Cooling System Performance Comparison of Refrigerant R-134a and MC- 134 on Ice Slush Machine

Received 01/10/2021 revision 21/04/2021 accepted 22/05/2021 Available online 29/05/2021 Ice Slush Machine uses a direct cooling vapor compression system. The primary refrigerant used in such a system mostly is hydrofluorocarbons (HFCs), such as R134a. R134a is a retrofit for refrigerant R-12 which is included in the chlorofluorocarbon (CFC) type of refrigerant. CFC-type refrigerants have a dangerous impact on the environment. Hydrocarbon refrigerant MC-134 is an alternative for R-134a because it has a low potential value for environmental damage. The secondary refrigerant used was propylene glycol and the product used was 3.5 liters of Coca-Cola. From the test results when the system using R134a had an average COPactual and an average COPcarnot of 2.6 and 4.55, respectively, and the energy consumption was 1.571 kWh with an average efficiency of 57%, while in a system with MC-hydrocarbon refrigerant 134 obtained an average COPactual and an average COPcarnot of 2.8 and 4.5, respectively and the energy consumption of 1.325 kWh with an average efficiency of 62%. Therefore, MC-134a had COP actual greater than R-134 and electrical energy consumption of MC134 was less than R-134a.


INTRODUCTION
Science and technology growth is rapidly developing, including in the field of refrigeration. The Ice Slush cooling process uses a vapor compression system with the brine cooling method in the cooling process [1,2].
The refrigerants used in this system are generally hydrofluorocarbon (HFCs), such as R-134a. Meanwhile, the secondary refrigerant that is often used is propylene glycol. R134a is a refrigerant that is often used in refrigeration systems because of its good performance as a medium for conducting heat. However, R134a is included in the hydrofluorocarbons (HFCs). R134a itself is an alternative refrigerant to replace R12, which is included in the chlorofluorocarbons (CFC) refrigerant [3][4][5]. Because refrigerants in the CFC class have an impact on the environment values, R12 refrigerant is replaced by R134a. As an alternative to CFC and HFC refrigerants in the refrigeration system, hydrocarbon refrigerants are being used [1][2][3] [6,7].
MC-134 is one of the refrigerants made by PT. PERTAMINA [5] with hydrocarbon as an alternative to R134a, MC-134 is derived from a mixture of propane (R290) and isobutane or R600a [8]. Apart from being environmentally friendly, MC-134 also has a good potential as a substitute for R134a.
The refrigerant had supported by Indonesia's Law No. 16 of 2016. This is an affirmation of Indonesia's participation in reducing the effects of climate change and global warming [1][2][3]6,7].

Experimental set up
The setup of the experiment is shown in Figure 1. The main components of the system were compressor, condenser, evaporator, and capillary tube. The tools used were ice slush machines with a vapor compression system and the cooling method was brine cooling [8]. The system used a capillary tube as an expansion tool. The process started with leak tests, vacuum, and charging. These steps can be simplified into one step called tools set-up. Nitrogen was filled to check for leaks in the system. After the system was confirmed that there were no leaks, the next step was the vacuuming process [9]. Then the R-134a refrigerant was charged into the system. The data collection process was done afterward. When the data collection process did not experience problems such as the pump was not running, it was continued with data processing. After that, the R-134a was removed and the vacuum process was carried out. Then the MC-134 refrigerant was charged. Then the data collection process was done. The analysis of the results was conducted.   R134a was used as the primary refrigerant and then replaced by MC-134 with a weight of 40% of the mass of R134a. The secondary refrigerant was a mixture of 30% propylene glycol and 70% water. The materials for the ice slush machine with cocacola products with its amounts are shown in Table  1.

Tools and equipment
Observation of the tools was used before performing a performance test of the performance comparison of the ice slush machine. The following are the specifications of the tools:

Procedure
The basic principle of work on this ice slush machine is the same as the vapor compression refrigeration system in general, the only difference lies in the use of secondary refrigerants as a medium for auxiliary absorption of heat [11]. Before the compressor works, the pump was first turned on so that the brine was evenly mixed. After a few minutes the pump started up, the next step was to turn on the compressor. The compressor pressed the vapor phase refrigerant so that the refrigerant was pressurized and had a high temperature. After that, the refrigerant flowed into the condenser where the heat was to be removed into the environment assisted by the condenser fan. The refrigerant, which was originally a vapor, changed its phase to liquid.
The liquid refrigerant flowed into the expansion device. In the expansion device, the refrigerant was lowered in pressure. The refrigerant phase then turned into a mixture. After that, the refrigerant went to the evaporator. In the evaporator the primary refrigerant absorbed the heat of the brine, then the brine circulated using a pump and absorbed heat from the cabin. During the absorption of heat in the evaporator, the primary refrigerant phase changed into a mixture of vapor and flowed back into the compressor so that the refrigeration cycle occurred [12].

Data Measurement
The time used for each data collection was 360 minutes. The data for calculating the ice slush machine used the average data when the product temperature was reached and before the system was turned off. The data can be seen in Table 2.

Calculation of the measurement data of R-134a
The measurement data in Table 1 was the measured data on the measuring instrument, while the data needed to plot the P-h diagram must be absolute pressure. Therefore, to get absolute pressure 1 bar must be added. The following are the results of the data that will be plotted on the Ph diagram: After that, the P-h diagram was plot on the cool pack software [13], which is shown in Figure 2. After knowing the actual COP and COPCarnot values, and then calculate the system efficiency value, so : η = 2,6 / 4,55 x 100 η = 0.57 x 100 = 57% (efficiency)

Calculation of MC-134 measurement data
The absolute pressure value and the refrigerant temperature were calculated using the same way as in the measurement data R134a. The following are the results of the data that will be plotted on the P-h diagram: The P-h diagram is shown in Figure 3;

COP Analysis
The measurement data used for the calculation of COP on the ice slush machine used the system average data when the product temperature was reached and before the system was turned off, COP measurement data can be seen in Figure 4. In Figure 4, it can be seen that the COPCarnot in both systems has a COP value greater than the actual COP due to several factors. Factors that can affect the actual COP value are the effect of refrigeration and compressor work [15]. In systems with the primary refrigerant R134a, the average COP-actual value is 2.6 and COPCarnot 4.55. While the primary refrigerant system MC-134 obtained a COP actual value of 2.8 and COPCarnot of 4.5. The graph above shows that the system with MC-134 primary refrigerant has a greater COP actual value than the system with R134a refrigerant [16].

Efficiency Analysis
The measurement data used to calculate the efficiency of the ice slush machine used the system average data when the product temperature was reached and before the system was turned off. Efficiency measurement data can be seen in graph Figure 5. From graph Figure 5 above, it can be seen that the efficiency values in the two systems have different values. The system using the primary refrigerant R134a has an efficiency value of 57%, while the system with the primary refrigerant MC-134 has an efficiency value of 62%. This shows that the system with the primary refrigerant MC-134 has a better efficiency value than the system using the primary refrigerant R134a [17].

Current versus time (analysis)
The results of data collection of electric current against time is shown by the Figure 6.  Figure 6 is a graph of the measured flow in the system. Compressor work greatly affects the electric current. The heavier the compressor works, the greater the current required [18]. In the graph above, it can be seen that systems using MC-134 primary refrigerant require a slightly smaller current than systems with primary refrigerant R134a, this is because the mass of MC-134 refrigerant is lighter than R134a so that the compressor works lighter when operating. In the graph above, the flow has decreased significantly, this is because the compressor has been cut off and the current will return to normal when the compressor is cut-in [19].

Time Analysis of Energy Consumption
The results of taking current and voltage data can be calculated using the formula as follows: 1. Based on data collection, the system used R134a refrigerant obtained an average voltage of 220 V, an average current of 1.8 A, an average cos phi of 0.85 (source from PLN), and a long system on for 280 minutes. The total energy consumption is [14]: From the results above, the electrical energy needed by the system with refrigerant R134a is 1.571 kWh, while the system with refrigerant MC-134 is 1.325 kWh. This shows that the system with MC-134 refrigerant is 16% more energy efficient than the system with R134a refrigerant [20,21].

CONCLUSION
From the results, the system using R-134a has an average COPactual and an average COPCarnot of 2.6 and 4,55 respectively, then the energy consumption is 1.571 kWh with an average efficiency of 57%, compared to the system with MC hydrocarbon refrigerant 134 which has an average COPactual and an average COPCarnot of 2.8 and 4.5 and energy consumption of 1.325 kWh with an average efficiency of 62%. Therefore, in terms of efficiency, COP, and electrical energy consumption, the MC-134 are better than R-134a.