I am working on an archive library that requires 50F and 35% RH indoor space conditions. The HVAC system in the proposed design is quite complex to maintain these conditions and includes a regenerative desiccant wheel, gas furnace to obtain high temperatures for the wheel, cold chilled water temperatures (36F), etc. This system is designed to deliver 25F dewpoint.
Appendix G defines the baseline system as System 5, but I may be able to apply an exception to use System 3. The proposed design is not part of a district energy system so the cooling type is DX. Appendix G states that space temperature and humidity conditions shall be consistent across the proposed and baseline designs. My question is what efficiency do I use for the baseline HVAC system? No systems in Table 6.8.1 of 90.1-2007 seem to apply. I understand that the baseline systems usually do not make "realistic sense", but if I am to use minimum efficiency requirements in Table 6.8.1 then there is no hope for energy savings.
Your advice and experience are much appreciated!
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5899 thumbs up
February 28, 2012 - 7:02 pm
For a Baseline system 5 you use the air cooled air conditioners in Table 6.8.1A. The air conditioning system in the Proposed is not relevant to the Baseline system selection.
Evelyn Dicks, EI, CxA
Mechanical EngineerMoses and Associates
83 thumbs up
February 29, 2012 - 9:19 am
Marcus, what about CRAC units? These typically have lower efficiencies than the minimum efficiency requriements of Table 6.8.1 because of their duty served. I know there have been posts about this in NC and other rating systems, but I don't think a consensus was made.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5899 thumbs up
March 1, 2012 - 8:12 am
All HVAC equipment used for conditioning spaces must meet the minimum efficiency requirements of Table 6.8.1A - 6.8.1J.