Test Bench for an Air Heat Pump Operating on an Inverse Brayton Cycle
Spike has designed and built a dedicated test bench for the experimental study of air-source heat pumps based on an inverse Brayton cycle, with the goal of analyzing efficiency, operational stability, and thermodynamic behavior in different configurations. The system integrates specific components for compression, expansion, heat exchange, and control, allowing the operating conditions of a real machine to be accurately replicated. The test bench was developed to offer maximum experimental flexibility and to enable comparative studies among regenerated closed-cycle configurations, non-regenerated closed-cycle configurations, and open-cycle configurations.
Test Bench Architecture and Operating Principle
The test bench is based on an air circuit that follows a complete inverse Brayton cycle, including compression, regeneration, cooling, and expansion. Compression is provided by two Rotrex compressors operating in parallel, while expansion is currently achieved via a throttling valve. In a future configuration, it may be carried out by a Garrett turbocharger-type turbine, equipped with a bypass to avoid surge conditions. The cooler reduces the temperature downstream of the compression stage, while the regenerator recovers heat in counterflow, improving efficiency in the regenerated closed-cycle configuration. The setup is fully modular and allows individual components to be activated or excluded depending on the type of test.
Role of the Cooling Water Loop
The water circuit is a key element of the test bench, ensuring thermal management of the entire system. It supplies hot fluid to the heater, removes heat from the cooler, and cools the compressor oil through dedicated heat exchangers. The entire loop is designed to maintain thermal stability even under variable loads, with multiple dry coolers in parallel, dedicated pumps, and redundancy logic to guarantee continuous operation.
Test Configurations and Operational Flexibility
The bench is designed to operate in three main configurations. In the regenerated closed cycle, the air and heat exchangers work in a circuit fully isolated from the environment, with thermal recovery via the regenerator. In the non-regenerated closed cycle, the same flow path is maintained but valves are set to bypass the regenerator. In the open cycle, air is drawn from and discharged to the surroundings. This versatility enables comparative testing of efficiency, dynamic response, and thermal behavior of the compressors, as well as analysis of system performance under varying ambient conditions.
Instrumentation and Control Systems
The test bench integrates an advanced measurement and control system; the supervision system manages the startup and shutdown of pumps, compressors, chillers, and dry coolers, and operates the three-way mixing valves through dedicated PID controllers. The main setpoints include the water supply temperature (40 °C), the air temperature at the outlet of the heater (15 °C), and the air temperature after the cooler (60 °C).
Twelve pressure sensors, twelve temperature sensors, and one airflow meter are installed on the air circuit. Data acquisition is carried out via a datalogger at 1 Hz, ensuring high temporal resolution suitable for transient analysis, diagnostics, and thermodynamic model validation.
Expected Results and Application Potential
This test bench represents a high-level experimental platform for the development of high-efficiency heat pumps based on Brayton technology. The ability to vary configurations, precisely monitor parameters, and dynamically control heat flows allows testing of next-generation compressors, optimization of heat exchangers, study of innovative cycles, and validation of digital twins of thermal machines.
The system’s potential includes the development of high-power heat pumps, integration into industrial heat-recovery systems, and evaluation of hybrid technologies, making the test bench a strategic asset for research and development in the HVAC sector and in the field of advanced thermal machinery.