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I presume that in doing so (eliminating the plenums) the consumption for both the baseline and proposed cases will be noticeably higher since you will have to make the conditioned zone volume larger to account for the exterior wall area contained in those plenums. (Exterior wall area and Window-to-Wall Ratio are defined to the bottom of roof deck not top of ceiling.) This could be a drastic change depending on how deep those plenums are, especially when dealing in terms of a simulation platform that treats a zone as uniformly conditioned (the zone volume is a uniform air temperature).

The increased consumption comes from this additional volume, but also comes from increased ventilation if one is not careful to specify the OA rate per zone based on what IEQp1 is saying. Again this is a comparison of modeling net vs. gross. I've seen GBCI call out modelers when the OA varies too much (too big and too small) from that scheduled on the MEP sheets and IEQp1.

I'm sure there are other considerations I am missing, but those are the big things off the top of my head that a reviewer will likely catch and would impact the accuracy of the model compared to one with plenums added. In my opinion, the issues above are the likely reason that most programs explicitly have plenums as a modeling feature.

Hope this helps some,

Nic

I presume that in doing so (eliminating the plenums) the consumption for both the baseline and proposed cases will be noticeably higher since you will have to make the conditioned zone volume larger to account for the exterior wall area contained in those plenums. (Exterior wall area and Window-to-Wall Ratio are defined to the bottom of roof deck not top of ceiling.) This could be a drastic change depending on how deep those plenums are, especially when dealing in terms of a simulation platform that treats a zone as uniformly conditioned (the zone volume is a uniform air temperature).

The increased consumption comes from this additional volume, but also comes from increased ventilation if one is not careful to specify the OA rate per zone based on what IEQp1 is saying. Again this is a comparison of modeling net vs. gross. I've seen GBCI call out modelers when the OA varies too much (too big and too small) from that scheduled on the MEP sheets and IEQp1.

I'm sure there are other considerations I am missing, but those are the big things off the top of my head that a reviewer will likely catch and would impact the accuracy of the model compared to one with plenums added. In my opinion, the issues above are the likely reason that most programs explicitly have plenums as a modeling feature.

Hope this helps some,

Nic