• Energy Research

Abstract The replacement of environmentally unfriendly refrigerants and the energy saving demand have recently caused changes of the components and operation of the vapour compression plants; in particular, the compressors have been experiencing upgrades and modifications. The compression systems are usually designed for working under maximum load conditions, but most of the time these plants work under partial load conditions with compressor on–off cycles regulated by a thermostat. As for the variable speed compressor, the speed is continuously controlled to match the compressor capacity to the load required; this allows to save energy when compared to the thermostatic control. The aim of this paper is to identify the compressor current frequency that optimizes the energy, exergy and economy aspects. The determination of the optimum frequency for each working condition is key to build a control algorithm that allows the compressor speed to be continuously regulated by an inverter. This analysis has been applied to the reciprocating and scroll compressors and high energy savings have been achieved.

Abstract Global warming is a worldwide common theme. Due to the Regulation (EU) no. 517/2014, refrigerants with a GWP (Global Warming Potential) higher than 150 are not allowed from January 1st, 2015 in new domestic refrigerators. Thus, a replacement for HFC134a is needed. In this paper attention is devoted to the drop-in substitution of HFC134a with HFO refrigerant fluids in a domestic refrigerator. An experimental evaluation of the environmental impact in term of the greenhouse effect of the substitution of HFC134a with HFOs has been reported. The greenhouse effect is accounted for the experimental evaluation of the LCCP (Life Cycle Climate Performance) index. The refrigerant fluids that have been tested as a drop-in are: pure HFO1234yf, the mixture HFO1234yf/HFC134a (90/10% in weight), pure HFO1234ze (E) and the mixture HFO1234ze (E)/HFC134a (90/10% in weight). The plant working with pure HFOs or with both mixtures achieves the same temperature levels of HFC134a in the freezer and the refrigerator cabinet. The experimental results clearly show that the lower environmental impact in term of global warming can be achieved with both mixtures. The lower LCCP index can be obtained with HFC134a/HFO1234yf (with a 17% reduction respect to HFC134a).

In this paper the experimental results of an autocascade refrigeration system for achieving ultra low temperature are presented. The plant is used to preserve tissue and cells. When the air temperature is equal to −150°C in 0.25 m3 space, the required refrigeration power is about 250 W. The influence of the most meaningful variables is discussed with regard to the design of the plant. The experimental results show an acceptable time to reach the steady state in dependence of the finality of the plant. The working substance is a non-azeotropic mixture consisting of hydrofluorocarbon (HFC) refrigerants in addition to argon and methane. Copyright © 2009 John Wiley & Sons, Ltd.

In the paper a pilot plant built to evaluate the comparative performances of R502 and its alternatives, is presented. Then, the first experimental results on R403B (ISCEON 69L, Rhone-Poulenc), obtained with evaporating temperatures around – 35°C are presented and discussed.

The industry of temperature-controlled transportation has shown significant growth in recent years, and this growth is expected to continue in the future. As the sector expands, it's crucial to focus on reducing energy consumption and greenhouse gas emissions related to transport refrigeration systems to meet the planned decarbonization goals. In this study, the energy and environmental benefits of implementing an electric Kinetic Energy Recovery System (KERS) on a refrigerated light-duty commercial van, equipped with a vapor compression refrigeration (VCR) system, are assessed by means of dynamic simulation. The KERS considered involves a LiFePO4 battery as electricity storage system, a brushless motor-generator unit and a hybrid inverter able to both charge the battery and power the refrigeration system. For each component of the system, i.e. the engine, the alternator, the transmission system and the KERS, the real efficiencies have been considered. The dynamic behaviour of the KERS is simulated by using data obtained by performing a real urban single-delivery 40 km mission, during which the vehicle operating conditions, as well as the electricity demand of the refrigeration system, have been measured. The estimation of the potential benefits of the proposed solution has been performed by comparing the electricity produced by the KERS (and available for use) and the measured energy demand of the refrigeration system. The results have shown that the electricity available for use could cover more than 47% of the total electricity demand. This means that nearly half of the primary energy/fuel consumption can be saved by employing a KERS in refrigerated-light duty vehicles. In particular, emissions savings ranging between 9 and 13 gCO2,e and cost savings between 0.4 and 0.7 c€ per kilometer travelled can be achieved, resulting in an average payback period of 8 years. In addition, when considering the entire useful life of a refrigerated van equal to 10 years, CO2,e savings of 4515–6710 kgCO2,e are obtained. The low complexity of the proposed system and the availability of the components on the market, together with the results obtained by simulation, make using KERS in refrigerated transport a promising solution throughout the decarbonization of the refrigerated transport sector.

Abstract The energy performances of an Active Caloric Refrigerator are reported in this paper. An ACR is tested under a vast number of solid-state refrigerants exhibiting one of the four main caloric effects considered for refrigeration (magnetocaloric, electrocaloric, elastocaloric and barocaloric effect). The analysis is performed numerically through a 2D model, experimentally validated, that can reproduce the behavior of an Active Caloric Regenerator. Temperature span, cooling power and coefficient of performance are the indexes through which the comparison is carried out. The tests are performed at a fixed AMR cycle frequency (1.25 Hz), in the temperature range 292–300 K, varying the mass flux in the range 150–250 kg s−1 m−2. The most promising caloric materials that have been tested as refrigerants are: Gd, Gd5Si2Ge2, LaFe11.384Mn0.356Si1.26H1.52, LaFe11.05Co0.94Si1.10 (magnetocaloric materials); P(VDF-TrFE-CFE)/BST polymer, 0.93PMN-0.07PT thin film, the Pb1-3x/2LaxZr0.85Ti0.15O3 with single and variable composition, PbTiO3, Pb0.8Ba0.2ZrO3, Pb0.97La0.02(Zr0.75Sn0.18Ti0.07)O3(electrocaloric materials); Cu68.13Zn15.74Al16.13, NiTi, PbTiO3 (elastocaloric materials); (NH4)2MoO2F4, MnCoGe0.99In0.01 (barocaloric materials). Among them, PLZT and in particular Pb0.97La0.02(Zr0.75Sn0.18Ti0.07)O3 show the best results, higher than every other caloric material tested, conferring to electrocaloric refrigeration globally the most promising behavior.

This paper addresses the problem of R314a substitution with a natural refrigerant fluid. Attention is devoted to the evaluation of the environmental impact, in terms of greenhouse effect. R134a and R744 (CO2) are compared to one another. The hydrofluorocarbon R134a has a large direct warming impact (GWP), whereas the R744 contribution is negligible. The greenhouse effect is determined by the experimental evaluation of the TEWI index (Total Equivalent Warming Impact) that takes into account both direct and indirect contributions to global warming. This paper compares a commercial R134a refrigeration plant and a prototype R744 system working in a trans-critical cycle. The experimental results clearly show that the latter has a larger TEWI than the system operating with R134a. The indirect contribution to global warming provided by R744 is always greater than that of R134a. This contribution prevails in most cases. Only few operating conditions corresponding to a refrigerating plant working as a classical split system benefits, in terms of greenhouse effect, of the substitution of R134a with R744.

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 50 Hz 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. Copyright © 2004 John Wiley & Sons, Ltd.