Metacentre DX Box
Page 3
1.3.2 Automatic Mode (Ar)
#1
#2
65%
35% = 100%
0%
-
-
35%
-
B
65%
A
-
100% A
B
A
B
Automatic mode can be used when the
compressor capacities are different. The DX
Box will utilise each compressor as required to
match output to demand. This mode enables
the compressor ‘group’ to behave in the same
manner as a single (multiple step) variable
output unit.
The set ‘Interval Time’ is ignored in this mode,
the DX Box will continuously evaluated
utilisation to match demand.
For example:
If demand can be satisfied by the smaller of
the two compressors (demand < 36%) the DX
Box will utilise the lower capacity compressor
(B). If demand increases above the output
capacity of the smaller compressor, but within
the capacity of the larger capacity compressor,
the DX Box will utilise the larger capacity
compressor (A). If demand exceeds to
capacity of the larger capacity compressor the
DX Box will load the larger compressor
continuously and utilise the smaller capacity
compressor to regulate as required.
1.3.3 Management System Integration
When integrated with a system management
unit the DX Box compressor ‘group’ will
respond in ‘Top-Up’ mode or ‘Base-Load’
mode as dictated by the management unit.
The assigned mode of response will change
from time-to-time dependant on the set
sequencing mode of the management unit.
In Top-Up’ mode the DX Box will allow
variable capacity control (as described above)
dependant on demand.
In ‘Base-Load’ mode the DX Box will fully load
both compressors to provide full base-load
capacity output.
The DX Box ‘group’ unit should be set as a
variable output unit on the management
system. The management system will fully
utilise the variable output capacity capability of
the DX Box ‘group’ and report the percentage
of utilisation of the ‘group’ in the same manner
as a single variable output compressor.
1.3.4 Percentage Capacity
The capacity of each compressor is
expressed, and set, as a percentage of the
combined output capacity of both
compressors.
For example:
If the larger compressor #1 (A) has an output
capacity of 13.0m
3
/min, and the smaller #2 (B)
compressor an output capacity of 7.0m
3
/min,
the total combined output of the DX Box
‘group’ equates to 20.0m
3
/min.
Total Capacity (20.0m
3
/min.) = 100%
Compressor #1 (A) = 65%
Compressor #2 (B) = 35%
1.3.5 Compressor Failure Mode
If one compressor in the DX Box ‘group’
suffers a shutdown failure, or is manually
stopped, the DX Box will indicate an ‘Alarm’
condition. The remaining compressor will
continue to function and the DX Box will
continue to operate at reduced capacity.
If both compressors suffer a shutdown failure,
or are manually stopped, the DX Box will
indicate a shutdown ‘Trip’ condition.
