I'm not sure of the Baseline envelope and HVAC system to use in hospital patient rooms. For one, Section 3.2 defines "residential" as including patient rooms in hospitals. If you believe this, then do you have to model patient rooms in your Baseline model with Residential envelope as defined in Table 5.5-x? This would require one type of Baseline envelope for patient rooms, and another type for non-patient rooms.
And do you have to model the Baseline HVAC systems for patient room thermal blocks using a residential system, such as System 1 or 2 in Table G3.1.1A? The footnotes to Table G3.1.1A do not refer to patient rooms as "residential," but Section 3.2 does. Also, while exception 'a' of G3.1.1 prescribes different Baseline systems for Residential areas (System Type #1 or #2), exception 'c' prescribes that System Type #3 or #4 be used for areas with code-required minimum circulation rates, which pertains to patient rooms as well.
If you believe that it is appropriate for the Baseline to have a Residential HVAC System type, it appears that the Proposed model will be unfairly penalized since G3.1.2.9 does not allow for a Pressure Drop Adjustment 'A' for System Type #1 or #2.
I would appreciate your input and experience as to the appropriate Baseline envelope and HVAC systems to use for patient rooms in hospitals.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
November 30, 2011 - 3:56 pm
Our interpretation would be to follow the residential column for the patient rooms in Table 5.5-x.
Since the note under Table G3.1.1A does not include hospitals in the list of residential facilities, the HVAC should not be #1 or #2 unless any of the exceptions under G3.1.1 apply. Sounds like you might have the option to use either exception "a" or "c" assuming you meet all the requirements. Our interpretation is that would be your choice.
Mark Benson
72 thumbs up
November 30, 2011 - 10:03 pm
Speaking of Baseline systems in hospitals: I find it interesting that the 'NREL Technical Support Document: 50% Energy Savings Design in Large Hospital Buildings' uses Multi-zone, constant volume, terminal reheat systems as a Baseline, while LEED for Healthcare prescribes that the Baseline be modeled as multiple Single-Zone systems (i.e. System Type #3 or #4).
Hope somebody fixes this before the TSD gets turned into an AEDG...
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
December 1, 2011 - 9:04 am
The prescriptive path in LEED 2009 for Healthcare (November 2011) references the Green Guide for Healthcare V2.2 and describes the HVAC system as follows: "The HVAC system serving all areas shall include Variable Air Volume (VAV) air handling units supplied by a central chilled water and boiler plant." This is a System #7. Maybe I am missing something?
Mark Benson
72 thumbs up
December 1, 2011 - 12:35 pm
Maybe it was my use of the word "prescribes."
You're correct about the prescriptive path in Option 3, Marcus, but I was referring to the Whole-Building Energy Simulation in Option 1, which requires that the Proposed design be compared to a Baseline simulation that uses HVAC system type 3 or 4. I was suggesting that the Baseline in LEED for Healthcare is different than the Baseline used in the AEDG.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
December 1, 2011 - 1:48 pm
Under Option 1 the HVAC system in the baseline is determined by 90.1-2007 Table G3.1.1A and will vary depending upon heating fuel and building size. Perhaps in your specific situation the Baseline is a system 3 or 4 but most hospitals are over 25,000 sf and the baseline would not be either of those system types.
I agree that the baselines can be different. The AEDG was based on a whole series of modeling assumptions so they had to pick a single baseline HVAC system. Under Option 1 the baseline varies depending upon your building design. So the two will not match in many cases. This is one of the differences between a prescriptive approach and a performance approach.