8
User
Guide RS8GR602 © Danfoss 2016-10
AK-CT
450A
Control of two compressors
(application 8)
The two compressors must be of the same size.
When the controller demands refrigeration it will first cut in
the compressor with the shortest operating time. After the time
delay the second compressor will be cut in.
When the temperature has dropped to ”the middle of the
differential”, the compressor with the longest operation time
will be cut out.
The running compressor will continue until the temperature
has reached the cutout value. Then it will cut out. When the
temperature again reaches the middle of the differential,
a compressor will again be started.
If one compressor cannot maintain the temperature within the
differential, the second compressor will also be started.
If one of the compressors has run on its own for two hours,
the compressors will be changed over so that operational time
is balanced.
The two compressors must be of a type that can start up against
a high pressure.
The compressors’s settings for ”Min On time” and ”Min Off time”
will always have top priority during normal regulation. But if one
of the override functions is activated, the ”Min On time” will be
disregarded.
Railheat
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
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%. (o87)
• One where the effect must be min. (o86).
At a dew point which is equal to or lower than the value in 086,
the effect will be the value indicated in o88.
In the area between the two dew point values the controller will
manage the power to be supplied to the rail heat.
During defrosting
The rail heating will be active during defrosting (as selected
in setting d27).
Dew point
Rail heat
