R32 which has a high volumetric capacity, and medium GWP 675. On the other hand, Olefins (R1234yf & R1234ze) have negligible GWP but low cooling effect and volumetric capacity. Both R32 and HFO have low flammability and toxicity. So, it is convenient to mix them in different ratios to make binary blends.

The thermophysical properties of refrigerant mixtures in mechanical vapor compression systems have been considered in order to provide successful condensation and evaporation processes. Due to the high value of the heat transfer coefficient, the condenser and evaporator will operate effectively when the thermal conductivity of both the liquid and vapor phases of the refrigerant mixture is high ( Lee et al., 2016 ; Mahmood et al., 2020 ). As a result, energy consumption will be reduced. The refrigerant charging amount is also influenced by some physical property.

Table 1 lists the properties of R410A, R32, R1234yf, and R1234ze refrigerants.

The thermodynamic analysis aids in predicting the performance of these refrigerants in systems as well as their environmental impact ( Abas et al., 2018 ). This study employed ten different refrigerants i.e., R410a, R32, R1234yf, R1234ze, and their mixtures with R32 considering 40%, 50%, and 60% of R1234yf and R1234ze.

GWP₁₀₀ indicates the heat traps in a refrigerant in the environment compared to the heat trap by the same mass of CO₂ over the 100-year horizon. Figure 2 depicts that the refrigerant mixtures show low GWP compared with widely used R410A.

The coefficient of performance (COP) is calculated theoretically using the thermophysical properties found in REFPROP database (V 9.1). In this work, average temperatures for evaporation and condensation are considered 7˚C and 35˚C, respectively. The adiabatic compression efficiency is considered 0.85. Figure 3 shows the pressure-enthalpy diagram of different refrigerants with their thermodynamic cycle.

The mathematical computations involved in the thermodynamic analysis are given. Isentropic compressor work is computed as

$w_c=h_2-h_1$ (1)

Refrigerating effect (Cooling effect) is calculated as

$RE=h_1-h_4$ (2)

Coefficient of performance (COP) is calculated as

$COP=\frac{RE}{w_c}$ (3)

Energy (Power) consumptionby the compressor per ton of refrigeration is computed by

$PPTR=\frac{3.5}{COP}$ (4)

Refrigerant mass flow rate is computed by

$\stackrel{\dot{}}{m}=\frac{\stackrel{\dot{}}{Q}}{RE}$ (5)

The pressure ratio (PR), also referred to as the compression ratio or system pressure ratio is a dimensionless parameter. It is obtained as the ratio of the absolute condensing pressure (P_cond, MNm⁻²) to the absolute evaporating pressure (P_evap, MNm⁻²) :

$P_R=\frac{P_{cond}}{P_{evap}}$ (6)

The compressor discharge temperature (T_d) is computed using superheated property tables and interpolating for the degree of superheat corresponding to the entropy difference.

The Volumetric cooling capacity (VC, kJm⁻³) is the refrigerating effect per unit volume of the refrigerant at the outlet of the evaporator. It is a value calculated from the vapor density (ρ, kgm⁻³) at the compressor’s inlet and the refrigerating effect (Q_evap, kJkg⁻¹)

Volumetric cooling capacity ( Uddin et al., 2021 ) is calculated as

$VC=\rho \times RE$ (7)

Figure 4 shows the cooling effect of various refrigerants considering 35°C condensing temperature. A higher mass fraction of R32 in R32/HFOs blend shows good result but, in that case, GWP value increases. Therefore, the calculation of total equivalent warming impact helps to determine the proper mass fraction.

Compared with R410A from Figure 4 , it is found that the cooling effect of mixtures R1234ze with R32 is higher than other blends and HFOs.

Figure 5 shows the compressor work for the mixtures. It is found that the compressor work is reasonable for R1234yf/R32 blends. The amount of R32 in the mixture helps to reduce the work done. 50% R32 with R1234yf shows less work done among the blends.

The high amount of COP is a crucial factor in selecting a refrigerant for a conventional air-conditioning system. It can be defined as the ratio of enthalpy difference in the evaporator and compressor sides ( Yang et al., 2021 ). Here, the COP of mixtures 40% R1234ze with 60% R32 is 9.16, on the contrary, 60% R1234ze with 40% R32 is 7.60, the lowest among the studied refrigerants. Besides, 50% of R1234yf and R1234ze have more COP than R410A. In Figure 6 , it may be perceived that by adding more R32 to the mixture, the value of COP is increased.

The change of COP with change of evaporation temperature is shown in Figure 7 . It is observed that with the increase in evaporation temperature, the COP increases. The foremost performance parameter of the conventional vapor compression system is COP which represents the overall cycle performance ( Bolaji, 2020 ). 40/60 ze/R32 mixture shows the highest COP among all the studied refrigerants.

Volumetric refrigeration capacity is influenced by the fluid’s refrigeration properties and the density of the refrigerant vapors. Figure 8 shows that the volumetric capacity of R1234yf and R1234ze is lower, which requires a broad-size compressor for the refrigerants. Since R32 has a higher volumetric capacity, the compressor needs to be redesigned or shortened to handle it. 60% of R32 in the mixture is good for the drop-in replacement.

The volumetric capacity of the refrigerant improves COP significantly for each refrigerant. Actually, the rise in the evaporator temperature of the blends induces the enhancement of volumetric capacity. COP of refrigerants exhibits an upward trend when the volumetric capacity is increased as shown in Figure 9 . The 40/60 ze/R32 shows the highest COP among the blends even in the same volumetric capacity.

In a refrigeration system, the mass flow rate plays a significant role in measuring how fast the fluid flows in the evaporator. By changing the compressor operation, this value can be modified ( Emani et al., 2017 ). A high mass flow rate of refrigerants ensures producing high cooling capacity. Figure 10 shows the mixture of R1234yf/R32 (60/40 by %wt) require the largest mass flow rate 1.082 kgs⁻¹ and R1234ze/R32 (40/60 by %wt) require the smallest mass flow rate, which is 0.8887 kgs⁻¹.

Figure 11 shows that the mass flow rate decreases with the increase in evaporation temperature. This is happening due to the increase of evaporation enthalpy at higher temperatures. The mixtures show better result than the widely used R410A.

A lower pressure ratio is desirable because the volumetric and isentropic efficiencies are expected to increase at pressure ratio. Figure 12 illustrates the relative pressure of R32/R1234ze and R32/R1234yf blends are more advantageous than R32/1234yf (40/60). Hence, the higher-pressure ratio means the reduction of compressor efficiency ( Uddin et al., 2019 ). Figure 12 delineates the operational pressure for R-32/R1234ze blend is slightly higher than that of R410A. Higher pressure ratio requires more compressor work to lift the evaporation pressure to the condensation pressure ( Pal et al., 2018 ).

It is crucial to investigate the stability and lifespan of the compressor before adding the new refrigerant to the system. Figure 13 shows the compressor discharge temperatures of all the investigated refrigerants. It is noticeable that compressor discharge temperatures of blends are higher. 40% R1234yf with 60% R32 shows lower discharge temperature among the blends.

The power per ton of refrigeration for the refrigerants demonstrates how much electrical work is put into producing one ton of refrigeration by the compressor. In Figure 14 , it can be shown that, among the ten examined refrigerants, mixture of 40/60 R1234ze/R32 uses the least amount of compressor energy per ton of refrigeration.

The environmental impacts of the air-conditioning and refrigeration system for its lifetime can be calculated by TEWI (Total Equivalent Warming Impact). TEWI is the result of direct and indirect emissions ( Uddin et al., 2019 ). The required time when the compressor runs on, as well as the coefficient of performance (COP) of refrigerant are the key parameters. The temperature at which cooling is required, for instance, application service, or process temperature of the space, along with the ambient temperature at which heat will be rejected is necessary to measure the TEWI. Each of the above variables can vary hour by hour and on a seasonal basis. It is therefore almost always necessary to use an Annual Load Model to calculate compressor energy consumption.

The electricity used to power cooling systems ( Deutsch & Harris, 2013 ) is primarily derived from fossil fuel-based power plants (such as coal and natural gas), which primarily emit global warming gases like CO₂ ( Craig, 2016 ). The GWP resulting from on-site electricity consumption is classified as an indirect emission ( Pierrehumbert, 2014 ).

The indirect emissions are influenced by the coefficients of performance. In the case of supermarkets, refrigerant leakage is a more serious source of emissions ( Islam et al., 2017 ). Its impact is correctly classified as a direct source of global warming gases ( Yang et al., 2021 ). Leakage rates are currently around 10% - 15% of on-site stock per year ( Uddin et al., 2021 ). This study calculated the TEWI value using the following equations ( Uddin et al., 2021 ):

$TEWI=DirectEmission+INndirectEmission$ (8)

$DE=GWP\times M\times \left[1-{\left(1-\frac{a}{100}\right)}^y\right]+GWP\times M\times {\left(1-\frac{a}{100}\right)}^y\times {\left(1-\frac{b}{100}\right)}^y$ (9)

$IDE=c\times Y\times CC\times \frac{t_c}{CO{P}_c}$ (10)

The system’s lifetime has been chosen as 10 years. The system is used in cooling mode for 3285 hours per year. The refrigerant charge amount is considered 0.75 kg for all refrigerants. The leakage rate is 2 percent per year and the recovery rate is 30 percent. CO₂ emissions to produce per kWh of electricity is 0.599 kg per kWh.

Rated cooling capacity was used at 2 KW for all refrigerants. The energy consumed by the refrigeration compressor(s) depends on various parameters ( Uddin et al., 2021 ; Uddin & Saha, 2022 ).

Figure 15 shows the direct emission for R410A is higher than all the studied refrigerants. Among the mixtures, R1234yf and R32 (40/60) show the highest amount of direct emission. TEWI is also the highest for refrigerant R410A. And among the blends R1234yf and R32 (40/60) show the lowest TEWI which is shown in Figure 16 .