We are working on getting an 8-story office building LEED EBOM certified. The system utilizes large built up air handlers to provide supply air to fan powered VAV boxes. The system is designed for full economizer when the ambient air conditions are sufficient. During occupied hours approximately 20% outside air is being provided through the outside air louver most of the time, but when ambient temperature is below 35 degF and above 85 degF the outside air damper closes because the building cannot maintain temperature set point. We have louver, fan, duct, ect. capacity to meet 62.1 flow rates, but the system cannot maintain set point at the mentioned ambient conditions.
It seems that meeting ASHRAE standard 62.1-2007 is infeasible because of physical constraints limiting the system to provide outside air when outside air is below 35 degF and above 85 degF. Therefore, I assume that we would pursue case 2 and provide 10 cfm of outside air per person. Case 2 states that we need to demonstrate that the current system cannot provide 62.1 outside air flow rates “under any operating condition even when functioning properly”.
My question is since we can provide the required outside air most of the time, does that mean we don’t meet the requirements of case 2 and are out of luck? Thank you for any help that you can provide!
Ben Stanley
Senior Sustainability ManagerWSP - Built Ecology
LEEDuser Expert
250 thumbs up
June 19, 2012 - 10:54 am
Darin,
The building will meet the prerequisite as long as the system provides at least 10 cfm per person under the worst case conditions and the systems are set to meet ASHRAE 62.1-2007 when they are physically able to do so.
I think that the rating system language you site above is meant to preclude situations where a building is only providing 10 cfm per person in all conditions, even if the systems can meet the ASHRAE standard during some or most conditions.
Darin Amsberry
Mechanical EngineerSystems Engineering
June 19, 2012 - 6:51 pm
Thanks for the response Ben. Just to clarify, the 10 cfm per person requirement is for FTE occupants and ASHRAE 62.1-2007 occupants, correct?
Ben Stanley
Senior Sustainability ManagerWSP - Built Ecology
LEEDuser Expert
250 thumbs up
June 20, 2012 - 12:30 pm
Sure, the 10 cfm per person requirement is for the maximum expected occupancy during typical operations. It's not supposed to be the ASHRAE default except in some circumstances when the project needs to follow the reduced occupancy guidelines (less than 90% average occupancy over the performance period). Those guidelines are posted on USGBC's website.
Peter Dahl
Associate PrincipalHGA
30 thumbs up
July 18, 2013 - 4:23 pm
Building on this thread...What is the population for the min OA calculation under Case 2?
I would expect this to be the Population of the area served by the AHU (accounting for diversity), or Cell I8 ("eye-eight") from the 62MZ calculator.
Alternatively, I could see an interpretation requiring the sum of Design Population from all zones (Sum of Row 18 in 62MZ calculator). However, this would overestimate maximum population expected during normal operations, since most buildings (especially office) have zones which share occupants.
For example, in Office buildings, an AHU may serve Conference Rooms and office areas. The Sum of all zones population might be on the order of double that of typical occupancy, if most conference room occupants are coming from nearby offices. Therefore, the actual population of the area served is more closely aligned with the Population adjusted for diversity.