Analysis of the Coefficient of Performance (COP) on the Car’s Air Cooling System Using a Training Kit with Constant Rotation

The performance of the air condition system is strongly influenced by the compressor work, the condenser cooling temperature. So that the compressor working pressure (suction) and condenser cooling play a very important role in the performance of the air conditioning system which will have an impact on compressor work, compressor power, refrigeration impact, isentropic efficiency and coefficient of performance (COP) of the car air conditioning system. From the research, data will be obtained which include the pressure value on the refrigerant, namely P1 and P2, the temperature on the refrigerant, namely T1, T2, T3 and Tcabin, at the point of installation of the Manifold Gauge and Thermocouple. The research data is then processed and analyzed to obtain performance at constant rotation with variations in compressor working time both actual and theoretical as well as the efficiency of the ac system. From the results of the study, it was found that the compressor rotation was 2300 rpm with a constant rotation then measured the pressure and temperature of the refrigerant, then temperature data was obtained and analyzed to obtain the enthalpy value, thus obtaining the coefficient of performance (COP) of the car air conditioning system. The coefficient of performance (COP) of the resulting system is greater than the actual COP, the optimal COP occurs at P1 30 psi and P2 340 psi working pressures, the actual COP is 3.4848 and the theoretical COP is 4.1500, with an efficiency of 83.97% at 360 seconds.


Introduction
In today's human life, whether in industry, household, mining or trade cannot be separated from the role of air conditioners, refrigeration equipment and food preservatives.Especially in the tropics, the level of comfort that people want is not met.Among the various uses mentioned above, the refrigeration system is very useful in human life.In the development of technology, we must prioritize safety, comfort and human safety, not forgetting the environmental aspect which is our main goal [1].
Air conditioning (AC) is a process of cooling the air so that it can reach the appropriate temperature and humidity required by the air conditions of a particular room.The condenser is used to dissipate heat in the refrigerant media using air media and is supported by a fan thrust; the refrigerant vapor released from the compressor will enter the high temperature steam condenser first. .To increase the working capacity of the COP (Coefficient of Performance), the condenser can be modified by using water-cooled refrigerant and the fan is no longer used to save fan driving power [2].A good heat dissipation process has good condensation (hot vapor from the refrigerant is liquid or condenses), and a good condensation process, especially the work of other components in the evaporator, has a heat absorption process (liquid evaporation).The price of COP (Coefficient of Performance) is higher because good refrigerant is removed from the room or object [3].Research on the manufacture of a car air conditioner simulator has been developed including the Arduino and LabVIEW-based Design and Build Adsorption Refrigeration Simulator Control Module which is to view and control the working principle of the cooling system optimally in computerized cooling (with the Arduino program) [4].Making a car air conditioner simulator to test the performance of the air conditioner by varying the refrigerant mass and cooling time [5].
Development of an AC simulator on the analysis of damage to the electrical system on the simulator [6].The development of an AC simulator on a car with CFD (Computational Fluids Dynamic) analysis has the same precise value and the simulator allows it to be developed because it has the same information when compared to the experiment [7].Research has been done on the manufacture of a car air conditioner simulator with a straight fin condenser type which is commonly used with a single phase electric motor drive with a series circuit that only produces 2 HP of power and which can be carried out with medium rotation [8].Heat transfer devices in cars are found in several cooling components including radiators, evaporators, condensers, these components have the same basic principle of releasing and absorbing heat so that the work process of a system on a car runs properly and normally [9].
From several previous studies, researchers were able to develop an air conditioning system training kit, where researchers wanted to know the COP (Coefficient of Performance) of the air conditioning system when it was transferred from the car to the training kit, then it was also carried out in constant rotation.This training kit is driven by a 2.3 KW electric motor.From this research, the opportunity to develop this training kit is to make a training kit driven by an electric motor that is more effective and efficient in operation.

Vapor compression cycle
Refrigeration engines most refrigeration engines work using a vapor compression cycle.Car air conditioner is a cooling machine that works by using a vapor compression cycle.The vapor compression cycle has four main components consisting of a compressor, condenser, expansion valve and evaporator [12].
The process that occurs in the vapor compression cycle is that the refrigerant absorbs heat from the environment which causes the refrigerant to evaporate so that refrigerant turns into gas.Refrigerant that has changed phase to gas compressed by the compressor to the condenser.Inside the condenser, refrigerant will undergo a condensation process.Refrigerant dissipates heat to environment so that the refrigerant changes its phase from hot gas to gas saturated, from saturated gas to saturated liquid and saturated liquid to further liquid.Then head to expansion valve.The expansion valve will lower the refrigerant pressure so that there is a phase change from saturated liquid to a liquid gas mixture, so that at when the refrigerant enters the evaporator, it is already in the form of a liquid and mixture gas.In the evaporator it there is a phase change from a mixture of liquid and gas becomes a hot gas which is accompanied by an increase in temperature before being sucked back in by the compressor.This process will take place repeatedly [10].The vapor compression cycle on the p-h diagram is presented in the Figure 1 below.[11] To find out the enthalpy value of each process that works in a cycle vapor compression, can use the ph diagram.With the help of pressure diagram enthalpy, an important quantity such as compressor work, condenser work, work evaporator, and COP in the vapor compression cycle with superheating and further cooling can be detected.In the enthalpy diagram the pressure depends on the type refrigerant used.For the enthalpy pressure diagram at refrigerant type 134a is presented in Figure 2 with refrigerant p-h R-134a.

Formulas and equations
The data obtained from the research will be analyzed using the following formulas and equations, In data analysis there are several formulas used with the following explanation: : The symbol above is used for the use of formulas and equations including to calculate the work of the compressor, the heat removed by the condenser, the heat absorbed by the evaporator, the COP value and efficiency.Calculating the work per unit mass on the refrigerant carried out by the compressor using the equation = - Calculate the heat released by the condenser per unit mass of refrigerant using the following equation Calculate the heat absorbed by the evaporator per unit mass of refrigerant ( ) using the following equation Calculate the actual value on the car ac trainer using the following equation: Calculating the value of ideal on a car ac trainer using the equation = (5) Calculating the efficiency (ƞ) of the vapor compression cycle engine used in car air conditioners using the following η = (COP actual : COP ideal ) × 100% (6)

Method
This research was conducted using an experimental method based on research and development of R&D.To make a simulator, design stages, design testing (validation), preparation of tools and materials, theoretical calculations and also mathematical analysis are carried out.  .The temperature and pressure data were collected on , and , and , using a thermocouple

Result and analysis
After doing the research, the data obtained in table 1.In table 1 presented data about the measurement of temperature and pressure contained in the air conditioning system in the training kit, for more details we can see in the table below.In the table above we can see the tendency of pressure at low pressure P 1 to be constant at 30 Psig, as well as at high pressure at P 2 also to be constant at 300 Psig.This condition is the same condition that occurs in the air conditioning system in real cars.For the temperature values for T 1 , T 2 and T 3 there are changes that are influenced by the operating time of the training kit; these changes are not significant but will affect the enthalpy value produced by each change in refrigerant conditions.
After we get data about the pressure and temperature of the refrigerant, we can determine the enthalpy value using a P-h diagram, for details we can see in table 2. In the table above we can see that the enthalpy value is influenced by pressure and temperature.We can compare the enthalpy values at points P 1 and T 1 which are lower than the enthalpy values at points P 2 and T 2 because the measurement points P 1 and T 1 are refrigerants originating from the evaporator which tend to be low pressure and low temperature, while at P 2 and T 2 the refrigerant is from the compressor.This has high pressure and temperature values.If we look at the variation in time, it tends to increase with increasing operational time.
Next we will see the compressor work (W in ), the heat released by the condenser (Q out ) and the amount of heat absorbed by the evaporator (Q in ) by entering the enthalpy value into the predetermined formula.For more details can be seen in table 3. The efficiency value is highly dependent on the compressor work value, the smaller the compressor work, the higher the efficiency value of an air conditioning system.For more clearly we can see in graph 2.
Graph 2. The value of efficiency in the air conditioning system training kit From graph 2 we can see that the efficiency value tends to increase and increase with the longer operational duration of the air conditioning system, the best efficiency value is found at 20 minutes with an efficiency value of 57.76%, this is influenced by when the conditioning system is operated, the refrigerant circulation has not operates perfectly and maximally and then the lowest efficiency is found at minute 6 with an efficiency value of 51.80% this condition is influenced by the condenser heat release and the heat absorption in the evaporator is not perfect.
From the results of this study it can be seen that the operation of the air conditioning system in the training kit using an electric motor is more effective and efficient, in this study it also has several limitations, namely the performance produced by the air conditioning system using the training kit is lower than that of the air conditioning system installed on the car.This is influenced by the position and installation of the condenser which does not get maximum cooling from the airflow and the cooling fan has not maximized in cooling the condenser.

Conclusion
From this research it can be concluded, the actual COP (coefficient of performance) value is strongly influenced by the ability of the condenser to lower the temperature of the refrigerant, the lower the temperature of the refrigerant, the faster the refrigerant changes form to a liquid.On the other hand, the heat absorption carried out by the evaporator to change the refrigerant form liquid to gas also affects the actual COP (coefficient of performance) value.The greater the absorption of heat, the faster the refrigerant turns into a gas.Then in increasing the actual COP (coefficient of performance) value, several things that can be done are engineering the condenser cooling or increasing heat absorption in the evaporator.The lower the compressor work also has a significant effect on the efficiency of the air cooling system, because this shows the less operating time of the compressor as a result energy consumption also decreases.
Pressure of refrigerant entering the compressor (Psi) : Pressure of refrigerant coming out of compressor (Psi) : The temperature of the refrigerant entering the compressor from the evaporator (℃) : The temperature of the refrigerant coming out of the compressor (℃) : The temperature of the refrigerant entering the expansion valve (℃) : The temperature of the refrigerant entering the evaporator (℃) I : The amount of compressor current in the air conditioning drive motor (A) V : Voltage on electric motor (A) Time: The time when the air conditioner compressor turns on and off (s)

Figure 2 .
Figure 2. Components of a conditioning system training kit on a car with an electric motor drive In Figure 2 above is the design of the air conditioning system training kit used for the research to be carried out.The training kit is driven by a 3-phase electric motor with a voltage of 380 volts.All components of the air conditioning system in the car are transferred to the training kit so that the air conditioning system can work according to the actual conditions in the car.

Figure 3 .
Figure 3. Research instruments on the air conditioning system training kit

Table 1 .
Data about the measurement of temperature and pressure

Table 3 .
Compressor work value (W in ), the heat released by the condenser (Q out ) and the amount of From table3we can see the best compressor work value at 4 to 6 minutes with a compressor working value of 54 Kg/Kj.for the heat release in the condenser the better with the longer operating time, namely in 20 minutes with a heat release value of 170 Kg/Kj, this condition shows the ability to release heat is getting better because it is suspected that the air flow is getting better and smoother.The best heat absorption capability in the evaporator occurs at 20 minutes, but the best COP aktual value occurs at 16 minutes with a COP aktual value of 2.31.This condition is where the compressor works the lowest at 15 Kg/Kj but the condenser value releases heat well with a value of 169 Kg. /Kj and is supported by the ability to absorb heat by a good evaporator with a value of 118 Kg/Kj.For more clearly we can see in graph 1.