Building Ventilation Air Balance
11 July 2016
Unbalanced HVAC systems in buildings are common, this occurs when the rate of make-up or replacement air into the space is less than the rate of exhaust air, thus creating a negative (-ve) pressure in the space.
Equilibrum must be maintained, so that negative pressure effect drags replacement air into the space, through any opening, gaps around doors and windows, and sometimes the only path of least resistance, through the drainage system.
In the short video, the bathroom room exhaust fan is ON, the bathroom door is shut, and we discover the door is almost air tight, therefore replacement air is drawn through the floor drain, the tell-tale streamer indicates the direction of the air flow into the room!
In tropical regions it is critcial, where buildings are air conditioned for comfort, negative (-ve) pressure must be avoided otherwise hot-humid outdoor air is drawn in to the space, giving rise to mold and moisture problems.
And along with the air from the sewer pipe, bacteria and foul odours enter the building. In this case the air flow through the floor drainage pipe because the water seal is inadequate, another common problem in Hong Kong (SARS 2003).
Therefore, the ventilation air balance is critical to maintain a healthy building, yet it is often overlooked.
Kelcroft takes the extra time and effort to review the air balance when commissioned to conducted an energy audit. And in our expereince, we find that most buildings have been modified by either owners or tenants, without providing sufficient make-up air, causing negative pressure, and the unwanted side effects.
About the Author
John A. Herbert is a veteran with more than 30 years engineering
experience, educated in the United Kingdom he has been working across
Asia for the last two decades for international and local companies.
He is a Hong Kong Registered Energy Assessor (REA), and BEAM