An "air balance" is a useful process for measuring the performance of a simple
or complex hvac system, and for providing the occupants with a comfortably
To understand how this process works, let's first look at the different types of
air balance by defining the two extremes: Comfort Balance and AABC Certified
A "comfort balance" is
simply checking to see whether the room feels comfortably conditioned. It
may be as easy as walking from room to room, holding a hand up to the ceiling
to see if sufficient air is coming out of the registers, and asking the
occupants if they are comfortable. If they are not, your journey starts
to discover how to resolve the HVAC problems associated with the
situation. It may involve adjusting/moving registers, installing
restrictors/dampers after the fact, or just insuring the air doesn't blow
directly on an occupant. Many occupant complaints are associated with air
circulation: too much and too little.
At the other end of the spectrum is the AABC Certified Air Balance. The
purpose of this type is to insure all components of the hvac (heating,
ventilating, air conditioning) system are working in harmony, at their optimum
performance, providing total occupant comfort. While the journey toward a
certified air balance starts before the testing stage, let's begin ours with
the mechanical engineer.
A mechanical engineer develops specifications and a set of mechanical drawings
from a mix of occupant desires, local codes, ASHRAE standards, and many years
of training. The correct ducting, airflow, registers, and unit
performance are brought together with consideration for ventilation
requirements and building exhaust needs.
The most important part of the mechanical plans used by the certified balance
company is the list of "cfm" requirements next to each supply, return, intake,
exhaust and ventilation opening. Without this important information a
certified balance is not possible.
To conduct an AABC Certified Air Balance, the building must first be totally
sealed/enclosed. Therefore this process would fall under the modular
dealer's scope of work. If your project is complex, or your customer
includes a certified air balance in the bid specs, be sure to include the
following cost allowances on the front end:
A mechanical engineer
A system with products capable of a certified balance
The cost for a balancing company
An HVAC contractor on site during balance.
The HVAC contractor is advisable because, according to their association, a true
AABC certified balance contractor must not be affiliated with any mechanical
contractors, design engineers, or equipment manufacturers. So if the HVAC
unit needs service during the air balance process, and an HVAC contractor is
not on site, the balance will most likely stop.
A total air balance requires an opposed blade damper (OBD) behind the face of
each intake and exhaust opening in each room and of the building. Other
balancing dampers are required at all branch locations of the duct system.
At the building site prior to occupation, the certified balance technician will
change all of the filters in the system, and insure that all dampers are fully
open. Readings are taken at every opening inside, on the roof, etc.
Slowly the dampers are closed in an effort to meet the cfm requirements set by
the mechanical engineer. Adjusting one damper changes the cfm at all
other openings. The air balance technician returns to every opening,
making new adjustments and readings based on the changes from the previous
one. Registers, grills, exhaust fans, and fresh air must all "balance" to
meet the system performance requirements.
After the technician believes the system is all in tune, he locks down all of
the dampers and other devices, so that the settings will not change.
While this should keep the system "balanced," the system can be thrown out of
balance by such things as dirty filters, the occupants changing the register
setting, office remodeling, and reconfiguring registers and ducting.
The cost to do an AABC Certified Air Balance ranges from $75-150 per
opening. You're paying for time, labor, expertise, equipment, and a
Certified Balance Report. A building with five supply openings, five
return openings, one exhaust fan, and one OSA intake has 12 openings to
verify. Depending on the complexity and location of the openings, you can
expect to pay $900-$2,000 for an AABC Certified Balance.
Is it worth it on large projects? Definitely. Remember, to avoid
wasting money on your balance, be sure to install registers that the occupants
Hiring a good air balance company with skillful technicians is also
important. Visit www.aabchq.com for more information on the Associated
Air Balance Council and a member list. The website also lists the
requirements for membership, the types of certified technicians, their code of
ethics, and their performance guarantee.
We have looked at the simple and the perfect air balance types, just hitting the
high spots toward explaining certified air balance requirements and
results. This understanding may help you avoid the temptation to put only
$50 in your bid when you see your customer specifications requiring an AABC
Certified Air Balance. The $50 only covers the cost of the "waving the
hand" comfort balance.
So stay tuned up and balanced until the next time we meet in . . . The Comfort