourly infiltration at the
space level, and each uses different inputs to determine the hourly
infiltration rate.  I am used to using the Air Change method, which
expects ACH inputs to be given at a 10mph windspeed (~13Pa).  eQuest
then varies this figure hourly considering the hourly temperature
differential and exterior wind speed (and I *think* surface height and
orientation)...  There's much, much more to read if you'll right-click
the infiltration method field for any space in detailed mode, so I'd
suggest perusing there if you haven't yet.


I'm browsing lightly through ASHRAE Fundamentals Ch. 27 (2005), there's
a lot here regarding infiltration model means/methods, but too much for
me to digest in a short period... so you might want to read further
there also.


Ultimately, if the goal is to take some CFM50 readings and get them into
your model, you may either find or make up some kind of conversion
factor that will account for the lowering effective leakage area from 50
down to 13 pascals 

(or some other reference pressure corresponding to another of the calc
methods that you like)... 

I'll be curious to hear your findings - please do share!








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From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Katie
Sent: Tuesday, June 29, 2010 10:35 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Airflow




I have two questions


1) For the air infiltration (both the building envelope and air flow
sections), does EQuest require CFM50 or CFM measurements?


2) Does anyone have any academic articles about how to convert from CFM
to CFM50?  I've found information on the LBL infiltration model (CFM =
CFM50/N, where N is the leakage-infiltration ratio) derived by M.
Sherman.  However, I can't find articles explaining the K-P model
derived by Kronval and Persily that just simply divides the annual
infiltration rate by 20. 


Thanks so much!


Katie MacKenzie
Smith College, Engineering 2011
Cell: 503.730.6354
E-mail: kmacken2 at smith.edu
Website: www.ktmackenzie.com

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