Effect of multi –stages vapor compression refrigeration cycle using refrigerant R32 for Air-Conditioning unit

Vapor compression cycle is mainly employed as a refrigeration cycle in the Air-Conditioning (AC) unit. In order to save energy, the Coefficient of Performance (COP) of the need to be improved. One of the potential solutions is to modify the system into the multi-stages vapor compression cycle. The present work deals with the investigation of single-stage and multi-stage vapor compression refrigeration cycle. A typical vapor compression cycle that is used in the AC unit is taken into consideration. The used refrigerants are difluoromethane R32. The analysis using the simulation process by utilizing software Aspen One. The performance parameters includes COP, the mass flow rate of the refrigerant and compressor power. It was shown that there exists a maximum COP for multi-stage. By taking these performance simulation results the multi-stage is the efficient method for the air conditioning system.


Introduction
The increase in population and industrialization had high an effect of greenhouse gasses emission. Air conditioning industry is growing rapidly throughout the Earth. The use of vapor compression cycle as air conditioning had impact of GHG emission. Air conditioning is maintained of temperature and humidity of a living for convenience, besides that, it is high consumption of energy. Most of the countries considered strategies for applied of vapor compression cycle with efficient and minimum impact for GHG emissions. There are several works related to increasing energy efficiency of a vapor compression cycle such as using heat recovery technique [1,2], multi-stages cycle, etc.
The present paper was focused in the compared a single-stage with a multi-stages vapor compression cycle. Adrian Mota-Babiloni et al. [3] analysis applied of refrigerant R32 can reduce GHG emissions. It value of GWP is 677, which is below the F-gas regulation limit in RAC equipment. Mahesh and Ravi [4] studied and compared by theoretically and experimentally refrigerant R22 and Refrigerant R290 for multistage vapor compression cycle. Nilesh, Dileep and Mani Sankar [5] studied performance of a two stage refrigeration cycle. This research used six common refrigerants, these are refrigerant R134a, R22 and R134a as synthetic refrigerants and propane, carbon dioxide and nitrous oxide as natural refrigerants. Jain et al. [6] showed that cascaded vapor compression-absorption system consist of a vapor compression refrigeration system coupled with a single effect vapor absorption refrigeration system. The effect of various operating parameters such as alternative refrigerant (R134a, R410A and R407C), superheating, sub-cooling, cooling capacity, inlet temperature and the product of effectiveness and heat capacitance of external fluids were investigated. Torella  al. [7] described a general methodology suitable for analyzing staged vapor compression refrigeration cycle by introducing two parameters related to the degree of sub-cooling and desuperheating parameters. Esfahani et al. [8] simulated a combined multi effect evaporationabsorption heat pump with vapor-compression refrigeration system using EES software. Manjili and Yavari [9] investigated a new two-stage multi intercooling transcritical CO2 refrigeration cycle with injector-expansion device (MIERC). At this study used two intercoolers. It can increase COP 15.3% to 19.6 % than standard compression cycle. Messineo [10] analysis a cascade refrigeration system using as refrigerant carbon dioxide in lowtemperature circuit and ammonia in high-temperature circuit. Results show that a carbon dioxide-ammonia cascade refrigeration system is an interesting alternative to R404A twostage refrigeration system for low evaporatingtemperatures (-30°C ÷ -50°C).
Those studies showed that single-stages and multi-stages technology for vapor compression refrigeration cycle has come under scrutiny. The present work focuses on the investigation of compare single stages and multi stages vapor compression refrigeration cycle with new refrigerant in ASPEN PLUS. The used refrigerant here is 100 % Difluoromethane (refrigerant R32) which is a new refrigerant. The results for multi stage refrigeration system are compared with the single stage refrigeration system using the refrigerant R32.It should provide all useful results, such as pressures, heat duties, cycle COP, mass flow rates, either directly or readilyavailable.

Solution Method
The governing equations of the systems are developed as follows. The power in the first (Ẇc1) annd second compressors (Ẇc2) are calculated by where h1, h2, h3, and h4 are enthalpy of the refrigerant at the inlet and the exit of first compressor and at inlet and the exit of the second compressor, respectively. The total of the power to system is calculated by The heat release by the system to ambient is given by equation (4).
where h4 and h5 are enthalpy of the refrigerant at the inlet and the exit of the condenser. Here mis defined as the flow rate of the refrigerant entering the condenser. The heat absorbed by the refrigerant in the evaporator, is given by: Refrigeration effect (ER) of the system is calculated by equation (6). 1 9 ER h h = − (6) The coefficient of performance of the system (COP) is given by Where e P and c P are the pressure of the evaporator and the condenser. A computer program has been developed to solve the above equations. The properties of the refrigerant is modeled using the data provided by American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE).

Description of the setup
For the evaluation of concept, the entire process was simulated with the engineering software Aspen Plus. In the literature, the Refrigerant Properties equation of state (REFPROP in Aspen Plus) is commonly used for the calculation of the thermo physical properties in refrigerant simulation. The analysis is carried out for refrigerant R32. Operating conditions, here after named as case, are analyzed, the first case is at temperature evaporation of -10 0 C and temperature condensation of 40 0 C. For all cases the cooling load is assumed to be constant at 1000 Ton.

Simulation result
The result the simulation are summarized in table 1. The total compressor power of single stage was Ptot=1048 kW, the two stage was Ptot= 955,7 kW, which coefficient of performance of single stage was COP = 3.35, coefficient of performance of single stage was COP = 3.67 In order to provide a convenient discussion, the value of COP was presented in Table 2. The data reveals that there is a discrepancy of the single stage with multi-stage. The results show that a significant decrease in the overall compression duty of the refrigeration cycle (8.8%) over the base case is obtained due to the reduction of the temperature lift (the temperature difference between the evaporator and condenser. This fact suggests that multistage using refrigerant R32 is effective than single stage

Conclusions
The result of this work show Difluoromethane (refrigerant R32) effective used for multistage, multi-stage using refrigerant R32 gives the high coefficient of performance and decreases the work of compressor. The multi-stage using refrigerant R32 can improve 8.8 % performance of the refrigeration cycle than single-stage. The multi-stage concept promises efficiency vapor compression cycle systems.