I seem to recall that, when fans are cycled during unoccupied periods per G3.1.2.4, ventilation should be zero - at least in the baseline. I have done this before in eQUEST by setting a MIN-AIR-SCH to zero during unoccupied hours. I can't find any reference to this requirement in Appendix G. However, in the mandatory provisions section 6.4.3.4.3 Shutoff Damper Controls, "Ventilation outdoor air dampers shall be capable of automatically shutting off during preoccupancy building warm-up, cool down, and setback..." (There are exceptions I'm not listing.) Is the general rule that Appendix G and/or LEED models have zero ventilation during unoccupied periods?
Thanks,
Bill
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Bill - an excellent question, one I haven't looking into too much before...
Here's a little logic, though:
1. All LEED buildings are required to meet Section 6.4 in its entirety. (per the pre-requisite language)
2. The ventilation rates are required to be identical between the proposed and baseline per G3.1.2.5
3. If there is a reason why the proposed building would need ventilation during unoccupied hours, both the proposed and the baseline shall have ventilation during those hours per G3.1.2.4
I think that's enough logic to make the case for what you've proposed. Thoughts?
Aaron
Aaron Dahlstrom , PE, LEED(r) AP
Thanks for the reply Aaron. I think Section 6.4 strongly implies, if not requires, Appendix G/LEED models to have zero ventilation during unoccupied hours, per your (our) logic. My particular case is a dormitory with proposed system of DOAS w/zonal induction units. I will verify the anticipated system fan schedule (which might be 24/7 when class is in session) but if there is any unoccupied fan cycling, the proposed design will be 100% OA and it might not meet any of the ASHRAE 90.1 exceptions. I could keep the baseline PTACs with the same ventilation rate during unoccupied hours but the actual cumulative ventilation rate will then vary with the number of hours of fan cycling, which will vary between the baseline and proposed cases due to envelope differences. Therefore, the G3.1.2.5 requirement cannot really be met (which is another reason to argue for no ventilation during fan cycling).
Bill
Concur!
Induction units for school occupancies can be tricky for that reason (fan power, ventilation during unocc periods).
I've seen a design where the zonal induction units have four-pipe coils, and the heating coil can be used for convective non-fan local heat during unoccupied hours. Cooling/humidity control is a different matter, and having a return on your DOAS might be useful for those hours. (To meet 6.4.3.4.3, while keeping the building under control...)
Of course, like you said, the dormitory unoccupied hours might be pretty minimal ... so the actual energy cost save from these dampers might be minimal. Wonder if the AHJ would accept a variance from 6.4 if the overall system still beats the ECB baseline?
Aaron Dahlstrom , PE, LEED(r) AP