A Comparative Performance Study of an Ejector-Expansion Refrigeration Cycle Using R134a and its Alternatives: Application of Automobile Air Conditioning

In this study, the performance of ejector-expansion refrigeration cycle (EERC) with R134a alternative refrigerants (R152a, R1234yf, R404A, R407C, R507A and R600a) for automobile air-conditioning application is investigated numerically. The ejector is modeled with a constant mixing-pressure assumption taking into consideration the friction effect in the ejector mixing section. The studied refrigerants are compared based on the optimum area ratio, discharge temperature, compressor input power, volumetric cooling capacity, exergy destruction, COP, exergy efficiency and COP improvement. The results show that R152a and R1234yf have the closest performance to R134a and can be considered the most suitable alternative refrigerants for R134a. The COP and exergy efficiency are improved by 2.26% and 2.27%, respectively, using R152a compared to the use of R134a, whereas they are reduced by 2.89% and 2.88% using R1234yf. The volumetric cooling capacity is reduced for both R152a and R1234yf by 6.14% and 6.8%, respectively. In addition, the effect of compressor rotational speed on the performances is reported.

Experimental Performance Analysis of R1234yf in an Air-Conditioning System as Substitute of R134a

In this work, R1234yf is tested in an air-conditioning system as a proposed alternative to R134a. The system is tested at 30, 35, 40, 45 and 50[Formula: see text]Hz evaporator fan frequency to cool the air entering into the evaporator section at a fixed temperature of 35∘C. The system is charged with 600, 700, 800, 1000 and 1200[Formula: see text]g of each refrigerant. The charge mass of 800 grams gives the best performance for both refrigerants. Also, R1234yf has higher COP, exergetic efficiency, second law efficiency, and lower compressor power consumption. Both refrigerants operate at a moderate range of compressor discharge temperature of 85∘C.

Methods based on a semi-empirical model for simulating scroll compressors with HFC and HFO refrigerants

The aim of this work is to evaluate three methodologies regarding semi-empirical scroll compressor modeling for different refrigerants and conduct a comparative analysis of their results and accuracy. The first step is to improve a semi-empirical model for scroll compressors based on established techniques, and further enhance the physical background of some of its sub-processes leading to more accurate predictions. Focus is then given on the compressor operation when changing the refrigerant, proposing three methods in total. The first method refers to the standard model, requiring an optimization process for the calibration of all the model parameters. The second method relies on a reference refrigerant, and also uses optimization procedures, but for the fine-tuning of a small subset of the parameters. The third method is more generalized, without the need of any optimization process for the parameters identification, when fluid change occurs, leading to a very fast approach. Το evaluate the accuracy and verify the applicability of each method also related to the necessary computational time, two scroll compressors each with three different refrigerants are considered (HFCs and HFOs and their blends). The model is evaluated with the available manufacturer data, using R134a as reference refrigerant. The results show that the first method predicts the key indicators with a very high accuracy, with the maximum discrepancy of 2.06%, 4.17% and 3.18 K for the mass flow rate, electric power and discharge temperature respectively. The accuracy of the other two methods is dropping, but within acceptable levels in most of the cases. Therefore, in cases that reduced accuracy can be accepted, the third method is preferred for compressor performance prediction when changing the refrigerant, which provides results at a small fraction of time compared with the other two methods, once the parameters are calibrated for a reference case.

Performance and Optimization Study of R290 as Alternative Refrigerant for R22 in Low Temperature Heat Pump System

This paper mainly studies the replacement performance of R290 in R22 low temperature heat pump system from the experimental point of view. By comparing the performance differences under different working conditions, it is found that when R22 is directly extracted from the original system and filled with R290, the heat capacity and COP of the system are attenuated, and the compressor discharge temperature and pressure of the R290 system are higher than those of the original R22 system in low temperature environment. Through the analysis of the system components, it can be considered that the main reason for the above phenomenon is that the compressor displacement of the R22 system is too large and does not match the R290 system. Therefore, in order to meet the safety requirements of the system and improve the overall performance of R290 in the low temperature heat pump system at the same time, it is considered to replace the compressor with a smaller displacement which is more matched with R290 in the system. The experimental results show that the compressor displacement optimization of the R290 low temperature heat pump system can effectively reduce the exhaust temperature and pressure of the system and improve the overall performance of the system. The COP of the optimized R290 low temperature heat pump system is 6.5% higher than that of the original R22 system, and the exhaust temperature in the low temperature environment is reduced by 36% to below 80 C.

Performance of Air Conditioning Unit under Constant Outdoor Wet-Bulb Temperature and Varied Dry-Bulb Temperature

An experiment has been carried out for examining the performance of an air conditioning unit under constant outdoor wet-bulb temperature and varied dry-bulb temperature. During the experiment, the wet-bulb temperature of the compartment for outdoor unit was maintained at 22℃ and the dry-bulb temperature was varied from 24℃ to 36℃. The increase of outdoor air temperature results in the increase of supply air temperature, discharge temperature, suction temperature, and liquid line temperature. These cause the degradation of the air conditioner performance. An increase of power consumption by 1.4% and decrease of cooling capacity by 0.8% were observed for each 1℃ increase of outdoor air temperature. As a result, the energy efficiency ratio drops by 2% for each 1℃ increase of outdoor air temperature.

Thermodynamic Analysis of Eco-Friendly Refrigerant Mixtures as an Alternative to HFC-134a in Household Refrigerator

Nowadays, research has been focused on refrigerants from Hydrofluorocarbons (HFCs), which are not harmful to the ozone layer. Because of replacing refrigerants from chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). HFCs are used in many applications, including refrigerants, aerosols, solvents, and blowing agents for insulating foams. However, some HFCs have relatively high global warming potential (GWP) and are subject to further examination due to growing concerns about global climate change. The present work’s main objective is to select eco-friendly refrigerants from AC5, R430A and R440A, combining two or more refrigerants from HC, HFC and HFO groups as a direct substitute HFC-134a in a household refrigerator. The performance of the domestic refrigerator with liquid suction heat exchanger (LSHX) was compared in terms of compressor discharge temperature, coefficient of performance (COP), volumetric cooling capacity (VCC), and power consumption of a compressor. It was found that the average COP of R440A and R430A was higher by approximately 2.5% and 1.47% than HFC-134a. However, the COP of AC5 was 6.1% lower than that of HFC-134a. The VCC of R430A is almost equal to HFC-134a. The results also show that AC5, R440A and R430A consume less power than HFC-134a. The compressor outlet temperature with R440A, AC5 provide higher values than HFC-134a, which affects the compressor life. The best overall performance was achieved with the refrigerant R430A in the household refrigerator and suggested an alternative to HFC134a, which also has a very low GWP from the environmental safety perspective.

Rack-Level Thermosyphon Cooling and Vapor-Compression Driven Heat Recovery: Compressor Model

This paper introduces a novel thermal management solution coupling in-rack cooling and heat recovery system. System-level modeling capabilities are the key to design and analyze thermal performance for different applications. In this study, a semi-empirical model for a hermetically sealed scroll compressor is developed and applied to different scroll geometries. The model parameters are tuned and validated such that the model is applicable to a variety of working fluids. The identified parameters are split into two groups: one group is dependent on the compressor geometry and independent of working fluid, whereas the other group is fluid dependent. By modifying the fluid-dependent parameters using the specific heat ratios of two refrigerants, the model shows promise in predicting the refrigerant mass flow rate, discharge temperature and compressor shaft power of a third refrigerant. Here, the approach has been applied using data for two refrigerants (R22 and R134a) to achieve predictions for a third refrigerant’s (R407c) mass flow rate, discharge temperature, and compressor shaft power, with normalized root mean square errors of 0.01, 0.04 and 0.020, respectively. The normalization is performed based on the minimum and maximum values of the measured variable data. The technique thus presented in this study can be used to accurately predict the primary variables of interest for a scroll compressor running on a given refrigerant for which data may be limited, enabling component-level design or analysis for different operating conditions and system requirements.

ENERGY EFFICIENCY IN CONSTANTA HARBOR- A THEORETICAL ASSESSMENT OF THE PERFORMANCE OF A HEAT PUMP FOR HEATING NEEDS, FOR A LESS POLLUTANT ADMINISTRATION OFFICE

In accordance with the present energetic exigencies, the energy consumption in port buildings is of a vital importance. From this perspective, heat pumps are less pollutant and more energy efficient options than the traditional heating technologies. This study focuses on an air source heat pump (ASHP), operating in an administration office located in Constanta harbor, Romania, in order to supply heated water during December of 2020. Electrically driven heat pumps are seen as a successful alternative to classical expensive heating means, such as electrical heating or the one based on fossil fuels combustion. Within this research, are investigated influences of the heated water temperatures and exterior air temperatures on the theoretical Coefficient of Performance, the compression ratio and the discharge temperature. The cycle is working with R134a, with 50C superheating and sub cooling. It will be considered that the heated water is supplied in the range (40-50) 0C, while the outdoor air temperature varies in the range (0-10) 0C. Obtained results show that the highest efficiency of the ASHP is obtained for the lowest value of the heated water temperature and for the highest value of the outdoor air temperature. This situation corresponds also to the good working of the compressor of the refrigeration plant, since are seen lowest values of the compression rate and the discharge temperature, as well. This means that the compressor do not consume high amounts of energy and the oil is not damaged because of high temperatures of the refrigerant vapors.

Thermodynamic Performance Analysis of Hydrocarbon Based Domestic Refrigeration System

The use of synthesized refrigerants has several environmental concerns. The most widely used substances like hydro fluorocarbons (HFCs), chlorofluorocarbons (CFCs) and hydro chlorofluorocarbons (HCFCs) have either high global warming potential (GWP), high ozone depletion potential (ODP) or long atmospheric life time. With the growing demand of healthier atmosphere, the study of other alternative substances is very important. This paper presents theoretical thermodynamic performance analysis of hydrocarbon based domestic vapour compression refrigeration system. Propane (R-290), isobutane (R-600a) and butane (R-600) were used. Then, the results were compared with the performance of currently most commonly used tetrafluoroethane (R-134a). These hydrocarbons have zero ODP and very negligible GWP. Different parameters, like coefficient of performance (COP), refrigeration effect, compressor work input and compressor discharge temperature were investigated. Evaporator and condenser temperatures, subcooling, superheating and compressor isentropic efficiency were the variables used for this study. MATLAB software has been used in the mathematical analysis. COP values were found comparable to that of R134a. All the hydrocarbons investigated gave beyond 150% refrigeration effect compared to R-134a for the same mass flow rate. But this was at the expense of higher compressor work input. This research also revealed that the compressor discharge temperature is much lower for R-600a and R-600. Generally, these hydrocarbons showed that they are a good alternative to R134a based on the thermodynamic point of view.