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While the global refrigeration capacity installed in ultra-low temperature applications is considerably lower than in standard refrigeration, the interest in such systems has risen during the last months due to their emerging demand for the preservation of mRNA vaccines. Several theoretical studies can be found in the literature for ultra-low temperature applications. However, there is still a lack of reliable experimental data that may be used for the models validation and, thereby, to perform more rigorous investigations. In light of this, the present manuscript proposes an ultra-low temperature refrigeration unit based on an indirect cascade system, developed by retrofitting a standard low-temperature R290 packaged unit. In this investigation, firstly, the suitability of the original components is assessed and, then, the unit is experimentally tested within a wide range of operating conditions. Thereby, the system's reliability is evaluated by assessing different parameters, such as discharge, condensing and evaporating temperatures and performance ratios. The main results showed a successful behaviour at the operating conditions tested, exhibiting a COP that ranged from 0.6 to 1.6 for cold room temperatures between -80 °C and -65 °C, respectively.

This work is focused on a case study of a small-scale Organic Rankine Cycle (ORC) adopted for electricity production from low-grade industrial waste heat recovery. This kind of applications raises a great interest due to the high amount of low-grade waste heat recoverable within industrial processes, but lacks of in-depth experimental investigations on the topic. The main reason is the difficulty to reach profitable small-scale projects, so more cost-effective solutions are being explored in the literature through thermo-economic optimizations. Nonetheless, the results obtained cannot be discussed with respect to actual operating data. In light of this, this paper proposes to conduct the thermo-economic optimization on the basis of an experimental application. In this manner, a comprehensive model of the facility is developed, calibrated, and validated from actual operating data. The model is used to conduct the thermo-economic optimization, revealing the influence of the organic fluid, cycle architecture, geometric parameters of main components, or control strategy used to obtain the best cost-effective solution. The main results show that, by means of a multivariable optimization using cost-effective ratios as objective function, a cheaper and powerful solution adapted to each specific project may be designed.

Europe is encouraging new buildings to minimize their primary energy dependence to be considered, from 2021, Nearly Zero Energy Buildings (NZEB). In this regard, solar thermal energy is being extensively used as a renewable source to produce Domestic Hot Water (DHW). However, solar thermal energy fields may be oversized during the warmest season of the year, rejecting the waste heat to the ambient while increasing the air conditioning demand. The Solar-driven Ejector Refrigeration System (SERS) may be a solution for solar cooling. Nevertheless, the SERS performance is constrained when low to medium temperature solar thermal collectors, commonly installed for DHW production, are used in warm climates. Consequently, this paper reformulates the SERS application as a novel fresh air pre-cooling system for air handling units. Thereby, greater evaporating temperatures that enable the SERS adoption in NZEB are explored. In doing so, the seasonal performance under severe operating conditions is analyzed considering the two-phase flow ejector geometry, as well as refrigerants with low global warming potential. Main results demonstrate a maximum seasonal COP of 0.37 by using R717. Moreover, an average cooling capacity of 28.3 kW could be produced per kW of electricity if an optimized multi-ejector solution with R600 is adopted.

An experimental evaluation of HFO-1336mzz-Z as a low global warming potential working fluid for ORC systems in micro-scale low temperature applications has been conducted. The energy performance in a fully monitored ORC module has been analyzed varying the heat source temperatures between 140 °C and 160 °C and heat sink temperatures between 25 °C and 40 °C. The ORC module uses a regenerative configuration allowing heat recovery not only from the heat source but also from the expanded vapor, thus improving the cycle thermal and electrical efficiency. The maximum gross electrical power generated was 1100 W, while the net electrical efficiency ranged from 5.5% to 8.3%. The volumetric expander performance was analyzed by means of the filling factor, while deviations of expander operation from ideal performance were evaluated by means of the isentropic and overall expander-generator efficiency. Net electrical efficiency, isentropic expander efficiency and volumetric expander performance obtained with HFO-1336mzz-Z in this work are higher than those obtained with HFC-245fa in a previous work using the same experimental facility.

The IHX (internal heat exchanger) is introduced in some refrigeration systems in order to achieve higher energy performances. Results obtained vary greatly depending on the refrigerant used and working conditions. This paper describes a drop-in analysis of IHX effects on the performance of a vapour compression system using R1234ze(E) and R450A (R134a/R1234ze(E) commercial mixture) as R134a low-GWP replacements. The tests were carried out in a completely monitored vapour compression system varying the condensing and evaporating temperature, with and without a counter-current flow tube-in-tube IHX. Because the cooling capacity rises and the power consumption remains similar, the conclusion is that the IHX has a positive influence on the energy efficiency for all refrigerants tested. The COP (coefficient of performance) gain using R1234ze(E) is the highest observed (overcomes the R134a COP for the same conditions). The R1234ze(E) and R450A discharge temperature increments are lower than those of R134a so does not reach dangerous values and the IHX pressure drops are also below than that of R134a., The authors thankfully acknowledge "Ministerio de Educacion, Cultura y Deporte - Gobierno de Espana" (Grant number FPU12/02841) for supporting this work through "Becas y Contratos de Formacion de Profesorado Universitario del Programa Nacional de Formacion de Recursos Humanos de Investigacion del ejercicio 2012".

[EN] Commercial Refrigeration comprises food freezing and conservation in retail stores and supermarkets, so, it is one of the most relevant energy consumption sectors, and its relevance is increasing. This paper reviews the most recent developments in commercial refrigeration available in literature and presents a good amount of results provided these systems, covering some advantages and disadvantages in systems and working fluids. Latest researches are focused on energy savings to reduce CO2 indirect emissions due to the burning of fossil fuels. They are focused on system modifications (as dedicated subcooling or the implementation of ejectors), trigeneration technologies (electrical, heating and cooling demand) and better evaporation conditions control. Motivated by latest GWP regulations that are intended to reduce high GWP HFC emissions; R404A and R507 are going to phase out. Besides hydrocarbons and HFO, CO2 appears as one of the most promising HFC replacements because its low contribution to global warming and high efficiencies when used in transcritical and low-stage of cascade systems., The authors thankfully acknowledge "Ministerio de Educacion, Cultura y Deporte" for supporting this work through "Becas y Contratos de Formacion de Profesorado Universitario del Programa Nacional de Formacion de Recursos Humanos de Investigacion del ejercicio 2012".

This paper deals about an experimental application of an ORC (organic Rankine cycle) in a ceramic industry for low grade waste heat recovery. The ORC module used in this application was initially designed and constructed to satisfy the main specifications for an efficient power system, highlighting a volumetric expander with large built-in volume ratio. Furthermore, the performance of the ORC was experimentally characterized in a test bench in a previous work, achieving a maximum gross electrical efficiency of 12.32%. Taking this as a starting point, the aim of this work is to verify the performance of this ORC operating in actual industrial conditions, besides to profiting the information extracted from the application to assess its profitability. For this, the system performance is experimentally characterized in the industry, discussing and comparing the results obtained to laboratory data. From these experimental results a model of the system is developed, which allows predicting the net electrical production of the system along a typical year of operation and quantifying the energy and environmental benefits of the project. Moreover, from the electrical generation, investment costs required and industrial electricity price, a feasibility study is conducted to address the profitability of the application., The authors are indebted to the Minister of industry of 'Generalitat Valenciana' (Spain) for its financial assistance under project INIDIV2010022 and Rank (R), the ORC manufacturer, for its support in this project. Also to thank greatly the Jaume I University for its financial support under the PhD grant PREDOC/2013/28 of 'Convocatoria d'ajudes predoctorals per a la formacio de personal investigador del Pla de promocio de la investigacio de la Universitat Jaume I de Castello (Spain)'.

An ORC (organic Rankine cycle) module, designed and built for a specific CHP (combined heat and power)) application, is tested in this paper. The aim of the work is to characterize the system performance in the operating range allowed by the ORC. For this purpose, a test procedure has been conducted in a test bench. The heat source has been simulated through a natural gas boiler and a thermal oil heat transfer loop to control the temperature in the low grade range of 90 °C 150 °C. The heat sink has been developed using a dry cooler to control the hot water temperature in the range of 30 °C, corresponding to a power application, to 80 °C, of a small-scale CHP application that provides hot water at 90 °C. Thereby, the results show that the thermal power captured by the ORC, electricity and useful heat produced, increase with the rise of the thermal oil temperature and larger pressure ratios. Moreover, the expander electrical isentropic effectiveness is maximized about 70% for a pressure ratio suitable for a CHP system. The cycle efficiency slightly continues increasing for higher pressure ratios, up to a net electrical efficiency of about 8%., The authors want to acknowledge all the invaluable cooperation of Rank (R), the ORC manufacturer, for its support in this project. Also to thank greatly the Jaume I University for its financial support under the PhD grant PREDOC/2013/28 of 'Convocatoria d'ajudes predoctorals per a la formacio de personal investigador del Pla de promocio de la investigacio de la Universitat Jaume I de Castello (Spain)'.

[EN] The EU Regulation No 517/2014 is going to phase-out most of the refrigerants commonly used in refrigeration and air conditioning systems (R134a, R404A and R410A) because of their extended use and their high GWP values. There are very different options to replace them; however, no refrigerant has yet imposed. In this paper we review and analyze the different mixtures proposed by the AHRI as alternative refrigerants to those employed currently. These mixtures are composed by HFC refrigerants: R32, R125, R152a and R134a; and HFO refrigerants: R1234yf and R1234ze(E). It is concluded, from the theoretical analysis, that most of the new HFO/HFC mixtures perform under the HFC analyzed (although some experimental studies show the contrary) and, in most cases, do not meet the GWP restrictions approved by the European normative. Furthermore, some of the mixtures proposed would have problems due to their flammability., The authors thankfully acknowledge "Ministerio de Educacion, Culture y Deporte" (Grant number FPU12/02841) for supporting this work through "Becas y Contratos de Formacion de Profesorado Universitario del Programa Nacional de Formacion de Recursos Humanos de Investigacion del ejercicio 2012".

R1234yf and R1234ze(E) have been proposed as alternatives for R134a in order to work with low GWP refrigerants, but this replacement results generally in a decrease of the performance. For this reason, it is interesting to explore ways to improve the system performance using these refrigerants. In this paper, a comparative study in terms of energy performance of different single stage vapour compression configurations using R1234yf and R1234ze(E) as working fluids has been carried out. The most efficient configuration is the one which uses an expander or an ejector as expansion device. On the other hand, using an internal heat exchanger in a cycle which replaces the expansion valve by an expander or an ejector could produce a detrimental effect on the COP. However, for all the configurations the introduction of an internal heat exchanger produces a significant increment on the cooling capacity.

Six refrigerants are evaluated as low GWP replacements for R404A using different configurations, including two-stage system architectures. These refrigerants are selected according to similar characteristics to R404A, and they are the mid-term alternatives R407A and R407F, and the long-term alternatives: L40 and DR-7 (with very low GWP and low flammability), N40 and DR-33 (with low GWP and no flammability). In order to have a complete comparison range, various operating conditions are considered, covering low and medium evaporator temperatures and two levels of condensation temperatures. Configurations selected are presented and the equations used to simulate the expected performance are shown. From a given cooling capacity, volumetric flow rate and COP are compared, taking R404A as baseline. The most efficient alternatives are the low-flammable refrigerants, L40 and DR-7, and when no flammability is acceptable, N40 and DR-33 are also very good options., The authors thankfully acknowledge "Ministerio de Educacion, Cultura y Deporte" for supporting this work through "Becas y Contratos de Formacion de Profesorado Universitario del Programa Nacional de Formacion de Recursos Humanos de Investigacion del ejercicio 2012" The authors also want to acknowledge Honeywell International Inc. for supporting this work.

[EN] This work presents an experimental analysis of a non-flammable R1234ze(E)/R134a mixture (R450A) as R134a drop-in replacement. While R134a has a high GWP value (1430), the R450A GWP is only 547. The experimental tests are carried out in a vapour compression plant equipped with a variable-speed compressor. The replacement suitability has been studied combining different operating conditions: evaporation temperature, condensation temperature and the use of an internal heat exchanger (IHX). The drop-in cooling capacity of R450A compared with R134a is 6% lower as average. R450A COP is even higher to those resulting with R134a (approximately 1%). The discharge temperature of R450A is lower than that of R134a, 2K as average. The IHX has a similar positive influence on the energy performance of both fluids. In conclusion, R450A can be considered as a good candidate to replace R134a., The authors thankfully acknowledge "Ministerio de Educacion, Cultura y Deporte" for supporting this work through "Becas y Contratos de Formacion de Profesorado Universitario del Programa Nacional de Formacion de Recursos Humanos de Investigacion del ejercicio 2012".

A moving-boundary dynamic model of a shell-and-tube condenser is presented. Within this approach, the mean void fraction is a relevant parameter which is obtained, in this work, using different correlations proposed in the literature for the flow pattern analyzed. In order to evaluate the performance of the model with each different mean void fraction correlation, a set of experimental tests using R134a as working fluid, varying the main operating variables (refrigerant mass flow rate, secondary fluid mass flow rate and inlet temperature), are performed. The model performance is analyzed from the system model outputs, namely, condensing pressure and refrigerant and secondary fluid outlet temperatures. The results, comparing model predictions and experimental data, show the great influence of the mean void fraction correlation on the model predictions with noticeable discrepancies depending on the correlation used. It is also observed that the model using the homogeneous correlation frequently provides acceptable results in all the tests analyzed, although the most appropriate correlation depends on the transient characteristics.