4.13.11* Door Opening Force. The maximum force for pushing or pulling open a door shall be as follows:
(2) Other doors.
(b) interior hinged doors: 5 lbf (22.2N)
Thank you very much...
According to the given codes, for a 3 x 7 hinged door P = 5 lbf / 21 sqft = 0.238 lbf/sqft which is exactly 0.05 in wg. PERFECT!
This means that the Differential Pressure could turn dependent on the door size, eg, Bigger doors less Delta P.
Smaller doors higher Delta P. Is that correct?
Interesting point is that Clean room Standards do not consider door size on their recommendations for Delta P.
Neither Pressure nor size change modifies the codes for reasoning this concept.
That's exactly the point. After the explanation tip I got (5 lbf) it seems that in theory it does matter (1/8" or 1/2", however from my practical experience this 0.05"wg value has likely been maintained from one project to the next, from one company to the other, along the time being. That means ....with so many issues during any HVAC project and a value for delta P at hand it is easier for the many just to accept and apply it.
Not sure where the numbers came from, buts its an FDA / ISPE / ISO requirement. The US has a requirement of 0.04 in wg to 0.06 in wg between classes, while Europe requires 0.05 in wg. So usually there is an airlock in between, so it could be construed as .25 in wg between doors, which we bump up to 0.03 in wg for a total of 0.06 in wg betrween classes as a buffer.
This is absolutely dependant on the door size and cracks and can be calculated using ASHRAE 2013 Fundamentals Equation 16.36
0.05 is not cast in stone.It is all right for clean rooms when it comes to containment situations(either clean room or lab) I have seen 20 to 25 Pa(0.08 to .1"wg)being used without much difficulty.Generally door swing is into the room of lower pressure so the greater pressure assists door opening.If the pressure differential is too low you do not have enough air flow when the door is fully open.Assume the leakage flow is 200 cfm for a standard 20 sq ft door.When it is fully open the air flow velocity across the door opening is around 10 fpm only.On the other hand too high a flow would mean turbulence and flow reversal.I am of the view that flow differential is more important than pressure differential because that is what affords you protection when the door is open.You can always get the differential you want by controlling the door leakage with the help of gaskets,seals etc.
I've used 0.05 IWC for dozens of years, as my main client was DoD biological safety and agent hood use. The 0.05 IWC is exactly spelled out in the DoD standards. Because leakiness standards are leaky, I've always relied on differential volume flow and availability of a Dwyer and damper for manual set or a photohelic for full control operation. The 0.05 IWG has worked well for setting high and low limits; typical would be to set a fast acting barometric damper on supply to avoid overpressure at about 0.02 IWC and 0.07 IWC as upper limt on VFD. Door open and close will make the control swing back and forth between 0.02-0.07 IWC in my expereince using air control valves and photohelics.
I wouldn't trust calculations as much as having a balancing damper and flow control. I've seen differential flows from anywhere between 60 CFM and up to 200 CFM depending on the leakiness. If you are on the high end, it might be time to get the silicon caulk out. Specifying good door hardware is important. The Phoenix valve web site may still have good tutorials for this.
No need to maintain 0.05 IWC under open door scenario, as long as positive volumetric flow is verified (smoke the door). If contaminants or viral/bacterial agent could swim against the flow, it would be a moot point.
