Potential energy savings - infiltration problem

[stormy013]

Hi,

I started using Green Building Studio with Revit one month ago and I am now trying to lower the energy use intensity of a residential building thanks to the potential energy savings tool.

I managed to improve the wall and roof insulation but meanwhile the losses due to infiltration kept on increasing (150%) and I cannot find a way to decrease them. I have tried to add air barriers and interior gypsum boards to better seal the building but it didn't seem to change anything. Does anybody has a clue about how to lower the infiltration losses?

Thanks a lot for your help!

Camille

[mstein7484]

See the Green Building Studio help pages for details on how to interpret the PES chart.

The size of the bar to the left of the centerline is the potential losses percentage. Losses of 150% due to infiltration merely indicates that this is potentially how much energy your project could lose if it's infiltration is very loose, due to poor construction. For the PES runs this value is set at 3.5 ACH for the low-end. The most energy efficient setting used for the PES run is 0.17 ACH. See GBS Run List page--the names of each PES run indicate the setting for that run.

Currently the constructions in your Revit model do not change the infiltration assumptions used for the energy analysis. You can manually change this setting by editing the gbXML file and upload the edited file directly to GBS.

Regards,

[adam.menter]

Question from Cal Poly students:

Several students are having trouble getting their infiltration numbers under control.  Any ideas on this?  Perhaps increasing the sliver space?  The students are not pro-modelers, so maybe there are modelling errors leading to this.  Any ideas you may have for helping them get infiltration under control would be much appreciated.  What items in the model/analysis settings control this?

ANSWER:

Good question. See Margie's answer above. To be clear: this isn’t something you can control in Revit. It actually has nothing to do with the Revit geometry... it’s a setting added by GBS (values documented here: http://help.autodesk.com/view/BUILDING_PERFORMANCE_ANALYSIS/ENU/?guid=GUID-D4BBD088-0E62-4B37-9CD8-5... ). Per Margie's answer above, infiltration is not even a setting you can control in GBS web.

VALUES SIMULATED:

Infiltration _3.5_ACH - Very loose envelope with 3.5 air changes per hour atwind speed of 10 mph

Infiltration _0.17_ACH - Very tight envelope with 0.17 air changes per hour atwind speed of 10 mph

[adam.menter]

ADDITIONAL DETAILS FROM AUTODESK BPA TEAM:

There’s a reason the infiltration value is not controllable.  Generally it’s not reasonable for an architect to define infiltration, as it’s something that has to do with construction systems and the skills and detailing of the contractor.  We feel it’s more appropriate to give a range always for what might occur due to infiltration, so that the architect knows how important it is and how much attention to pay to detail drawings and specs and construction administration.  

That said, we may need to refine the ranges we run by what constructions are chosen. 

The analysis engine DOES take weather and wind and HVAC operation into account to vary the base infiltration according to conditions.