HVAC Control Conflict

[ThePunisher]

Hi all, I have a situation where I have a switchgear building which is located within the reach of a gas cloud. We are not able to locate the building away. The HVAC system intake damper will close in the event of 30% LEL to prevent gases from being introduced into the building. On the other hand, the building requires pressurization to be maintained which requires air intake. Hence, there is control conflict. In this case, I am hoping anyone had the same situation and was able to mitigate by engineering controls and share them. Worst case we want to avoid is to shutdown the electrical building. Thank you in advance.

 

[waross]

You may have to duct-in make-up air from outside the hazardous area.

Bill
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"Why not the best?"
Jimmy Carter

 

[GroovyGuy]

howdy,
Bill is correct; you need a clean source of pressurization air brought into the bldg. This is a typical solution to a common problem. If your gases are heavier than air, an 20ft length of vertical ducting is all that is required to get at a clean source of air.

You also should have redundant LEL xmitters located within the electrical room. 30% is too high in my opinion, you should alarm @ 10% and shutdown at 20%.

API-505 has some good info wrt this type of solution.

GG

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[JensenDrive]

Look into molecular sieve for emergency makeup air when gas is detected. Seal the room well so low makup air is needed.