Danfoss Turbocor TT Series, Installation Manual

Page: 53 / 108

Page 53 of 108
M-AP-001-EN Rev. N
Control Logic Guidelines For Multiple Compressors
Due to the nature of centrifugal compression, special control logic must be implemented for
proper staging of multiple Turbocor compressors when installed on a common circuit. This
section is intended only as a guide without going into details. Control details are specific
to each OEM’s individual control strategy. The Turbocor centrifugal compressors can be
controlled by staging compressors and running the on line compressors in parallel.
Staging valve:
The Staging valve is piped in upstream of the check valve to provide a low
pressure bypass path and is used to reduce the pressure ratio in the system to assist in
starting a compressor. Staging valve is mandatory with all DTC compressors required to start
against a pressure ratio of 2.4 or greater.
Load balancing valve (hot gas bypass):
the LBV is piped downstream of the check valve
and is primarily used in low load conditions to keep the compressor Online instead of
cycling off. It is possible to use a staging valve as a load balance valve (HGBP) but sizing
and control can be a little more challenging and for that reason they are both frequently
installed in many systems.
NOTE
The hot gas evacuated by the staging valve must be injected downstream of the main EXV in order to de-superheat the gas
prior to entering the suction of the compressor.
• • • CAUTION • • •
If the staging valve is used as load balancing valve (HGBP) there are two major risks:
•
Check valve chattering if the bypassed flow is too high, this chattering will lead to bearing faults due to vibrations (Please
contact DTC for further information)
•
High suction superheat which may lead to compressor trip
10 Control Logic Guidelines
for Multiple Compressors