# ASHRAE 90.1-2007 Exception G3.1.1 (a)

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A CIR I found for a residential project refers to the Exception G3.1.1(a) applied in a Business Hotel Building, the CIR is very clear in the application of the exception but there is a paragraph that I fund confusing when calculation the area and number of floors of the additional HVAC system type, the CIR states that: "this separate Baseline system type shall be determined based on the conditioned floor area and number of floors containing non-residential space functions; however, corridors may be excluded when identifying the number of floors of unconditioned space."

Does this means that for example if I have a Hotel Building of 7 floors and the first level lobby, restaurant, back of house, meeting room, corridors, etc. total conditioned area is 23,000sf the system type for the additional system will a system 3 or 4 or as it has conditioned corridors in the room floors (2 to 7) it will be a system 5 or 6
I think maybe the word unconditioned in the underline sentence was meant to be "conditioned", but I am not sure about it.

Can some help me interpret this CIR correctly???

CIR:

1) Question: Is it possible to use the fan
power limitation pressure drop adjustment for the baseline fan power of PTAC/PTHP? Answer: Per
AHRAE 90.1-2007 Table G3.1.2.9, the baseline fan brake horsepower for constant volume systems 3 or 4
and variable volume systems 5 through 8 can be adjusted by factor A, and factor A is calculated
according to Section 6.5.3.1.1 using the pressure drop adjustment from the proposed building design and
the design flow rate of the baseline building system. PTAC is system 1 and PTHP is system 2 based on
Table G3.1.1A, and therefore can#t use fan power limitation pressure drop adjustment. However, If the
business hotel building include more than 20,000 square feet of conditioned non-residential space (such
as restaurant, meeting rooms, business center, laundry, back of house, kitchen, corridors, etc.) and meets
the requirements of Exception G3.1.1 (a), then the project should reflect a separate Baseline Case
system type serving these spaces. This separate Baseline system type shall be determined based on the
conditioned floor area and number of floors containing non-residential space functions; however, corridors
may be excluded when identifying the number of floors of unconditioned space. Since the system types
serving non-residential spaces are system types 3 through 8, the fan power limitation pressure drop
adjustments may be applied per Table G3.1.2.9. Please refer to Table 6.5.3.1.1B for a list of devices
which are eligible for the fan power limitation pressure drop adjustment. Note that pressure adjustments in
the Baseline Case for energy recovery devices and for evaporative cooling devices are only allowed if the
devices are required to be included in the Baseline Case model.

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Oh I see you answered you're own question. Thanks for sharing

Be Sustainable -- Never let today use up tomorrow!.

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I think what they mean by unconditioned corridor area might have been "conditioned", but that part is irrelevant. I think what they meant is this:

If you have a mixed use facility, the hotel is usually a tower. Let's say that is 20 stories, and you have 2 stories of conference rooms outside of the tower (or below it)

They are simply saying that you don't count the corridor when you are determining the number of floors in the secondary system, or you would end up with 20 stories in your secondary system (by counting the non-residential spaces) - which of course would have a great impact on the system type.

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