Parallel operation with economiser

Parallel operation requires an individual and careful assessment and design with respect to oil return and oil equalisation between compressors.

Parallel compounding with individual liquid subcoolers

The use of individual liquid subcoolers is governed by the same directives as that of single compressors. Both solenoid valves in the subcooling circuit are activated by an auxiliary contact in parallel to the compressor contactor. If the compressors are operated with capacity control and the ECO connection is only active at full load, the solenoid valves have to be switched off in case of part load.

Parallel compounding with ECO and an individual subcooler
Parallel compounding with ECO and an individual subcooler

Parallel compounding with a common liquid subcooler

When using a common subcooler, a solenoid valve and a check valve as well as a suction gas filter must be provided in each pipe section leading to the ECO connection of a compressor. The solenoid valve is activated in parallel to the compressor contactor via an auxiliary contact.

For part load operation, the common subcooler and the expansion valve must be designed very carefully. In particular, the refrigerant distribution and gas flow velocity must be taken into account. For operation over a larger capacity range, it may be advantageous to use two expansion valves (e.g. 33% and 66%) which are alternatively charged with liquid via the corresponding solenoid valves depending on the load condition. For extreme conditions, a subcooler with subdivision on the evaporator side is recommended.

If the compressors are operated with capacity control, an evaporator pressure regulator (EPR) must be installed in the ECO suction gas line downstream of the subcooler. It should be adjusted to a pressure slightly below the value for full-load conditions. A suitable adjustment of the regulator also makes it possible to keep the liquid temperature at a defined value.

➀ When operated with capacity control

➁ When operated with 2 expansion valves of different capacities

Parallel compounding with ECO and a common subcooler
Parallel compounding with ECO and a common subcooler

Parallel operation with economiser in R717 systems