[Equest-users] How to Model Infiltration based on Pressure

[David Reddy]

Steve-

Here is a link to a paper published by PNNL discussing some guidelines 
for converting building leakage rates at a known pressure to energy 
model infiltration inputs.

http://www.pnl.gov/main/publications/external/technical_reports/PNNL-18898.pdf

It is written in the context of EnergyPlus, but eQUEST/DOE-2 includes 
the same infiltration model (AIR-CHANGE -> AIR-CHANGES/HR).  In my 
experience using this guideline, you'll have to do some calculations of 
exterior wall area and perimeter zone floor area to come up with the 
correct infiltration inputs for each SPACE; keyword defaulting can come 
in handy for this task...  Also, this guideline doesn't go into depth on 
how to develop infiltration schedules that reflect the design capacity 
and control of different types of ventilation systems.  Rather from what 
I gleaned, the guideline is simply 1.0 when fans are off, and 0.25 when 
fans are on.  Finally, keep in mind that DOE-2 calculates a local wind 
speed from weather file wind speed and SITE-PARAMETER inputs that 
describe characteristics of both the weather station and the terrain 
local to the building.  These parameters (which I overlooked until 
researching these infiltration models), do have an impact on the 
calculation of hourly SPACE loads, since the local wind speed 
calculation not impacts the wind-dependent infiltration model, but also 
exterior (wall and window) film conductance.

The authors acknowledges that the recommended model addresses only 
"wind-driven" infiltration, so if stack-driven flow is a major component 
in your building, you may want to figure out a way to adjust your 
inputs/schedules to account for this; a combination of AIR-CHANGES/HR 
and the other model input, INF-FLOW/AREA, could be one approach for 
dealing with this.  The DOE-2 Crack model does attempt to account for 
stack driven flow, but this model is sensitive to it's many, 
component-specific inputs, which are often difficult to characterize.

-David

-- 
David Reddy

360 Analytics
Building Energy Analysis Consultants
mail:	12354 16th Ave NE, Seattle, WA 98125
office: 206.420.7918
mobile:	206.406.9856
web:	www.360-Analytics.com



On 4/13/2011 5:39 AM, Steve Burley wrote:
>
> As part of the Estidama, the local ABU Dhabi requirements, we are 
> required to model "building air leakage rates" on 2l/s/m² at 75Pa. Is 
> it possible to model this in equest? The help file would suggest so if 
> AIR-CHANGES/HR is used but this is corrected for wind speed.
>
> Are the corrections held in the P-Inf and C-Inf (perimeter and core 
> infiltration?) schedules or are they calculated during the simulation run?
>
> Any help would be gratefully received.
>
> Regards,
>
> Steve
>
>
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