4 WEEKS INDUSTRIAL TRAINING REPORT ON “REFRIGERATION & A/C” (Submitted to Mechanical Engineering Department for the partial fulfillment of)DIPLOMA IN MECHANICAL ENGINEERINGSUBMITTED BY………………. SUBMITTED TO: HOD (ME) APC, ABOHAR
ACKNOWLEDGEMENTIt is worth to do anything without mentioning the names of persons who made it possible.I am very thankful to Our Principal Er. Tilak Raj and HOD Er Chhinder Pal who give usopportunity to go for industrial training. I am also thankful to our training Incharge Er SudhirBansal and Er Harvinder Singh for their value able guidance to accomplish our training ontime.I thank all those who are directly or indirectly assisted us to complete this
INDEXIntroduction to RefrigerationMethods of RefrigerationUnits of RefrigerationVCR System ComponentsAir conditioningApplication of refrigeration
IntroductionRefrigeration is a process in which work is done to move heat from a low temperature to a hightemperature and typically also from one location to another. The work of heat transport istraditionally driven by mechanical work, but can also be driven byheat, magnetism, electricity, laser, or other means. Refrigeration has many applications,including, but not limited to: household refrigerators, industrial freezers, cryogenics, and airconditioning. Heat pumps may use the heat output of the refrigeration process, and also may bedesigned to be reversible, but are otherwise similar to refrigeration unitsCycles Prof. U.S.P. Shet , Prof. T. Sundararajan and Prof. J.M . MallikarjunaIndian Institute of Technology Madras 6.2 Methods of Refrigeration:a) Natural Method:The natural method includes the utilization of ice or snow obtained naturally in coldclimate. Ice melts at 00C. So when it is placed in space or system warmer than 00C,heat is absorbed by the ice and the space is cooled. The ice then melts into water byabsorbing its latent heat at the rate of 324 kJ/kg. But, now-a-days, refrigerationrequirements have become so high that the natural methods are inadequate andtherefore obsolete.b) Mechanical or Artificial Refrigeration:Atmosphere(T1)RefrigeratedSystem (T3)T2δQ1Refrigerating System (R)δWδQ2A mechanical refrigeration system works on the principle of reversed Carnot cycle asshown in Fig.6.2. Work δw is delivered to the refrigerating system, causing it to removeRefrigeration Cycles Prof. U.S.P. Shet , Prof. T. Sundararajan and Prof. J.M . MallikarjunaIndian Institute of Technology Madrasheat δQ2 from the body or system (at lower temperature T3) and to deliver it along withwork, δw, to another body at higher temperature, T1, so that,δQ1 = δw + δQ2There can be two methods by which the temperature T2 < T3 may be attained within therefrigerating system.i) By lowering the temperature of the working substance in the refrigerating
system to the level of T2. In this case, the heat will be absorbed due totemperature difference and T3 will decrease as heat δQ2 flows out.ii) By evaporating some fluid at an appropriate pressure. In this case, a constanttemperature T2 will be maintained and latent heat of fluid will be absorbed asδQ2.Depending upon the above method used, there are two types of mechanicalrefrigerating systems :i) Air systems: Uses air as a working fluid. Air does not undergo any change ofphase, but absorbs heat due to temperature difference.ii) Chemical Agent Systems: The working fluid changing its phase while boilingfrom liquid to vapor state, thereby it absorbs the latent heat. Unit of Refrigeration:Capacity of refrigeration unit is generally defined in ton of refrigeration. A ton ofrefrigeration is defined as the quantity of heat to be removed in order to form one ton(1000 kg) of ice at 00C in 24 hrs, from liquid water at 00C. This is equivalent to 3.5 kJ/s(3.5 kW) or 210 kJ/min.Methods of refrigeration can be classified as non-cyclic, cyclic, thermoelectric and magnetic.Non-cyclic refrigerationIn non-cyclic refrigeration, cooling is accomplished by melting ice or by subliming dryice (frozen carbon dioxide). These methods are used for small-scale refrigeration such as inlaboratories and workshops, or in portable coolers.Ice owes its effectiveness as a cooling agent to its melting point of 0 °C (32 °F) at sea level. Tomelt, ice must absorb 333.55 kJ/kg (about 144 Btu/lb) of heat. Foodstuffs maintained near thistemperature have an increased storage life.Solid carbon dioxide has no liquid phase at normal atmospheric pressure, and sublimes directlyfrom the solid to vapor phase at a temperature of -78.5 °C (-109.3 °F), and is effective formaintaining products at low temperatures during sublimation. Systems such as this where therefrigerant evaporates and is vented to the atmosphere are known as "total loss refrigeration".Cyclic refrigerationHeat pump and refrigeration cycleThis consists of a refrigeration cycle, where heat is removed from a low-temperature space orsource and rejected to a high-temperature sink with the help of external work, and its inverse,the thermodynamic power cycle. In the power cycle, heat is supplied from a high-temperaturesource to the engine, part of the heat being used to produce work and the rest being rejected to alow-temperature sink. This satisfies the second law of thermodynamics.A refrigeration cycle describes the changes that take place in the refrigerant as it alternatelyabsorbs and rejects heat as it circulates through a refrigerator. It is also appliedtoHVACR work, when describing the "process" of refrigerant flow through an HVACR unit,whether it is a packaged or split system.
Heat naturally flows from hot to cold. Work is applied to cool a living space or storage volumeby pumping heat from a lower temperature heat source into a higher temperature heatsink. Insulation is used to reduce the work and energy needed to achieve and maintain a lowertemperature in the cooled space. The operating principle of the refrigeration cycle wasdescribed mathematically by Sadi Carnot in 1824 as a heat engine.The most common types of refrigeration systems use the reverse-Rankine vapor-compressionrefrigeration cycle, although absorption heat pumps are used in a minority of applications.Cyclic refrigeration can be classified as: 1. Vapor cycle, and 2. Gas cycleVapor cycle refrigeration can further be classified as: 1. Vapor-compression refrigeration 2. Vapor-absorption refrigerationVapor-compression cycle (See Heat pump and refrigeration cycle and Vapor-compression refrigeration for more details) The vapor-compression cycle is used in most household refrigerators as well as in many large commercial and industrial refrigeration systems. Figure 1 provides a schematic diagram of the components of a typical vapor-compression refrigeration system. Figure 1: Vapor compression refrigeration
The thermodynamics of the cycle can be analyzed on a diagram as shown in Figure 2. Inthis cycle, a circulating refrigerant such as Freon enters the compressor as a vapor. Frompoint 1 to point 2, the vapor is compressed at constant entropy and exits the compressor as avapor at a higher temperature, but still below the vapor pressure at that temperature. Frompoint 2 to point 3 and on to point 4, the vapor travels through the condenser which cools thevapor until it starts condensing, and then condenses the vapor into a liquid by removingadditional heat at constant pressure and temperature. Between points 4 and 5, the liquidrefrigerant goes through the expansion valve (also called a throttle valve) where its pressureabruptly decreases, causing flash evaporation and auto-refrigeration of, typically, less thanhalf of the liquid. Figure 2: Temperature–Entropy diagramThat results in a mixture of liquid and vapor at a lower temperature and pressure as shownat point 5. The cold liquid-vapor mixture then travels through the evaporator coil or tubesand is completely vaporized by cooling the warm air (from the space being refrigerated)being blown by a fan across the evaporator coil or tubes. The resulting refrigerant vaporreturns to the compressor inlet at point 1 to complete the thermodynamic cycle.The above discussion is based on the ideal vapor-compression refrigeration cycle, and doesnot take into account real-world effects like frictional pressure drop in the system,slight thermodynamic irreversibility during the compression of the refrigerant vapor,or non-ideal gas behavior (if any).More information about the design and performance of vapor-compression refrigerationsystems is available in the classicPerrys Chemical Engineers Handbook.Vapor absorption cycle
Main article: Absorption refrigeratorIn the early years of the twentieth century, the vapor absorption cycle using water-ammoniasystems was popular and widely used. After the development of the vapor compressioncycle, the vapor absorption cycle lost much of its importance because of its low coefficientof performance (about one fifth of that of the vapor compression cycle). Today, the vaporabsorption cycle is used mainly where fuel for heating is available but electricity is not,such as in recreational vehicles that carry LP gas. It is also used in industrial environmentswhere plentiful waste heat overcomes its inefficiency.The absorption cycle is similar to the compression cycle, except for the method of raisingthe pressure of the refrigerant vapor. In the absorption system, the compressor is replacedby an absorber which dissolves the refrigerant in a suitable liquid, a liquid pump whichraises the pressure and a generator which, on heat addition, drives off the refrigerant vaporfrom the high-pressure liquid. Some work is needed by the liquid pump but, for a givenquantity of refrigerant, it is much smaller than needed by the compressor in the vaporcompression cycle. In an absorption refrigerator, a suitable combination of refrigerant andabsorbent is used. The most common combinations are ammonia (refrigerant) with water(absorbent), and water (refrigerant) with lithium bromide (absorbent).Gas cycleWhen the working fluid is a gas that is compressed and expanded but doesnt change phase,the refrigeration cycle is called a gas cycle. Air is most often this working fluid. As there isno condensation and evaporation intended in a gas cycle, components corresponding to thecondenser and evaporator in a vapor compression cycle are the hot and cold gas-to-gas heatexchangers in gas cycles.The gas cycle is less efficient than the vapor compression cycle because the gas cycle workson the reverse Brayton cycle instead of the reverse Rankine cycle. As such the workingfluid does not receive and reject heat at constant temperature. In the gas cycle, therefrigeration effect is equal to the product of the specific heat of the gas and the rise intemperature of the gas in the low temperature side. Therefore, for the same cooling load, agas refrigeration cycle needs a large mass flow rate and is bulky.Because of their lower efficiency and larger bulk, air cycle coolers are not often usednowadays in terrestrial cooling devices. However, the air cycle machine is very commonon gas turbine-powered jet aircraft as cooling and ventilation units, because compressed airis readily available from the engines compressor sections. Such units also serve the purposeof pressurizing the aircraft.Thermoelectric refrigerationThermoelectric cooling uses the Peltier effect to create a heat flux between the junction oftwo different types of materials. This effect is commonly used in camping and portablecoolers and for cooling electronic components and small instruments.Magnetic refrigerationMain article: Magnetic refrigeration
Magnetic refrigeration, or adiabatic demagnetization, is a cooling technology based on the magnetocaloric effect, an intrinsic property of magnetic solids. The refrigerant is often aparamagnetic salt, such as cerium magnesium nitrate. The active magnetic dipoles in this case are those of the electron shells of the paramagnetic atoms. A strong magnetic field is applied to the refrigerant, forcing its various magnetic dipoles to align and putting these degrees of freedom of the refrigerant into a state of loweredentropy. A heat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermal contact with the heat sink is then broken so that the system is insulated, and the magnetic field is switched off. This increases the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the heat sink. Because few materials exhibit the needed properties at room temperature, applications have so far been limited to cryogenics and research. Other methods Other methods of refrigeration include the air cycle machine used in aircraft; the vortex tube used for spot cooling, when compressed air is available; and thermoacoustic refrigeration using sound waves in a pressurized gas to drive heat transfer and heat exchange; steam jet cooling popular in the early 1930s for air conditioning large buildings; thermoelastic cooling using a smart metal alloy stretching and relaxing. Many Stirling cycle heat engines can be run backwards to act as a refrigerator, and therefore these engines have a niche use in cryogenics. In addition there are other types of cryo coolers such as Gifford-McMahon coolers, Joule-Thomson coolers, pulse-tube refrigerators and, for temperatures between 2 mK and 500 mK, dilution refrigerators.VCR SystemThere are six main components in a refrigeration system The Compressor The Condenser The Metering Device or expansion valve The Evaporator Piping material RefrigerantCompressorIt is heart of the refrigeration system as it circulates the refrigerant in the system like the heartof a human being circulating the blood in the body. • Two different pressures exist in the refrigeration cycle. The evaporator or low pressure, and the condenser, or high pressure. These pressure areas are divided by the other two components. On one end, is the metering device which controls the refrigerant flow, and on the other end, is the compressor.
The compressor is the heart of the system. The compressor does just what its name is. It compresses the low pressure refrigerant vapor from the evaporator and compresses it into a high pressure vapor. • The inlet to the compressor is called the “Suction Line”. It brings the low pressure vapor into the compressor. • After the compressor compresses the refrigerant into a high pressure Vapor, and the outlet of the compressor is called the “Discharge Line”. There are three types of compressors namely reciprocating, rotary and centrifugal. The type ofcompressor depends on the pressure difference between the high pressure side (condenser)and low pressure side (evaporator) of the refrigeration system. This further depends onthe refrigerant selected for the application under consideration.Condenser • The “Discharge Line” leaves the compressor and runs to the inlet of the condenser. • Because the refrigerant was compressed, it is a hot high pressure vapor. • The hot vapor enters the condenser and starts to flow through the tubes. • Cool air is blown across the outside of the finned tubes of the condenser (usually air by a fan or water with a pump). • Since the air is cooler than the refrigerant, heat jumps from the tubing to the cooler air (energy goes from hot to cold – “latent heat”). • As the heat is removed from the refrigerant, it reaches its “saturated temperature” and starts to change state, into a high pressure liquid. • The high pressure liquid leaves the condenser through the “liquid line” and travels to the “metering device” through a filter dryer to remove any dirt or foreign particles. The condenser can be free air cooled (domestic refrigerator), forced air cooled (window airconditioner), water cooled (Central air conditioning plant in a library, cinema house andevaporative cooled (ice plant unit or a cold storage unit).
Expansion Device • Metering devices regulate how much liquid refrigerant enters the evaporator as per heat load on evaporator. • Common used metering devices are, small thin copper tubes referred to as “capillary tubes”, thermally controller diaphragm valves” (thermostatic expansion valves, called “TXV’s. This valve has the capability of controlling the refrigerant flow. If the load on the evaporator changes, the valve can respond to the change and increase or decrease the flow accordingly. The TXV has a sensing bulb attached to the outlet of the evaporator. This bulb senses the suction line temperature and sends a signal to the TXV allowing it to adjust the flow rate. This is important because, if not all, the refrigerant in the evaporator changes state into a gas, there could be liquid refrigerant content returning to the compressor. This can be fatal to the compressor. Liquid cannot be compressed and when a compressor tries to compress a liquid, mechanical failing can happen. The compressor can suffer mechanical damage in the valves and bearings. This is called” liquid slugging”. Normally TXVs are set to maintain 10 degrees of superheat. That means that the gas returning to the compressor is at least 10 degrees away from the risk of having any liquid. The metering device tries to maintain a preset degree of superheat at the outlet openings of the evaporator. As the metering devices regulates the amount of refrigerant going into the evaporator, the device lets small amounts of refrigerant out into the line and looses the high pressure to low pressure. • Now we have a low pressure, cooler liquid refrigerant entering the evaporative coil. These are of five type namely capillary tube (domestic fridge), Automatic expansion valve (ice plant unit), Thermostatic expansion valve (Library refrigeration plant, theatre air conditioning unit and many more), Low side float valve (industrial cooling units) and high pressure float valve (industrial cooling units). These causes the required pressure drop between the high and low pressure sides and also control the flow of refrigerant as per cooling requirements.
Evaporator The evaporator is where the heat is removed from your house, business or products to be cooled. • Low pressure liquid leaves the metering device and enters the evaporator. • Usually, a fan will move warm air from the conditioned space across the evaporator finned coils. • The cooler refrigerant in the evaporator tubes, absorb the warm room air. The change of temperature causes the refrigerant to “flash” or “boil”, and changes from a low pressure liquid to a low pressure cold vapor. • The low pressure vapor is pulled into the compressor and the cycle starts over. • Evaporators are two types i.e. flooded evaporators necessitating the use of accumulators to permit only vapors to the compressor and dry expansion type evaporators. Flooded types are used in industrial units whereas dry expansion types are used in domestic and commercial refrigeration units.Piping MaterialsPipe material should have high thermal conductivity, low cost, easy working and inertness withthe refrigerant. Till date most commonly used pipe material is soft copper with all refrigerantsexcept ammonia. The pipe material used with ammonia is mild steel as ammonia is highlycorrosive to copper.Refrigerant It is working substance in a refrigeration unit like blood in the human body. Its selectiondepends on many considerations like temperature to be produced, latent heat, ozone depletionpotential, global warming potential, toxicity, inflammability, inertness, corrosion, erosion,action with water and lubricating oil, cost, availability, leak detection and power requirementsfor a certain amount of cooling needed. Various commonly used refrigerants are halogenatedsaturated hydrocarbons like R-134, R-22 and inorganic compounds like ammonia and air. Mostcommon previously used refrigerants like R-12 and R-11 has been banned because of their highozone depletion and global warming potentials. Mixed refrigerants and zoetrope’s are also inuse. Refrigerants can be primary, secondary and tertiary type depending where and how thesebeing used are. The same substance, for example, air can be primary in aircraft refrigeration;can be secondary as in a window air conditioner and tertiary in a central air conditioning plant.
Air conditioningAir conditioning is the process of altering the properties of air (primarily temperature andhumidity) to more favourable conditions. More generally, air conditioning can refer to any formof technological cooling, heating, ventilation, or disinfection that modifies the condition ofair.An air conditioner (often referred to as AC) is a major or home appliance, system, ormechanism designed to change the air temperature and humidity within an area (used forcooling and sometimes heating depending on the air properties at a given time). The cooling istypically done using a simple refrigeration cycle, but sometimes evaporation is used, commonlyfor comfort cooling in buildings and motor vehicles. In construction, a complete system ofheating, ventilation and air conditioning is referred to as "HVAC".The basic concept behind air conditioning is known to have been applied in ancient Egyptwhere reeds hung in windows had water trickling down. The evaporation of water cooled theair blowing through the window, though this process also made the air more humid. In AncientRome, water from aqueducts was circulated through the walls of certain houses to cool themdown. Other techniques in medieval Persia involved the use of cisterns and wind towers to coolbuildings during the hot season. Modern air conditioning emerged from advances in chemistryduring the 19th century, and the first large-scale electrical air conditioning was invented andused in 1911 by Willis Haviland Carrier. The introduction of residential air conditioning in the1920s helped start the great migration to the Sunbelt.Pre-industrial coolingThe 2nd-century Chinese inventor Ding Huan (fl 180) of the Han Dynasty invented a rotary fanfor air conditioning, with seven wheels 3 m (9.8 ft) in diameter and manually powered. In747, Emperor Xuanzong (r. 712–762) of the Tang Dynasty (618–907) had the Cool Hall (LiangTian) built in the imperial palace, which the Tang Yulin describes as having water-powered fanwheels for air conditioning as well as rising jet streams of water from fountains. During thesubsequent Song Dynasty (960–1279), written sources mentioned the air-conditioning rotaryfan as even more widely used.In the 17th century, Cornelis Drebbel demonstrated "turning Summer into Winter" for James Iof England by adding salt to water.In 1758, Benjamin Franklin and John Hadley, a chemistry professor at Cambridge University,conducted an experiment to explore the principle of evaporation as a means to rapidly cool anobject. Franklin and Hadley confirmed that evaporation of highly volatile liquids such asalcohol and ether could be used to drive down the temperature of an object past the freezingpoint of water. They conducted their experiment with the bulb of a mercury thermometer astheir object and with a bellows used to "quicken" the evaporation; they lowered the temperatureof the thermometer bulb down to −14 °C (7 °F) while the ambient temperature was 18 °C
(64 °F). Franklin noted that, soon after they passed the freezing point of water 0 °C (32 °F), athin film of ice formed on the surface of the thermometers bulb and that the ice mass was abouta quarter-inch thick when they stopped the experiment upon reaching −14 °C (7 °F). Franklinconcluded, "From this experiment one may see the possibility of freezing a man to death on awarm summers day"...Mechanical coolingThree-quarters scale model of Gorries ice machine. John Gorrie State Museum, FloridaIn 1820, British scientist and inventor Michael Faraday discovered that compressing andliquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate. In1842, Florida physician John Gorrie used compressor technology to create ice, which he usedto cool air for his patients in his hospital in Apalachicola, Florida. He hoped eventually to usehis ice-making machine to regulate the temperature of buildings. He even envisionedcentralized air conditioning that could cool entire cities. Though his prototype leaked andperformed irregularly, Gorrie was granted a patent in 1851 for his ice-making machine. Hishopes for its success vanished soon afterwards when his chief financial backer died; Gorrie didnot get the money he needed to develop the machine. According to his biographer, Vivian M.Sherlock, he blamed the "Ice King", Frederic Tudor, for his failure, suspecting that Tudor hadlaunched a smear campaign against his invention. Dr. Gorrie died impoverished in 1855, andthe idea of air conditioning faded away for 50 years.James Harrisons first mechanical ice-making machine began operation in 1851 on the banks ofthe Barwon River at Rocky Point in Geelong (Australia). His first commercial ice-makingmachine followed in 1854, and his patent for an ether vapor-compression refrigeration systemwas granted in 1855. This novel system used a compressor to force the refrigeration gas to pass
through a condenser, where it cooled down and liquefied. The liquefied gas then circulatedthrough the refrigeration coils and vaporised again, cooling down the surrounding system. Themachine employed a 5 m (16 ft.) flywheel and produced 3,000 kilograms (6,600 lb) of ice perday.Though Harrison had commercial success establishing a second ice company back in Sydney in1860, he later entered the debate of how to compete against the American advantage ofunrefrigerated beef sales to the United Kingdom. He wrote Fresh Meat frozen and packed as iffor a voyage, so that the refrigerating process may be continued for any required period, and in1873 prepared the sailing ship Norfolk for an experimental beef shipment to the UnitedKingdom. His choice of a cold room system instead of installing a refrigeration system uponthe ship itself proved disastrous when the ice was consumed faster than expected.Electromechanical coolingWillis CarrierIn 1902, the first modern electrical air conditioning unit was invented by Willis HavilandCarrier in Buffalo, New York. After graduating from Cornell University, Carrier, a native ofAngola, New York, found a job at the Buffalo Forge Company. While there, Carrier beganexperimenting with air conditioning as a way to solve an application problem for the Sackett-Wilhelms Lithographing and Publishing Company in Brooklyn, New York, and the first "airconditioner", designed and built in Buffalo by Carrier, began working on 17 July 1902.Designed to improve manufacturing process control in a printing plant, Carriers inventioncontrolled not only temperature but also humidity. Carrier used his knowledge of the heating ofobjects with steam and reversed the process. Instead of sending air through hot coils, he sent itthrough cold coils (ones filled with cold water). The air blowing over the cold coils cooled theair, and one could thereby control the amount of moisture the colder air could hold. In turn, the
humidity in the room could be controlled. The low heat and humidity helped maintainconsistent paper dimensions and ink alignment. Later, Carriers technology was applied toincrease productivity in the workplace, and The Carrier Air Conditioning Company of Americawas formed to meet rising demand. Over time, air conditioning came to be used to improvecomfort in homes and automobiles as well. Residential sales expanded dramatically in the1950s.In 1906, Stuart W. Cramer of Charlotte, North Carolina was exploring ways to add moisture tothe air in his textile mill. Cramer coined the term "air conditioning", using it in a patent claimhe filed that year as an analogue to "water conditioning", then a well-known process for makingtextiles easier to process. He combined moisture with ventilation to "condition" and change theair in the factories, controlling the humidity so necessary in textile plants. Willis Carrieradopted the term and incorporated it into the name of his company. The evaporation of water inair, to provide a cooling effect, is now known as evaporative cooling.Evaporative cooling was the first real air-conditioning and shortly thereafter the first privatehome to have air conditioning (The Dubose House) was built in Chapel Hill, North Carolina.Realizing that air conditioning would one day be a standard feature of private homes,particularly in the South, DuBose designed an ingenious network of ductwork and vents, allpainstakingly disguised behind intricate and attractive Georgian-style open moldings.Meadowmont is believed to be one of the first private homes in the United States equipped forcentral air conditioning.Refrigerant developmentThe first air conditioners and refrigerators employed toxic or flammable gases, such asammonia, methyl chloride, or propane, that could result in fatal accidents when they leaked.Thomas Midgley, Jr created the first non-flammable, non-toxic chlorofluorocarbon gas, Freon,in 1928."Freon" is a trademark name owned by DuPont for any Chlorofluorocarbon (CFC),Hydrochlorofluorocarbon (HCFC), or Hydrofluorocarbon (HFC) refrigerant, the name of eachincluding a number indicating molecular composition (R-11, R-12, R-22, R-134A). The blendmost used in direct-expansion home and building comfort cooling is an HCFC known as R-22.It was to be phased out for use in new equipment by 2010, and is to be completely discontinuedby 2020.R-12 was the most common blend used in automobiles in the US until 1994, when most designschanged to R-134A. R-11 and R-12 are no longer manufactured in the US for this type ofapplication, the only source for air-conditioning repair purposes being the cleaned and purifiedgas recovered from other air-conditioner systems. Several non-ozone-depleting refrigerantshave been developed as alternatives, including R-410A, invented by Honeywell (formerlyAlliedSignal) in Buffalo, and sold under the Genetron (R) AZ-20 name. It was firstcommercially used by Carrier under the brand name Puron.
Innovation in air-conditioning technologies continues, with much recent emphasis placed onenergy efficiency and on improving indoor air quality. Reducing climate-change impact is animportant area of innovation because, in addition to greenhouse-gas emissions associated withenergy use, CFCs, HCFCs, and HFCs are, themselves, potent greenhouse gases when leaked tothe atmosphere. For example, R-22 (also known as HCFC-22) has a global warming potentialabout 1,800 times higher than CO2. As an alternative to conventional refrigerants, naturalalternatives, such as carbon dioxide (CO2. R-744), have been proposed.Humidity controlAir conditioning units outside a classroom building at the University of North Carolina in Chapel Hill,North CarolinaSee also: DehumidifierRefrigeration air-conditioning equipment usually reduces the absolute humidity of the airprocessed by the system. The relatively cold (below the dewpoint) evaporator coil condenseswater vapor from the processed air (much like an ice-cold drink will condense water on theoutside of a glass), sending the water to a drain and removing water vapor from the cooledspace and lowering the relative humidity in the room. Since humans perspire to provide naturalcooling by the evaporation of perspiration from the skin, drier air (up to a point) improves thecomfort provided. The comfort air conditioner is designed to create a 40% to 60% relativehumidity in the occupied space. In food-retailing establishments, large open chiller cabinets actas highly effective air dehumidifying units.A specific type of air conditioner that is used only for dehumidifying is called a dehumidifier.A dehumidifier is different from a regular air conditioner in that both the evaporator andcondenser coils are placed in the same air path, and the entire unit is placed in the environmentthat is intended to be conditioned (in this case dehumidified), rather than requiring the
condenser coil to be outdoors. Having the condenser coil in the same air path as the evaporatorcoil produces warm, dehumidified air. The evaporator (cold) coil is placed first in the air path,dehumidifying the air exactly as a regular air conditioner does. The air next passes over thecondenser coil, re-warming the now dehumidified air. Having the condenser coil in the main airpath rather than in a separate, outdoor air path (as with a regular air conditioner) results in twoconsequences: the output air is warm rather than cold, and the unit is able to be placedanywhere in the environment to be conditioned, without a need to have the condenser outdoors.Unlike a regular air conditioner, a dehumidifier will actually heat a room just as an electricheater that draws the same amount of power (watts) as the dehumidifier would. A regular airconditioner transfers energy out of the room by means of the condenser coil, which is outsidethe room (outdoors). That is, the room can be considered a thermodynamic system from whichenergy is transferred to the external environment. Conversely, with a dehumidifier, no energy istransferred out of the thermodynamic system (room) because the air conditioning unit(dehumidifier) is entirely inside the room. Therefore all of the power consumed by thedehumidifier is energy that is input into the thermodynamic system (the room) and remains inthe room (as heat). In addition, if the condensed water has been removed from the room, theamount of heat needed to boil that water has been added to the room. This is the inverse ofadding water to the room with an evaporative cooler.Dehumidifiers are commonly used in cold, damp climates to prevent mold growth indoors,especially in basements. They are also used to protect sensitive equipment from the adverseeffects of excessive humidity in tropical countries.The engineering of physical and thermodynamic properties of gas–vapor mixtures is calledpsychrometrics.EnergyIn a thermodynamically closed system, any power dissipated into the system that is beingmaintained at a set temperature (which is a standard mode of operation for modern airconditioners) requires that the rate of energy removal by the air conditioner increase. Thisincrease has the effect that, for each unit of energy input into the system (say to power a lightbulb in the closed system), the air conditioner removes that energy. In order to do so, the airconditioner must increase its power consumption by the inverse of its "efficiency" (coefficientof performance) times the amount of power dissipated into the system. As an example, assumethat inside the closed system a 100 W heating element is activated, and the air conditioner hasan coefficient of performance of 200%. The air conditioners power consumption will increaseby 50 W to compensate for this, thus making the 100 W heating element cost a total of 150 Wof power.It is typical for air conditioners to operate at "efficiencies" of significantly greater than100%. However, it may be noted that the input electrical energy is of higher thermodynamicquality (lower entropy) than the output thermal energy (heat energy).
Air conditioner equipment power in the U.S. is often described in terms of "tons ofrefrigeration". A ton of refrigeration is approximately equal to the cooling power of one shortton (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. The value is defined as12,000 BTU per hour, or 3517 watts. Residential central air systems are usually from 1 to 5tons (3 to 20 kilowatts (kW)) in capacity.In an automobile, the A/C system will use around 4 horsepower (3 kW) of the engines powerSeasonal energy efficiency ratioMain article: Seasonal energy efficiency ratioFor residential homes, some countries set minimum requirements for energy efficiency. In theUnited States, the efficiency of air conditioners is often (but not always) rated by the seasonalenergy efficiency ratio (SEER). The higher the SEER rating, the more energy efficient is the airconditioner. The SEER rating is the BTU of cooling output during its normal annual usagedivided by the total electric energy input in watt hours (W·h) during the same period. SEER = BTU ÷ (W·h)this can also be rewritten as: SEER = (BTU / h) ÷ W, where "W" is the average electrical power in Watts, and (BTU/h) is the rated cooling power.For example, a 5000 BTU/h air-conditioning unit, with a SEER of 10, would consume 5000/10= 500 Watts of power on average.The electrical energy consumed per year can be calculated as the average power multiplied bythe annual operating time: 500 W × 1000 h = 500,000 W·h = 500 kWhAssuming 1000 hours of operation during a typical cooling season (i.e., 8 hours per day for 125days per year).Another method that yields the same result, is to calculate the total annual cooling output: 5000 BTU/h × 1000 h = 5,000,000 BTUThen, for a SEER of 10, the annual electrical energy usage would be: 5,000,000 BTU ÷ 10 = 500,000 W·h = 500 kWh
SEER is related to the coefficient of performance (COP) commonly used in thermodynamicsand also to the Energy Efficiency Ratio (EER). The EER is the efficiency rating for theequipment at a particular pair of external and internal temperatures, while SEER is calculatedover a whole range of external temperatures (i.e., the temperature distribution for thegeographical location of the SEER test). SEER is unusual in that it is composed of an Imperialunit divided by an SI unit. The COP is a ratio with the same metric units of energy (joules) inboth the numerator and denominator. They cancel out, leaving a dimensionless quantity.Formulas for the approximate conversion between SEER and EER or COP are available fromthe Pacific Gas and Electric Company: (1) SEER = EER ÷ 0.9 (2) SEER = COP × 3.792 (3) EER = COP × 3.413From equation (2) above, a SEER of 13 is equivalent to a COP of 3.43, which means that 3.43units of heat energy are pumped per unit of work energy.The United States now requires that residential systems manufactured in 2006 have a minimumSEER rating of 13 (although window-box systems are exempt from this law, so their SEER isstill around 10).
ConstructionA typical home air conditioning unitRefrigerantsMain article: Refrigerant
A modern R-134a hermetic refrigeration compressor"Freon" is a trade name for a family of haloalkane refrigerants manufactured by DuPont andother companies. These refrigerants were commonly used due to their superior stability andsafety properties. However, these chlorine-bearing refrigerants reach the upper atmospherewhen they escape. Once the refrigerant reaches the stratosphere, UV radiation from the Suncleaves the chlorine-carbon bond, yielding a chlorine radical. These chlorine atoms catalyze thebreakdown of ozone into diatomic oxygen, depleting the ozone layer that shields the Earthssurface from strong UV radiation. Each chlorine radical remains active as a catalyst unless itbinds with another chlorine radical, forming a stable molecule and breaking the chain reaction.The use of CFC as a refrigerant was once common, being used in the refrigerants R-11 and R-12. In most countries the manufacture and use of CFCs has been banned or severely restricteddue to concerns about ozone depletion. In light of these environmental concerns, beginningon November 14, 1994, the U.S. Environmental Protection Agency has restricted the sale,possession and use of refrigerant to only licensed technicians, per Rules 608 and 609 of theEPA rules and regulations; failure to comply may result in criminal and civil sanctions.Newer and more environmentally safe refrigerants such as HCFCs (R-22, used in most homestoday) and HFCs (R-134a, used in most cars) have replaced most CFC use. HCFCs, in turn, arebeing phased out under the Montreal Protocol and replaced by hydrofluorocarbons (HFCs) suchas R-410A, which lack chlorine. Carbon dioxide (R-744) is being rapidly adopted as arefrigerant in Europe and Japan. R-744 is an effective refrigerant with a global warmingpotential of 1. It must use higher compression to produce an equivalent cooling effect.
TypesThe external section of a typical single-room air conditioning unit. For ease of installation, these arefrequently placed in a window. This one was installed through a hole cut in the wall.The internal section of the above unit. The front panel swings down to reveal the controls.Window and through-wallRoom air conditioners come in two forms: unitary and packaged terminal PTAC systems.Unitary systems, the common one room air conditioners, sit in a window or wall opening, withinterior controls. Interior air is cooled as a fan blows it over the evaporator. On the exterior theair is heated as a second fan blows it over the condenser. In this process, heat is drawn from theroom and discharged to the environment. A large house or building may have several suchunits, permitting each room be cooled separately.PTAC systems are also known as wall split air conditioning systems or ductless systems.These PTAC systems which are frequently used in hotels have two separate units (terminalpackages), the evaporative unit on the interior and the condensing unit on the exterior, withtubing passing through the wall and connecting them. This minimizes the interior systemfootprint and allows each room to be adjusted independently. PTAC systems may be adapted toprovide heating in cold weather, either directly by using an electric strip, gas or other heater, orby reversing the refrigerant flow to heat the interior and draw heat from the exterior air,converting the air conditioner into a heat pump. While room air conditioning providesmaximum flexibility, when used to cool many rooms at a time it is generally more expensivethan central air conditioning.
The first practical through the wall air conditioning unit was invented by engineers at ChryslerMotors and offered for sale starting in 1935.Window unitEvaporative coolersMain article: Evaporative coolerIn very dry climates, evaporative coolers, sometimes referred to as swamp coolers or desertcoolers, are popular for improving coolness during hot weather.An evaporative cooler is a device that draws outside air through a wet pad, such as a largesponge soaked with water. The sensible heat of the incoming air, as measured by a dry bulbthermometer, is reduced. The total heat (sensible heat plus latent heat) of the entering air isunchanged. Some of the sensible heat of the entering air is converted to latent heat by theevaporation of water in the wet cooler pads. If the entering air is dry enough, the results can bequite cooling; evaporative coolers tend to feel as if they are not working during times of highhumidity, when there is not much dry air with which the coolers can work to make the air ascool as possible for dwelling occupants. Unlike air conditioners, evaporative coolers rely on theoutside air to be channeled through cooler pads that cool the air before it reaches the inside of ahouse through its air duct system; this cooled outside air must be allowed to push the warmerair within the house out through an exhaust opening such as an open door or window.These coolers cost less and are mechanically simple to understand and maintain.An early type of cooler, using ice for a further effect, was patented by John Gorrie ofApalachicola, Florida in 1842. He used the device to cool the patients in his malaria hospital.Portable unitsA portable air conditioner is one on wheels that can be easily transported inside a home oroffice. They are currently available with capacities of about 5,000–60,000 BTU/h (1,800–
18,000 W output) and with and without electric-resistance heaters. Portable air conditioners areeither evaporative or refrigerative.Portable refrigerative air conditioners come in two forms, split and hose. These compressor-based refrigerant systems are air-cooled, meaning they use air to exchange heat, in the sameway as a car or typical household air conditioner does. Such a system dehumidifies the air as itcools it. It collects water condensed from the cooled air and produces hot air which must bevented outside the cooled area; doing so transfers heat from the air in the cooled area to theoutside air.A portable split system has an indoor unit on wheels connected to an outdoor unit via flexiblepipes, similar to a permanently fixed installed unit.Hose systems, which can be monoblock or air-to-air, are vented to the outside via air ducts.The monoblock type collects the water in a bucket or tray and stops when full. The air-to-airtype re-evaporates the water and discharges it through the ducted hose and can runcontinuously.A single-duct unit uses air from within the room to cool its condenser, and then vents it outside.This air is replaced by hot air from outside or other rooms, thus reducing the unitseffectiveness. Modern units might have a coefficient of performance (COP, sometimes called"efficiency") of approximately 3 (i.e., 1 kW of electricity will produce 3 kW of cooling). Adual-duct unit draws air to cool its condenser from outside instead of from inside the room, andthus is more effective than most single-duct units.Evaporative air coolers, sometimes called "swamp coolers", do not have a compressor orcondenser. Liquid water is evaporated on the cooling fins, releasing the vapour into the cooledarea. Evaporating water absorbs a significant amount of heat, the latent heat of vaporisation,cooling the air: humans and other animals use the same mechanism to cool themselves bysweating. They have the advantage of needing no hoses to vent heat outside the cooled area,making them truly portable; and they are very cheap to install and use less energy thanrefrigerative air conditioners. Disadvantages are that unless ambient humidity is low (as in adry climate) cooling is limited and the cooled air is very humid and can feel clammy. Also, theyuse a lot of water, which is often at a premium in the dry climates where they work best.A typical single hosed portable air conditioner can cool a room that is 475 sq ft (44.1 m2) orsmaller and has at most a cooling power of 15,000 BTUs/h (4.3 kW). However, single hosedunits cool a room less effectively than dual hosed as the air expelled from the room through thesingle hose creates negative pressure inside the room. Because of this, air (potentially warm air)from neighboring rooms is pulled into the room with the cooling unit to compensate.
Heat pumpsMain article: Heat pump"Heat pump" is a term for a type of air conditioner in which the refrigeration cycle can bereversed, producing heating instead of cooling in the indoor environment. They are alsocommonly referred to, and marketed as, a "reverse cycle air conditioner". Using an airconditioner in this way to produce heat is significantly more energy efficient than electricresistance heating. Some homeowners elect to have a heat pump system installed, which issimply a central air conditioner with heat pump functionality (the refrigeration cycle can bereversed in cold weather). When the heat pump is in heating mode, the indoor evaporator coilswitches roles and becomes the condenser coil, producing heat. The outdoor condenser unitalso switches roles to serve as the evaporator, and discharges cold air (colder than the ambientoutdoor air).Heat pumps are more popular in milder winter climates where the temperature is frequently inthe range of 40–55°F (4–13°C), because heat pumps become inefficient in more extreme cold.This is due to the problem of ice forming on the outdoor units heat exchanger coil, whichblocks air flow over the coil. To compensate for this, the heat pump system must temporarilyswitch back into the regular air conditioning mode to switch the outdoor evaporator coil back tobeing the condenser coil, so that it can heat up and de-ice. A heat pump system will thereforehave a form of electric resistance heating in the indoor air path that is activated only in thismode in order to compensate for the temporary indoor air cooling, which would otherwise beuncomfortable in the winter. The icing problem becomes much more severe with lower outdoortemperatures, so heat pumps are commonly installed in tandem with a more conventional formof heating, such as a natural gas or oil furnace, which is used instead of the heat pump duringharsher winter temperatures. In this case, the heat pump is used efficiently during the mildertemperatures, and the system is switched to the conventional heat source when the outdoortemperature is lower.Absorption heat pumps are actually a kind of air-source heat pump, but they do not depend onelectricity to power them. Instead, gas, solar power, or heated water is used as a main powersource. Additionally, refrigerant is not used at all in the process.[dubious – discuss] An absorptionpump absorbs ammonia into water.[further explanation needed] Next, the water and ammonia mixture isdepressurized to induce boiling, and the ammonia is boiled off, resulting in cooling.Some more expensive window air conditioning units have a true heat pump function. However,a window unit that has a "heat" selection is not necessarily a heat pump because some units useonly electric resistance heat when heating is desired. A unit that has true heat pumpfunctionality will be indicated its specifications by the term "heat pump".
Health issuesAir-conditioning systems can promote the growth and spread of microorganisms, such asLegionella pneumophila, the infectious agent responsible for Legionnaires disease, orthermophilic actinomycetes; however, this is only prevalent in poorly-maintained water coolingtowers. As long as the cooling tower is kept clean (usually by means of a chlorine treatment),these health hazards can be avoided.Conversely, air conditioning (including filtration, humidification, cooling and disinfection) canbe used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms andother environments where an appropriate atmosphere is critical to patient safety and well-being.Air conditioning can have a negative effect on skin, drying it out, and can also causedehydration. Air conditioning may have a positive effect on sufferers of allergies andasthma.Prior to 1994, most automotive air conditioning systems used Dichlorodifluoromethane (R-12)as a refrigerant. It was usually sold under the brand name Freon-12 and is a chlorofluorocarbonhalomethane (CFC). The manufacture of R-12 was banned in many countries in 1994 becauseof environmental concerns, in compliance with the Montreal Protocol. The R-12 was replacedwith R-134a refrigerant, which has a lower ozone depletion potential. Old R-12 systems can beretrofitted to R-134a by a complete flush and filter/dryer replacement to remove the mineral oil,which is not compatible with R-134a.
REFERENCESwww.wikipedia.comRefrigeration and air conditioning by DomkudwarRefrigeration by N Singh