Suction Groups; Controlling Sensor; Reference - Danfoss AK-PC 772A User Manual

Suction groups

Controlling sensor

The capacity distributor can regulate according to the suction
pressure P0.
The IT compressors are also regulated according to the suction
pressure, but the signal is received from the receiver - Prec. See
page 108 for IT description
An error in the controlling sensor will mean that regulation con-
tinues with fx. 50% cutin in daily operation and fx. 25% cut-in at
night, but for a minimum of one step.

Reference

The reference for the regulation can be defined in 2 ways:
Either
P0Ref = P0 setting + P0 optimization
or
P0Ref = P0 setting + night displacement + Ext. Ref
P0 setting
A basic value for the suction pressure is set.
P0 optimization
This function displaces the reference so that regulation will not
take place with a lower suction pressure than required.
The function cooperates with controllers on the individual
refrigeration appliances and a system manager. The system
manager obtains data from the individual regulations and adapts
the suction pressure to the optimum energy level. The function is
described in the manual for the System manager.
With this function you can read which appliance is most heavily
loaded at the moment as well as the displacement allowed for the
suction pressure reference.
Night displacement
The function is used to change the suction pressure reference for
night time operation as an energy saving function.
With this function the reference can be displaced by up to 25 K
in positive or negative direction. (When you displace to a higher
suction pressure, a positive value is set).
Displacement can be activated in three ways:
• Signal on an input
• From a master gateway's override function
• Internal time schedule
The "night displacement" function should not be used when
regulation with the override function "P0-optimisation" is performed.
(Here the override function will itself adapt the suction pressure to the
max. permissible).
88 Capacity controller RS8HF102 © Danfoss 2017-07
If a short change in the suction pressure is needed (for example,
up to 15 minutes in connection with defrosting) the functions
can be applied. Here the PO-optimisation will not have time to
compensate for the change.
Override with a 0 - 10 V signal
When a voltage signal is connected to the controller the reference
can be displaced. In the setup it is defined how big a displacement
is to take place at max. signal (10 V) and at min. signal.
Limitation of reference
To safeguard yourself against a too high or too low regulation
reference, a limitation of the reference must be set.
P0 ref
Max.
Min.
Forced operation of the compressor capacity in the suction
group
A forced operation of the capacity can be carried out which
disregards the normal regulation.
Depending on the selected form of forced operation, the safety
functions will be cancelled.
Forced operation via overload of requested capacity
The control is set to manual and the desired capacity is set in % of
the possible compressor capacity.
Forced operation via overload of digital outlets
The individual outputs can be set to MAN ON or MAN OFF in the
software. The control function disregards this but an alarm is sent
out that the outlet is being overridden.
Forced operation via change-over switches
If the forced operation is done with the switch-over on the front of
an expansion model, this is not registered by the control func-
tion and no alarm is sounded. The controller continues to run and
couples with the other relays.
AK-PC 772A