I have put together an eQuest model for a LEED project where there is no cooling installed for the proposed design. This spurred the following GBCI reviewer comment:
According to the primary HVAC system input and Table 1.4, no cooling has been provided for in the Baseline or Proposed buildings; However, cooling equipment should be modeled in both cases if the spaces are considered conditioned per the definition in Section 3 (page 13) of ASHRAE 90.1?2004. Please refer to the definition of conditioned space, semi?heated space, and unconditioned space in Section 3. If the heating output capacity is greater than or equal to 15 Btu/h?sq. ft. then the space is considered conditioned so cooling should be included in the Baseline and Proposed Case models. The cooling should be modeled using the Baseline cooling system type (system type # 3)in both the Baseline and Proposed Case models, using identical cooling capacity ratios and efficiencies in the Baseline and Proposed Case. If the heating output capacity is less than 15 Btu/h*sq. ft., then the space is considered semi?heated or unconditioned, so only heating equipment should be included in the Proposed and Baseline models; the heating type, capacity ratios, fan volume, and fan power for these spaces should be modeled identically between the Baseline and Proposed Case. Please revise the Proposed model and Baseline model as needed so the correct system type is modeled in all spaces. Please also indicate the total heating capacity and building area for semi-conditioned spaces to verify that they qualify as semi-conditioned spaces. In addition, please update Table 1.2 and Table 1.4 as needed reflecting the changes.
I have read and re-read the ASHRAE section referenced with regards to the definitions of a space and what would make a building required to be modeled with cooling but I am not seeing what the reviewer is seeing. Any help or insight would be appreciated.
A little background of the building: non-traditional school building with no summer use. Proposed design uses radiant floor heating. Climate zone 6B. Heating output for the different zones within the building is between 15-20 Btu/h*sq.ft.
I do not get into modeling very often, but I have found this forum to be an extremely valuable resource. Hopefully I will be able to contribute something for someone else in the future.
Thanks
Travis Miller
Basically, if the space is provided with heating, of a capacity greater than
15 btu/h-sq ft, then it is a conditioned space. Appendix G requires that
all conditioned spaces be provided with heating and cooling for modeling
purposes.
In the past, when I have a building that is not occupied during the summer,
I have done the following:
In the proposed design model:
1. model the heating plant as designed
2. model a cooling system equal to the baseline cooling system
In the baseline model:
model the building with heating and cooling, determining the baseline system
following the usual method
IN BOTH MODELS:
create a thermostat schedule where, the cooling setpoint is set-back during
unoccupied hours. Usually, I set the thermostat back to 90F +/-. If your
building truly doesn't need cooling, the cooling plant will never come on.
--
Karen
2010/12/29 Travis Miller
Note ? the upper limit of the semi-heated definition varies by climate zone. It appears the reviewer cited the wrong value, but pointed you in the right direction to look. Table 3.1 in ASHRAE 90.1-2004 lists the upper limit for semi-heated conditions by climate zone. For Zone 6B a semi-heated space would be one that has a system with a maximum heating output between 3.4 btuh/sf and 20 btuh/sf. The italics are my emphasis ? I?m sure there is a difference of opinion on the email lists here, but in my experience the reviewers interpret the values to be the maximum rated capacity of the system, not the design output. They don?t want to reward a system that can be operated as if the space were conditioned by considering the system to be serving a semi-heated space, only to have the occupants later jack the thermostats back up and result in real energy use exceeding the 20 btuh/sf (in your specific case).
In your response you need to show you?ve done the analysis for the spaces you consider semi-heated and that the space calculates out as a semi-heated space and not a conditioned space. Otherwise, you need to design in a cooling system that meets the requirements of Appendix G, but you are allowed to set the thermostat to 100F so that the system never turns on in either the baseline or design model.
Jeremy R. Poling, PE, LEED AP+BDC
Hi All,
If a building has an overall area greater than 25,000 sq ft, but has
distinct wings each less than 25,000 sq ft and each has independent HVAC
systems, would one use System 6 (overall) or use System 4 (based on each
wing) to determine baseline type?
Thanks,
Jeffrey G Ross-Bain, PE, LEED, BEMP