How to calculate room pressurisation
How to calculate room pressurisation
Say you have a 200sqm room, how do you calculate or estimate the air flow required to maintain pressurisation in the room?
We must first estimate the leakage area including doors, windows and walls. If we want positive pressurisation we must introduce more supply air into the room more than the exhaust and relief via door undercut and leakages from cracks on wall, and infiltration from windows. For negative pressure it will be more exhaust than supply air.
Then use the table below to work out the required flow rates based on ΔP and leakage area.
It can also be estimated from the formula below.
C = flow coefficient, usually 0.65
A = flow area 0r leakage area, m2
ΔP = pressure difference across path, Pa
V = volumetric flow, m3/s
ρ = gas density in path, kg/m3
All the above will require the leakage are be determined. Another popular way to establish positive or negative pressurisation is to first work out the room volume. Say the room height is 4m; the above room volume will be 800m2.
To sustain room pressure, we have established that we need 2 to 3 air change per hour.
Low estimate: 1600m3/hr or about 450L/s
High estimate: 2400m3/hr or about 650L/s
Pressurisation make up or exhaust air required is between 450 to 650L/s. This flowrate is the basis for the room pressurisation, it is very important the both the supply and exhaust outlets are provided with balancing dampers to adjust the actual flowrate for the room pressure required. If any of the dampers is missing you will not be able to balance the flowrate to achieve the pressurisation needed.
You may also us Contam software to estimate room pressurisation, the download link is below
https://www.nist.gov/el/energy-and-environment-division-73200/nist-multizone-modeling/software/contam/download
