These charts are actual Test and Balance data collected prior
to the redesign and implementation of numerous systems corrections
to the supply, return and outside air distribution systems of
a new heart hospital, and are indicative of issues plaguing
air distribution systems in general. The outside air system
utilized one large “passive” (not forced air) outside air duct
that was tapped into for each individual air handling units’
ventilation requirement. Several of the air handling units had
100% (airside economizer) outside air capability, making the
corrective measures much more complicated. Modifications included:
- Replacement of the existing outside air ducts supplying each
air handling unit with much smaller (with higher, controllable
velocities) ducts equipped with airflow measuring stations.
- DDC system sequences of operations modifications that incorporated
a positive method of outside air control, including actuation
of the outside air and mixed air dampers and return air fans
to maintain the pressure relationships required for outside
air control.
From the charts below, it is obvious that severe issues existed
with the supply air distribution system. Those included:
• Enormous (up to approximately 1”) pressure drops across numerous
smoke fire dampers throughout the facility.
• Excessive pressure drops due to system effect losses at
the air handling units’ discharge duct configurations and
general ductwork practices
• Use of inlet guide vanes for capacity control on some of
the supply air and return air fans
• Supply air and return air fan tracking algorithms that were
completely (used a % of speed to control the return air fans)
substandard
These conditions shifted the system curve
as shown above. Obviously, even at 100% speed, the fans were
unable to deliver design airflow. As a result, the air distribution
system was not only unable to take advantage of variable airflow
capabilities it was also seriously deficient in maintaining
temperature and humidity control throughout the facility. The
charts below are indicative of this condition.
This HVAC air distribution system - click
here to read more of the innovative analysis and design
practices used to correct these issues – vividly illustrates
the variety of ills experienced by air distribution systems
in general. We often encounter systems using unnecessary, energy
consuming return air fans. We often encounter systems using
unnecessary fan-powered VAV boxes that present other tests to
system efficiency. Energy-Environment-Economics
is uniquely qualified to solve all of your HVAC system related
operational and energy efficiency challenges.
