Maintaining Positive Pressure inside an Office Area
Maintaining Positive Pressure inside an Office Area
(OP)
Dear Friends,
I am designing an Office Space air-conditioning system with the following estimates:
Cooling Load : 25 Ton
Conditioned air flow into Office space: 10000 CFM
Fresh air supply: 1000 CFM (ambient air from outside for maintaining IAQ - added in the mixing plenum of the return air from office)
Toilet Extract: 1000 CFM (transfer via Toilet door louvers)
But the specification requires the office space to be maintained at 5 Pa pressure difference with respect to the ambient.
Would anyone please suggest me some guidelines to achieve the intent?
Thanks in advance for the support.
I am designing an Office Space air-conditioning system with the following estimates:
Cooling Load : 25 Ton
Conditioned air flow into Office space: 10000 CFM
Fresh air supply: 1000 CFM (ambient air from outside for maintaining IAQ - added in the mixing plenum of the return air from office)
Toilet Extract: 1000 CFM (transfer via Toilet door louvers)
But the specification requires the office space to be maintained at 5 Pa pressure difference with respect to the ambient.
Would anyone please suggest me some guidelines to achieve the intent?
Thanks in advance for the support.





RE: Maintaining Positive Pressure inside an Office Area
Measure the pressure inside and out side the space with all doors and windows in the space closed. This is where to start.
RE: Maintaining Positive Pressure inside an Office Area
There are no guidelines but meeting the 5 Pa intent could be adjusted by changing your makeup vs. exhaust ratio.
RE: Maintaining Positive Pressure inside an Office Area
RE: Maintaining Positive Pressure inside an Office Area
RE: Maintaining Positive Pressure inside an Office Area
With 1000 cfm ventilation and 1000 cfm exhaust, your building is essentially neutral, although you'll still get infiltration due to effects like wind pressure. Also if you don't have dedicated equipment or fans providing the outdoor air, or reheat, your building pressure will swing negative when supply air fans shut off or slow down due to the reduced fresh air intake.
RE: Maintaining Positive Pressure inside an Office Area
Also to maintain positive pressure, I typically design to provide 10-20% more OA than EA. Will this result in the 5 Pa difference? I don't know, it depends an the variables listed by Willard. I don't usually have the time to analyze things to that degree.
If you will have intermittent exhaust or you want to be super critical of maintaining that pressure difference, then using indoor/outdoor pressure differential sensor with variable dampers/VFDs is the way to go.
RE: Maintaining Positive Pressure inside an Office Area