|Nyayu Aisyah||Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|Muhammad Idrus Alhamid||Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|Nasruddin||Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
Scientists have worked assiduously to find low GWP refrigerants for HVAC systems that specifically address the environmental problems of ozone depletion and global warming. R1234ze and R1234yf were considered as potential alternatives to conventional refrigerants such as R410A. Thermodynamic analysis of 4 kW air conditioning systems was conducted to assess system performance of R1234ze and R1234yf. Furthermore, exergy and exergo-environmental analysis were carried out for the heat pump system using selected environmentally friendly refrigerants. Finally, by using a multi-objective genetic algorithm, the optimum operating condition, including evaporation temperature, condensing temperature and mass flow refrigerant was determined. The result showed that the optimum operating condition of 20oC evaporation temperature, 42.57oC condensation temperature and 0.02 kg/s mass flow rate, led to exergy efficiency of 51.92% and an exergo-environmental value of 101.925 mPts/h. R1234ze has a comparable performance to R410A or performs even better.
Exergo-environmental; Exergy; Heat pump; Low GWP refrigerants
The search for alternative refrigerants has been, and still remains, a prevalent topic in the history of Heating Ventilating Air Conditioning systems (HVAC systems) (Mohd-Ghazali et al., 2011; Alhamid et al., 2013). Chlorofluorocarbon (CFC), as the first refrigerant used in HVAC systems was banned by the Montreal Protocol in 1987 to be replaced by Hydrofluorocarbon (HFC) and Hydrochlorofluorocarbon (HCFC). In 1996, the phase-out of CFC refrigerants was completed, and HFC and HCFC were recommended as CFC alternatives because of their low Ozone Depletion Potential (ODP). However, in 1990 it was found that both of these low ODP refrigerants actually contribute to the global warming phenomenon. Consequently, the Kyoto Protocol, issued in 1997, aimed to reduce global warming by decreasing greenhouse gases with the use of low Global Warming Potential (GWP) refrigerants (Yildirim et al., 2017).
Many alternative refrigerants were introduced to replace conventional refrigerants. For example, due to its low GWP value, low flammability, and comparable performance, the R1234 refrigerant series was widely touted as a potential alternative to replace the conventional refrigerant R134a (Fukuda et al., 2014; Kondou & Koyama, 2015; Nawaz et al., 2017; Wu et al., 2018).
R32 and L41a have also been recommended as candidates to replace R410A because not only do they have a low GWP value, but they also closely resemble the characteristics of R410A and perform well. (Alabdulkarem et al., 2015; Cho et al., 2016; Yildirim et al., 2017; Botticella et al., 2018; Cremaschi et al., 2018).
Recently, some researchers have shown interest in pursuing a return to natural refrigerants as alternative to commercial refrigerants. Nasruddin et al. (2018) conducted research using a working fluid mixture of 86% R601 and 14% R744 for binary cycle systems. Yamaguchi et al. (2011) investigated the use of R744 for heat pump systems. Natural refrigerants such as hydrocarbons are considered non-toxic, non-flammable harmless working fluids, and furthermore, they do not contribute to global warming (Park et al., 2007; Sarkar & Bhattacharyya, 2009; Mohanraj et al., 2009; Antunes & Filho, 2016; Badache et al., 2018).
In order to ascertain whether an alternative refrigerant could be an option to replace conventional ones, a thermodynamic analysis is required. Park et al. (2007) conducted a thermodynamic analysis of a residential heat pump system using R433A as a replacement for HCFC22. R433A has zero ODP and a GWP of less than 5. The results revealed that the coefficient of performance for the system using R433A is 4.9% higher than a system using HCFC22. In conclusion, R433A is a good substitute for the conventional refrigerant has better performance (Park et al., 2007). Dopazo et al. (2009) also reported on the COP and exergy efficiency of a cooling system using alternative refrigerant R744 with an analysis and parametric study of the system. The result showed that the system has COP varied from 1.5–2.5 and can be increased 70% by doing optimization procedure. Nawaz et al. (2017) made a performance evaluation of a residential heat pump system in order to compare R600a and R290 refrigerants to HFC refrigerant, R134a. The analysis suggested that both refrigerants could be viable options with comparable performance (Nawaz et al., 2017).
But in previous literature that mentioned above, the analysis still not considers the effect of the system on the environment. So in this work, the exergoenvironmental analysis is discussed, and it becomes the novelty of this paper. The purpose of this work is to perform exergy and exergoenvironmental analyses of low GWP refrigerant R1234ze and R1234yf theoretically and compare it with R410A. After that, the multi-objective optimization is conducted by using the best refrigerant selected by exergy and exergoenvironmental analyses. From the result of the optimization procedure, the optimum condition including evaporation and condensation temperature, as well as the mass flow rate of refrigerant can be determined.
Exergy and exergo-environmental analysis and optimization were conducted in this study. The refrigerant R1234ze was chosen based on the evaluation of its thermophysical properties, the TEWI analysis method, and exergy and exergo-environmental analyses. After conducting this analysis, an optimization procedure was performed. By using a multivariable genetic algorithm, the system was optimized. In the optimization procedure, the exergy efficiency and exergo-environmental were choosen as the objective functions, while evaporating temperature, condensing temperature, and refrigerant mass flow rate were selected as constraints. The results showed that the heat pump system using environmentally friendly refrigerant R1234ze has a good performance with an exergy efficiency of 51.92% and a 101.925 mPts/h exergo-environmental value with an evaporating temperature of 20oC, a condensing temperature of 42.57oC, and a mass flow rate of 0.02 kg/s.
The authors gratefully acknowledge Universitas Indonesia for supporting this research under the Tugas Akhir Mahasiswa Doktor (TADOK) research grant 2018 number 1356/UN2.R3.1/HKP.05.00/2018 dated March 21, 2018.
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