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NC-2009 EAp2:Minimum Energy Performance

Modeling HVAC System #8: VAV with PFP boxes

Dear Forum, We are modeling a high rise building in order to comply with EAp2 minimum energy performance. The corresponding HVAC system for the baseline design is system #8, VAV with PFP Boxes. Section G3.1.1 of Appendix G of ASHRAE 90.1 2007 states: For systems 5, 6, 7, and 8, each floor shall be modeled with a separate HVAC system. Floors with identical thermal blocks can be grouped for modeling purposes. So, according to this section, I have to model a VAV system with PFP boxes for each floor (it would have its own chiller, cooling tower, pump and its corresponding air loop). For the project I modeling, this means a lot of work, since we have 23 floors! The floors are not identical in size but have the same thermal zone configuration. Is it acceptable to group them all together? Many thanks in advance

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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
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Tue, 10/22/2013 - 21:47

Your assumption is not quite correct. You model a central chilled water plant for the whole building including towers, pumps, etc.. You model a system per floor (air handling, chilled water coils, electric heat, etc.). So one central plant with 23 systems (unless you can justify lumping some systems together).

Tue, 10/22/2013 - 22:04

Thank you Marcus I got it clear now. In my opinion section G3.1.1 should be explained in more detail because when it says: each floor shall be modeled with a separate HVAC system, it is not clear that it should exclude the central plant. Regards, Santiago

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