Installation Guide Manual

If there is a call for reheat to maintain room temperature, the primary airflow
is set to the value of Auxiliary Flow.
Warm Air Available
In the heating mode, as the Heating Loop increases
from 0% to 100%, Primary Airflow Setpoint is proportionally calculated
between Minimum Heating Airflow and Maximum Heating Airflow.
See also the topics, Changeover on page 62 and Input sources on page 58.
Changeover
The Discharge Air Temperature input is used by the controller to determine
the type of air that is being supplied by the AHU. The sensor is required for
applications that require automatic change over between cooling and heating.
When the Heating loop is inactive, the Discharge Air Temperature input is
compared to the SAT Changeover Temp. If the Discharge Air Temperature is
below the SAT Changeover Temp minus 2°, the SAT Changeover Mode is set
to Cool. If the Discharge Air Temperature is above the SAT Changeover Temp
plus 2° Fahrenheit, the SAT Changeover Mode is set to Heat. The default
changeover temperature is 74° Fahrenheit.
See the topic Discharge Air Temperature (DAT) limiting on page 62 and Input
sources on page 58.
Discharge Air
Temperature (DAT)
limiting
A Discharge Air Temperature senor and DAT limiting is required to control
VAV units with reheat. If a Discharge Air Temperature (DAT) sensor is
detected and DAT Limiting is enabled, the VAV terminal will be controlled
by the DAT loop. The unit will also limit the Discharge Air Temperature to
within 15° F of the Space Temp Reference.
When there is a call for heat and the primary air is cool air, the reheat outputs
are directly controlled by the DAT Loop and the DAT Setpoint reset based
on the output of the Heating loop. As the Heating loop increases from 0% to
50%, DAT Setpoint is proportionally calculated between Space Temp
Reference and Space Temp Reference + 15° F up to maximum 90° F. This
allows the reheat to be controlled by the DAT loop over the first 50% of a call
for heating.
Section 7: Sequences of operation SimplyVAV
62 Revision E