Version 2.02 15.05.2007
Function of VS 3000
24
HP monitoring is shown diagrammatically in the following illustration:
t
Limit HDS limiter
ZNR.
51203
78
030
E0
t
c
Limit HP limiter
tc OFF COMPR.
tc ON COMPR.
Compressor lock (no load of any stages)
Compressor shut down until max. 40% power
Enabling compressor lock
Enabling unseated compressors
Alarm delay High HP
VS 3000 HP Monitoring
(tc OFF COMPR. - tc ON COMPR.)
4
dt =
dt
3.24 CO
2
cascade
When the refrigerant of a CO2 LT pack is condensed with one or two NT systems in a plate-type heat exchanger
cascade, HP fault conditions can occur on the LT pack on shutting down NT compressors. This frequently oc-
curs during the nighttime in winter when only one NT capacity stage is required and it is disabled for example
due to long start delay intervals or limiting of compressor starts.
To avoid such HP faults, the pack controller of the LT circuit needs to be able to perform forced loading of NT
compressors via the CAN bus in critical cases. For this purpose the LT circuit pack controller can activate two
different NT pack controllers.
The Node Nos. of the NT pack controllers can be defined by the parameters
NT Cascade 1
xxx and
NT Cas-
cade 2
xxx (Menu 3-3). The function is deactivated when ”---” is entered for both Node Nos. Only one pack con-
troller is activated if only one Node No. is entered. When both Node Nos. are entered, compressors can be con-
trolled by two NT pack controllers. If the same NT pack controller is selected for both Node Nos., the second
address will be ignored. These parameters are only shown for LT systems working with CO2 as the refrigerant
and the function is not active for all other systems
Demand for NT compressors is made by the condensing temperature, tc. A temperature difference dt is formed
from the monitoring parameters
tc OFF Comp
. (Menu 3-3) and
tc ON Comp
. (Menu 3-3) for computing the re-
quired limits:
d
t
=
(
t
c
OFF Comp
−
t
c
ON Comp
)
4
tc OFF Comp:
t
c
limit for compressor shutdown
tc ON Comp:
t
c
limit for compressor enabling
If temperature tc exceeds the defined limit
tc OFF Comp - 2*d
t, the LT pack controller immediately transmits a
compressor demand signal at 1 second intervals to the NT pack controller assigned Node No.
NT Cascade 1
x
xx. If a Node No.
NT Cascade 2 xxx
has been entered and temperature tc exceeds the limit tc OFF Comp - dt,
the LT pack controller immediately transmits a further compressor demand signal at 1 second intervals to the NT
pack controller assigned Node No.
NT Cascade 2 xxx.