TAB Journal Summer 2019 - 19

The next step, after OA airflow calibration has been
completed, is to drive all VAV boxes to maximum airflow
to determine the "worst case scenario" VAV box. This VAV
box will be the one with the lowest percentage of design
maximum airflow or the highest percentage of damper open
per the control system display. Once the worst case scenario
box has been determined, increase AHU VFD speed, or close
surrounding VAV boxes until it achieves design maximum
airflow at a 90 percent open, per the control system display. In
going through this process, it is understood that the worst case
scenario VAV box is operating under control. The next step is
to verify what AHU down-duct SP was required to satisfy the
worst-case scenario VAV box. This SP value then becomes the
AHU static pressure setpoint.

which VAV boxes need to be set at maximum airflow, and
which ones need to be at minimum airflow, and set the VAV
boxes accordingly, such that the total airflow equals the
AHU's scheduled maximum airflow. If maximum airflow
is not achieved at this point adjust the AHU VFD speed to
get back to maximum airflow. Please note that if any speed
changes are required, the system static pressure setpoint
needs to be re-evaluated and the minimum outdoor airflow
reverified before AHU testing is completed. Measure, read
and record all final AHU airflows (i.e. SA, OA and RA),
and take a SP profile across all unit components. The VAV
AHU setup is now complete.

Once the AHU SP setpoint has been established, the next step
is to drive all VAV boxes to maximum airflow and allow the
AHU system to settle out (reach steady state). Once steady
state operation has been achieved, verify that the OA airflow
is still at the specified design minimum airflow value. With
the AHU operating at maximum airflow, and the OA airflow
correct, the RA airflow system can now be balanced. It should
be noted that in the last step, you only drive all VAV boxes to
maximum airflow if the system has no diversity.

As I stated previously, the correct setup of a VAV system
is not rocket science, but it does require a deliberate,
methodical approach combined with a systematic protocol
to achieve correct results. This summary has presented
such a protocol, and I have used this same protocol to
accomplish the successful setup of numerous VAV systems.
Feel free to use it, and I would welcome any feedback. It
should be understood that the protocol presented here is
the most basic and straightforward protocol for setting up
a simple VAV system. With today's more sophisticated
control systems, more "bells and whistles" have been
added, and many more control strategies now exist, such
as VAV box static pressure reset. In addition, there are also
other energy saving strategies, such as optimizing the AHU
SP setpoint for minimum airf low, like what was done for
maximum airf low.

After the RA airflow system has been balanced, the next
step is final AHU setup. Prior to final setup, check the
condition of the AHU filters (prefilters and final filters if
applicable), and have the installing contractor install a clean
set of filters. Set the AHU for maximum airflow and wait
for the VAV boxes to settle out. For final airflow setup,
if the AHU has been specified with diversity, determine

Conclusion

Need a Better

Test & Balance Spec?
AABC CAN HELP!

■ Specify for Independence ■ Recommended, achievable
tolerances
■ Detailed contractor
responsibilities to ensure ■ Detailed procedural requirements
readiness for T&B
■ AIA format, MasterSpec approved
For more information: www.aabc.com/specifications
Email headquarters@aabc.com, or call 202-737-0202

TAB Journal Summer 2019

19


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TAB Journal Summer 2019

Table of Contents for the Digital Edition of TAB Journal Summer 2019

TAB Journal Summer 2019 - Cover1
TAB Journal Summer 2019 - Cover2
TAB Journal Summer 2019 - 1
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TAB Journal Summer 2019 - Cover3
TAB Journal Summer 2019 - Cover4
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