Configuration Manual

Version Document
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001
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ccess V4.X Configuration manual
22 (56) 2018-07-11
DX cooling with exchanger control
When running cascade control, the supply air controller setpoint is normally
controlled by the room/extract air controller output signal.
When DX cooling is activated, the supply air controller setpoint is lowered to five
degrees (adjustable) below the setpoint given by the room/extract air controller.
This prevents the DX cooling from being activated/deactivated too often. 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 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).
Blocking of DX cooling at low outdoor temperature
DX cooling can be blocked when the outdoor temperature is low. It is possible to
block the three cooling steps individually or to block all DX cooling. The
temperature limits are adjustable (+13°C default) and have a fixed one degree
hysteresis.
When two DX cooling steps are used with binary function, the cooling effect is
divided into three steps. The desired blocking level can be set individually for each
of these steps.
When three DX cooling steps are used with binary function, the cooling effect is
divided into seven steps. However, the controller still only has three blocking level
settings. Therefore, Blocking step 1 will apply to binary steps 1 and 2, Blocking
step 2 to binary steps 3 and 4, and Blocking step 3 to binary steps 5, 6..etc.
Blocking of DX cooling at low supply air fan speed
When DX cooling is used in conjunction with pressure controlled or flow controlled
fans it is possible to block DX cooling if the supply air fan control signal falls below
a preset values. For sequential control, the blocking level is individually settable for
each DX cooling step.
When two DX cooling steps are used with binary function, the cooling effect is
divided into three steps. The desired blocking level can be set individually for each
of these steps.
When three DX cooling steps are used with binary function, the cooling effect is
divided into seven steps. However, the controller still only has three blocking level