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Tolerance for Differential Pressure
- Thread starter SAK9
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) even when doors are opened for short spans.- Thread starter
- #3
Quark ,thanks for your reply.I need to maintain the space at a differential pressure of 15 pa.So what should be the acceptable tolerance range I should specify to the controls specialist? is it +/-1 pa or +/-2 pa.Is this a difficult tolerance level to achieve? Hope to hear from you again.
If I have to believe Cleanroom International Magazine(A free magazine for which you can subscribe online), ISO/FDIS 13408-1 has given guidance value from room to room pressurisation of 10 to 15 Pascals.
Even +/-2 Pascals seems quite critical to me, for the typical time of control for pneumatic pressure controller is 4 seconds and that of electric controller is 6 seconds. But the pressure change in the system is more faster. Anyhow it is always better to specifiy best parameters.
What I suggest you is to take a video of air flow direction by using Titanium Tetrachloride near doors. This helped us very much and Inspectors easily get satisfied.
Secondly, while specifying room pressures in your qualificatin documentation give range of pressure for each room (ex. 5 to 15 pascals etc.)
Even +/-2 Pascals seems quite critical to me, for the typical time of control for pneumatic pressure controller is 4 seconds and that of electric controller is 6 seconds. But the pressure change in the system is more faster. Anyhow it is always better to specifiy best parameters.
What I suggest you is to take a video of air flow direction by using Titanium Tetrachloride near doors. This helped us very much and Inspectors easily get satisfied.
Secondly, while specifying room pressures in your qualificatin documentation give range of pressure for each room (ex. 5 to 15 pascals etc.)
SAK9 - the simplest solution is to give the controls contractor an offset flow rate between supply and exhaust. The design condition (15 Pa) would be established by door gasketing and adjustable sweeps. This would give you the desired room pressure during a closed door condition. Accept the fact that pressure will drop (although flow will still be in the right direction) when a door is opened.
The more complex alternative would be to have the room controls operate the HVAC in/out volumes based on maintaining the room differential pressure at 15 Pa (with some deadband, e.g., ±2 Pa.). A device such as a TSI Sureflow can incorporate the pressure differential signal into a signal that drives volume control dampers to attempt to maintain room pressure. With most control systems, this requires higher-end, more rapidly responding control damper actuation to try to maintain a given pressure with door or transfer hatch shutting/opening. The spring-loaded mechanical actuation of the Phoenix valve system is probably the best on the market in maintaining such a condition. Keep in mind that maintaining 15 Pa with a door wide open may not be achievable, even at maximum supply and minimum exhaust airflow.
The more complex alternative would be to have the room controls operate the HVAC in/out volumes based on maintaining the room differential pressure at 15 Pa (with some deadband, e.g., ±2 Pa.). A device such as a TSI Sureflow can incorporate the pressure differential signal into a signal that drives volume control dampers to attempt to maintain room pressure. With most control systems, this requires higher-end, more rapidly responding control damper actuation to try to maintain a given pressure with door or transfer hatch shutting/opening. The spring-loaded mechanical actuation of the Phoenix valve system is probably the best on the market in maintaining such a condition. Keep in mind that maintaining 15 Pa with a door wide open may not be achievable, even at maximum supply and minimum exhaust airflow.
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