Search

Lower GWP refrigerants are essential to mitigate the impact of refrigeration systems on climate change. HFO/HFC mixtures are currently considered to replace HFCs in refrigeration and air conditioning systems. The aim of this paper is to present the main operating and performance differences between R513A (GWP of 573) and R134a (GWP of 1300), the most used refrigerants for medium evaporation temperature refrigeration systems and mobile air conditioners. To perform the experimental comparison, 36 tests are carried out with each refrigerant at evaporating temperatures between −15 and 12.5°C and condensing temperatures between 25 and 35°C. The conclusion of the experimental comparison is that R513A can substitute R134a with only a thermostatic expansion valve adjustment, achieving better performance and higher cooling capacity. The discharge temperature of R513A is always lower than that of R134a. The authors thankfully acknowledge the Ministry of Education, Culture and Sports, Spain for supporting this work through “Becas y Contratos de Formación de Profesorado Universitario del Programa Nacional de Formación de Recursos Humanos de Investigación del ejercicio 2012 (Grant number FPU12/02841)” and “Ayudas complementarias para beneficiarios de ayudas (FPU): Estancias Breves. Convocatoria 2015 (Grant number EST15/00154)”. This research is also done within the Effsys Expand P08 project that is funded by the Swedish Refrigeration Cooperation Foundation, KYS and Swedish Energy Agency with the support of Bosch Thermoteknik AB, Danfoss Värmepumpar AB, Nibe AB, Nowab, Svensk Energi & Kylanalys AB and Svenska Kyltekniska Föreningen.

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.

Because air conditioning and heat pump systems contribute greatly to greenhouse gas emissions, equipment with both lower global warming potential (GWP) working fluids and a higher level of performance should be used. R32 (difluoromethane) has been proposed to substitute R410A, particularly in residential air conditioning (RAC) systems. This study collected the most relevant and recent researches into R32 as a refrigerant so as to assess its viability in RAC systems in both Europe and the USA, as compared to R410A and other lower GWP RAC alternatives. The R32 value of GWP is 677, which is below the F-gas regulation limit in RAC equipment (750). According to ASHRAE standard 34, R32 is less flammable than hydrocarbons, and the amount of charge permitted for R32 is above the necessary level in RAC equipment. It can be concluded that R32 has significantly good heat transfer characteristics and a level of performance that make it acceptable at low condensing temperatures, thereby avoiding overly high compressor discharge temperatures. Its performance is very similar to that of R410A across the entire operating range, and it is therefore believed that R32 will be utilized in RAC systems in the remaining countries that prioritize lower GWP fluids but are less strict in their security regulations. To replace R410A under extreme conditions, some system modifications can be conducted, or R32 mixtures with hydrofluoroolefins (HFOs) can be used. Such mixtures achieve a lower performance than R32, but are acceptable replacements when considering their lower GWP compared to that of R32, and similar level of flammability. Finally, other (R32-based) alternative mixtures have also been developed and their behaviours studied under a wide range of operating conditions. The authors thankfully acknowledge the Spanish Ministry of Education, Culture, and Sport for supporting this work through “Becas y Contratos de Formación de Profesorado Universitario del Programa Nacional de Formación de Recursos Humanos de Investigación del ejercicio 2012 (Grant number FPU12/02841)” and “Ayudas complementarias para beneficiarios de ayudas (FPU): Estancias Breves. Convocatoria 2015 (Grant number EST15/00154)”. The authors are also grateful to the Swedish Energy Agency for supporting this study under the “EFFSYS EXPAND P08” research program.

A comparative energetic evaluation of R1234yf, R1234ze(E) and R450A as alternatives to R134a in a variable speed compressor is carried out. A compressor model based on dimensionless numbers was obtained using the Buckingham p -theorem, which was validated with experimental data; showing that the prediction error of the model is lower than ± 10% and ± 2 K for temperature. The experimental data were obtained by testing R134a, R1234yf, R1234ze(E) and R450A for a wide range of operating condi- tions. Results obtained with the validated model, show that the dimensionless approach provides a similar estimation of energy parameters compared with the experimental results, such as power con- sumption, refrigerant mass fl ow rate, cooling capacity, COP, discharge temperature and compressor ef- fi ciencies for each refrigerant tested using the dimensionless approach proposed. The comparative evaluation of the compressor predictions shows a reduction in the cooling capacity obtained with R1234yf, R450A and R1234ze(E), in comparison with R134a. Also, COP values for R1234yf, R450A, and R1234ze(E) are lower than those obtained from R134a. Finally, results shows that the dimensionless correlation compressor model can be used to predict the performance of other reciprocating compres- sors, at similar operating conditions for a wide range of compressor rotation speed, with a reasonable accuracy. The authors thankfully acknowledge to the "Consejo Nacional deCiencia y Tecnología (CONACYT)” for their support to this study, and to the “Ministerio de Educación, Cultura y Deporte” (Grant number FPU12/02841) for sponsoring this work through “Becas y Contratosde Formación de Profesorado Universitario del Programa Nacional de Formación de Recursos Humanos de Investigación del ejercicio 2012”.

Nowadays, a high amount of industrial thermal energy is still lost due to the lack of competitive solutions for energy revalorization. Facing this challenge, this paper presents a novel technology, based on a reversible High-Temperature Heat Pump (HTHP) and Organic Rankine Cycle (ORC). The proposed system recovers low-grade waste heat to generate electricity or useful heat in accordance with consumer demand. Compressor and expander semi-empirical models have been considered for the reversible system computational simulation, being HFC-245fa the working fluid selected. The built-in volume ratio and Internal Heat Exchanger (IHX) effectiveness have been optimized to reach the maximum energy efficiency in each operating condition. Although HFC-245fa exhibits energy performance attributes, its high Global Warming Potential (GWP) is an issue for climate change mitigation. Hence, multi-objective optimisation of the environmentally friendly working fluids Butane, Pentane, HFO-1336mzz(Z), R-514A, HCFO-1233zd(E) and HCFO-1224yd(Z) has been carried out. The results show that the system proposed, working with HFC-245fa, achieves a Coefficient of Performance (COP) of 2.44 for condensing temperature of 140 °C, operating in HTHP mode, whereas the ORC mode provides a net electrical efficiency of 8.7% at condensing temperature of 40 °C. Besides, HCFO-1233zd(E) and HCFO-1224yd(Z) are both appropriate alternatives for the HFC-245fa replacement. These working fluids provide a COP improvement of 9.7% and 5.8% and electrical net efficiency improvement of 2.1% and 0.8%, respectively, compared to HFC-245fa. This paper provides a reference study for further designs and developments of reversible HTHP-ORC systems used for industrial low-grade waste heat recovery.

This work is focused on waste heat recovery of jacket cooling water from Internal Combustion Engines (ICEs). Cooling water heat does not always find use due to its low temperature, typically around 90 °C, and usually is rejected to the ambient despite its high thermal power. An efficient way to take benefit from the ICE cooling water waste heat can be to increase the power output through suitable bottoming Organic Rankine Cycles (ORCs). Thereby, this work simulates six configurations using ten non flammable working fluids and evaluates their performances in efficiency, safety, cost and environmental terms. Results show that the Double Regenerative ORC using SES36 gets the maximum net efficiency of 7.15%, incrementing the ICE electrical efficiency up to 5.3%, although requires duplicating the number of main components and high turbine size. A more rigorous analysis, based on the system feasibility, shows that small improvements in the basic cycle provide similar gains compared to the most complex schemes proposed. So, the single Regenerative ORC using R236fa and the Reheat Regenerative ORC using R134a seem suitable cycles which provide a net efficiency of 6.55%, incrementing the ICE electrical efficiency up to 4.9%.

This paper presents an experimental analysis of the influence of an internal heat exchanger on the performance of a vapour compression system using R1234yf as a drop-in replacement for R134a. In this work, we compare the energy performance of a monitored vapour compression system using both refrigerants, R134a and R1234yf, with and without the presence of an internal heat exchanger under a wide range of working conditions. A set of experimental tests are carried out varying the condensing temperature, the evaporating temperature and the internal heat exchanger use. From the experimental results, reductions in cooling capacity and COP between 6 and 13% have been observed when R134a is replaced by the drop-in fluid R1234yf, although the presence of an IHX can help to lessen these reductions between 2 and 6%. Finally, the experimental results obtained agree with the theoretical evaluations developed neglecting the pressure drops.

[EN] This paper presents an experimental analysis of a vapor compression system using R1234yf as a drop-in replacement for R134a. In this work, we compare the energy performance of both refrigerants, R134a and R1234yf, in a monitored vapor compression system under a wide range of working conditions. So, the experimental tests are carried out varying the condensing temperature, the evaporating temperature, the superheating degree, the compressor speed, and the internal heat exchanger use. Comparisons are made taking refrigerant R134a as baseline, and the results show that the cooling capacity obtained with R1234yf in a R134a vapor compression system is about 9% lower than that obtained with R134a in the studied range. Also, when using R1234yf, the system shows values of COP about 19% lower than those obtained using R134a, being the minor difference for higher condensing temperatures. Finally, using an internal heat exchanger these differences in the energy performance are significantly reduced., This study was sponsored by Fundacio Caixa Castello-Bancaixa under the project P11B2010-24 "Aplicacion de nuevos refrigerantes con bajo potencial de efecto invemadero en sistemas de frio comercial y climatizacion".

[EN] In this work an experimental evaluation of the working fluid HCFO-1233zd-E as HFC-245fa replacement in ORC systems for low temperature heat sources has been conducted. A fully monitored ORC module has been used to test both working fluids at different operating conditions. Due to the different densities of the working fluids, the mass flow rate for HCFO-1233zd-E is approximately 20% lower than for HFC-245fa. This causes thermal and electrical powers to be lower for HCF0-1233zd-E than for HFC245fa. However, net electrical efficiency is similar for both working fluids, ranging from 5% to 9.7% in the tested operating conditions. Regarding the expander performance, various performance indicators are addressed. The expander isentropic performance has a maximum value of 75%, with higher values for HCFO-1233zd-E than for HFC-245fa. The overall efficiency of the expander, similar for both working fluids, ranges from 44% to 57% in the experimental test range. (C) 2016 Elsevier Ltd. All rights reserved., The authors thankfully acknowledge the cooperation of Rank (R) for its support in this project.

[EN] Climate change is demonstrated through global surface temperatures increase in the last century. To stop this phenomenon, new regulations that ban or tax greenhouse gas fluids (HFC among them) have been approved. In the medium term, only low-GWP refrigerants will be permitted in developed countries. HFO fluids and most used HFCs as refrigerants in HVACR systems possess similar thermophysical properties. Among them, one of the most promising is R1234ze(E). This refrigerant presents good environmental properties and can be used in most of HVACR applications, pure or mixed with HFC or natural refrigerants (mainly CO2). This paper collects the most relevant research about R1234ze(E) thermophysical and compatibility properties, heat transfer and pressure drop characteristics, and vapor compression system performance; separating those works that consider R1234ze(E) pure or blended. Once the available literature is analyzed, it can be concluded that pure R1234ze(E) is a good option only in new HVACR systems. Nevertheless, if it is combined with other refrigerants, the final GWP value is also considerably reduced, maintaining efficiency parameters at levels that allow them to replace R134a, R404A or R410A in existing systems with minor modifications., The authors thankfully acknowledge the “Ministerio de Educación, Cultura y Deporte” (Grant Number FPU12/02841) for supporting this work through “Becas y Contratos de Formación de Profesorado Universitario del Programa Nacional de Formación de Recursos Humanos de Investigación del ejercicio 2012”.

We have developed a computational method for analysis of refrigeration cycles. The method is well suited for automated analysis of complex refrigeration systems. The refrigerator is specified through a description of flows representing thermodynamic sates at system locations; components that modify the thermodynamic state of a flow; and controls that specify flow characteristics at selected points in the diagram. A system of equations is then established for the refrigerator, based on mass, energy and momentum balances for each of the system components. Controls specify the values of certain system variables, thereby reducing the number of unknowns. It is found that the system of equations for the refrigerator may contain a number of redundant or duplicate equations, and therefore further equations are necessary for a full characterization. The number of additional equations is related to the number of loops in the cycle, and this is calculated by a matrix-based topological method. The methodology is demonstrated through an analysis of a two-stage refrigeration cycle. © 2009 Elsevier Ltd. All rights reserved.

In this work a model of a vapour compression refrigeration system with a variable-speed compressor, based on a black-box modelling technique, is presented. The kernel of the model consists of a full customized radial basis function network, which has been developed to accurately predict the performance of the system with low cost data requirement in terms of input variables and training data. The work also presents a steady state validation of the model inside and outside the training data set, finding, in both cases, a good agreement between experimental values and those predicted by the model. These results constitute a first step to go through future research on fault detection and energy optimisation in variable-speed refrigeration systems.

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".

In this paper, the influence of different mean void fraction correlations on a shell-and-tube evaporator dynamic model performance has been evaluated. The model proposed is based on the moving boundary approach and includes the expansion valve modelling. Several transient tests, using R134a as working fluid, have been carried out varying refrigerant mass flow, inlet enthalpy and secondary fluid flow. Then, the model performance, using different mean void fractions, is analysed from the system model outputs (evaporating pressure, refrigerant outlet temperature and condensing water outlet temperature). The slip ratio expressions selected are: homogenous, momentum flux model, Zivi's, Chisholm's and Smith's correlations. The results of the comparison between experimental and model predictions depend on the transient characteristics and there is not a single slip ratio correlation that provides the best performance in all the cases analysed.

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".

In this paper the performance of an Organic Rankine Cycle (ORC) module, which was designed and built for a specific power application, is experimentally characterized. The ORC tested satisfies the main specifications for an efficient power system, highlighting a volumetric expander with large built-in volume ratio. For tests development, a monitored test bench has been used and adapted to the planned test procedure, which consisted of varying the thermal power input for different condensing conditions. Thereby, 10 steady state points are achieved and analyzed according to thermal power input, gross and net electrical powers, electrical cycle efficiencies and expander effectiveness. The results show that the ORC performances are improved for higher thermal oil temperatures, capturing more thermal power, producing more electricity and achieving better cycle efficiencies. The maximum gross electrical efficiency obtained is 12.32%, for a heat source temperature about 155 °C and a direct dissipation to the ambient. Moreover, the expander reaches an electrical isentropic effectiveness about 65% for an optimum pressure ratio around 7, being a suitable system for power applications from low grade heat sources., 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)'.

This paper presents a model of shell and tube evaporator with micro-fin tubes using R1234yf and R134a. The model developed for this evaporator uses the ε-NTU method to predict the evaporating pressure, the refrigerant outlet enthalpy and the outlet temperature of the secondary fluid. The model accuracy is evaluated using different two-phase flow boiling correlations for micro-fin tubes and comparing predicted and experimental data. The experimental tests were carried out for a wide range of operating conditions using R134a and R1234yf as working fluids. The predicted parameter with maximum deviations, between the predicted and experimental data, is the evaporating pressure. The correlation of Akhavan– Behabadi et al. was used to predict flow boiling heat transfer, with an error on cooling capacity prediction below 5%. Simulations, carried out with this validated model, show that the overall heat transfer coefficient of R1234yf has a maximum decrease of 10% compared with R134a. The authors are grateful to University of Guanajuato, the ISTENER research group of University Jaume I, and the Consejo Nacional de Ciencia y Tecnologia (CONACYT) for their support to this study. Finally, the linguistic support of Dr. Carlos Montoro is appreciated.

The present paper presents experimental results obtained from a refrigerating vapour-compression plant’s shell-and-tube (1–2) evaporator working with R407C. Several tests have been carried out to study the influence of the evaporating pressure and the refrigerant’s mass flow rate on the refrigerant’s boiling heat-transfer coefficient inside horizontal tubes. This work has been performed by analyzing the variations of the evaporator’s overall thermal-resistance, computed using the effectiveness-NTU method, considering the influence of pressure drops and glide at the evaporator, and finally transferring the results and conclusions to the boiling heat-transfer coefficient. It has been observed that the variations of the boiling heat-transfer coefficient show a dependence on the evaporating temperature and the refrigerant’s mass-flow rate, which has been analyzed in the test range.

This paper deals with the control of the heat exchangers. Due to the resonant effect on this systems, simplified lumped parameters models obtained from the step response can be not enough appropriate to controller design if high performance is required. To design the control, instead of looking for a precise heat exchanger model obtained through complex experiments and sophisticated parameter estimation methods, the use of an iterative approach is suggested.

Up to now, the use of ammonia/water absorption cycles has been mainly limited to the production of refrigeration or air conditioning but due to the relatively high generator pressure some authors have proposed the integration in parallel of an expander to produce cooling and power simultaneously. This feature could provide many benefits in the future such as the use of solar thermal energy to partially cover the heating, cooling and electricity demand of a building. In the other hand the life cycle cost of the absorption system is improved because of the increase in the number of running hours in periods in which there is no demand for cooling but the demand for electrical power is still important. This paper shows a new combined absorption system using a scroll expander and three different working fluids using ammonia as refrigerant: ammonia/water, ammonia/lithium nitrate and ammonia/sodium thiocyanate. The scroll expander performance maps were obtained experimentally and modeled to predict the power production, rotational speed and exhaust temperature of the expander and included in the complete absorption cycle model build using Engineering Equation Solver (EES) Software. This system produces different amounts of cooling and power at the desired power/cooling ratio to cover varying demand profiles.

Internal or liquid-suction heat exchangers are used in many refrigeration and air conditioning systems based on the vapour compression cycle, with the basic objective of assuring the entrance of refrigerant in liquid phase to the expansion device. This purpose is achieved by exchanging energy between the cool gaseous refrigerant leaving the evaporator and warm liquid refrigerant exiting the condenser. These devices can have positive or negative influences on the plant overall energy efficiency, depending on the working fluid and the operating conditions. In this paper the experimental results obtained from a refrigeration test facility with and without the presence of an internal heat exchanger, using R22, R134a and R407C as working fluids, are presented and analyzed, including the impact of pressure drops and variations of refrigerant mass flow rate. A comparison between experimental and theoretical results is also enclosed.

In this paper, the predicted performance of a shell-and-tube (1-2) evaporator installed in a vapour compression liquid chiller is analysed. The classical thermal design methods are applied to the evaporator performance with two HFC refrigerants, a pure fluid (R134a) and a zeotropic blend with an appreciable glide (R407C). From the experimental results obtained it is possible to discuss the validation of the simplificatory assumptions usually taken, evaluating the resulting error introduced due to the no consideration of pressure drops and temperature glide (in the case of zeotropic blends) at the evaporator. Concluding that is not possible to consider the behaviour of a zeotropic refrigerant as a pure refrigerant, rejecting the glide. Whereas the assumption of no pressure drops in evaporator, leads to an error of about 5% in cooling capacity calculation. Copyright © 2004 John Wiley & Sons, Ltd.

In this paper, the influence of the main operating variables on the energetic characteristics of a vapour compression plant, based on experimental results, is addressed. The experimental tests are performed on a single-stage vapour compression plant using three different working fluids, R134a, R407C and R22. The operating variables considered are the evaporating pressure, the condensing pressure and the superheating degree at the compressor inlet. The performance characteristics followed to analyse the energetic performance are the refrigerating capacity and the power requirements of the reciprocating compressor, presenting and discussing in this work the main experimental results obtained.

Adaptive methods are system identification methods which are commonly used to analyze nonlinear and nonstationary signals. The use of three of these methods to study the time dependence evolution of the linear stability parameters of a Boiling Water Reactor using neutronic noise signals has been analyzed. Both simulated and real neutronic signals have been considered to perform the analysis.

In this work we present several tools to study the time dependence of the linear stability parameters of a BWR using neutron noise analysis. Particularly, we have studied the variation in time of the fundamental frequency of a signal using the short-time Fourier transform and we have compared this method with the calculation of a time dependent Power Spectral Density (PSD) function. The temporal variation of the decay ratio is analysed using a method based on an autoregressive model to fit the different blocks of the signal. The performance of the tools presented is compared analysing analytic signals and a real signal of Forsmark 1&2 Stability Benchmark.

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] HFC-245fa is a common working fluid used in Organic Rankine Cycles generating mechanical power from low temperature heat. This paper compares the predicted ORC performance of two novel low GWP working fluids, HCFO-1233zd-E and HFO-1336mzz-Z, to HFC-245fa over a wide range of evaporating temperatures, condensing temperatures and vapour superheat values. Expander power output, required pump power input, net cycle efficiencies, mass flow rates and turbine size parameters with HCFO-1233zd-E, HFO-1336mzz-Z and HFC-245fa were compared for a given thermal power input. HCFO-1233zd-E and HFO-1336mzz-Z are predicted to have attractive thermodynamic Rankine power cycle performance. HCFO-1233zd-E would require 10.3%-17.3% lower pump power and would enable up to 10.6% higher net cycle efficiencies than HFC-245fa over the range of cycle conditions examined in this paper. The turbine size required with HCFO-1233zd-E would be up to about 7.5%-10.2% larger than with HFC-245fa. HFO-1336mzz-Z would require 36.5%-41% lower pump power and would enable up to 17% higher net cycle efficiencies than HFC-245fa over the range of cycle conditions examined in this paper. The turbine size required with HFO-1336mzz-Z would be up to about 30.9%-41.5% larger than with HFC-245fa. HFO-1336mzz-Z cycle efficiency is benefitted substantially by a recuperator. The net cycle efficiency increases and the required turbine size decreases relative to HFC-245fa for HCFO-1233zd-E and for HFO-1336mzz-Z at higher evaporating and condensing temperatures. (C) 2014 Elsevier Ltd. All rights reserved., The authors thankfully acknowledge DuPont Corporation 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".

[EN] This paper presents an energy performance evaluation of two low-GWP refrigerants, R1234yf and R1234ze(E), as drop-in replacements for R134a. Tests are carried out in a monitored vapor compression system combining different values of evaporation and condensation temperature, and without/with the adoption of an internal heat exchanger. The parameters analyzed are volumetric efficiency, cooling capacity and COP and they are presented taking R134a as baseline. Results show that without IHX the average volumetric efficiency for R1234yf and R1234ze is 4% and 5% lower compared with R134a. The cooling capacity obtained with R1234yf and R1234ze is reduced, with an average difference of 9% and 30% without IHX. Also, COP values are about 7% lower for R1234yf and 6% lower for R1234ze than those obtained using R134a. Finally, the use of an internal heat exchanger reduces the COP differences for both replacements. (C) 2014 Elsevier Ltd. All rights reserved., 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 work presents a model of a shell-and-tube evaporator using R1234yf and R134a as working fluids. The model uses the effectiveness-NTU method to predict the evaporation pressure and the refrigerant and secondary fluid temperatures at the evaporator outlet, using as inputs the geometry of the evaporator, the refrigerant mass flow rate and evaporator inlet enthalpy, and the secondary fluid volumetric flow rate and evaporator inlet temperature. The model performance is evaluated using different two-phase flow heat transfer correlations through model outputs, comparing predicted and experimental data. The output parameter with maximum deviations between the predicted and experimental data is the evaporating pressure, being the deviations in outlet temperatures less than 3%. The evaporator model using Kandlikar's correlation obtains the highest precision and the lowest absolute mean error, with 4.87% in the evaporating pressure, 0.45% in the refrigerant outlet temperature and 0.03% in the secondary fluid outlet temperature.

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.

Despite of the excellent efficiency of the CO2 transcritical cycle in heat pump mode, there is a loss of efficiency in refrigeration mode compared with the subcritical vapor compression cycle with HFC refrigerants. This reason has lead several researches to propose ways to improve the transcritical cycle performance using CO2 as refrigerant in refrigeration mode, mainly associated to cycle configurations changes. In this paper, a comparative study and energetic simulation of most common configurations for transcritical single stage cycle using CO2 as refrigerant has been carried out. In order to make the comparison, a cycle components modelization has been proposed and the simulation results are used to find the optimum configuration for a single stage vapor compression transcritical system.

The aim of this work is to propose a black-box model to accurately predict the chilled water temperature dynamic response of a vapour compression chiller. The model is oriented to be of value in determining an adequate control algorithm based on compressor speed regulation. The model uses variables that are easily obtained in any commercial or industrial facility, such as the water inlet temperature and the compressor speed, to predict the chilled water outlet temperature. Several linear black-box model structures are proposed and their ability to describe the process behaviour is validated with experimental data from a monitored test bench. Finally, the Box–Jenkins structure shows the best fits, obtaining promising results.

This work presents a model for a variable-speed vapour compression system that is able to predict accurately the system performance using data easily obtained from an industrial facility. The model uses information on the secondary fluids input conditions and the compressor speed to predict the secondary fluids output temperatures, the operating pressures, the compressor power consumption and the system overall energy performance. This model has been validated experimentally with steady state tests, presenting a prediction error lower than 10%. Finally, an application of the model to evaluate the influence of the operating variables on the energy performance of a chiller is presented. © 2009.

This work presents a mathematical model of a shell-and-tube evaporator based on mass continuity, energy conservation and heat transfer physical fundamentals. The model is formulated as a control volume combination that represents the different refrigerant states along the evaporator. Since the model is based on refrigerant and secondary fluid states prediction, it can be easily adapted for modelling any type of evaporator. The strategy of working with physical fundamentals allows the steady- and dynamic-state analysis of any of its performance variables. The paper presents a steady-state validation made with two pure refrigerants (HCFC-22, HFC-134a) and with a zeotropic blend (HFC-407C), and a dynamic validation with transient experimental tests using HCFC-22. The model prediction error is lower than 5% and it is well in accordance with actual dynamic behaviour. Copyright © 2006 John Wiley & Sons, Ltd.

[EN] Based on a previously developed and validated steady-state model of a single-stage vapour compression plant, the present paper describes an in-depth study directed to examine the consequences of changes in the operating conditions in such a plant. These include modifications of condensing and evaporating temperatures and the total superheating degree at compressor suction, which are the main energy parameters in a refrigeration plant. The aim of this work is not to determine the final energy state when the operating conditions are modified, which could be achieved using the steady-state model, but to study the mechanism that explains the variation. The pursuit of this goal implies conducting a detailed analysis of the performance and influence of several intermediate variables, the evolution of which has a direct effect on the final cooling capacity, compression power and COP values. The results obtained show the significant influence of the suction pressure (through the specific suction volume) on the compression power and cooling capacity, while the condensing and evaporating temperatures have a similar influence on the COP., The authors are indebted to the Generalitat Valenciana for partial support under project GV05/091

Summarization: Successful planning and operation of a solid waste management system depends on municipal solid waste (MSW) generation process knowledge and on accurate predictions of solid waste quantities produced. Conventional analysis and prediction models are based on demographic and socioeconomic factors. However, this kind of analysis is related to mean generation data. Dynamic MSW generation analysis can be done using time series data of solid waste generated quantities. In this paper some tools for time series analysis and forecasting are proposed to study MSW generation. A prediction technique based on non-linear dynamics is proposed, comparing its performance with a seasonal AutoRegressive and Moving Average (sARIMA) methodology, dealing with short and medium term forecasting. Finally, a practical implementation consisting of the study of MSW time series of three cities in Spain and Greece is presented. Presented on: Resources, Conservation and Recycling

Lower global warming potential (GWP) refrigerants must be used in refrigeration education to integrate the environmentally responsible engineering principles in class. However, most of the refrigeration educational laboratories are still using hydrofluorocarbons (HFCs) as working fluids, which are considered as greenhouse gases. This paper shows the procedure to adapt the new refrigerant R513A in a refrigeration system used for a cooling capacity educational laboratory. First, the paper describes the organization of the laboratory session, and the characteristics of the different methods of cooling capacity calculation taught to the master’s degree students. Then, the benefits of including new sensors in the experimental setup to obtain more accurate results are explained. Later, accurate new graphics and an equation to calculate the R513A cooling capacity are provided. Finally, the educational aspects worked with the students in this session, and each cooling capacity method are assessed. The procedure explained in this paper can be used as a guide for introducing lower GWP refrigerants in similar educational refrigeration laboratories.

This paper reviews different techniques to analyze BWR's stability regime from neutronic power signals, and alternative methodologies based on the singular value decomposition (SVD) of a given matrix are proposed. The results obtained from experimental signals using two different constructions of the embedding space of the system have been compared. SVD-based AR models have been studied and the results obtained with these methods have been compared with those of a standard AR model for short neutronic power signals.