# Investigation of the Environmentally-Friendly Refrigerant R152a for Air Conditioning Purposes
## 1 Introduction  
Refrigeration is responsible for the 20% of the global energy consumption [1]. Moreover, the refrigeration process is associated with a series of environmental problems such as the ozone layer depletion and the global warming phenomenon due to the harmful refrigerants [2]. Therefore, there is a need for establishing a refrigeration system with high efficiency and with environmentally-friendly refrigerants [3, 4]. According to the European Parliament Directive 517/2014 [5], the use of refrigerants with high global warming potential (GWP) has to be reduced. A general limit in the GWP can be selected at 150 [5], especially for the domestic refrigeration systems and so the use of refrigerants with lower GWP has to be used in the new systems or to replace the existing refrigerants. At this time, the most usual refrigerants are the R134a and the R404a [6] which have GWP equal to 1430 and 3922 respectively. The next generation of the refrigerants have to be friendlier to the environment and so a lot of interest has been focused on R32 with GWP = 675. However, this refrigerant has a medium and not a low GWP; a fact that creates a great criticism about this [1]. The alternative refrigerant R152a presents GWP = 138 and it is a promising choice according to this criterion. However, it presents relatively higher flammability and it belongs to the A2 ASHRAE group. The refrigerants R1234 yf and R1234 ze have GWP equal to 4 and 6 respectively and they are good choices, yet their chemical stability problems for long-term operation and their high costs make their utilization questionable. The last and the most promising category for the future are the natural refrigerants which have extremely low GWP. The R717 (NH\({}_{3}\)) is a promising refrigerant but it is toxic (B1 ASHRAE group). The R290 (propane) and the R600a (iso-butane) are also natural refrigerants butthey have high flammability (A3 ASHRAE group). The last choice is CO2 which has GWP = 1 and it is not flammable and toxic, but it has a low critical temperature (~31 \({}^{\circ}\)C) which leads to transcritical cycle with relatively low efficiency and high-pressure levels. Table 1 summarizes the previous refrigerants and their characteristics [7; 8; 9]. The previous analysis indicates that there is no optimum refrigerant without any drawback. The use of CO2 seems to be a promising choice for the future, especially with the modified system with parallel compression, subcooling, and ejector devices [10; 11] but there is a need for efficiency enhancement and creating certified personnel [1]. Among the HFC, the use of R152a seems to be a promising choice because of the low GWP which is lower than 150. Only the flammability problems have to be faced in order to establish it. However, it is important to state that R152a belongs to the A2 category and it is less flammable than the R290 and R600a which are also promising and used refrigerants. Therefore, the use of R152a has to be performed with experienced personnel and with the proper safety rules. The last years, a lot of studies have been conducted about the use of the R152a and they compare it with the existing refrigerants and with other promising. Also, it is useful to state that the R152a is a component in many blends (for instance R444A). [PERSON] [12] studied a simple refrigeration system with R152a, R134a and R32. It is found that the use of R152a leads to 8.5% higher coefficient of performance (COP) than R134a, while R32 is the less efficient refrigerant. Moreover, [PERSON] et al. [13] found the R152a more efficient than R134a, R143a, and R32. [PERSON] et al. [14] examined the use of R152a as a substitute for R134a for the system with and without an internal heat exchanger. They found 13% higher COP with R152a, while a decrease in the cooling capacity. [PERSON] et al. [15] examined various refrigerants and they found that R152a is more efficient than R134a, R600a, R1234 vf, and R1234 ze.