CNT-SVX04A-EN
Sequence of operation
66
Four-pipe changeover units capable of both hydronic heating and hydronic
cooling with the main coil determine their mode based on the following
sequence (summarized in Table 38):
1
If the controlled space requires heating or cooling, the controller changes
from heating to cooling and cooling to heating based on the space
temperature, active setpoint and the integrated error between the two. Once
the controller changes modes, it verifies the entering water temperature.
If the controller does not have available
the entering water temperature, either
communicated or hardwired on a
changeover coil, the controller restricts the
hydronic cooling capacity to 0% and only
allows heating.
2
When the main/primary coil entering water temperature is not appropriate
for cooling, the controller can change to cooling mode, but remains at 0%
capacity for hydronic capacity. When the main/primary coil entering water
temperature is not appropriate for heating, the controller can change to
heating mode and use the auxiliary coil for heating.
3
When the entering water temperature is appropriate to deliver the desired
heating or cooling, the controller selects the primary coil to deliver heating
or cooling and resumes normal operation.
Table 38
4-pipe main and auxiliary coil operation
Note
1
:
The entering water temperature sensor is normally applied to changeover units on the main
coil. Since the controller cannot determine the auxiliary coil water temperature, the auxiliary coil is
assumed hot.
For more information about 4-pipe operation, see
Coil changeover
on page 58.
Two-position damper operation
The Tracer ZN.520 zone controller does not support 2-position outdoor air
damper.
A form of 2-position control can be accomplished using a modulating outdoor
air damper actuator and the damper minimum position value. This is
accomplished by not providing an outdoor air temperature, either hardwired or
communicated, to the controller, and using the Roverservice tool to set the
damper minimum position to the desired value.
Unit
Entering water
temperature
Main coil
Auxiliary coil
Operation
4-pipe
Not present
Cold
Assumed hot
1
Main coil cooling,
Auxiliary coil heating
4-pipe changeover
Cold
Cold
Assumed hot
1
Main coil cooling,
Auxiliary coil heating
Hot
Hot
Assumed hot
1
Main coil heating,
Auxiliary coil not used
