Changeover Relay Operation; Comfort Ventilation Operation - York J Series Manual

CHANGEOVER RELAY OPERATION

The Changeover Relay (COR) is an external relay
driven by the controller that allows the controller to
operate 6 stages of cooling and 6 stages of heating from
6 controller outputs. The COR routes the stage signals
from the controller to the compressors when mechanical
cooling is required or to the staged heaters when heat-
ing is required.
The control of the Changeover Relay will be:
• For cooling operation: energize the COR output.
• For heating operation: deenergize the COR out-
put.
Verification of the COR operation is done through the
COR Status binary input (BI #15).

COMFORT VENTILATION OPERATION

Comfort Ventilation is applicable in CV unit configu-
rations where:
• Space temperature is sensed through a Thermostat
or Space Sensor.
• Economizer is installed.
Comfort Ventilation will operate when:
• Comfort Vent Mode is ON.
• Occupied is ON (occupancy detected).
• There is no call for heating or cooling due to the
Thermostat or Space Sensor.
• If Demand Ventilation and/or Outdoor Airflow Con-
trol are enabled, these control modes are the first
priority in establishing the OA Damper position.
Comfort Ventilation will operate as follows when
enabled:
• Supply Fan will remain ON when mechanical re-
frigeration or heating are OFF.
• The Outdoor Air Damper will be modulated be-
tween the Comfort Ventilation Maximum Damper
Position and the OA Damper Minimum Position
#1.
Economizer Control During Comfort Ventilation
Economizer control will use a PI controller that controls
SAT within the specified SAT band by repositioning the
economizer dampers. The PI controller setpoint will
be calculated as a midpoint between the programmed
JOHNSON CONTROLS
Cmfrt Vent High SAT setpoint and Cmfrt Vent Low SAT
setpoint. As the controller uses outside air to maintain
the SAT at the setpoint, it must be capable of self-
configuration for direct or reverse action, depending
on the relationship of the OAT to the specified SAT
control band:
• If the OAT is below the specified Cmfrt Vent Low
SAT setpoint, the action will be direct acting. In this
case, the economizer control can lower the SAT tem-
perature just by opening the economizer damper and
using more outdoor air. However, if the economizer
controller can not prevent the SAT from dropping
below the bottom control band limit by closing the
economizer damper to its programmed minimum
position, one or more heating stages are turned ON
as required. Similarly, if the economizer controller
can not prevent the SAT from increasing above the
top control band limit by opening the economizer
damper to its programmed Cmfrt Vent High SAT
setpoint, one or more compressors will be turned
ON as required.
• If the OAT is above the specified Cmfrt Vent High
SAT setpoint, the action will be Reverse Acting. In
this case, the economizer control can increase the
SAT temperature just by opening the economizer
damper and using more outdoor air. However, if
the economizer controller can not prevent the SAT
from increasing above the top control band limit by
closing the economizer damper to its programmed
minimum position, one or more compressors will be
turned ON as required. Similarly, if the economizer
controller can not prevent the SAT from dropping
below the bottom control band limit by opening the
economizer damper to its programmed Cmfrt Vent
Low SAT setpoint, one or more heating stages will
be turned ON as required.
• If the OAT is within the SAT control band, (i.e.
between the programmed Cmfrt Vent High SAT
setpoint and Cmfrt Vent Low SAT setpoint), the
economizer damper will be overridden to fully
open position subject to OA flow requirements if
installed and enabled. In this case, no other control
action needs to be taken to maintain the SAT within
the specified control band.
Staging Control During Comfort Ventilation
The economizer control alone may not be able to
maintain the SAT within the specified control band.
A separate staging control algorithm supplements the
economizer control and will stage heating or mechanical
cooling as necessary.
FORM 100.50-NOM7 (808)
35
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