Danfoss ADAP-KOOL AK-PC 783, Design Manual, Page: 101 / 128

AK-PC 783 Capacity controller RS8GN202 © Danfoss 11-2013 101
Compressor timers
Time delays for cutins and cutouts
To protect the compressor against frequent restarts three time
delays can be put in.
- A minimum time to run from a compressor’s startup and until it
may be restarted.
- A minimum time (ON-time) for the compressor to operate before
it may be stopped again.
- A minimum OFF time to run from a compressor stops and until it
may be restarted
When unloaders are cut in and out, the time delays will not be
used.
Timer
The operating time of a compressor motor is registered continu-
ously. You can read out:
- operating time for the previous 24-hour period
- total operating time since the timer was last set to zero-set.
Coupling counter
The number of relay cutins and cutouts is registered continuously.
The number of starts can be read out here:
- Number during the previous 24-hour period
- Total number since the counter was last set to zero-set.
Example:
- Two speed-regulated compressors with a nominal capacity of
20 kW and frequency range 25-60 Hz
- Two one-step compressors, each of 20 kW
Best fit
During best-fit operations, the speed-regulated compressors can
have different sizes and they will be handled in such a way that
the best possible capacity adjustment is achieved. The smallest
compressor will be started first, then the first will be cut-out and
the second compressor will cut in. Finally, both compressors will
be cut in together and will run in parallel.
The following one-step compressors will, in every case, be
handled in accordance with the best-fit coupling pattern.
Example:
- Two speed-regulated compressors with a nominal capacity of
10 kW and 20 kW respectively
- Frequency range of 25-60 Hz
- Two one-step compressors of 20 and 40 kW respectively
Screw compressor with pulse width modulation (PWM)
The compressor can be connected as follows:
The PWM signal must be obtained from a solid state output.
The compressor motor and unloaders must be connected to the
relay outputs as shown.
Refrigeration
No refrigeration
The capacity from the digital scroll compres-
sor
The capacity is divided into period times as "PWM per". 100% ca-
pacity is delivered when cooling takes place for the whole period.
An off time is required by the by-pass valve within the period and
an on time is also permitted. There is "no cooling" when the valve
is on.
The controller itself calculates the capacity needed and will then
vary it according to the cut-in time of the by-pass valve.
A limit is introduced if low capacity is needed so that the cooling
does not go below 10%. This is because the compressor can cool
itself. This value can be increased if necessary.
The capacity can similarly be limited so that the compressor can-
not deliver 100% capacity. It is not normally necessary to limit this
max. capacity.