Filter
Top Products
70 TRG-TRC014-EN
notes
period five
Application Considerations
With all three components, DDC controls on the VAV terminal units and air
handler, a method to measure outdoor airflow at the air handler, and a
communicating building automation system (BAS), a VAV system can use the
multiple-spaces equation (Equation 6-1) from Standard 62 to dynamically
operate the VAV system.
Each VAV terminal unit continuously monitors primary airflow. The DDC
controller also knows the ventilation air requirement. With this information, the
controller can continuously calculate the space ventilation fraction of the space,
or (the ventilation airflow required divided by the primary airflow being
delivered). The BAS periodically gathers this data from all the VAV terminal
units and solves Equation 6-1. This determines the amount of outdoor airflow
that must be introduced at the system level, at the central air handler, to satisfy
the ventilation requirements. The BAS then resets the outdoor airflow set point,
and the outdoor airflow measuring device controls the damper accordingly.
This method, called ventilation reset, ensures that all spaces are properly
ventilated at all load conditions while minimizing wasteful overventilation.
Ventilation Reset
VAV terminal units
VAV terminal units
with DDC controls
with DDC controls
OA
RA
PA
central air handler
central air handler
with controls
with controls
outdoor airflow
outdoor airflow
measurement
measurement
and control
and control
communicating BAS
communicating BAS
Figure 97