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AIR DISTRIBUTION SYSTEM ISSUES


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.

 

 

      Copyright Energy Environment Economics - 2003