Comparative performance analysis of the low GWP refrigerants HFO1234yf,HFO1234ze(E) and HC600a inside a roll-bond evaporator

This paper presents the comparative performance analysis of the low GWP refrigerants HFO1234yf, HFO1234ze(E) and HC600a inside a commercial roll-bond evaporator for household refrigerators. The vaporisation performances were evaluated at two evaporation temperatures, −15 and −20 °C, and different refrigerant mass flow rates and compared with those of the traditional refrigerant for domestic refrigeration HFC134a. The performance analysis was carried out using both thermocouples installed on the rear side of the roll-bond evaporator and an IR thermo-camera. Each of the low GWP refrigerants tested can be considered a good substitute for HFC134a, provided that the compressor displacement is adjusted to deliver the proper refrigerant mass flow rate. Only HFO1234yf exhibits performance similar to HFC134a at the same mass flow rate, therefore it can be considered a direct drop-in substitute for HFC134a.     

An experimental investigation of the energetic performances of HFO1234yf and its binary mixtures with HFC134a in a household refrigerator

In this paper, a comparative experimental analysis between HFC134a, HFO1234yf and a refrigerant mixture of HFC134a/HFO1234yf (10/90% weight) implemented in a domestic refrigerator is introduced. Adding 10% of HFC134a to HFO1234yf, the mixture becomes non-flammable with GWP still less than 150. The experimental tests have been conducted under sub-tropical conditions in accordance with the UNI-EN-ISO15502 standard. Two kinds of tests have been shown: pull down and 1-day energy consumption. The results show that HFC134a/HFO1234yf (10/90% weight) is the best drop-in refrigerant fluid for HFC134a in the domestic refrigerator used for the experimental tests. The refrigerant mixture has the closest behaviour to that of HFC134a in terms of temperatures and pressures. Furthermore, the cycle working with the optimal charge of the mixture shows an energy saving of 16 and 14% with respect to HFC134a and HFO1234yf, respectively.     

Experimental assessment of R134a and its lower GWP alternative R513A

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.     

R1234yf and R1234ze(E) as low-GWP refrigerants for residential heat pump water heaters

Owing to the growing concerns about the relatively high global warming potential (GWP) of current refrigerants, a serious effort is in progress to find lower-GWP substitutes. The hydrofluoroolefin (HFO)-based refrigerants R1234yf and R1234ze(E) are being considered for use in multiple heating, ventilation, air conditioning, and refrigeration applications because of their very low GWP. A study was conducted to model a residential heat pump water heater using these HFOs. A system model was calibrated using experimental data and the calibrated model was used to evaluate the potential of HFOs to replace R134a. A series of parametric analyses were used to investigate the impacts of condenser wrap pattern, condenser tube size, evaporator size, and heat loss factor from the storage tank. It has been shown that both R1234yf and R1234ze(E) can be substituted for R134a with comparable performance and no substantial modifications to the original system. This study presents a detailed feasibility analysis for successful replacement of high-GWP refrigerants with low-GWP refrigerants with acceptable performance.     

新型制冷剂R1234ze(E)及其混合工质研究进展

低GWP值制冷剂R1234ze(E)(trans-1,3,3,3-tetrafluoropropene)作为R134a较为理想的替代品而被关注,但其单一成分的热力学性能和传输特性并不理想,在R1234ze(E)中混入R32成分可以有效改善其热力学性能。本文概述了低GWP值工质R1234ze(E)及其与R32混合物的热物性特征、传输特性及系统运行性能方面的研究现状,并与目前常用的制冷工质进行比较分析,指出R1234ze(E)与R32混合工质有望成为新型低GWP值替代工质。     

Analysis of alternatives to high GWP refrigerants for eutectic refrigerating systems

The EU Regulation No 517/2014 is going to phase-out R507A and R404A refrigerants because of their high GWP values. Different alternative refrigerants are under consideration, with the research results available for various applications. However, the eutectic refrigerating system operates at specific conditions, which are analysed in the paper. The applicability of the alternative refrigerants in the eutectic systems is analysed, focusing on performance and availability of components.The analysed alternatives are hydrocarbons, CO₂ and HFC/HFO mixtures. The hydrocarbons would be a good alternative, but the required system components are not available. The HFC/HFO mixtures are the alternative with the available system components. The drop-in replacement test results with R448A refrigerant demonstrate significant performance degradation. At 25 °C ambient temperature the pull-down time increased by 24% and the power consumption increased by 9%. Also, due to the glide and lower evaporation pressure, the retrofitted system cannot reach the required evaporation temperatures.     

欧盟汽车空调指令对汽车企业的影响分析

欧盟汽车空调指令2006/40/EC要求汽车空调制冷剂GWP值≤150,目前,广泛使用的R134a制冷剂的GWP值为1300,因此,R134a逐渐会被禁用,新型制冷剂HFO-1234yf逐步被推广,取代R134a.重点研究了两种制冷剂的性能差异,替代趋势,及空调指令在欧盟的执行情况,以及国内自主汽车企业的应对措施.     

Comparative experimental study of low GWP alternative for R134a in a walk-in cold room

The environmental problems induced by the ongoing increase in the global worming potential (GWP) pose a significant interest among researchers. It was found that, the currently used refrigerants are with high GWP (National Refrigerants Inc., 2004), so that it becomes necessary to search for alternatives to these refrigerants that can properly operate on the same systems but with low GWP. Therefore a walk-in cold room working with vapor compression cycle is constructed and tested in this paper. The performance of R134a refrigerant with high GWP is compared to another low GWP refrigerant R1234ze in a trail to provide a solution of the problem of high GWP of refrigerants currently used in cold rooms. The results obtained in this study have shown that, the cooling capacity of R1234ze was lower than that of R134a by 2% to 13%. The lowest evaporating temperature that could be reached for R1234ze is −13 °C while the lowest temperature of R134a is −30 °C. Regarding the power consumption, R1234ze has lower power consumption than R134a by about 9% to 15% therefore it can be concluded that R 1234ze can be recommended to be used at high and medium evaporating temperature after carrying out the suitable modifications on the refrigeration cycle.     

冰淇淋机制冷系统性能及新型环保制冷剂热力学分析

针对软冰淇淋机首先确定了其计算工况，在分析冰淇淋机制冷循环的基础上，应用NIST的REFPROPV6.0软件编写了通用的计算程序，对不同工质的冰淇淋机循环过程进行了计算。经过计算可以发现，纯质HFC134a,HFC125,HFC143a,HFC32和HFC152a等中没有一种工质的热工性能，安全性能和环境性能可以完全满足替代要求，根据蒸气压相似原则，考虑各纯质的优缺点及混合制冷剂配对原则，确定了混合工质HFC134a/HFC32(70/30mass%)作为冰淇淋机的替代制冷剂。     

Nucleate boiling heat transfer coefficients of HFO1234yf on various enhanced surfaces

In this study, nucleate boiling heat transfer coefficients (HTCs) of HFO1234yf HFC134a are measured on a flat plain, Turbo-B, Turbo-C, and Thermoexcel-E surfaces. All data are taken at the liquid pool temperature of 7 °C on small flat horizontal square copper plates (9.53 mm × 9.53 mm) at heat fluxes from 10 kW m⁻² to 200 kW m⁻² with an interval of 10 kW m⁻². Test results show that nucleate boiling HTCs of HFO1234yf on all four surfaces are similar to those of HFC134a at all heat fluxes tested in this study. At heat fluxes below 150 kW m⁻², Thermoexcel-E surface shows the highest heat transfer performance and hence is the best surface for the manufacture of the evaporators in refrigeration and air-conditioning equipment. On the other hand, at high heat fluxes above 150 kW m⁻², Turbo-B and Turbo-C show better heat transfer performance than Thermoexcel-E and hence are good for electronic cooling applications. Overall, HFO1234yf is a good long term candidate with excellent environmental properties to replace successfully HFC134a from the view point of pool boiling heat transfer. Hence HFO1234yf can be readily applied to the conventional evaporators designed for HFC134a.     

Commercial refrigeration – An overview of current status

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.     

HCFC123与HFC134a离心式冷水机组特性比较

从离心式冷水机组的特性角度出发,阐述冷水机组2种替代制冷剂HFC134a和HCFC123的选择使用,比较分析这2种制冷剂的性能,及其机组性能和其他一些因素。其中制冷剂的环境特性包括毒性、GWP和ODP等。机组性能特性包括产品能耗比及单位质量制冷量比的比较等。其他特性包括产品尺寸、使用维护等。综合考虑上述因素,尤其应考虑2007年9月修订的《蒙特利尔议定书》加速淘汰HCFCs的现实要求,认为在我国对新的离心机组使用HCFC123应持十分谨慎的态度。     

Theoretical energy performance evaluation of different single stage vapour compression refrigeration configurations using R1234yf and R1234ze(E) as working fluids

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.     

HFO1234ze(E) vaporisation inside a Brazed Plate Heat Exchanger (BPHE): Comparison with HFC134a and HFO1234yf

This paper investigates the effects of heat flux, saturation temperature, and outlet conditions on HFO1234ze(E) boiling inside a Brazed Plate Heat Exchanger (BPHE). The effect of the heat flux on the heat transfer coefficients was remarkable. Similar consideration applies for outlet condition effects whereas the impact of saturation temperature was found to be lower. The frictional pressure drop shows a linear dependence on the refrigerant kinetic energy per unit volume. The two-phase flow boiling heat transfer coefficients were compared with a new model for refrigerant boiling inside BPHE (Longo et al., 2015): the mean absolute percentage deviation between calculated and experimental data is 7.2%. The present data points were compared with those of HFC134a and HFO1234yf previously measured inside the same BPHE under the same operating conditions: HFO1234ze(E) exhibits heat transfer coefficients very similar to HFC134a and HFO1234yf and frictional pressure drops slightly higher than HFC134a and HFO1234yf.     

HFC125/HCs二元混合工质理论制冷循环性能分析

利用NIST REFPROP数据库计算HFC125/HCs(包括丙烷、丁烷、异丁烷)三类二元混合工质的热力学性质,并对其理论制冷循环性能进行分析计算,筛选出最佳配比.结果显示其理论循环性能比HCFC22高16.9%,并且压缩机排气温度也有所降低.     

R1234yf as a substitute of R134a in automotive air conditioning. Solubility measurements in two commercial PAG oils

Starting from January 1st 2011, as stated by the Directive 2006/40/EC, fluorinated greenhouse gases with a global warming potential (GWP) higher than 150 can not be used in automotive applications any more. For this reason, 1,1,1,2-tetrafluoroethane (R134a), commonly used for these applications, will be abandoned and substituted by refrigerants with lower GWP. In recent times, a new fluid, 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) has been proposed as an interesting alternative, since it has a very low GWP and thermodynamic properties very similar to R134a. At the moment, only few data can be found on the thermodynamic properties of this new refrigerant and, in particular, its behaviour in solution with commonly used compressor lubricants is still to be evaluated. Here, solubility experimental data of R1234yf in a Polyalkylene Glycol (PAG) and in a specifically modified Double-Capped PAG (DC-PAG) commercial lubricants are measured with a static synthetic method at isothermal conditions, in the temperature range between 258 K and 338 K.     

Formation Conditions of Clathrates Between HFC Alternative Refrigerants and Water

There are two promising candidates as alternative refrigerants for air-conditioners and heat pumps. The first is R407C, which is composed of HFC-32 (23 mass%), HFC-125 (25 mass%), and HFC-134a (52 mass%). The second is R410A, which is composed of HFC-32 (50 mass%) and HFC-125 (50 mass%). In this study, formation conditions of clathrate compounds between water and HFC alternative refrigerants such as HFC-32, HFC-125, HFC-134a, and their mixtures, R407C and R410A, were investigated. Phase diagrams of clathrates of these HFC alternative refrigerants and their mixtures were determined. From the phase diagrams, the critical decomposition temperature and the critical decomposition pressure were determined. The relationship between the critical decomposition points for the clathrates of HFC-32, HFC-125, HFC-134a, R410A, and R407C were studied. It is found that R407C and R410A form clathrate compounds with water under the evaporating temperature condition in the refrigeration cycle of air-conditioners and heat pumps.     

混合制冷剂R1234yf/R134a PVTx性质的实验研究

为了获得混合制冷剂R1234yf/R134a的热物性数据,本文利用Burnett法为基础搭建的高精度PVTx实验台,在温度为268~323 K时,测定了质量分数为55%/45%,50%/50%和45%/55%混合制冷剂R1234yf/R134a的PVT性质,最终拟合了三种不同配比的混合工质的气态维里方程,方程和实验数据具有较高的重合度。     

Drop-in replacement in a R134 ejector refrigeration cycle by HFO refrigerants

The present work reports a numerical analysis of a single-phase supersonic ejector working with R134a as well as hydrofluoroolefin (HFO) refrigerants R1234yf and R1234ze(E). Comparisons were made regarding the ejector performances under varying operating conditions and refrigerant mixture proportions. The calculations have been then extended to an existing ejector heat driven refrigeration cycle (EHDRC). R1234yf appears to be a good candidate for drop-in replacement of R134a in a real EHDRC, while using R1234ze(E) would induce some modifications due to its thermodynamic properties. Maintaining the same pressure ratio for the ejector would lead on one hand to better entrainment ratio using R1234ze(E) and on the other hand to reduced coefficient of performance (COP) and cooling power by 4.2% and 26.6% in average, respectively. Using R1234yf under the same conditions induces a decrease of 5.2% for the entrainment ratio, 9.6% for the COP and 19.8% for the cooling power in average.