Air Balance Basics for Existing Facilities


Author: Darren Witter –

We all understand the concept of the “band-aid approach” whereby you find a quick cover-up to a problem without actually investigating the root of the it.  This concept applies very frequently in the context of a Facility Manager or Building Owner wrestling with HVAC emergencies that are being caused by negative building pressure. They will tackle issues such as condensation, hot/cold spots, humidity, odor, and difficult to open doors with band-aids of increased air conditioning, dehumidifiers, wet floor caution signs, door mechanisms, air fresheners, apologizing to patrons, comping customers’ bills, and so on.  This is understandable when you’re managing 80+ facilities, all with problems that stretch far beyond just HVAC.  However it comes with a cost of spending a lot of time, money, energy, and reputation just to have the issues continuing to come back.  While balanced airflow is not a tangible product that is easily seen or touched, the consequences of an unbalanced building are very perceptible.

Facility Managers are ready to de-mystify their HVAC issues with understanding of the root causes.  Use the air balance basics below to recognize when an issue is airflow-related.

What does it mean to have a balanced airflow?

Think of a financial statement with income listed in one column and expenses in the other.  Much like a budget where you want cash coming in to be at least equal to or greater than cash going out, you typically want the air going into a building to be slightly greater than the air going out.  Similarly, think of a balanced scale.  In the graphic below, air is being drawn out of the building by exhaust fans, to remove heat and smoke from kitchen cooking appliances and foul air from the restrooms, at a rate of 4000 CFM (cubic feet per minute).  Air is also being introduced into the building through an outside air fan, to provide fresh breathing air for the occupants and to replace the exhausted air, at a rate of 4500 CFM.  The result is a slightly positive building pressure of 500 CFM (4500 – 4000 = 500), which signifies a balanced airflow.  Conversely, if the air coming into the building is slightly less than the air leaving the building, then you have a negative building pressure, which is the frequent culprit of many HVAC problems.

Which brings us to a crucial pairing to the air balance concept.  That is if balanced airflow is peanut butter, than a performance test is the jelly.

What is an air test & balance service?\
 

An air balance testing service is the process by which the performance of HVAC airflow is measured.  Once it is tested, the systems are then adjusted, or balanced, so that the air brought into a building is slightly greater than the air being pulled out of the building.  The benefit for testing and balancing being a combined service is explained by Rob Falke, President of the National Comfort Institute, “This [positive] pressure condition can be designed, but to be sure it actually happens requires air diagnostic testing.  However, it’s hard to say how great the positive pressure reading in the building will be. It depends on how tight (or leaky) the envelope of the building is, and what other pressure generating forces exist, including the wind, appliances, exhaust fans, and the stack effect of the building.”  The result is a comfortable, healthy indoor environment with an HVAC system that is optimized to perform efficiently.

 Sources:

  • Digital image. Air Concepts LLC. N.p., n.d. Web.  Nov 25 2015.
  • Falke, Rob. “How to Measure Building Pressures.” Contracting Business, 1 May 2006. Web. 25 Nov. 2015.

Authored By: Darren Witter

Darren Witter is the Vice President and General Manager of Melink T&B and has been with the company since 1996. Darren received his Mechanical Engineering degree from University of Cincinnati and is a State of Ohio Professional Engineer (PE). He is also certified as a LEED-accredited professional and an NEBB-certified professional. For more than 25 years, Melink T&B has been providing independent testing and balancing, and installation verification services to help building owners reduce operating costs and improve comfort.