Special Maintenance Considerations - Effective Building Maintenance: Protection of Capital Assets - page 90

(3) Determine the entering pressure to each terminal unit. If
this pressure is more than 15% higher than the sum of ter-
minal unit pressure loss and the downstream low pressure
ductwork losses, the fan is producing excess pressure that
can be reduced by changing the static pressure controller
setpoint (for VAV systems) or slowing the fan (for constant
volume systems).
(4) Finally, check the static pressure drop across each terminal
unit and compare this value to the design values in the orig-
inal balancing report or equipment submittal. If this value is
higher, the unit may need cleaning or repair.
— Water piping systems :
(1) Usingasingle,highqualitypressuregauge that is moved from
point to point, determine the pressure drop for each heat
exchanger in the system. Compare these values to the de-
sign values in the original balancing report or equipment
submittal. If any value is more than 15% higher, the heat
exchanger may need cleaning or repair.
(2) Check the pressure drop across strainers and clean if re-
quired.
(3) Sometimes, the pressure drop through the index circuit will
significantly exceed the pressure drop through the other cir-
cuits in the system. If this is the case, determine if the index
circuit can be re-piped to reduce losses. Another option is to
use a booster pump in this one circuit and shave the impel-
ler of the main pump(s) to reduce the available head to the
remaining circuits and, thus, save energy.
• Add/Remove an Airside Economizer Cycle : Airside economizers,
which provide “free” cooling using cold outdoor air, should not be
applied to dual duct or multizone secondary HVAC systems. If this
is the case, energy savings will result by eliminating the economizer.
(Note, however, that if the chiller must now run in the winter, modi-
fications to the chiller and its cooling tower may be required and a
waterside economizer may be more cost effective.)
For other types of air systems that require cooling during the
winter, though, an airside economizer can reduce cooling energy
consumption by 10-30%. For systems without return fans, imple-
menting an airside economizer cycle requires the addition of a re-