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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. Change over 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 Setpoint + 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 Setpoint + 3ºF, and it
has been 5 minutes since the last active call for heating has been terminated.
Figure 74. Heating/Cooling Changeover
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