INTERNAL ROOM PRESSURE REGULATON WITH MOTORIZED DAMPER

[schola]

Hi friends!

I have been asking me about what practical is controlling internal positive room pressure using arrangaement composed by Internal Pressure Sensor (as Magnahelic) + modulating motorized damper.

How quick is the control response? Is a realiable design? Wath level of precise control is achieved?

Thanks,

schola

 

[tombmech]

Some of these other guys are more expert at the actual controls components - especially the old pneumatic stuff. If you use a PLC, it's a simple matter to plug-in a square root multiplier.

The problem is that pressure and flow are not linear. The pressure varies by the square of the cross-sectional area. So, a simple sensor and modulating actuator will constantly overshoot/undershoot.

You can measure this yourself. Typically, you will find that with a simple butterfly damper, there is no reduction in flow (pressure) until the last ~25% of movement. Multi-bladed, opposed blade, and airfoil-blade dampers will minimize this somewhat, but cannot remove the essential squared relationship.

Venturi valves, such as those made by Phoenix, are inherently linear by virtue of their geometric design.

 

[quark]

I had used these for pressure control in the areas. The dampers were provided by Belimo and the control system was of Honeywell. The main problem is with the opening of the doors. You should carefully study the duration through which the room pressure is unstable, during a door opening, and offset this effect, room by room. The accuracy was with in +/-5Pa. It is practically impossible that you can maintain room pressures when the doors are open. When the doors are closed, it is a simple job.

If you balance the system manually first and also if you have variable volume systems, this may not be a difficult task.

 

[SAK9]

Tombmech's observation is spot on.I have done pressure control using manual dampers,VAV boxes(butterfly damper inside),Motorised OBDs and phoenix valves.Nothing can venturi valves(Phoenix) in terms of accuracy,speed and stability.

I think the criticality of your application dictates what solution you need to apply.For eg,if it is a biocontanined lab,the investment on venturi valve is well worth it.On the other extreme,if it is a control room, a manual damper can do the job.