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Topic under discussion is the required air changes per hour (ACH) for a warehouse space in Phoenix, AZ. I'm an architect, not an engineer but my consultation with engineers on this topic has yielded a wide range of answers, and google search is even less productive. For the record, I'm speaking about leased warehouse facilities, not warehouses that are owned, occupied and operated by the same entity. The owner/landlord may have a records storage tenant now, but could lease to a manufacturing tenant in the next 5 years, then metal parts storage facility for the next, and so on...
ASHRAE appears to list the recommended air changes for warehouses as a range of 6 to 30 changes per hour. That is a massive spread in the range. In a warehouse served by evaporative coolers, trying to get to 30 air changes would take an insane amount of specialized evap cooler equipment, and in reality, most leased evap-cooled warehouse space in the Phoenix metro area are providing no more than 3 to 5 air changes per hour. Just look at the google aerial view of the warehouses in Phoenix. Very very few of them have that amount of equipment on the roof.
Here's a real life example in Phoenix. An existing 64,000sf warehouse building is currently served by 12 evap coolers that each push 20,000cfm. After crunching all the miscellaneous factors in, the air change calculation yields 7.5 air changes per hour existing. Just to get to 14 air changes, one might think a conservatively prudent midpoint, the owner or tenant would have to add another 12 evap coolers to the building.
The threshold for IMC Table 403.3.1.1 OSA compliance is much much lower at 0.06cfm per sf. A 64,000sf warehouse only requires 3,840 cfm of OSA to be compliant. Each evap cooler in our example provides 20,000cfm and there are 12 existing on the roof, so obviously, OSA is not an issue, but recommended air changes is a whole other story.
So, my questions are:
1. What is a realistic recommendation for number of air changes in a warehouse space in Phoenix, AZ? For you practicing mechanical engineers out there, what do you use as your guideline here? If the space described above was not cooling as effectively as the tenant would like in the summer, is the recommendation they need to add 12 more units to get to the the midpoint of the max recommendation of 30?? Adding 12 more units is a very costly alteration, and comes with a LOT more annual maintenance. The space is "code compliant" so there's no mandate here, right? The only required calculation required by the AHJ is an OSA calc which is an easy hurdle with evaps. We don't have to demonstrate compliance with ACH rates.
2. Given the extreme range in the ASHRAE recommendation, is it prudent to use ASHRAE recommended ACH rates as a basis of design for new evap cooled warehouse space, and if so, again where in the 6 to 30 range do you start?
Thank you in advance for your feedback...
ASHRAE appears to list the recommended air changes for warehouses as a range of 6 to 30 changes per hour. That is a massive spread in the range. In a warehouse served by evaporative coolers, trying to get to 30 air changes would take an insane amount of specialized evap cooler equipment, and in reality, most leased evap-cooled warehouse space in the Phoenix metro area are providing no more than 3 to 5 air changes per hour. Just look at the google aerial view of the warehouses in Phoenix. Very very few of them have that amount of equipment on the roof.
Here's a real life example in Phoenix. An existing 64,000sf warehouse building is currently served by 12 evap coolers that each push 20,000cfm. After crunching all the miscellaneous factors in, the air change calculation yields 7.5 air changes per hour existing. Just to get to 14 air changes, one might think a conservatively prudent midpoint, the owner or tenant would have to add another 12 evap coolers to the building.
The threshold for IMC Table 403.3.1.1 OSA compliance is much much lower at 0.06cfm per sf. A 64,000sf warehouse only requires 3,840 cfm of OSA to be compliant. Each evap cooler in our example provides 20,000cfm and there are 12 existing on the roof, so obviously, OSA is not an issue, but recommended air changes is a whole other story.
So, my questions are:
1. What is a realistic recommendation for number of air changes in a warehouse space in Phoenix, AZ? For you practicing mechanical engineers out there, what do you use as your guideline here? If the space described above was not cooling as effectively as the tenant would like in the summer, is the recommendation they need to add 12 more units to get to the the midpoint of the max recommendation of 30?? Adding 12 more units is a very costly alteration, and comes with a LOT more annual maintenance. The space is "code compliant" so there's no mandate here, right? The only required calculation required by the AHJ is an OSA calc which is an easy hurdle with evaps. We don't have to demonstrate compliance with ACH rates.
2. Given the extreme range in the ASHRAE recommendation, is it prudent to use ASHRAE recommended ACH rates as a basis of design for new evap cooled warehouse space, and if so, again where in the 6 to 30 range do you start?
Thank you in advance for your feedback...
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