Special Maintenance Considerations - Effective Building Maintenance: Protection of Capital Assets - page 89

The first step in converting the either system is to modify termi-
nal units for variable airflow. This can be done by either replacing
existing terminal units with new VAV units (the preferred method)
or adding a new VAV air valve upstream of the existing terminal
unit. If the second option is selected, it will be necessary to remove
the constant volume regulator in the exiting terminal unit which, for
older mechanical type regulators, will reduce the system static pres-
sure requirement by as much as 1” wg.
The terminal unit controls, then, must be modified to allow
50-70% airflow reduction before the heating/reheating coil is ener-
gized.
At the AHU, a variable frequency drive (VFD) is required for
each supply and return fan, controlled on the basis of supply duct
static pressure.
The savings from this conversion can be as much as a 50% re-
duction in air transport, heating, and cooling energy consumption.
• Reduce Distribution Pressure Losses : Excess pressure losses in air
duct and water piping systems increase transport energy consump-
tion. The resistance to flow in a duct or piping system is the sum of
the resistances in the index path or circuit, i.e., the path or circuit
with the largest resistance to flow. By locating and improving the
pressure losses in the index path or circuit, fan or pump energy can
be reduced. To determine the index path or circuit and identify high
losses that can be addressed, the following procedures can be used:
— Duct systems :
(1) Using a magnahelic pressure gauge with flexible tubes and
simple ¼” copper tube static pressure probes, measure the
pressure drop across the primary AHU components (coils,
filters, fan, etc.) Compare these values against the “new”
values in the original balancing report or equipment sub-
mittals. If the measured values are more than 10% higher,
maintenance of filters, coils, fans, etc. is required.
(2) Starting at the AHU, measure the duct static pressure up-
stream and downstream of each change of direction (elbow)
or branch connection (tee) to determine if there are excess
pressure drops. Check on each side of every fire and/or
smoke damper to determine if the fire damper is partially
(or completely!) closed.