But the cost to install a VFD — or retrofit an existing system
— has come down significantly to be comparable to the cost of
installing a constant speed hydrant system. Additionally, systems
that may have functioned properly and made sense 10 or
20 years ago are now likely to be in need of repairs or
replacement, making this the prime time to explore how a VFD
system might be the best solution for aircraft fueling needs.
Preconditioned Air Systems
Keeping Passengers Comfortable
By Janelle Burd, PE, LEED AP,
and Grant Smith, PG
Preconditioned air (PCA) systems cool and heat aircraft
parked at the gate and pre-cool/pre-heat the passenger
boarding bridges for passenger comfort during loading and
off-loading operations. A life cycle cost analysis study can
identify the most economical option for each airport based
on number of gates, gate usage schedule, local utility rates,
initial capital cost and terminal space availability.
For equipment to be effective, it must be sized so that it
can accommodate varying sizes of aircraft serviced at each
gate, and account for design temperatures assigned to its
To determine a system’s size, designers:
• Consult gated flight schedules to see what types of planes
each gate serves, and when such planes arrive and depart.
• Obtain the maximum ambient design temperature for the
airport’s location, then calculate planes’ conductive and
solar load conditions.
• Identify the largest type of plane to be served, during the
hottest and coldest times of day during the hottest and
coldest days of the year.
• Factor in heat gained when planes are full, have most of
their electrical equipment operating, and are absorbing
heat (or cold) from the outside.
PCA systems cool — or heat, if it’s winter — outside air
to a range of 30 to 35 degrees, to be pumped into each
connected plane and passenger bridge. Such air comes in at
relatively high pressure so that it can make its way through
the plane’s small ductwork for supply air.
The maximum volume of supply air is the pounds per minute
of outside air cooled to 30 degrees (leaving coil temperature)
required to meet aircraft cabin cooling load.
VFD systems operate between 120 psi and 145 psi, do not
require pressure control valves in the hydrant system, and
use motor-operated valves for emergency fuel shut-off.
A simplified view of the advantages VFD systems bring shows
reduced speed during off-peak times, which translates to
significant savings on energy and operation costs.