Sequence Of Operation; Cooling Mode - Danfoss MCX-RTU User Manual

User Guide | MCX-RTU Rooftop

Sequence of Operation

© Danfoss | ADAP-KOOL® | 2018.11

Cooling Mode

The Controller is in Cooling Mode when the Zone Temperature is above Cool1 Target minus two
times the programmed Cool Range. At this point Free Cooling will be active if the Damper and
Free Cooling are enabled. The Damper will modulate to maintain the Supply Air or Mixed Air
target temperature. Free Cooling is enabled when Zone Enthalpy is above Outdoor Enthalpy and
the above conditions are met. Free Cooling will lockout if the Outdoor Enthalpy, Temperature or
Relative Humidity are above their specific lockout values.
The Cooling stages will become active when the Zone Temperature is above Cool1 Target minus
the Cool Range. Before any cooling stages are activated, the fan must be proofed by either a
digital input or analog input to insure the fan is operational. The method of operation depends
on the Cooling stages configuration. It is required for the previous stage of Cooling be ON prior
to the next stage activating.
If all Cooling stages are configured to use Relay Outputs, then the stages will turn on at Cool
Target plus the Range and off at Cool Target minus the Range. Each stage has a Target, PreDelay
and PostDelay. PreDelay is the delay period once the conditions have been met for the stage to
activate. PostDelay is the period the output will stay on once the conditions have been met for
the stage to deactivate.
If any cooling stages are configured to use an Analog Output, the sequence of operation chan-
ges. All stages that use an Analog Output must precede stages that use Relay Outputs. In this
configuration, the first stage will start when the Zone Temperature reaches the Cool 1 Target
minus the Range. The Analog Output will be set to the Min Compr1 Speed. The speed ramps to
100% when the Zone Temperature reaches the Cool 1 Target plus the Range. When Zone Tempe-
rature reaches the Cool 2 Target minus the Range the second stage activates, and the first stage
reduces to Min Compr1 Speed. If the second stage uses an Analog Output, then the output will
use the same value used by Cool Stage 1. If there are more than 2 stages, Min Compr Speed will
adjust so the total cooling capacity will equal the maximum capacity of the previous cooling
stage. All the Cooling Analog Outputs will always be in sync as they rise.
Fan control during Cooling Mode depends on the type of fan controlled. For Single Speed Fan,
the fan will be ON whenever there is a demand for cooling. If the fan is configured for con-
tinuous operation, then the fan runs all the time. For Two Speed Fan, the fan will be on high
speed whenever there is a demand for cooling. If the fan is configured for continuous operation,
the fan will switch to Low Speed with no demand for cooling. If the fan is configured for On
Demand, the fan switches off when there is no demand for cooling. For Variable Speed Fan, the
fan modulates to maintain the Cooling Supply Air Target with a demand for cooling. If the fan
is configured for continuous operation the fan modulates to the Cool Min Fan Speed with no
demand for cooling. If the fan is configured for On Demand, and there is no demand for cooling,
the fan either modulate to Cool Min Fan Speed or turns OFF, depending on setting of the Fan
Control Demand parameter.
Note: On DOAS units with more than 2 stages of cooling, the first two stages turn ON together.
With the balance of the stages turning ON sequentially.
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