STL: IMPROVING EFFICIENCY OF
Lambert-St. Louis International Airport (STL) spent
2011 in the midst of a major renovation of its Terminal
1 building, including upgrades to the terminal’s main
air handlers. The terminal, originally designed in 1953,
hadn’t seen a comprehensive renovation since 1978.
The project included full replacement of four of the
terminal’s main air handlers, including associated
controls. The units had control concepts common
in the 1970s: constant-volume airflow, three-way
hydronic valves, and dual-deck multi-zone
configurations. Of particular concern: the multizone
The multizone units served multiple independent
zones of the building by simultaneously heating
and cooling air. The system relied upon dampers
to mix the air to meet each zone’s specific needs.
While the system did work, it worked all the time —
simultaneously heating and cooling air for 365 days
per year, resulting in high energy costs.
In a perfect situation, the multizone equipment could
be replaced with a modern variable air volume (VAV)
control strategy by adding air terminal devices in
individual zones. But there simply wasn’t enough
space in the 1950s building to accommodate
Having ruled out the typical approach, the project
team opted to implement modern controls.
First came replacement of thermostats and addition
of a full DDC system to affected equipment, followed
by reproduction of the functionality of a VAV air
terminal device inside the existing ducts within the
mechanical rooms themselves.
This second part of the approach proved the most
challenging. Fitting components into the space
already was difficult, but the location of terminal
devices within the mechanical room made system
controllability even more difficult. In a typical VAV
system the controller senses duct pressure from a
location far downstream from the mechanical room,
then uses that information to obtain a smooth input
signal. If the sensor is near the mechanical room,
pressure fluctuations from the fan can result in a
The project team overcame the problem of noisy
pressure measurements by putting it to a vote,
literally. Fan speed, and therefore system pressure,
was set to an initial value and then changed on a
regular interval – about every five minutes — based
on votes received from each air terminal controller.
If an air terminal closed more often than expected,
the controller would vote for lower system pressure.
Likewise, if an air terminal was open too far, its
controller would vote for higher system pressure.
Making the system smarter enabled the system to
adapt to a situation where a traditional approach
would have failed.
JIM ROSICK, firstname.lastname@example.org, is a project
manager and manager of the Aviation Group for
Burns & McDonnell in St. Louis. ROSS TRUITT,
email@example.com, is a project manager
for the firm in Chicago.
Air-handling systems helped Lambert-St. Louis International Airport adapt.