Modeling an Exterior Chase

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Is it good modeling practice to model a small chase in a building if it is
on the exterior? Should I simply add it to the space nearby or create its
own space and let it float and push the loads via heat transfer to the
interior spaces? Does adding this little bit of detail make enough
difference? See my attachment for a little view as to what I am talking

Any help would be appreciated!

Rob Hudson

rdh4176's picture
Joined: 2011-02-14
Reputation: 0

I vote "Ignore it". It's a small construction difference in a small portion
of the overall envelope and will not affect your overall results at all,
especially considering the myriad of other assumption you are making.

James V. Dirkes II, P.E., BEMP , LEED AP

James V Dirkes II, PE's picture
Joined: 2011-10-02
Reputation: 203


Tracing the footprint as you have - you are setting up flexibility to
revisit this decision later if you should desire to. You could easily
come back and define an alternate layered construction to apply to the
associated exterior surfaces later if you need to enhance the model's
accuracy ;). I also suspect the net effect is probably negligible.


Nick-Caton's picture
Joined: 2011-09-30
Reputation: 805

Dear Rob,

To me the idea of modeling these spaces as extra zones is a bit overkill, especially looking at their floor area in comparison to the adjacent room. The "detailed" approach you discussed would probably work, but probably doesn't gain you much in accuracy. It is difficult to tell from the drawings provided what the construction of these chases might be, but since they are so thin relative to the room, you might be able to approximate them by creating a special envelope construction with an air gap. You don't need to have a temperature node in your model for the chase, just capture their basic heat conduction properties.

Good luck!

Peter May-Ostendorp, EIT, LEED AP

Peter T. May-Ostendorp's picture
Joined: 2011-11-10
Reputation: 0