Our project is an existing 36,000 sf museum with a planned 18,000 sf addition. The existing portion is served by a dual-duct HVAC system with a boiler and chiller plant. The boilers and chillers will be replaced as part of the LEED scope of work, but the airside equipment will remain. The addition will be served by a new multizone system, also connected to the new boiler/chiller plant.
Based on 90.1 and reviewing LEED User, the baseline energy model would include the existing dual-duct system for the existing building and System 3 - PSZ for the addition. But it seems ambiguous how to model the heating and cooling plant serving the dual duct system in the baseline model.
Two strategies have occurred to me:
1. In the baseline, model a central plant that mirrors the proposed plant but with minimum efficiencies and mandatory controlsfrom section 6 only -
2. In the baseline, model a central plant based on Appendix G requirements for boilers and chillers - i.e. two natural draft boilers, one screw chiller, etc
Has anyone dealt with a similar situation or have an opinion about those two approaches?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5869 thumbs up
February 22, 2012 - 11:18 am
None of the above. I would recommend #3 below.
Model the whole building baseline as a system 5 from Table G3.1.1A. Since you are only keeping the airside equipment and not a complete system, I would default to the Appendix G defined baseline. The 90.1-2007 User's Manual indicates that if there is a complete existing HVAC system it should be modeled identically in both models. It does not address a situation where part of the system will be retained. To base the baseline in any other way creates a very awkward hybrid that would be difficult to justify.