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For the Ventilation system consider a closed circuit with a single fan to recirculate air. The circuit pressure drop will equal the fan pressure rise. Now place a fan blowing in to the circuit rated at the leakage rate (plus a margin) with a pressure rise of 30Pa from ambient. This will effectivly now pressurise the room system.
Mechanical. Oct 1, 2003. 1,283. US. Positive pressure will occur when the pressure in the pipe/duct/room is greater than the pressure outside of it - so flow would go out of a room. Negative pressure means the pressure in the pipe/duct/room is less so flow would go into the room.
Normally, the pressure level is obtained from pressurizator manufacturers index,or trough basic practices coming from enginnering consulting and/or installing firms. The "standard" pressurization value ranges from 0.05 to 0.15 "H2O. Take in account, the wind speed an incidence angle over windows, doors and cracks belonging to the MCC room.
For a +ve pressure room, if the leak rate is 100 cfm, say, and the recirculation rate is 1000 cfm then supply air flow is 1100 cfm and return air flow is 1000 cfm. If you are maintaining +0.25" pressure in the controlled space then pressure at inlet to the plenum should also be +0.25". Any other pressure contradicts the maintained room pressure.
Room should be negative instead of positive because of the Class II type B2 biosafety cabinet. With sealed isolation rooms we have found that 400 CFM should be the design CFM differential to hold minimum 0.001 in. wg pressure differential. 1 pascal is 0.0040865 in wg.
The 15000cfm is produced from the VFD itself and is blown into the room where the vfd exists. You're going to have a wind tunnel for a room to keep it cool. Forced draft (fan forcing air into the room) will keep a positive pressure on it. I think 0.25-0.5 inWC is a typical positive room pressure but I'm no HVAC expert.
If positive, I count air changes by supply for the ISO ACH requirement, and look for a 0.05 IWG at balance by dampering the exhaust. For negative I go by ISO ACH requirement on the supply side, and damper back the exhuast at balance for the 0.05 IWG. A magnahelic on the wall before entry should be considered for operations.
The room is maintained at 38-40F with DX cooling racks. What the owner would like a make-up unit to maintain the room at a positive pressure of 5 pascals. The unit to be control by a VFD and pressure sensor located in the space and adjacent control space, location ideas needed!!!!
The positive pressure may not help you keep the washing area dry. I would rather focus on containment issue and keep it negative. In pharmaceutical plants, laundries are kept at negative pressure w.r.to adjacent spaces. sathanasiou (Mechanical) 6 Oct 05 05:34. I would keep the pressure negative and use a dehumidifier in order to keep the room dry.
Sounds like you're on the right track. If you want to maintain a slightly positive pressure in the enclosure compared to outside the enclosure (0.0 to 0.1" w.g) , you are going to need to introduce make-up air (as you say), and of course, ideally, upstream of the fan intake and filters.