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RS8HP102 © Danfoss 2018-09
AK-CC 750A
Fan control
To obtain energy savings it is possible to reduce the power supply
to the fans at the evaporators. The reduction can be done:
- during the thermostat’s cutout period (cold room)
- during night operation and during the thermostat’s cutout pe-
riod (appliance with Night blind)
It can be controlled by one of the following 4 fan types:
Single speed fan
One relay is used here to control the fans. This relay can be pulse
controlled, but only when all sections/evaporators are cut out
.
A period of time is set as well as the percentage of this period of
time where the fans have to be operating.
2-speed fans
Two relays are used here to control the fans. One relay will pro-
vide full speed for the fans, and when the second relay triggers,
the speed of the fan motors is reduced. The relay for reduced
speed will be referred to as 'eco' in the setup of outputs.
Fan with EC motor
Here the controller must use an analogue output module that
can deliver the desired voltage to the EC motor. 0 - 10 V, 2 - 10 V,
0 - 5 V or 1 - 5 V.
The desired fan speed is given as a percentage of the output
signal i.e. 0 - 100 %. For example, 90 % during normal daytime
operation and 70 % during eco operation.
Different values can be set for the four operating modes: Normal
day, Normal night, Day with thermostat disconnected, Night with
disconnected thermostat.
A minimum start speed can be set. This setting will only apply for
10 seconds after the start.
Fans that are controlled by a frequency converter (VSD)
The controller must use an analog output module for these with a
starting relay for on/off control of the converter.
The settings are the same as for EC motors
Stop of fans if cooling is missing
If the refrigeration in a breakdown situation stops, the temperature
in the cold room may rise quickly as a result of the power supply
from large fans. In order to prevent this situation the controller can
stop the fans if the temperature at S5 exceeds a set limit value.
The function can also be used as a sort of MOP function during
start-up with a hot evaporator. The fans will not start until the S5
temperature has been reached below the set limit value. In other
words, the evaporator and hence the compressor wll not be so
heavily loaded during the startup phase.
The function uses the S5 sensor from section A.
The function is not active when refrigeration has stopped.
Rail heat control
It is possible to pulse-control the power to the rail heat in order to
save energy. Pulse control can either be controlled according to
day/night load or dew point.
Pulse control according to day and night
Various ON periods can be set for day and night operation.
A period time is set as well as the percentage part of the period in
which the rail heat is ON.
Pulse control according to dew point
In order to use this function a system manager of the type AK-SM
720, 850, AK-SC 255 or 355 is required which can measure dew
point and distribute the current dew point to the appliance
controllers. For this the rail heat’s ON period is controlled from the
current dew point.
Two dew point values are set in the appliance control:
• One where the effect must be max. i.e.100%.
• One where the effect must be min.
At a dew point which is equal to or lower than the value, the effect
will be the value indicated in "Rail heat min ON%".
In the area between the two dew point values the controller will
manage the power to be supplied to the rail heat.
The current dew point and duty cycle for rail heat can be read off
as status values.
If the dew point signal cannot be distributed to a controller, the
rail heat will revert to day/night control.
During defrost the rail heat will always be 100% ON.
If rail heat ON is selected, it will run at 100% during d the
time after defrost if the thermostat temperature is above the cut-
in limit (but max. 15 minutes).
Common functions
Railheat.
Min. ON%
Effect
Dew point
