Lg AHU serving multiple floors, perform calcs at zone level?

March 20, 2012

AAME User

LEEDuser Basic Member

12 thumbs up

March 20, 2012

I was brought on to a project to complete the ASHRAE 62.1 calculator after the project was denied LEED EBOM IEQp1. The project consists of two high rise office buildings. Tower "A" is conditioned via one air handler per floor with mixed use and occupancy. Tower "B" is conditioned via 4 large air handlers, each serving multiple floors with mixed use and occupancy. I understand after reading through leeduser.com that ventilation readings need only be taken at the air handler at minimum OSA. The owner/F&M staff are having a hard time tracking down the mechanical as-builts which would assist in determining mins and zoning. So, my questions is as follows: am I required to perform the ventilation calcs at the zone level (i.e. determine critical zones such as interior conference rooms)? I just want to be sure that politely demanding as-builts from the client to determine potentially critical zones and the associated mins is appropriate.

Thanks in advance for your help.

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AAME User

LEEDuser Basic Member

12 thumbs up

March 29, 2012 - 10:45 am

So the lack of response to this question leads me to think that maybe my original question wasn't clear enough. Basically, I'm wondering if anywhere in the LEED EBOM or ASHRAE 62.1 documentation, there exists any exceptions to performing calcs at the zone level and allowances to only perform measurements at the Air Handlers. i.e., if the Air Handler is seeing a minimum of 20% outside air during normal operating conditions, all zones are also seeing a minimum of 20% outside air.

Thanks again in advance for any help.

Ben Stanley

Senior Sustainability Manager
WSP - Built Ecology

LEEDuser Expert

250 thumbs up

March 29, 2012 - 12:06 pm

Both the ASHRAE 62.1 calculations and the outside air testing need to be done at the system level (AHUs). But, the ASHRAE 62.1 calculations do need to incorporate the critical zones for each system. So, somehow you will need to determine the critical zones for each system and collect the relevant data points for those zone. We've seen that typically a handfull of critical zones for each system should be sufficient for the calculations and the LEED review.

Samantha Harrell

LEED Project Reviewer certificate holder

LEEDuser Basic Member

115 thumbs up

March 29, 2012 - 12:14 pm

Hi Roger,

When identifying the required minimum ventilation (IEQp1) at the system level, documentation must be provided to demonstrate that all occupiable zones have been accounted for in the calculations, and that the critical zone for each system has been correctly determined. However, the 30% increase in OA for compliance of IEQc2 must be provided at the zone level to ensure that breathing zone outside airflow is increased adequately.