Deployment of Scroll Compressor in an Air Conditioning System of an SUV

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1 172 Published By: Deployment of Scroll Compressor in an Air Conditioning System of an SUV Ravi Kumar, Santosh G. Taji, GVS Sastry Abstract Most current Sports Utility Vehicles in India use fixed or variable displacement type piston compressors in air conditioning system which consumes a lot of power from engine. The AC compressor is the highest consumer of engine power among all the air conditioning system components. It is evident that any effort of reducing power consumption will not have fruitful result without reducing compressor power consumption. The conventional piston compressors are not only higher in weight, its volumetric efficiency is less too. The objective of this work is to derive analytical methodology to select a suitable Scroll Compressor without having any compromise on cooling performance of the vehicle and to articulate benefits by giving objective values for weight reduction, parasitic load reduction and above all fuel economy improvement of the vehicle. In cognizance of the Scroll technology, in the current work piston compressor has been replaced with an energy efficient Scroll compressor of an existing SUV vehicle to achieve weight reduction of 2 Kg, power consumption reduction up to 0.4 Kwatt which has resulted in fuel economy improvement by 0.5 Kmpl. Unlike previous works done on this topic the compressor selection procedure can be applied to all kinds of passenger vehicle to achieve similar objectives. Index Terms Climate Control, Scroll Compressor, Piston Compressor. I. INTRODUCTION Nowadays public awareness of environmental protection on a global scale has increased and efforts to combat global warming have accelerated in both the public and private sectors. In addition, the rising prices of crude oil and materials have prompted further energy and resource conservation. The demand for saving energy in a passenger vehicle is increasing in terms of environmental conservation against global warming. Since most energy in vehicle air-conditioning systems is consumed in compressor to compress refrigerant, the efficiency improvement in compressor is indispensable. Due to substantial power consumption by a/c compressors vehicles use to experience low pick-up when the AC is switched on. The car is perceived to be under powered with AC and sometimes the compressor has to be switched off while overtaking or climbing a gradient. In the classical reciprocating piston type compressors, the reciprocating motion of pistons results into higher frictional losses thereby lowering efficiency. The scroll compressor consists of two helices with one lying within the other. They are both mounted in a cylindrical housing. One helix is fixed and the other is attached to the drive shaft of the compressor. The driven helix does not rotate itself but does orbit the other helix. The two helices through movement create crescent-shaped compression chambers. Manuscript received February Ravi Kumar, Research Scholar, PES s Modern College of Engineering, Pune University, India. S.G. Taji, Astt. Prof., PES s Modern College of Engineering, Pune University, India. GVS Sastry, Product Engineering, Tata Technologies Ltd., Pune, India. A. The volume within the compressor increases with the movement of the driven helix. This allows refrigerant to enter the compression chamber. The shape of the helix and its movement mean that no physical inlet valve is required. Induction or the suction phase ends when the position of the helix is at the bottom of its eccentric movement. B. Compression occurs by trapping the refrigerant in the centre of the helix and then reducing the volume. This reduction will increase the pressure and temperature of the refrigerant to the required state. C. Discharge occurs at the centre of the helix where a valve is positioned to ensure that no refrigerant is allowed to flow back into the compressor when not being operated.. This method of compressing refrigerant results in lower frictional losses thereby increasing efficiency. During operation all gas spaces are in various states of compression which results in a continuous inlet and outlet flow. The compressor has few moving parts which mean less wear. Literature survey shows that the works done on compressor efficiency enhancement and power consumption reduction have been done to show component level improvement. The work done by S. Barbusse, L. Gagnepain, in the paper named Automobile Air-conditioning Its Energy and Environmental Impact explains the importance of energy saving. Similarly M. Takeuchi, T. Ukai, H. Yamazaki, K. Watanabe, T. Moro, S. Mishima, have done excellent work in An Environmentally Friendly, Highly Efficient, Lightweight Scroll Compressor for Car Air Conditioners to show how scroll compressor can become very important tool to reduce power consumption. The work done by S. H. Kapoor, S. Paramane, and G. Arora, named Application of Energy Efficient Scroll Compressor for Small Cars have presented work to show advantages for small cars. The present work has been done on a vehicle originally equipped with 150 cc/rev reciprocating piston compressor. Considering higher efficiency of scroll compressor the same type of compressor has been considered to achieve power consumption reduction goal of the present work. The most exciting part of the present work is the analytical method derived to finalize the suitable scroll compressor to provide the desired cooling and stabilize cabin temperatures to comfortable levels in hot climatic conditions. Above all the present work has taken the work started by earlier researchers to way ahead and has been reached to its destiny. The present work clearly shows vehicle level fuel economy improvement achieved by replacing 150cc piston compressor with a suitable 90cc Scroll Compressor.

= Temperature of medium to be cooled T1 = Saturation temperature refrigerant at evap. pressure 1/U = 1/h 1 + x 1 /k 1 + x 2 /k 2 +.

2 173 Published By: Deployment of Scroll Compressor in an Air Conditioning System of an SUV II. DESIGN CALCULATION TO FINALIZE OPTIMIZED CAPACITY COMPRESOR FOR A VEICLE AIR CONDITIONING SYSTEM Q = U A T E U = Overall heat transfer coefficient in w/m 2 k A = Area of evaporator surface in m 2 T2 = Temperature of medium to be cooled T1 = Saturation temperature refrigerant at evap. pressure 1/U = 1/h 1 + x 1 /k 1 + x 2 /k /h h i = Inner heat transfer film coefficient (w/mk) h o = Outer heat transfer film coefficient (w/mk) k = Thermal conductivity of wall material (w/mk) x = Thickness of each layer (m) Q= α A t [ cosθ] / U g A [T o T i ] α is Absorptivity of Glass A is area of Glass surface t is Transmissivity of Glass surface θ is Glass incidence angle T o is outside glass surface temperature T i is inside glass surface temperature OASH = [cmm] o [t o t i ] OALH = 50 [cmm] o [ω o ω i ] t o = Outside temperature ( C) t i = Inside temperature ( C) ω o = Outside specific Humidity ωi = Inside Specific Humidity (cmm) o = Outside Air Quantity entering the room (m3/min) [cmm] o = [V/60 ] A c [cmm] i = cmm / Crack length in meter P V = Volume of air conditioned space A c = No. of air changes per hour P = Perimeter of windows and doors Q evap = m R [H 2 H 1 ] N e = [V G r FDR ] / [2 π R r 60] V = vehicle speed G r = Gear ratio FDR = Final drive ratio R r = Dynamic rolling radius 6 Heat Load of vehicle 5.0 Kwatt 7 Evaporator Capacity 5.5 Kwatt 8 Suction Pressure [ absolute ] 2.96 bar 9 Discharge Pressure [ absolute ] 15.9 bar 10 Engine Speed at 3 rd gear 40 kmph 1750 rpm 11 Compressor clutch pulley ratio Compressor speed calculated at 40 kmph 2227 rpm 13 Refrigerant Mass flow through Evaporator kg/s 14 Refrigerant mass flow per revolution of compressor kg/s 15 Swept volume of compressor (theoretical) 82.7 cm 3 16 Swept Volume Scroll Compressor (actual) cm 3 17 Swept Volume Reciprocating Compressor (actual) 155 cm 3 III. PERFORMANCE COMPARISON: PISTON VS. SCROLL COMPRESSOR 3.1 COMPONENT LEVEL TESTING: COMPRESSOR CALORIMETER TEST The calorimeter measures capacity by means of a heat balance. The compressor suction pressure is adjusted by controlling the liquid refrigerant at the expansion device, and the temperature of the refrigerant vapor entering the compressor is adjusted by varying the electrical heat input. The discharge pressure is adjusted by varying the temperature and flow of the condensing medium, or by a pressure control device in the discharge line. Compressor calorimeter test is done to know performance parameters of compressor in standalone condition not balance dimensionally. If you must use mixed units, clearly state the units for each quantity in an equation. 4 condenser Design Calculation to select A/C Compressor for a vehicle 1 Type of Vehicle SUV 2 No. of Occupants 7 3 Vehicle Cabin 3.87 m 3 4 Ambient Temperature 35 C,40% RH 5 Cabin Temperature Target 20 C,50% RH The test conditions like Suction pressure =1.96bar, Discharge Pressure = 16.4bar, Super Heat =10 C, Sub cooling =5 C have been used for performance comparison of both the compressors. The test conditions selected for compressor calorimeter test represent actual operating conditions on the vehicle, under moderate climatic conditions. The compressor speed was set corresponding to engine speed as on the vehicle. The compressor cooling capacity, power consumption and volumetric efficiency were evaluated at various compressor speeds which is equal to the actual compressor speed when fitted in a vehicle and operating across all driving conditions.

174 Published By: 3.1.1 COOLING CAPACITY COMPARISON: 150cc Piston vs. 90cc Scroll 3.1.4 COP COMPARISON: Figure 4: compressor COP: component level Figure1: Compressor Cooling Capacity: component level 3.

3 174 Published By: COOLING CAPACITY COMPARISON: 150cc Piston vs. 90cc Scroll COP COMPARISON: Figure 4: compressor COP: component level Figure1: Compressor Cooling Capacity: component level POWER CONSUMPTION COMPARISON: 3.2 SYSTEM LEVEL TESTING: SYTEM TEST BENCH On System Test bench actual performance check of particular a/c component is done when it is functioning with all other components like evaporator, compressor and condenser etc. Many times it happens that due to other components capacity constrains the test component performs low. The system test bench is used to do system balancing and fine tuning of components to achieve an optimum design of ac system. Figure 2: Compressor Power Consumption :component level VOLUMETRIC EFFICIENCY COMPARISON: 150cc. Piston vs. 90cc Scroll Compressor Figure3: compressor volumetric efficiency: component level Figure 5: system test bench HVAC On the test bench, the compressor speeds for both compressors were set corresponding to engine speed as on the vehicle. There are five engine speeds from 750 rpm to 2500 rpm simulating vehicle idling to high cruising speeds. There are two ambient conditions for the compressor (70 C and 100 C) and the condenser (35 C and 45 C). Air flow rate across the condenser is related to vehicle speed. In stationary idling condition, the velocity was restricted to 1m/s whereas at cruising speed of 80 kmph, the velocity was set to 4 m/s. There are two conditions for the evaporator (27 C / 50% RH and 35 C / 60% RH). Air flow rate over the evaporator was set at 450m3/hr. This typically is the air flow rate at the maximum blower speed on a SUV. In the bench test, cooling capacity, air discharge temperature at the outlet of evaporator, power consumption, AC system pressures and COP have been evaluated across engine speeds.

175 Published By: Deployment of Scroll Compressor in an Air Conditioning System of an SUV 3.

4 175 Published By: Deployment of Scroll Compressor in an Air Conditioning System of an SUV COOLING CAPACITY COMPARISON: [System Test Bench results-severe Test Condition] VEHICLE LEVEL POWER CONSUMPTION TEST: The vehicle is tested on a chassis dynamometer with the existing 150cc piston compressor and the proposed 90cc Scroll Compressor. The Chassis dynamometer tests have been conducted to evaluate the AC power consumption under identical test conditions. Figure 6: cooling capacity compressor: system level POWER CONSUMPTION COMPARISON: [System Test Bench results-severe Test Condition] Figure 9: vehicle level compressor power consumption VEHICLE LEVEL A/C STUMBLE TEST: The above test shows that the use of Scroll Compressor gives clear advantage of power consumption reduction in terms of minimal drop in engine speed which would give advantage in drivability of the vehicle. Figure 7: power consumption compressor: system level 3.3 VEHICLE LEVEL TEST: Subject SUV was tested on a chassis dynamometer with the reciprocating and scroll compressors. The tests were conducted under identical test conditions to evaluate the load from AC system. The test was done at five vehicle speeds, in 5th gear and full throttle condition. To ensure that the AC system is fully loaded and the compressor works continuously during the test, the windows were kept open and the anti-icing device was bypassed, load on engine from AC system reduces by 11.8 to 20% with use of scroll compressor VEHICLE LEVEL AIR CONDITIONING SYSTEM PERFORMANCE: COOLDOWN TEST Figure 10: vehicle engine speed reduction due to compressor load VEHICLE LEVEL FUEL CONSUMPTION TEST: It is clear from the fuel economy test that the compressor selected in the present work increases the fuel economy of the vehicle by 0.25 to 0.5 kmpl. With an average usage of 25,000 kms per year there will be average annual fuel cost saving of Rs 6060 [Diesel price in Pune Rs/lit] Figure 8: a/c performance test [transient cool down] Figure 11: vehicle fuel economy with a/c on

5 176 Published By: IV. CONCLUSION: The main focus of the present work is To derive an analytical method to finalize compressor capacity based on cooling load of a vehicle. To produce vehicle level advantages of Scroll Compressor by giving objective values of fuel economy improvement achieved with the help of the present work. Weight reduction of 2kg is also helping in reducing co2 emission. The annual saving on fuel cost of Rs approx. for an average usages of 2500 Kms. REFERENCES [1] S. Barbusse, L. Gagnepain, Automobile Air-conditioning Its Energy and Environmental Impact. [2] M. Wang, M. J. Zima and P. S. Kadle, Energy-Efficient Air Conditioning Systems Utilizing Pneumatic Variable Compressor. [3] M. Takeuchi, T. Ukai, H. Yamazaki, K. Watanabe, T. Moro, S. Mishima, An Environmentally Friendly, Highly Efficient, Lightweight Scroll Compressor for Car Air Conditioners. [4] S. H. Kapoor, S. Paramane, G. Arora, Application of Energy Efficient Scroll Compressor for Small Cars. [5] J. P. Elson, and S.W. Vehr Horizontal Scroll Compressor for Transport Application. [6] Automotive Air-Conditioning and Climate Control by Steven Daly [7] Automotive Heating and Air Conditioning Haynes Techbook. [8] Automotive Air-Conditioning Training Manual Aria Zone NOMENCLATURE: N e Engine speed rpm P r Power consumption of reciprocating compressor kw P s Power consumption of scroll compressor kw Q r Cooling capacity of reciprocating compressor kw Q s Cooling capacity of scroll compressor kw η vr Volumetric efficiency of reciprocating compressor % η vs Volumetric efficiency of scroll compressor % ABBREVIATIONS: AC Air Conditioning COP Coefficient of Performance HP High pressure LP Low pressure RH Relative Humidity SC Sub cooling SH Superheating ACKNOWLEDGEMENT: The authors gratefully acknowledge the support provided to this work by Behr India Limited and specially Mr. G. Parthasarathi for his kind support in doing component level and system level tests. The authors also acknowledge the guidance and support given by Mr. H. Mukherjee from MHI, India

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