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Can LEED 2009 projects elect to follow ASHRAE 62.1-2010 for this prerequisite?

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NC-2009 IEQp1:Minimum IAQ Performance

ASHRAE 62.1 - 2007 Occupant Density vs T24

I am trying to show that we meet the required ventilation rates for compliance with ASHRAE 62.1-2007 in order to meet the prereq for the LEED credit. Our project is in the state of California, and in some cases in design our assumed "occupant density" was based on CBC which is more stringent. We must meet Title-24 which also typically has more stringent ventilation rates. In order to prove that I meet ASHRAE 62.1, do I only need to use the default occupant density listed in Table 6-1, even though I have used a more dense occupant density for determing actual ventilation (as Title-24 requires the more greater density)? Or do I need to combine my actually used occupant density to comply with the more strict code with the ventilation rates specified in Table 1 and then use that to determine required ventilation to meet 62.1? I hope that is clear. Basically I am just getting tripped up on which occupant density to use to show 62.1 compliance when I may have used a greater density for Title-24 compliance. Thanks in advance!

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Wed, 06/05/2013 - 18:00

Juani, if you already have the CBC Calculations documented then it would probably be the easiest course of action to just go ahead and upload those. That being said, if you want to use the ASHRAE compliance method then you should use the actual number of occupants in each space. If you don't know the number of occupants then you should use the default occupant density. If your CBC calculation is more stringent than the ASHRAE 62.1 requirements then using the ASHRAE compliance may help you achieve the Increased OA credit IEQc2. I hope that helps.

Wed, 06/05/2013 - 18:19

The CBC Mechanical Code requires compliance with ASHRAE 62.1-2007. The T24 Calculations use simplified assumptions that sometimes exceed the ASHRAE requirements, but not for some space types. EQp1 requires use of the more stringent requirements between local code and ASHRAE. You're stuck having to do ASHRAE calculations to prove which is more stringent. Proving T24 compliance is not hard if you have a T24 energy model which documents the compliance. You'll have to use the LEED tools to document the ASHRAE side of the requirements.

Wed, 06/05/2013 - 18:28

ASHRAE 62.1 requirements are from the CBC Title 24, Part 4, California Mechanical Code. From the 2010 version of the Code: CHAPTER 4 - 403.1.1 Breathing Zone Outdoor Airflow. The design outdoor airflow required in the breathing zone of the occupiable space or spaces in a zone, i.e., the breathing zone outdoor airflow (Vbz), shall be determined in accordance with Equation 4-1. [ASHRAE 62.1:6.2.2.1] Vbz = RpPz + RaAz The reference to the 2007 version of ASHRAE 62.1 occurs in the Chapter 17, Standards (Page 292 of the Code).

Wed, 06/05/2013 - 18:31

...and as Andrew stated, you do not have to use T24 Energy Code occupancies for ASHRAE 62.1 compliance.

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