EFFECT OF USING R-22 , R 404 AND R-407 C ON PERFORMANCE OF AN AIR-CONDITIONING SYSTEM

Due to the environment depletion, replacing chlorofluorocarbons in refrigeration industry was an important problem. In the experimental study a (1.0 TR) vapor compression system were used with original working fluid of R-22 and compared to alternatives refrigerant R-407C and R-22. The effects of the main parameters of performance analysis such as refrigerant type, compressor pressure ratio, outlet air evaporative temperature, coefficient of performance were investigated for various ambient temperatures above 50 oC. The results showed that the compressor ratio of system using R404 and R-407C is more than the compressor ratio of system using R22 by 2% and 4% respectively. Also, the outlet air evaporative temperature of system using the alternative refrigerant R-22 is more than the outlet air evaporative temperature with system using R-407C and R-404 by 8% and 5% respectively. The coefficient of performance of R-407C was measured with the same reciprocating compressor that was supplied with the R-22 system. It could be concluded that there is a decrease of 8% in system COP as friendly environment R407C compared with system using R-22 and a decrease of 12% in system COP when using R-404. However; the result showed that R407C have thermodynamic performance similar to R-22. Engineering Equation Solver (EES) software is used for draw (p-h) diagram for the cycle.


Introduction
According to the Montreal Protocol the phase out of R-22 will commence in 1996 with a consumption cap, followed by a 35% reduction in consumption starting in 2004, and a complete phase-out is slated for 2020 in Canada.The phase out for R-22 has already been advanced in Europe, with Germany having a phase-out for new equipment starting in 2000.
When using refrigerant alternatives, it has an advantage that it needs no large change of the compressor dimension for R22 use.It is important to compare the performance of different mechanism compressors to supply most appropriate type according to cooling capacity range after R22 is replaced with alternatives.
By considering current compressor losses and its alternation by changing refrigerant, it should be studied technique about compressor dimensional optimization, and estimated efficiency of optimized compressor in the case that R22 is replaced with R407C or R410A, but in this paper there is no any change in the compressor mechanism.
Replacing chlorofluorocarbons in refrigeration industry is an important problem because of environment depletion.There are many types are suitable refrigerant blends as a replacement of R-22.R407 represented in this paper: R-407C, a zeotrope of HFC-32/HFC-125/HFC-134a (23/25/52 wt.%) .R407C is a mixture refrigerant and its thermodynamic and physical properties are like as R22.This refrigerant has been introduced as an alternative for R22 with zero ozone depletion potential and less greenhouse warming potential than R22.A comparison of performance of different refrigerants in the vapor compression cycle can be carried out on the basis of the internal temperatures of the refrigerant or on the basis of the external temperatures of the heat transfer fluids which acts as a heat source and a heat sink.Herbert et.al [1], present the experimental performance study of an air-conditioning unit with M20 (a refrigerant mixture of R407C, R600a and R290 in the mass fraction 80:10.96:9.04respectively).Experiments were conducted in a 5.25 kW window airconditioner to assess the potential of M20 as a retrofit refrigerant without making any system alteration other than changing the capillary.The results presents that the system had 4.18% to 7.47% lower cooling capacity with respect to that of R22 when using M20.The COP for the M20 refrigerant was lower, in the range of 0.58% to 7.78% than that of R22.So, M20 can be used as a drop-in-substitute for R22 in window airconditioners.
Saber et.al [2], investigated advantages and disadvantages of R407C as an alternative refrigerant for replacing R22 in refrigeration systems.Also, studied the effect of various parameters on cycle performance by modeled refrigerants thermodynamic properties, condenser and evaporator secondary fluid using artificial neural network, then reducing complicated computation and without using state equations.Also, a comparison of refrigeration cycle using R22 and R407C refrigerants with Wilson-Plot method.
Vaisman [3], presents a comparison of Computational performance of a rotary vane compressor air conditioning unit operates with R22 and R407C is produced taking into account actual system configurations.It is appeared that the cooling capacity of an air-conditioning unit using R407C is higher than system operating with R22 by factor of 1.038.also, the system COP of an air-conditioning unit operates with R-407C is lower than system operates with R-22 by factor of 0.984, for outdoor temperature of 95˚ F and indoor temperature of 80.6 ˚ F, while the relative humidity is about 47%.Anders and Lundqvist [4], present a comparison of COP, compressor efficiency and cooling capacity of the air-conditioning system when using the refrigerants (R-407C, R-404a, R-417A, R-134a and R290 with respect to R-22)."Fig.1" shows the relationship between the relative COP's with relative capacity.Kato et.al [5], show an experimental and theoretical comparison of compressor efficiency between rotary and scroll type using R-22 and its alternative refrigerants, R407C and R410A. it is showed that the upper limit of cooling capacity range, in which efficiency of rotary type is higher than that of scroll type, is about 8,000 Btu/h with R22 and R407C.In the case with R410A, rotary type is superior to scroll type in the range approximately up to 24,000 Btu/h. it shows that the range in which rotary type operates more efficiently than scroll type will expand up to small capacity range of unitary air conditioners in the case with R410A.
Linton et.al [6], made a comparison between performance of two long term replacements R-407C (HFC-32/125/134a (23%/25%/52%)) and R-410A (HFC-32/125 (50%/50%)) with R-22 using 10.5 kW (3.0 TR) residential central heat pump.The performance evaluations were carried out in a psychometric calorimeter test facility located at NRC using the Canadian Standards Association (GSA)/Air-Conditioning and Refrigeration Institute (ARI) rating conditions.The performance of R-407C was measured with the same reciprocating compressor that was supplied with the R-22 system.Performance characteristics were measured including compressor power, cooling and heating capacity, mass flow rate of a refrigerant, cooling energy efficiency ratio (EER) and heating coefficient of performance (COP).The optimization included Changing the direction of the air flow (inverting the evaporator coil) to get an approximation of a counter-flow heat exchanger to take advantage of R-407C's temperature glide.
Yunting and Cropper [7], developed a simulation model of steady-state case of a finned-tube air-cooled condenser by using the distributed modelling method.The model can be used to predict 3-D variations of parameters for both air and refrigerant sides.The model has been validated by comparing outputs from the model with test data, given in reference papers, derived from air-cooled condensers with differing dimensions and refrigerants.Application of the model is concentrated on optimization and exploration of existing and new control strategies for controlling refrigerant dischargepressures in retail refrigeration systems, where air-cooled condensers are being utilized.Meaningful results are obtained for both the optimal design and development of the new control strategies and for performance comparisons when different refrigerants are employed in the condensers.
The aim of current work is comparing COP and evaporative temperature between the two types of alternatives (R-407C & R-404) with R-22 experimentally.

General Equipment Layout
In this work, a (1TR) air-conditioning split unit was used with three type of refrigerants, R-22, R-404 and R407C with same type of compressor and same amount of lubricating oil, the air condition unit consist of a compressor, condenser, capillary tube and evaporator are shown in "Fig.2".Pair of high pressure gauges (type PM-500psi) are fixed after the compressor and condenser, while the others of low pressure gauges (type PM-250psi) are fixed after capillary tube and evaporator.Calibrated thermocouples type (pt100 with multi-reader and type k with selector switch) are used and shown in "Fig.3", for measuring pressure and temperature around the cycle."Fig.4", shows the parameters used in the system.

Theoretical Model
Rotary type, positive displacement compressor, has been used in current study.The amount of specific, isentropic work done by an ideal compressor can be found by the energy equation: Since the finned-tube heat exchangers are most commonly used for residential air conditioning applications, a plate finned-tube type has been used in this work."Fig.5", shows the Z-type, finnedtube, staggered condenser used in this work.The condenser can be separated into three sections: superheated, saturated, and subcooled shown in "Fig.6".The specific heat rejected from each section can be found by evaluating the refrigerant enthalpies at the inlets and outlets, so the equations (2 to 4) presented the heat rejection.

Out
Ref.

In Air Flow
Space with a font size 10 Then the heat transfer of the air across the condenser can be calculated according to the difference bulb temperature between the air inlet and air outlet temperatures was given in the following equation [8].
Space with a font size 10 Space with a font size 10 Where, Space with a font size 10 Space with a font size 10 Also the air mass flow rate that effect on the condenser coil can be calculated from the following expression: Space with a font size 10 Space with a font size 10 While the surface temperature ( ) is constant across the condenser, then the heat balance can be expressed by [8].
Space with a font size 10 Space with a font size 10 Where, Space with a font size 10 (11) Space with a font size 10 Where, Number of refrigerant pipe in condenser All the air properties can be taken at of the inlet and outlet of an air duct.
Space with a font size 10 The heat transfer coefficient for the air side of the condenser can be calculated from the following equation ( 16) [9].Also ̇ is the mass flow rate of the air, could be calculated from the following equation: Space with a font size 10 Also the heat transfer coefficient can be calculated using equation ( 18).
Space with a font size 10 (18) Space with a font size 10 If the number of rows less than 10, so the following equation can be calculates the Nusselt number [8]: Space with a font size 10 Space with a font size 10 The constants ( n) are depends on the ratio of ( ⁄ ) & ( ⁄ ), that's shown in "Table 1", and ( ) depends on the number of horizontal rows, as shown in "Table 2" below [10]: Mass flow rate of the air to be assumed as a uniform distributed over the whole coil face regardless of the coil and fan respective locations.So each coil was associated with the same air mass flow rate.Also it was assumed that the air stream passing through the coil with a sufficient turbulence status so that the air with uniform properties was enters each tube bank.
For Turbulence flow, Dittus-Boelter correlation [9] has been used to calculate heat transfer coefficient for refrigerant side.The heat transfer coefficient is represented as: Space with a font size 10 The heat transfer rate over the condenser of refrigerant side can be calculated from the following equation: Space with a font size 10 Space with a font size 10

Capillary Tube
Space with a font size 6 Under normal operating conditions, there is a thermostat connected with capillary tube to maintain a fixed superheat exiting the evaporator.The energy equation assumes that the enthalpy is constant across the expansion valve.
Space with a font size 10 Space with a font size 16

Evaporator
Space with a font size 6 In this study an air-cooled evaporator was used.To keep the evaporator model simple, the coil is assumed to be dry, so the air-side heat transfer coefficient is not affected, but the specific heat is corrected to account for condensation.Because the air flowing over the evaporator is cooled below the wet bulb temperature, some of the heat rejected by the air results in condensing water out of the air rather than lowering the temperature.The total enthalpy change of the air is the sum of the enthalpy change due to temperature drop, or sensible heat, and the enthalpy change due to condensation, or latent heat.itThe coefficient of performance (COP) is the ratio of the heat absorbed by the evaporator to the amount of compressor work as shown in the following equations: Space with a font size 10

Results and Discussion
Space with a font size 6 "Fig.8", shows comparison between compression pressure ratio for the three of refrigerants (R-22 , R-407C and R404).It is clear that when using R-404 and R-407C gives satisfied compressor pressure ratio compared with R-22, the compression ratio increases when the ambient temperature increased, this due to the ambient temperature leads to raise the compressor pressure ratio.However, the compressor ratio of system using R404 and R407C is more than the compressor ratio of system with R22 by 2% and 4% respectively.
Space with a font size 12 before the figure Space with a font size 12 before the figure "Fig.9", shows the evaporator temperature comparison between the two type of refrigerants R-407C and R-404 compared with R-22.It is clear that there is an increase in outlet air evaporative temperature of system using R-22 compared to outlet air evaporative temperature of system using R-407C and R-404 by a percentage of 8% and 5% respectively.In this figure, a convergence in data measured from the unit that leads to possibility of replacing the refrigerant R-22 by R-407C and R-404.
Space with a font size 12 before the figure before the figure "Fig.13", shows the COP behavior of the three types of the refrigerants R22, R407C and R404.However; The system using R407C has COP of 8% less than COP of system using R22, also; there is about COP of 12% for system using R404 compared with system using R22.So, it can be concluded that it is applicable to replace R-22 by R407C or R-404 in same air-conditioning unit.
Space with a font size 12 before the figure Space with a font size 16

Conclusions
Space with a font size 6 It is found that there are data convergence between the results of the compressor ratio of system using R-22 and system with R407C and R404.The compressor ratio of system using R407C is more than the compressor ratio of system using R22 by 4% and The compression ratio for R-404 is more than R-22 by 2%.The outlet air temperature of the evaporator for system using R-22 is more than the outlet air evaporative temperature with system using R-407C and R-404 by 8% and 5% respectively.The COP of the system using R-22 is more than the system using R-407C and R-404 by 8% and 12% respectively.So it can be concluded that it is possible to replace system refrigerant using R-22 by R-407C and R-404 as an alternative refrigerant that considered friendlier to environment.

FilterFigure 3 .
Figure 3. Schematic Diagram of system equipment with measurement devices

Figure 6 .
P-h Diagram of the cycleSpace with a font size 10