An experimental analysis of a thermodynamic model of a vapour compression refrigeration plant on varying the compressor speed

Abstract

The principal aim of this paper is the study of a thermodynamic model that simulates the working of a vapour compression refrigeration plant. The model allows the evaluation of plant performances when the compressor capacity is regulated varying its velocity by means of an inverter inserted into the compressor electric motor feeder. This type of control allows to match continuously the compressor refrigeration capacity to the load, determining an energy saving in comparison with the classical thermostatic control. In particular, in this paper the outputs of the model are compared with the experimental results. The vapour compression experimental refrigeration plant, whose evaporator is located in a commercially available cold store, presents a semi-hermetic reciprocating compressor able to work with the R22 and some its substitutes, and designed for a revolution speed corresponding to a 50Hz frequency of a compressor electric motor supply current. The comparison of model and experimental results is realized by varying the supply current frequency of the compressor in the range 30–50 Hz using the R407C (R32/R125/R134a 23/25/52% in mass) that represents the most suitable working fluid for the R22 substitution. The model experimental comparison results reported in terms of condensation temperature, compression ratio, condensation power and Coefficient Of Performance are completely acceptable. Moreover, an exergetic analysis is realized to explain the performances of the plant components when the compressor speed is varied

Exergetic performance assessment of a variable-speed R404a refrigeration system

“…Additionally, Aprea and Renno [9] have used semi-hermetic compressor in their variable-speed experimental refrigeration cycle and found that the irreversibility rates were 37% at the compressor, 27% at the condenser, 23% at the evaporator and 13% at the expansion valve using R407c as the working fluid. Figure 5 shows the graphical representations of the exergy balance (Grassmann diagram) for the refrigeration system at different frequencies.…”

A review on recent developments in new refrigerant mixtures for vapour compression-based refrigeration, air-conditioning and heat pump units

“…Aprea and Renno [40] investigated the performance of variable speed vapour compression refrigeration system Developments in new refrigerant mixtures M. Mohanraj, C. Muraleedharan and S. Jayaraj working with R407C used for cold storage applications. Their results concluded that exergy loss in the components of the system increases with increase in compressor speed.…”

“…Joudi et al [33] investigated the performance of an automobile air-conditioning system working with R12 and HC mixture (composed of R290 and R600a, in the ratio of 62:38, by mole percentage). They performed the experiments at three different ambient temperatures (35,40 and 501C) with six speeds 700, 1000, 1500, 2000, 2500 and 3000 rpm. During their experiments the evaporator chamber was maintained at 45, 50, 55, 60 and 651C.…”

Experimental and numerical investigations of the energy efficiency of conventional air conditioning systems in cooling mode and comfort assurance in office buildings

“…Variable speed control is another approach to decreasing compressor power because the motor efficiency can be improved at lower speeds when the chiller compressor is operating under a partial load [22,23]. When a variable speed control is applied to the condenser fans, each fan can be operated at a lower speed with a large reduction in power while the condensing temperature remains at its set point.…”