The building I am working on has a large main sales area which is served by 8 AHUs, all bringing in 100% fresh air. In this case, is the proper protocol to first divide total peak customer and worker population numbers and total size of the sales floor by 8, and then use these numbers to calculate the required Vbz for each AHU, which in this case would be identical for each?
You rely on LEEDuser. Can we rely on you?
LEEDuser is supported by our premium members, not by advertisers.
Go premium for
Peter Dahl
Associate PrincipalHGA
30 thumbs up
March 23, 2011 - 10:56 am
The System Ventilation Efficiency factor (Zp) of the Ventilation Rate Procedure is not correctly accounted for if you do not consider the 26 recirculating AHUs. The method for completing this calculation also strongly depends on whether the AHUs are CV or VAV.
While measuring the OA rates is sufficient at the system level (in your case measure OA rates at each AHU providing OA), you'll need to more accurately determine the zones for each OA AHU to correctly calculate minimum OA requirements per ASHRAE 62.1-2007 Ventilation Rate Procedure. These zones will depend on the air distribution system, partition walls or any air barriers, and loads in the space.
Zachary Goodnough
32 thumbs up
March 23, 2011 - 11:07 pm
My understanding is that this issue comes down to whether or not the area can be considered a single ventilation zone, since it appears Zp only needs to be accounted for in Multiple-Zone Recirculating Systems. The sales area I am calculating ventilation rates for has similar occupancy category, occupancy density, distribution effectiveness and primary airflow per unit area. Although there are many "occupiable spaces", by definition, ventilation zones can have one or more. The air distribution system is a ceiling supply of cool air, and while there are aisles, the length of the space between the top of the aisles and the ceiling is large enough where it doesn't seem necessary to consider the aisles air barriers. That all being said, I am inexperienced working with this standard, so please let me know if something in here is incorrect.
For what it's worth, and I'm not sure if it is possible to take this into account, because I'm treating the whole area as one zone, the recirculating AHUs will be working as a CV CO2 demand system, controlled by the building automation system. Since the area is very large, and it is probable that at certain times customer population density will fluctuate from store area to store area, depending on special sales or other retail related factors, this will move the fresh air to where it is needed if the circumstance requires it. The fresh air AHUs, however, will be constantly providing the calculated minimum outdoor airflow volume sufficient for the entire ventilation zone.
So, I guess the fundamental question is, do you think I can I consider the sales area to be one ventilation zone?
Thanks