I have reviewed the list archives on this issue and found some conflicting opinions for residential buildings. To give some background, I am working on a model for a large adaptive reuse project that includes the conversion of a warehouse building to residential apartments. The proposed design includes split system heat pumps in the units (Electric Heat) and several RTUs (fossil fuel heat) serving as DOASs w/ energy recovery conditioning the corridor spaces and supplying/exhausting air from the residential apartment spaces. The corridor spaces exceed 25,000 square feet and 5 floors. I have the proposed design squared away, but I was hoping for an endorsement of my approach to the baseline before reconfiguring almost everything under my air-side HVAC tab.

For the baseline systems my strict reading of Table G3.1.1A along with the exceptions under G3.1.1 would indicate that for my baseline design I would do the following:

-Apartment spaces: System 2 PTHP.
-Corridor spaces: System 7 VAV w/ Reheat.

I am hesitant to plunge forward, as System 7 seems an unrealistic baseline for this application. I am also a bit confused as to how I should model the outside air delivery in my baseline. I believe I should deliver outside air via the central systems as I did in the proposed design rather than directly at the PTHP in each unit. Since the building is in Climate Zone 3A, I would not include an economizer, but I might have to include exhaust air heat recovery for cooling if the design supply air capacity for these systems exceeds 5,000 CFM, per G3.1.2.10. Am I interpreting that correctly?

To top it off, there was also a school of thought within the archives that one should model the whole baseline building with System 2 for this situation. It would certainly be less complicated, but create issues around fuel use type and fan power.

Any feedback is much appreciated.

Robert Stephenson