Exergetic Analysis of a Refrigeration System with Mechanical Vapors Compression

The 
main purpose of this study is to improve the energy efficiency of a 
refrigerated facility by means of exergetic analysis. In order to achieve this 
goal, we have evaluated the input exergy flows of the whole system to deduce 
the exergetic yields, which are compared to the degree of irreversibility in order 
to have a qualitative measurement of energy losses. The concept of exergy is 
the part of energy that is virtually converted into work. The exergetic 
analysis was performed on a refrigeration 
unit ZR22K3E Copeland Scroll. The results of this analysis are consistent with 
the condition, that the exergetic performance, which is: 36.57% and it is 
approximately equal to the degree of irreversibility which is 37.50%. This 
approach provides a comprehensive, standard and rigorous framework for the 
analysis of energy systems, and thus for the understanding and systemic 
management of the energy challenge.

pinches to the exchangers, load losses, overheating), etc. [2] [3] [4] [5] [6]. Radcenco and Canivet show that the exergetic measure the availability that may be extracted from a reservoir or energy flux and it indicates that spontaneous processes tend to consume this exergy. Joule effect, Foucault current, viscosity, turbulence, heat transfer and friction deteriorate the energy but unlike energy, exergy is not preserved during natural transformation. The idea of dissipation of exergy is directly related to idea of creation of entropy and irreversibility. The exergy is the part of the energy that is virtually convertible into work. This is a consequence of the second principle of thermodynamics. The first to introduce this concept is G. Gouy, who, in the late nineteenth century, defined the concept of exergy. Numerous studies give useful information for practitioners about the exergy efficiency of different types of systems, I quote here: [7] [8]. Professor V.
Radcenko, former Doyen of the Faculty of Mechanics, at the Polytechnic's University of Bucharest, who was also my thesis' supervisor, has published numerous books on the exergy, in which I will quote only: [2] [3]. In one of the chapters of my Ph.D. thesis, which is entitled "Contribution to the Study of the Optimization of Air Conditioning Systems" [9], an exergetic analysis of the air conditioning facility was treated. We applied this exergetic analysis to a small power plant in the case of, the ZR22K3E Copeland Scroll (Figure 1), in order to improve energy efficiency, by determining energy balance and exergy balance in order to obtain an exergetic yield that will be compared to the degree of reversibility of the plant, thus allowing a qualitative measure of energy losses that degrade efficiency installation. The energy as well as the different quantities involved in determining the energy balance are obtained in the logP-h. Figure 2 diagram is presented in Table 1. The exegetic balance of the installation shall be carried out after the completion of the energy balance which consists of determining and summing all the energy involved, namely: • the work of compressor inst W ; • heat losed to the condenser cD q ; • cold thermal production o q ; • heat absorbed sc q to the overheating [4] [5] [10].
To establish the exergetic balance sheet, one calculates all losses which appear during the transformations, namely: • the losses due to the compression process irC π ; • the losses due to the relaxation process irD π ; • the losses due to the condensation process irCd π ; • the losses due to the spray process irEv π ; • the losses due to the overheating process irSc

Material
The refrigeration system which is the subject of the exergetic analysis (Figure 1), is a designated refrigeration unit: ZR22K3E Copeland Scroll composed of a compressor, a condenser and an evaporator having a vaporization temperature of T 0 = 268 K and ambient temperature T a = 305 K.

Method
To calculate the exergy yield of the installation, it is first necessary to determine the characteristic quantities of the refrigeration cycle allowing the realization of the exergy balance which shows for each organ the loss that it generates.
• Determination of the dimension's characteristics of the cold cycle R134a The coefficient of performance (C.O.P.) of the Carnot cycle, limited by the temperature T a and T 0 , is determined by the following the relationship: The cycle in (  [ ] They will be sucked by compressor, process 6-1.
The Coefficient of Performance of the installation is determined by the relationship: The degree of irreversibility through the relationship: The mechanical work of the Carnot cycle of the installation is calculated by the relationship: where: , is the sum of the exergetic losses due to the irreversibility of the cold production system plant.
• Calculation of the losses due to the irreversibility of cycle R134a During the process in the refrigeration system, a number of irreversibility losses appear which can be calculated by the following relationships: [7] [8] [10] -Loss of exergy during the relaxation process: Then the weight of exergetic loss during the relaxation process will be: -Loss of exergy during compression process: Then the weight of exergetic loss during the compression process will be: -Loss of exergy during the heat transfer process in the condenser: Then the weight of exergetic loss during the condensation process will be: -Loss of exergy during overheating process:

Results and Discussion
In order to establish the energy balance, it is assumed that the sum of energy absorbed by the evaporator, the overheating energy and the energy absorbed by the compressor is equal to the energy released to the condenser. The energy balance in (Figure 3) and in Table 2  In Figure 3 and Table 3, the drill balance expressed by the relationship: , takes into account both the qualitative and quantitative aspects of the energies involved in the installation processes of refrigeration production. Indeed, the degree of reversibility as shown in Table 2 [11]. For very high loss percentages, the installation nevertheless produces cold with much higher energy consumption.

Conclusion
The results of this analysis are in fact consistent with the condition, that the ex- . The identification of losses helps to rationalize energy resources and also reduce the environmental impact of these resources into the atmosphere. It should also be noted that the analysis was carried out on a new installation. If the analysis is carried out on a facility that has already been in operation for some time, on the one hand, the losses will be very high and on the other hand the economic losses will become noticeable and significant due to or interest in an exergetic analysis. This analysis shows that the losses are greater in the old installation. The size of the data involved in the exergy requires a numeric treatment of all incoming flows from the whole refrigeration system.