I am currently modeling a 51,000 sq.ft., two story building. The baseline HVAC system per ASHRAE Appendix G, is a type 5 (PVAV). The baseline model incorporates one PVAV per floor. The proposed building will use four pipe fan coils in each zone and a dedicated OA/ERV system which deliveres conditioned OA to each fan coil.
Ashrae 62.1 requires the total ventilation rate in the baseline system to be increased in order to satisfy the critical zone, as all ventilation air is introduced in the PVAV unit. This adjustment is not requried in the proposed system as the correct amount of OA is ducted directly to each zone.
Tables used for EaP2, Section 1.4 state that the ventilation in the baseline and proposed systems must be same unless we are using Demmand Control Ventilation. The lower ventilation rate in the proposed system is not due to Demmand Control Ventilation, but rather the use of a completely seperate, OA/ERV system supplying the proper ventilation to each space.
How do I present this savings to the reviewrs? Adding ventilation to the proposed system, so that it is equal to the baseline, does not reconize the savings of the design. Decreasing the ventilation in the Baseline model, so it matches the proposed, would be modeling a system that does not meed code, and is therefore unrealistic.
All help is appreciated.
Christopher Schaffner
CEO & FounderThe Green Engineer
LEEDuser Expert
963 thumbs up
January 27, 2011 - 12:09 pm
Even though it "does not meed code, and is therefore unrealistic", I think for LEED, you need to decrease the ventilation rate in the Baseline case, so that the ventilation rates match.
Appendix G is very clear that the ventilation rates must match.