My company is working on a study for an existing building and wanted to take a look at performance of the existing equipment. The building is a dual-duct system with (3) cooling-only units serving the cold deck and (3) heating units on the roof serving the hot deck. The interior spaces are served by single-duct VAV boxes while the perimeter spaces are served by dual-duct VAV boxes.
We originally thought of modeling central systems in the tree that have the cooling performance from the cooling only units and heating performance from the heaters, but this doesn’t necessarily account for differences in fan performance. We also thought of copying over identical zones to the heating units, but that would inflate anything calculating off of conditioned floor area.
We’re also looking through the software to see if we would need to have the heating units be their own central systems and tell the perimeter zones (modeled under the cooling units) to get heating from those, but I expect we would run into an error stating that the heating central systems would need their own zones.
I could not find any guides on modeling dual duct systems since they aren’t common anymore – are there any recommendations on how to model this type of system?
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