Arizona System Analysis Professionals, LLC

Common TAB Problems for Facility Managers


Sometimes HVAC problems are not what they first appear to be. A common problem that we run into, in usually but not always older facilities, is the air handling units not operating to capacity. You may have consulted with a mechanical contractor or even a mechanical engineer and their solutions may be to speed up the fan or possibly add a supplemental additional unit, or to add a whole new air handler.


Before you spend money on sheave changes or worse, a TAB mechanical survey can end up being an incredible money savings. Investing a little money in a survey and repairs to a duct system can save big money when compared to buying a new air handler and installing it on the same duct system that still needs repairs. Bigger fans or fan speed increases may ease a comfort issue, but keep in mind that an increase of 20% in flow will equal a 73% increase in power.


Over the years, facility personnel, usually in an effort to please one occupant will make an adjustment to one damper. At first this seems harmless but when you think about the consequences, this just becomes the first step in the long process of playing “chase the air”. Remember, most of the air you’re shutting down goes somewhere, if this additional air is not wanted where it ended up, then the adjustment process starts over again until every outlet on the system is somewhat closed, causing the total air from the air handler to reduce. This plus flex ducts that have become detached or kinked, ductwork that has developed leaks where it connects to a fan coil or VAV units, inaccurate outside air flow and more will all be caught and identified during a TAB Survey.


We have actually balanced a facility that had additional fan coil units installed to keep up with the cooling demand that their unbalanced VAV system could not keep up with. After the re-balance we had them turn off those unneeded fan coils. This facility paid to have these fan coils installed and ran these additional fans for 12 hours a day for multiple years. This building owner also paid for the additional maintenance costs to maintain these units, all because their system fell victim to facility personnel closing dampers over the years, to accomplish a quick fix for an uncomfortable occupant.