Control Building Pressurization 1

[butelja]

An existing Engineering Standard for HVAC systems in control rooms located in a "low risk" area of a chemical plant states the following with respect to building pressurization: The system shall maintain a positive pressure within the building of 0.05" WC with all doors closed, and alarm (after a 2 minute delay) when the pressure falls below 0.025" WC. Other systems located in "moderate risk" areas are pressurized according to NFPA 496, which has values of 0.25" WC setpoint and 0.125" WC alarm.

I don't have a lot of practical HVAC experience, but my gut feeling is that these pressures for the "low risk" areas are too low to be practical and might lead to many nuisance alarms. Does anyone with experience in this area have any comments? [sig][/sig]

 

NFPA 496 allows a pressure of 0.1"wc for controls rooms and is used effectively for maintaining a positve pressure without the risk associated with opening a personnel size door to an area pressurized to 0.25"wc. The .25"wc pressure is satisfactory for smaller enclosures but for rooms the lower pressure is much easier to maintain.