My question is regarding how the proposed hvac system should be modeled when the C&S design includes a DOAS w/a DX CC and gas HC which is capped at the shafts, therefore there are no ductwork branches or terminals. A plant has been designed with CHW and HHW capped at each floor as well (obviously for serving terminals and not the DOAS). My understanding is that the proposed model must match the baseline for the parts that are not yet designed. Therefore if the baseline is system 5/7 is it true that the proposed DOAS must be modeled with VAV terminals? The DOAS would not meet the space loads of the shell space using only VAV terminals with the design capacity and airflow rates since it has been designed to be used with chilled beams and fptu/fcu terminals (hence the CHW and HHW taps). Can I model the shell space with FCUs since the design clearly requires a terminal unit with CHW and HHW? Would I need some sort of document from the owner that states the shell spaces must be designed with terminals of a certain type to avoid modeling VAV terminals in the proposed? If I can't get this document, will the leed reviewer accept a submission with a bunch of unmet load hours because the modeling guidance has required the proposed to be modeled in that manner?
Furthermore the first two floors will be occupied by the building owner and the fit out has been designed by my AE firm, therefore I have access to permit drawings for those spaces, but no TSLA since the owner is the occupant. Can I model the first two floors with the spaces zoned and served by chilled beams and FPTUs as designed in the fit out documents (which clearly demonstrate the design intent of the DOAS and plant)?
Tyler Thumma
7GroupLEEDuser Expert
67 thumbs up
February 17, 2022 - 10:43 am
For the shelled floors, the most straightforward option would be to model the DOAS as-designed, supplying OA to a System 5/7 per floor. In order to reduce the potential fan energy penalty, you could consider the DOAS fan power as part of the Baseline fan power allowance and therefore subtract it from the System 5/7 fan power.
The other option would be to use a TSLA requiring a specific kind of terminal unit, but the TSLA would need to be signed by the owner and tenant(s). Any parameters for the terminal units which were not specifically defined by the TSLA (such as specific fan power, fan speed, minimum airflows, etc.) would revert to the Baseline requirements.
In no case would a LEED reviewer accept a model with greater than 300 unmet load hours.
As for the floors with owner fit-out, these could be modeled based on the permit drawings. This would be a similar situation to the one allowed by LEED Interpretation 10129.