Danfoss AK-PC 781A

132 Capacity controller RS8HE202 © Danfoss 2017-07 AK-PC 781A
Example 1
In this example, the speed-regulated compressors are of the same
size and the following one-step compressors are of different sizes
Increasing capacity:
- The speed-regulated compressor with the least operating hours
(C1) starts when the desired capacity equals the start speed
- When the first speed-regulated compressor (C1) has reached
max. speed (60 Hz), the second speed-regulated compressor
(C2) cuts in so that the compressors run in parallel
- When the two speed-regulated compressors reach full speed
(60 Hz), the small one-step compressor (C3) is cut in
- When the two speed-regulated compressors again reach full
speed (60 Hz), the large one-step compressor (C4) is cut in and
the small one-step compressor (C3) is cut out
- When the two speed-regulated compressors again reach full
speed (60 Hz), the small one-step compressor (C4) is cut in
again.
- When the one-step compressor is cut in, the speed is reduced
on the speed-regulated compressor (35 Hz) corresponding to
the cut in capacity
Decreasing capacity:
- The small one-step compressor (C3) is cut out when the speed-
regulated compressor reaches the min. speed (25 Hz)
- When the two speed-regulated compressors again reach min.
speed (25 Hz), the big one-step compressor (C4) is cut out and
the small one-step compressor (C3) is cut in
- When the two speed-regulated compressors again reach min.
speed (25 Hz), the small one-step compressor (C3) is cut out
- When the two speed-regulated compressors again reach min
speed (25 Hz), the speed-regulated compressor with the most
operating hours (C1) is cut out
- The last speed-regulated compressor (C2) is cut out when the
requirements for this are fulfilled
- When one-step compressors cut out, the speed-regulated
compressors increase speed (50 Hz), corresponding to the cut
out capacity
Example 2:
In this example, the speed-regulated compressors are of different
sizes and the following one-step compressors are also of different
sizes.
Increasing capacity:
- The smallest speed-regulated compressor (C1) starts when the
desired capacity equals the start speed
- When the smallest speed-regulated compressor (C1) has
reached max. speed (90 Hz), the large speed-regulated com-
pressor (C2) cuts in and the small speed-regulated compressor
cuts out.
- When the large speed-regulated compressor reaches max.
speed (90 Hz), the small speed-regulated compressor (C1) cuts
in again so that the compressors run in parallel
- When the two speed-regulated compressors reach full speed
(90 Hz), the small one-step compressor (C3) is cut in
- When the two speed-regulated compressors again reach full
speed (90 Hz), the big one-step compressor (C4) cuts in and
then the small one-step compressor (C3) cuts out
- When the two speed-regulated compressors again reach full
speed (90 Hz), the small one-step compressor (C3) is cut in
again.
- When the one-step compressors are cut in, the speed decreases
on the speed-regulated compressor (56.7 Hz) corresponding to
the cut in capacity
Decreasing capacity:
- The small one-step compressor (C3) is cut out when the speed-
regulated compressor reaches min. speed (30 Hz)
- When the two speed-regulated compressors again reach min.
speed (30 Hz) the big one-step compressor (C4) cuts out and
the small one-step compressor (C3) cuts in.
- When the two speed-regulated compressors again reach min.
speed (30 Hz), and the small one-step compressor (C3) cuts
out.
- When the two speed-regulated compressors again reach min.
speed (30 Hz), the small speed-regulated compressor (C1) cuts
out.
- When the big speed-regulated compressor reaches min. speed
(30 Hz), it is cut out and the small speed-regulated compressor
is cut in (C1)
- The small speed-regulated compressor (C1) is cut out when the
conditions for this are met.
- When the one-step compressors are cut out, the speed-regulat-
ed compressors' speed increases (63.3 Hz) equivalent to the cut
out capacity.