VDH Products MC 785-SC, Руководство по эксплуатации, Страница: 24 / 32

Operating manual Document nr. : 022091 Version : V2.3
MC 785-SC Client : General Page : 24 of 32
Step Compressor-1 ,
3-cylinder model 1kW
Compressor-2 ,
2-cyl.model 2kW
Total
0-cyl. 1-cyl. 2-cyl. 3-cyl. kW 0-cyl. 1-cyl. 2-cyl. kW kW %
0% 33% 66% 100
% 0% 50% 100
%
1 x 0 x 0 0 0
2
x 0.33 x 0 0.33 11
3
x 0.66 x 0 0.66 22
4
x 1 x 0 1 33
5
x 0 x 1 1 33
6
x 0.33 x 1 1.33 44
7
x 0.66 x 1 1.66 55
8 x 1 x 1 2 66
9 x 0 x 2 2 66
10
x 0.33 x 2 2.33 77
11
x 0.66 x 2 2.66 88
12
x 1 x 2 3 100
Example-1 overview of the control steps with the cooling capacity in percentages ( x=active)
Increasing compressors:
When two or more steps result in the same capacity the step leading to the switching down of
the fewest compressors is first selected. If the steps are then still equal the step with the
shortest increase delay is selected. If the steps are then still equal the step with the fewest
running hours is selected. If this still does not lead to an unambiguous step then the first step is
increased.
Decreasing compressors:
When two or more steps result in the same capacity the step leading to the switching down of
the fewest compressors is selected. If the steps are then still equal the step with the shortest
switching down delay is selected. If the steps are then still equal the step with the most running
hours is selected. If this still does not lead to an unambiguous step then the first step is
increased. If the minimum on and off times are longer than the switching up and down times
this can result in an unstable system. When the switching down time is over there must
always
be a switching down (provided that the minimum on-time is over).
Example-3: Three compressors (1kW, 2kW, 4kW) run in the stand 1-1-0 (step-4=3kW)
The suction pressure is still too high so the next step is 0-0-1 (step-5=4kW)
Now the suction pressure will fall to the switching down point.
If the compressors1 and 2 are still running in their minimum off-time, then the
control will still decrease compressor 3. The result of this is that all compressors
are now off.
When compressors have to be switched on during the switching down process
they
will always continue to run for their minimum on-time.