Modelica-based modeling and simulation of a twin screw compressor for heat pump applications

• Difficulties related to the compressor limit the development of a high temperature heat pump using water as refrigerant.
• A new water vapor double screw compressor has been developed to overcome compression problems.
• A dynamic model of this compressor has been developed and simulated using Modelica.
• The behavior of the compressor has been identified all along the compression cycle and efficiencies have been calculated.

A new twin screw compressor has been developed by SRM (Svenska Rotor Maskiner) for use in a new high temperature heat pump using water as refrigerant. This article presents a mathematical model of the thermodynamic process of compression in twin screw compressors. Using a special discretization method, a transient twin screw compressor model has been developed using Modelica in order to study the dry compression cycle of this machine at high temperature levels. The pressure and enthalpy evolution in the control volumes of the model are calculated as a function of the rotational angle of the male rotor using energy and continuity equations. In addition, associated processes encountered in real machines such as variable fluid leakages, water injection and heat losses are modeled and implemented in the main compressor model. A comparison is performed using the model developed, demonstrating the behavior of the compressor and the evolution of its different parameters in different configurations with and without water injection. This comparison shows the need for water injection to avoid compressor failure and improve its efficiency.