Evaluation of reversible screw compressors with an adaptable built-in volume ratio in reversible heat pumps

Reversible heat pumps consisting of a high-temperature heat pump and an Organic Rankine Cycle have been subject to increasing academic interest in recent years. Early experimental studies suggested the use of separate compression and expansion devices due to different process conditions in both operating modes. While this concept enables higher machine efficiencies, it also drives up the system cost and can make the concept economically unattractive. In recent years, twin-screw compressors with an adaptable built-in volume ratio (BVR) have become available, allowing efficient machine operation over a wider range of operating conditions. Since this type of compressor is inherently reversible (allowing operation as an expander), it should be considered for use in reversible heat pumps with a single compressor/expander unit. This work makes use of a recently developed model for volumetric screw compressors and expanders to evaluate the potential of machines with an adaptable BVR. A reversible heat pump with a single compressor/expander unit is deployed within a geothermal CHP plant model and annual simulations are performed based on the adapted load profiles of an existing district heating plant. The yearly net electricity production is compared for adaptable BVR machines and the more established fixed-BVR machines. For the observed scenario, the yearly net electricity production rises by 3.1 % due to the deployment of adaptable BVR machines.     «

Reversible heat pumps consisting of a high-temperature heat pump and an Organic Rankine Cycle have been subject to increasing academic interest in recent years. Early experimental studies suggested the use of separate compression and expansion devices due to different process conditions in both operating modes. While this concept enables higher machine efficiencies, it also drives up the system cost and can make the concept economically unattractive. In recent years, twin-screw compressors with...     »