VDH MC3-SC, Manual, Page: 22 / 45

MC3-SC Stepped Controller
Document no.: 140744 version 1.3
Page 22 of 45
4 Explanation of the parameters
4.1 Compressor section
P 10 & P 11 The range that the suction pressure setpoint can be set between from the front
P 12 The proportional band. This is symmetrical around the setpoint. As long as the
pressure is within this bandwidth, no compressor levels will be enabled or disabled.
P 13
Delay for switching on the next compressor. It will always wait at least this long
before a new compressor is added. If the current waiting time (P15) is greater than
P13, the current waiting time will be used.
P 14 Delay for switching on the next compressor level. It will always wait at least this long
before a new compressor step is switched on. If the current waiting time (P15) is
greater than P13, the current waiting time will be used.
P 15 Step-up time between the compressors / levels. This time starts at the moment a
compressor or level is switched on Note! This is not a switch-on delay. For example,
take a step-up time of 2 minutes. Compressor 1 comes online and the pressure
stays constant. The timer now begins to run. If the pressure now begins to rise after
2 minutes, compressor 2 will come on straight away. However, if the pressure begins
to rise within the first 2 minutes, the timer will first have to expire before the next
compressor can come online.
P 16 Step-down time between the compressors / levels. Works in the same way as P15.
P 17 In this type of regulation, the compressors are switched in such a way that the
lowest possible capacity is switched on. If there is more than one combination of
capacities that yields the same power, then the first one switched on will be the one
that is allowed to start first. If that is also the same, the one started will be the one
with the least runtime.
P 18 To avoid unwanted switching of the compressors, restrictions can be assigned. If
zero is filled in for this parameter, then there are no restriction.
If this parameter is set to 1, then a compressor that has started running will keep
going. For example, compressor 1 is a 33/66/100 compressor and the second
compressor is a 50/100 compressor. The capacities of the two compressors are the
same. Compressor 1 will now start up first, at 33%. If there are no restrictions,
compressor 1 will switch off and compressor 2 will start at 50% when the suction
pressure increases. However, if the parameter is set to 1, compressor 1 will remain
switched on and will step up to the 66% and 100% levels before compressor 2
comes online.
If this parameter is set to 2, the regulation operates in much the same way as for
setting 1, except that in this case no capacities get switched off.
There will however be a step down if the pressure drops outside the P band, of
course.
P 19 If a step up is required, the step chosen will always yield at least the required gain in
capacity. Combinations that result in less gain will be skipped. This is done to prevent
unnecessary stepping down in compressor levels.
P 20 To avoid having a compressor come back on very shortly after it has been turned off,
a time can be specified here stating how long a compressor must have been off
before it can be switched on again.