Shutdown CRAC Unit for Clean Agent Discharge?

2/20/2020

Our common CRAC Units (Cooling, Refrigeration and A/C) for data centers only cool the air directly from the data center and back into the data center.

Do these need to be shutdown with the use of a total-flooding clean agent system?

If the CRAC unit is only exchanging air within the same space then I'm not sure what harm it would do if it's running during or after clean agent discharge. I'm curious if I'm off the mark here, thanks!

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6 Comments

Jocelyn

2/20/2020 10:56:48 am

Per NFPA 2001 5.3.6.1 (2018 ed), if the CRAC is not shut down, the volume of the ventilation system needs to be considered as part of the total hazard volume.

Jen

2/20/2020 11:26:56 am

I think the unit he is referring to is just an heating/cooling unit and brings in no ventilation air since the air it heats/cools is from the space itself.

Mike

2/20/2020 11:33:28 am

The CRAC units are typically wired to the fire alarm so upon activation, the CRAC unit is shut down.

Jen

2/20/2020 11:46:10 am

Hi Mike,

If the unit is not wired to the fire alarm, and the unit continues running during the agent discharge, would the unit continuing to run impact the clean agent system performance at all? I cant imagine there would be any significant temperature changes between before discharge and after discharge caused by the CRAC unit that would impact the system, but I don't know for sure.

JOnathan D Griffin

2/20/2020 12:05:49 pm

If the CRAC is serving only the protected space, then it is allowed to continue to run. A Room Integrity Test would test as a "Mixing Volume" for agent concentration purposes, as when the CRAC unit is running, a descending interface is not established.

I do this a lot (Leaving the CRAC running for the client, and using the Continual Mixing Interface option when testing the room integrity).

Travis De Goei

2/20/2020 02:11:30 pm

I completed our enclosure integrity testing for many years. I agree that the mixing method of testing is an option that considers retention conditions while the fans in are in operation.

I always found mixing to be detrimental to getting a room to pass an enclosure test. The retention time with descending interface is the time it takes the descending interface to descend from the maximum protected height to the height of the protected equipment. With Mixing the design concentration is assumed achieved after discharge then decreases based upon the room leakage. The retention time with mixing is the time between design concentration and I think the minimum extinguishing concentration. I never tested a room no matter how tight where additional agent wasn't required to make a room pass. The system almost has to be designed at a higher concentration than the design concentration which requires more agent and has an impact on tank size, pipe size, and labor. Sales people will avoid additional costs every time unless the specification demands. Curious if you encountered the same?

I always focused on sealing the room, shutting down the air, and keeping the max distance possible from the ceiling to the protected equipment to get our rooms to pass.

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