Pressure of Room with door open

[robgallentine]

I have been asked to provide a flow of at least 60 fpm thru all openings of my presurized room. I need to check the flow when my 3' door is open. I have a constant running fan w/ variable control for 200 to 600 cfm output. I am not sure how to check my flow. I have attached technical data of HVAC unit. Can anyone help?

 

[VerneE]

If your door is 3' wide and 7' tall, and if the average flow through the door is 60 fpm, then the total flow is 1260 cfm.

If you want an average of 60 fpm across an opening, have one side of the opening be 0.00022 inches water guage lower in pressure than the other.

The formula v = 4005 x sqrt(vp) where v is velocity in fpm, vp is velocity pressure in inches water gauge is the relationship between velocity and pressure for dry air. The velocity pressure is the energy the system must convert from pressure into momentum to go from 0 fpm to 60 fpm.

Doing the math, a 60 fpm average velocity across the opening. requires a pressure difference of 0.00022"w.c. This is approximate, but is close enough for most purposes.

 

[ChasBean1]

"I have been asked to provide a flow of at least 60 fpm thru all openings of my presurized room. I need to check the flow when my 3' door is open."

Design around cracks and leakage with the door closed; don't design for a pressure or velocity with an open door. Who asked you to provide a flow of "at least 60 fpm thru all openings of my pressurized room?"

VerneE showed you the flow difference needed under this condition. This would overpressurize the room with the door closed.

 

[boo1]

close the door

 

[Waramanga]

is 0.00022"WC a commissionable figure, it is a tiny pressure, like a 100th of a pascal. I think a velocity meter accross the door will be a better bet.....

 

[mauricestoker]

If you have 600 CFM maximum available, an area of 21 SF, how would you expect to get 60 FPM? Start with the algebra.

An easy way might be to put a Dwyer dP across the door, turn off supply, put exhaust VFD in bypass, point to the Dwyer, and show maximum available dP. Specify good door hardware, especially the door closer. If the customer meant "with door closed" you could run the exhaust VFD off a duct dP corresponding to the dP desired accross the perimeter.

 

[cry22]

1. what is the application? TB isolation room in a hospital? how critical is it to have this pressure at al times? do you require alarm when deviating form DP? etc.. If it is the equipment manufacturer that requires this DP, I suggest you move to another MFTR without CYA attached to their equipment.

2. Agree with waramanga: 0.00022" DP - I do not know of any DP equipment capable of sensing such a number. Next is the engineer's liability in providing a set point? be aware that if the set point does not do the job (that dp is not achieved with your set point anyway), you're in a hot seat.

3. TSI type DP instruments recommend between -0.02 and + 0.02 sensitivity I think - The set point in DP has always been a legal nightmare for engineering firms, even CDC does not issue a set point for TB patient rooms for example. We tpically call for manufacturer (such as TSI) set point as CYA in our documents.

4. I would not use Dwyer equipment for such a small DP (will work during air balance with door closed but is out of wack when the door opens). I would use equipment such as TSI type control with VAV box on Supply and Exhaust/return to control DP between room and adjacent space at an achievable and readable DP set point.
Your primary concern is to have in place MEANS of controlling the air flow, such as VAV boxes and equipment with VFD's.

5. Agree with most people here - Close the darn door.

 

[mauricestoker]

If maintaining the dP is crucial during door opening, use a double door vesibule. For 60 fpm that would probably take 60-100 CFM differential volume flow.