DX system is controlled by a separate controller. DX cooling is normally used in conjunction with room cascade temperature control or extract air cascade temperature control.

When running cascade control, setpoint of the supply air controller is controlled by the output signal of the room/extract air controller .

When DX cooling is activated, the supply air controller setpoint is lowered to five degrees (adjustable). This prevents the DX cooling from being activated/deactivated too often.


DX cooling can be set to include exchanger control (type of cooler: DX cooling with exchanger control).


If the supply air temperature falls below the setpoint given by the room/extract air controller, the heat exchanger output will be activated in order to try to maintain the supply air setpoint given by the room/extract air controller. The output uses P-control with a P-band of half the setpoint lowering (adjustable, 2.5 °C as a default). The setpoint given by the room/extract air controller cannot drop below the set min limit. When there is no longer a cooling demand, the supply air controller setpoint will return to the value given by the room/extract air controller.


Note: The function cannot be used if the exchanger signal controls a mixing damper.


Example:        

The room controller gives a supply air setpoint of 16 °C. If there is a cooling demand, the supply air controller setpoint is lowered to 11 °C (16-5) and DX cooling is activated. Should the supply air temperature fall below 16 °C, the exchanger output will be activated and reach 100 % output when the supply air temperature has fallen to 13.5 °C (16-2.5).


The table below shows a configuration example of the DX cooler control with alarm monitoring.



Variable

Available options & Selection

Note


Sequence selection

Configuration > Functions > Function activation > Heating/Cooling sequence setup

Sequence for cooling

| SEQ-A | SEQ-B | SEQ-C Cooling |...|



Sequence settings

Configuration > Functions > Function activation > Heating/Cooling sequence setup > Cooling

Type of sequence

|Cooling | Exchanger | Heating | Damper | Fan setpoint compensation |


Type of cooler

| Water | DX | DX with exchanger control |


Type of feedback

| None | Alarm | Run indication |


Digital start output

| No | Yes |


Sequence output when recirculation/support

| 0% | 100% | Auto |


Sequence output min limit

0%


Sequence output max limit

100%


Sequence output when the unit is stopped

0%



PID Settings

Configuration > PID controllers > Cooling

P-band

10 oC

PID settings for the sequence

I-time

100 s

D-time

0 s


Hardwired interface to the pump & valve

Configuration > I/O allocation settings >

Digital inputs > Feedback cooling (SEQ-C)

Any available I/O


Digital outputs > Cooling start (SEQ-C)


Analog outputs > Cooling (SEQ-C)

Cooling sequence output (input for DX)


Cooling control settings

Data & Settings > Temperature control > Cooling

Digital start output start point

10%

Output of the supply controller to start and stop the DX cooler

Digital start output stop point

1%


Block DX-cooling if outdoor temperature <

0 oC


Block DX-cooling if supply air fan output signal <

0%


Hysteresis if outdoor temperature block

1 oC


Reduction of min limit supply air is active DX-cooling

5 oC


Valve flowrate at fully open position

100.00 l/s

value used for internal calculation


Flowchart setup

Configuration > Functions > Flow chart setup

Type of DX cooler

|DX coil | SoftCooler |



Graphical representation

Flowchart


35% - indication of sequence output


Alternatively DX coil can be displayed as integrated cooler (soft cooler)


Variable

Available options & Selection

Note


Flowchart setup

Configuration > Functions > Flow chart setup

Type of DX cooler

|DX coil | SoftCooler |



Graphical representation

Flowchart


35% - indication of sequence output