Control-oriented model of refrigeration units for residential and industrial applications

The Vapour Compression System (VCS) is the leading technology in the refrigeration sector, and it is also employed for Heat Pump (HP). The dynamical modelling could play a paramount role in the optimisation of such systems, from the design phase to the development of real-time control applications as Digital Twins. In this context, this work describes in detail the realisation of a dynamical model of a VCS in Simulink®. The model is validated employing experimental data obtained with a test machine, composed of a reciprocating compressor, two brazed-plate Heat Exchangers (HEXs) in counterflow arrangement, the electronic expansion valve and some auxiliaries. The HP behaviour is investigated during different transients of compressor speed and valve opening. The test ring is analysed, and the reliability of the available measurements for the investigation of transients is assessed. The model of each component is developed and validated experimentally; a numerical verification is proposed where suitable data are not avail able. The model of the compressor, the expansion valve, the piping and the vessels are faced with a lumped parameter approach. Much effort is devoted to the HEXs model using a finite volume approach. The work proposes some measures useful to enhance its accuracy and stability and reduce its computational load. The full machine model can predict the process variables with reasonable accuracy. The refrigerant mass flow rate is calculated within 5% of the experimental data. The average pressure deviation in the two HEX settles around 20-40 kPa, corresponding to less than 1 °C in the estimation of the saturation temperature. All the temperatures of the working fluids are estimated with an absolute deviation of less than 1 °C.