CHAPTER 1 INTRODUCTION

Transcription

1 1 CHAPTER 1 INTRODUCTION 1.1 Background The science which deals with creating a controlled climate in indoor space is called air conditioning. Earlier days the air-conditioning was treated as a luxury, but in present scenario due to change in environmental conditions the air conditioning system has become part and parcel of human life. In tropical and subtropical countries cooling by means of air conditioning is necessary features of modern development. At present comfort air conditions is widely used in residence, office and commercial applications. One of the major transformations of 20 th century is widespread usage of modern, environmental friendly and effective air conditioning system. Thus, it is necessary to develop modern air conditioning system to meet the requirements comfort conditions. As the importance of refrigeration and air conditioning is increasing day by day there is need to study about the thermal comfort at any range of environmental conditions. Most of the air conditioning system uses either vapour compression system or vapour absorption system. The capacity may vary from a few kilowatts to megawatts. The vapour compression refrigeration cycle is widely used for room air condition because of its better performance. The working fluid used in the vapour compression cycle is known as refrigerant, which absorbs heat from the refrigerated space and rejects in the heat source. Last eight decades, the synthetic refrigerants like Chlorofluorocarbons (CFCs) and Hydro chlorofluorocarbons (HCFCs) are doing well because of every specific application, and however CFCs and HCFCs are not Ecofriendly [102]. There are two international agreements in this regards, namely Montreal and Kyoto protocol, the Montreal protocol is an international treaty that controls the production of

2 2 Ozone Depletion Substances (ODS). The original protocol was signed September 16 th, 1987 by the European Economic Community presently known as European Union and 24 nations including United States. Kyoto protocol concentrated on the Global worming impacts, the successful implementation of various components of the Montreal and Kyoto protocol will lead to an effective phase-out of ODP (Ozone Depletion potential) and GWP (Global warming potential) substances. CFCs and HCFCs causes ozone depletion and all of them cause global warming by green house effect, the CFC refrigerants containing chlorine which spoil the ozone layer, hence; Montreal protocol banned the CFC refrigerants in Subsequently, HCFC phase-out scheduled has been given for developed countries 2010 and for the developing countries dead line has been given up to 2030 [43]. The major disadvantage of R22 is having ozone layer depletion potential and global warming effect, which causes a lot of ill health and diseases for living and non living things. The ozone friendly refrigerant like R410A and R32 Hydro fluorocarbon group refrigerants emerging in the field of refrigeration and Air-Conditioning systems which are emerging as next generation refrigerants, because of their Zero Ozone Depletion Potential and low Global Warming Potential and favorable performance with less environmental impacts[96]. Most of the early refrigerant materials have been discarded for safety reasons or lack of chemical and thermal stability. Now, many refrigerants are used for air conditioning and refrigeration applications. R32 is expected to mildly flammable with an ASHRAE A2L (American Society of Heating, Refrigeration and Air-conditioning Engineers) flammability safety ratings and involve significant tradeoff among efficiency and cost. Besides the human comfort, air conditioning is used in industries for efficient functioning of machines, in cold storage to preserve food

3 3 products, in textile industry for better product and pharmaceuticals [50].In designing Airconditioning system the various factors which affect the human comfort are, Effective temperature (Dry bulb temperature, Wet bulb temperature), Heat production and regulation in human body, Relative Humidity, quality and quantity of air and Air Stratification. 1.2 Applications of Refrigeration and Air Conditioning The purpose of this section is to provide the various applications of refrigeration and air conditioning industry. Over the span of last few decades, refrigeration industry has grown into full-fledged industry in urbanized or northern countries. The refrigeration has become as vital feature rather than a luxury. It has brought much more success and comforts to human beings than any other devices of human comfort. The application of refrigeration can be classified in the following six categories: 1. Domestic Refrigeration / Appliance Servicing 2. Commercial Refrigeration 3. Industrial refrigeration 4. Transport and Marine 5. Comfort Air- conditioning 6. Processing Air Conditioning The primary function of the refrigerator or freezer is to provide and maintain food storage space at lower temperature for preservation of food. The mechanical vapour compression cycle as well as absorption system may use for domestic refrigerator or freezer. Appliance industry covers the domestic refrigerators, freezer; the commercial refrigeration covers the commercial and industrial applications for example merchandising cabinet, cool rooms, freezers rooms and air

4 4 conditioning systems, the air conditioning industry covers residential installation, shopping centres and hospitals, where as industrial process such as textile, printing, drug manufacturing and for drying of products. 1.3 Refrigerant and Refrigeration Cycle Refrigeration is a process of maintaining system temperature lower than that of surrounding temperature. The refrigeration cycle describes the changes that take place in the refrigerant as it alternately absorbs and rejects heat as it circulates through the refrigeration cycle. Heat naturally flows from hot to cold. Work is applied to cool a living space or storage volume by pumping heat from a lower temperature heat source into a higher temperature heat sink. Insulation is used to reduce the work and energy needed to achieve and maintain a lower temperature in the cooled space. The operating principle of the refrigeration cycle was described mathematically by Carnot in 1824 as a heat engine. In the refrigeration cycle, four important essential parts are compressor, condenser, expansion device and evaporator. In the refrigeration system these refrigerants absorb heat at low temperature system and reject the heat at high temperature system [103]. The suitability of a particular refrigerant for a certain application is determined by its thermo physical, chemical properties and various practical factors. Natural Ice, Air and water were the first refrigerants known to man. Subsequently, refrigerants such as ammonia (NH 3 ), Carbon dioxide (CO 2 ), sulphur dioxide (SO 2 ), Methyl chloride and dry ice were developed in nineteenth century. Presently in the field of refrigeration and air conditioning the synthetic refrigerants with a trade name of Freon s group refrigerants like CFCs, HCFCs, HFCs, FCs and HCs. The refrigerant changes its phase and absorbs more heat thus improving Coefficient of Performance of the unit,

5 5 thus; these refrigerants became very popular in vapour compression system. However, due to the environmental issues because of ozone layer depletion and Global Warming some of the refrigerants were banned and in several countries. Refrigerants may be classified into two types 1. Primary refrigerants 2. Secondary refrigerants The basic requirement of refrigerant Non flammable and non explosive (i)safe and non toxic, (ii)low cost (iii)easy to condense at moderate pressure and temperature,(iv)easy to detect leaks either by odor or indicator, (v)ability to operate on above atmospheric pressures and (vi) ability to Mix well with oil. The thermo physical properties are shown in Appendix-A. The refrigeration cycle can also be applied for air conditioning system, now days there are various methods of cooling systems are available, but vapour compression refrigeration system is better and efficient method for air conditioning purpose. Vapour compression refrigeration cycles have two advantages. First, a large amount of thermal energy is required to change a liquid to a vapour, and therefore a lot of heat can be removed from the air-conditioned space. Second, the isothermal nature of the vaporization allows extraction of heat without raising the temperature of the working fluid to the temperature of whatever is being cooled. This means that the heat transfer rate remains high, because the closer the working fluid temperature approaches that of the surroundings, the lower the rate of heat transfer. The applicability of this system ranges from a household refrigerator to a window air conditioner and from central air conditioning plants to large storage.

6 6 1.4 Air-Conditioning System The air conditioning is the process of simultaneous control of temperature, humidity, flow of air and purity of air. It needs the controlling the properties of atmospheric air and distributing through the space to be conditioned. Air conditioner which works on vapour compression refrigeration cycle consists of compressor, condenser (heat exchanger), expansion valve and evaporator (heat exchanger).refrigerant is a working medium in refrigeration cycle used for heat transfer; it picks up heat (latent or Sensible heat) from the source at lower temperature and pressure and gives up heat (latent or Sensible heat) at higher temperature and pressure. Selecting refrigerant for a particular purpose its characteristics must be considered and the selection must be made on the basis of its compatibility with the system [105]. An air conditioning system is assembly different parts to be used to produce specified conditions of air with in a room or space. The important parts and equipments of an air-conditioner are a unit of refrigeration cycle components (vapour compression system) i.e. 1. Compressor 2. Condenser 3. Expansion device 4. Evaporator In addition to these parts there exists Air-Cleaning and Air-filters, humidifiers, dehumidifiers, fan and Blowers and grills for space to be conditioned. The equipment working and the mechanism of maintaining comfort conditions will be discussed in detail chapter 5.The general classification of air conditioning system is as follows I. According to the purpose of the system 1. Industrial Air conditioning System

7 7 2. Comfort air conditioning system II According to the seasonal use. 1. Summer air conditioning system 2. Winter air conditioning system 3. Year round air conditioning system III. According to the arrangement of the equipment. 1. Central air conditioning system 2. Unitary air conditioning system IV.According to working substance used in the system. 1. All air system 2. Air water system 3. Chilled water system. The America Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) define it as the condition of mind which expresses satisfaction with thermal conditions. The comfort may be described as a condition in which the human body feels neither warm nor cold an absence of excess sensation or comfort air conditioning deals with creating optimum conditions for human comfort where as industrial air conditioning deals with providing conditions necessary for some industrial process. There are temperature and humidity conditions taken into consideration by air conditioning engineers to design their system and select the equipment. Design conditions differ from place to place and depend upon the type of application. The first important step for designing air conditioning is fixing the design conditions, the indoor conditions are based on human comfort and outdoor design conditions are based on average ambient temperatures and humidity data.

8 8 1.5 Simulation Tool for Refrigeration and Air-Conditioning Chapter 4 has been discussed about simulation methodology, in which the different simulation tools like REFPROP version 6.01 and cool pack version 1.49 has been discussed. For simulation, REFPROP version 6.01[89] (REFPROP is an acronym for Refrigerant Properties) used for finding out the properties of selected refrigerants i.e. R22, R410A and R32, which gives the most accurate properties for simulation and to draw high quality property plots, which has been developed by the National Institute of Standards and Technology (NIST) provides the thermodynamic and transport properties of refrigerants REFPROP also provides high accuracy data for pure refrigerants and refrigerant mixtures. Cool Pack (version 1.49) is a collection of simulation programs used for designing, dimensioning, analyzing and optimizing the refrigeration and air conditioning systems. The program consists of three main groups (i) Refrigeration Utility, (ii) EES Cool Tool and (iii) Dynamic analysis Tool. The program in refrigeration utility consists of calculation of refrigeration properties like thermodynamic and thermo physical properties and property plots, EES refers to Engineering Equation Solver, The group EES cool tools is a collection of program for both refrigeration systems and cycle components for solving the system operating conditions of compressor, condenser, pressure reducer and evaporator. EES covers both single stage and multi stage cycle analysis; design and dimensioning consists of component size and operating conditions and energy analysis consists of compressor performance, condenser and evaporator temperature levels, pressure loss and suction gas heat exchange type of refrigerant, and cooling capacity, if the input for the capacity is given out put related to capacity are found like mass flow rate, COP and volume fowl of refrigerant. Dynamic cooling models consist of cooling and system stabilization time with on/ off controls of the compressors and condenser and transient cooling of the room.

9 9 1.6 Experimental Methodology The experimental test has been conducted with calorimeter test for air conditioning and vapou compression cycle performance test, the calorimeter has the facility to conduct from small airconditioners unit to large chillers. The Balanced Ambient Test Facility Lab (BATF lab) has the ability to conduct the various tests for Window and Split Air-Conditioning systems [38]. The test facility having range from 0.5kW to 10 kw capacities with heat balance within 4% for the test units when the test rooms are completely stabilized. The calorimeter test facility is equipped with a highly advanced data acquisition system, the computer programme is written in the programming language of Lab VIEW, which is developed by National Instruments as per standards of National Institute of Standards and Technology. The lab VIEW software has a graphic user interface that controls and monitors various parameters. The present equipment used for testing is having calibrated by TRANSCAL which has been established as a Micro Service Industry in the year 2002 to provide services for calibration of test and measuring instrumrnts to meet the quality requirement with highly qualified engineers. The simulated results of R32, R410A and R22, thus obtained are compared with the experimental test data of R32, R410A and R22.The performance parameters like power consumption, coefficient of performance, mass flow rate and Pressure ratios, energy efficiency ratio and cooling capacity are compared for both simulated and experimental. In the present research the range of cooling capacity, condenser and evaporator temperature has been considered from 3.5 kw to 7.5kW, condenser temperature from 35 C to 55 C, evaporator temperature from -10 C to +10 C, for both experimental and simulation analysis for the components of HCFC-22, HFC group refrigerants like R32 and R410A refrigerants in vapour compression refrigeration system.

10 Structure of the Dissertation This thesis (dissertation) comprises a comprehensive analysis of window air conditioning system which works on vapour compression refrigeration system. For performance comparison three different group refrigerants were selected. The whole thesis has been divided into 7 chapters; chapter 1 describes the importance of ozone layer, Global warming, environmental impacts and refrigeration and air conditioning. Also describes the various applications and methods of air conditioning. The chapter 2 describes about the motivation to take up this research work, problem formulation and defining of the objectives of this research work. As part of research work, the vast literature has been reviewed from the natural ice methods to present modern mechanical methods. Also discussed about the HCFC phase-out scheduled, research gaps and scope of research work, particularly in the field of alternative refrigerants to replace R22 in vapour compression refrigeration system. Chapter 3 describes the working of vapour compression system, in which the different components are explained with their functional aspects. Refrigerant is the working medium in the system for which the detailed configuration of system components and the properties of refrigerants, refrigerant designation and selection of refrigerants are explained. The system simulation methodology has been described in chapter 4, for analysis REFPROP and cool pack software tools are used, the tool are being used for refrigeration and air conditioning purpose. Also, described about mathematical computation for balancing of mass flow rate through capillary tube and compressor.

11 11 Chapter 5 describes the experimental plan to conduct experiments for which Balanced Ambient Test Facility (BATF) lab, calorimeter test, Test Room Accessories and Helping Devices, Test Unit Air Sampling System, System Measurements, NABL for testing and Calibration, Error Analysis, validation methodology, Lubricants in Refrigeration System, Miscibility of oil with Refrigerant, Leak Detection methods has been explained for R22, R32 and R410A data base. Chapter 6 presents the results for the components studied and discussion, in which the critical parameters like temperature, pressure, density, freezing point of refrigerant, boiling point of refrigerant discussed. The system performance parameters like Coefficient of performance, Cooling Capacity, Mass flow rate of refrigerant, compressor power consumption, energy efficiency Ratio (EER) has been discussed, time response graph for different Parameters, Psychrometric Properties Stabilization Plot, normalized performance parameters from set values are also discussed. Chapter 7 presents, closing remarks and recommendation for future scope of work particularly related to the optimum design for various components and suitability of refrigerants to enhance the performance of the system. Other important parameter like compressor discharge temperature also explained. Appendices i.e. (Appendix: A to M) provides the additional data which has been used as part of present research work for various test conditions, which includes, the thermo physical properties of the refrigerants, calorimeter test report, general servicing and maintenance, Trouble shooting chart, room air conditioner, refrigerant safety standards and handling and Storage.