Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
Here in Vermont, the commercial building code calls for a maximum infiltration of 0.3CFM/ft2@75 Pa. Since this is a code requirement, new buildings should be getting blower door tested to ensure compliance and, in VT, they do. We have found the the quality of building here is very good and we easily meet the code minimum. Architects often call for target infiltrations to be significantly better than 0.3CFM75. I'm working on a project now where the target infiltration is 0.1CFM75. Since you are an architect, I would ensure that the building envelope assembly details drive tight buildings. Then, I would specify target infiltration levels that match recent completed building blower door test results. I use DesignBuilder and use scheduled natural ventilation. This means that the infiltration rate is fixed at the level I input. I input with units of CFM/ft2@50Pa (so I need to convert from 75Pa). Design builder then converts this to typical air pressure differentials (I think 4 Pa is used).
So how do you determine your infiltration rate in EnergyPlus? Is it with a baseline, with a code/certification target, or with historical data from past projects? If the architect doesn't have a target and defaults to me, I often use historical data from past projects, or just an assumption that the new design will be 10%, 20%... better than code maximum. I would ask you favorite MEP firm or mechanical contractor for some of their latest blower door test results from new projects.
