Ingersoll-Rand ReliaTel, Manual, Page: 150 / 176

150 RT-SVD03L-EN
Heating/Cooling Changeover
The change over from heating to cooling is
accomplished in two different ways. The first drawing
below illustrates change over in a system without an
economizer, and the second drawing illustrates change
over in a system with an economizer. Changeover from
cooling to heating is accomplished in the same manner
for both economizer and non-economizer systems.
If the unit is in the cooling mode and the zone
temperature is falling, the unit will change to the
heating mode when the zone temperature is less than
the heating set point and it has been 5 minutes since
the last active call for cooling was terminated. For
systems without economizers or with economizers, but
the economizer is enthalpy disabled, if the unit is in the
heating mode, and the zone temperature is rising, the
unit will change to the cooling mode when the zone
temperature is greater than the greater of the Active
Cooling Setpoint or Active Heating Se 3ºF, and
it has been 5 minutes since the last active call for
heating has been terminated. For systems with
economizers and the economizer is enthalpy enabled, if
the unit is in the heating mode, and the zone
temperature is rising, the unit will change to the
cooling mode when the zone temperature is greater
than the greater of the economizer setpoint or the
Active Heating Se 3ºF, and it has been 5
minutes since the last active call for heating has been
terminated.
Figure 97. Heating/cooling changeover
ZTEMP
falling
ZTEMP
falling
CSP
CSP
ESP
HSP + 3F
HSP
HSP + 3F
HSP
ZTEMP
rising
ZTEMP
rising
without economizer
with economizer
change
to heating
change
to heating