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Building Pressurization, You Know, Basic Stuff

Building Pressurization, you know, Basic Stuff

Quality, Consequences and the Construction Industrial Complex (part 188).

In the excitement of IOT, AI and Smart buildings why are we ignoring the fact that BMS (BAS in North America) doesn’t prevent simultaneous heating & cooling and building & room pressurization is not achieved, stable, tested or monitored? 

The property industry is a bit like the mining industry, it is full of carnival barking promotors promising outcomes that ignore reality. I think it was Mark Twain who said bitterly, “a mine is a hole in the ground, covered by a lie”. The property version might be, “this development, is leasing fast, it is “Green”, low cost to run and fully automated”. 

We have all been in hotel lobbies and felt the inrush of air as we enter or seen air diffusers dripping water. In a humid climate, dripping air diffusers are a sure sign of a negatively pressurized building. I don’t know why, but hotel building services design and construction really does suck and this lobby pressurization issue is not complicated. It does not get more basic than building pressurization. Simply, the ventilation systems need to provide a positive building pressure to ensure there is slightly more air leaving the building than entering. All this takes is easy arithmetic and basic controls, IMHO. 

So why does negative building pressurization matter? Negative building pressurization allows uncontrolled infiltration of:

  • Moisture leading to mould growth.
  • Air.
  • Pollutants i.e. unfiltered air.
  • Additional heating and cooling temperature load.

Given property developers sell a dream of a controlled, comfortable environment, none of this is good for the user experience, facilities manager nor energy costs. For hotels and residential buildings, negative building pressurization is irritating but not mission critical. For a Bio-hazard Lab, hospital or data centre the consequences are more serious. So what to do? 

Building Services Designers

  • Design with intention to address building pressurization.
  • Take into account wind pressure effect i.e. cross wind, direct wind and interior door effects. 
  • Use Air Flow Monitors and VFD’s to control on air flow and ensure building pressurization is maintained as filters load.
  • Specify duct leakage testing. 
  • Specify enclosure testing in mission critical applications.
  • Include air flow and building pressurization alarms in the BMS points list.
  • Produce a building “Air Balance Diagram” (See example below).

Example Building Air Flow Diagram


  • Build with air infiltration in mind i.e follow the construction details and sample test quality.
  • Do not value engineer out the AHU and fan VFD’s or air flow monitoring devices.
  • Understand the quality of your work impacts the performance of the building plus its environmental and air-conditioning systems.

Testing, Adjusting & Balancing Team

  • Reconcile and report test results against the building Air Balance Diagram.
  • Test building pressurization at ground level in simulated maximum heating and cooling scenarios.

Commissioning Team

  • Verify ductwork leakage testing.
  • Verify and report test results against the building Air Balance Diagram.
  • Functionally test and monitor building pressurization in all systems mode of operation including a simulation of fully loaded AHU and air systems filters.

This may all seem a bit too much, however, consider this info graphic I saw on LinkedIn recently:

Graphic by: 

Shout out to Purpose Building in Canada. The graphic speaks for itself and they note, focusing on compartmentalization, air-tightness and pressurization may be more effective than envelop upgrades!

If you want your building to work, perform and have a minimal energy footprint then everything matters, including building pressurization.

Twitter: @BLDWhisperer  

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