Room Pressure
Room Pressure
(OP)
Hello,
Please can you help me, I have a room 2,2m x 2,3m x 2,55 and I need it to be pressurized to 15 Pascals, the volume of the room would be 12.9 or say 13 Cubic m
Please can you help me, I have a room 2,2m x 2,3m x 2,55 and I need it to be pressurized to 15 Pascals, the volume of the room would be 12.9 or say 13 Cubic m





RE: Room Pressure
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RE: Room Pressure
RE: Room Pressure
B.E.
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RE: Room Pressure
RE: Room Pressure
15pa is equivalent to 1 point 53 mm water guage (!)
Of course this only applies if not a single molecule of air leaks out of your room.
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RE: Room Pressure
RE: Room Pressure
RE: Room Pressure
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RE: Room Pressure
RE: Room Pressure
http://www.airflowdirection.com/ASHRAE%20Original%...
http://w3.usa.siemens.com/buildingtechnologies/us/...
https://www.allergycosmos.co.uk/blog/positive-nega...
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Room Pressure
Airflow Through Large Intentional Openings
The relationship describing the airflow through a large intentional opening is based on the Bernoulli equation with steady, incompressible flow. The general form that includes stack, wind,
and mechanical ventilation pressures across the opening is
Q = 776*C*A * SQRT(2* delta-p / density
(This is equation 36 in Ch 16 of 2013 Ashrae Fundamentals in English units)
where:
Q = airflow rate, cfm
C = discharge coefficient for opening, dimensionless (usually 1.0 for a door)
A = cross-sectional area of opening, ft2 (Single door with 1/4 crack, = 0.23 ft^2)
p = air density, lbm/ft3 (0.075)
dp = pressure difference across opening, in. of water (convert 15 pascals to English)
776 = unit conversion factor
knowledge is power
RE: Room Pressure
your maths works well for discharging into open space, which i doubt you use as a method of pressurizing pharma areas.
normally, there you have rooms with excess supply and rooms with excess exhaust where pressurizing is coming out of flow differences and pressure loss rates related to flow.
you can desire any flow through transition opening, but real flow will depend on real pressure loss, which makes process iterative, and i doubt much you can achieve exact overpressure without pressure dampers, differential pressure-controlled supply and exhaust fans, or both. you cannot use dp control for central fans if you have rooms with differing requirements so damper remains the only option imho.
RE: Room Pressure
- build the rooms needing positive or negative pressure as tight as possible
- use exhaust and inflow flow meters, like Accutrol air valves (can't use pitot-tube devices for dirt and accuracy reasons)
- supply or exhaust a few % of flow more.
- see if the pressure relationship is as you want it.
- in some cases you also may use dP sensors between those rooms.
You also need to set up control so that if a flow station or a dP sensor fails, the room fails in the extreme of the pressure. i mean if you space is supposed to be 0.01" negative, failure of control should not make it positive. i once had to fix a shooting range pressure control (designed by someone else) and that would fail in being positive to adjacent rooms, not good for a room that is supposed to be negative. Murphy's law dictates failures will happen, prepare for them.
RE: Room Pressure
RE: Room Pressure
B.E.
You are judged not by what you know, but by what you can do.
RE: Room Pressure
Energy explains the issues that you need to think of to make it work in practice.
I have only done "static" systems with a hard balance. There are "dynamic" systems that are constantly hunting. You need top quality air valves, and even then it is difficult, because the accuracy is so small that the sensor technology is not there yet, when put in practice (from what I was told).
Berk, that switch does sot have the accuracy required. You usually have rooms at 0.03 in wc difference required.
knowledge is power
RE: Room Pressure
RE: Room Pressure
So here is an interesting question with an answer based in experience:
If you are pressurizing a room positive (lets say a typical amount is 0.03-0.07" w.c.), how much "less" return air do you return in rooms for balancing?
I have been taught 100 CFM per door, or 10% less than SA, with judgement being used for both.
Anyone else?
RE: Room Pressure
I have my answer to my question, can someone tell me how to close this topic
RE: Room Pressure
THIS IS THE OUTDOOR AIR.
YOU MUST ALSO SEAL THE CEILING AND CRACKS WITH SIKA OR SILICONE.
IF YOU HAVE SUCTION AIR FROM THE ROOM ADD IT TO THE FRESH AIR.
ALSO NOTTICE THAT THE DOORS ARE OPENED TO THE ROOM AND NOT OPENED TO THE OUTSIDE OF THE ROOM BECAUSE , SO THE HIGH PRESSURE WILL "CLOSE" THE DOOR AND NOT "OPEN" IT (IN THIS CASE AIR WILL RUN AWAY FROM THE DOOR