RefrigerationPlants combine carbon dioxide from atmosphere, moisture and traces of chemicals from the soil to form all constituents they need. Energy from sunlight and green parts of plants can effect this synthesis. Animals cannot do this They have to get food from plants or other animals. From their food they absorb hat they re!uire in their digestive system and re"ect the rest. #any micro$organisms live on the same food as men. %ur battle is to get the food before the micro$organisms. &n this battle the micro$organisms are ell placed si'e so small they are ever present in the atmosphere. Any food exposed to atmosphere at ordinary temperature appropriate organisms ill start to gro. They consume the food li(e animal absorbing hat they li(e and re"ecting the remainder. )e"ected remainder is often toxic leading to food poisoning.#icro$organisms can be divided in three groups moulds, yeast and bacteria. #oulds start microscopic can develop into clearly visible groths.*east reproduce into microscopic individuals presence (non by the alcohol their digestive process re"ects leading to fermentation.+acteria $ also multiply as microscopic individuals$ their aste products often giving rise to evil smells of putrefaction as ell as being toxic.Each type of micro$organisms has its on environment of temperature, atmosphere ,gaseous composition and humidity- and food for optimum groth..ater is re!uired by everyone. /ence drying can also lead to food preservation.0ontrol of micro$organisms by sub"ecting them to lo temp. is basis of refrigerated carriage of foodstuffs.There are three main temperature group of micro$organisms 1. 23.45 0 for optimal groth. This group includes bacteria. They practically cease groth at 55 0.6. %ptimal groth at 615 0, hich are capable of rapid groth at 55 0 and hich ill gro on unfro'en substances belo this temperature. This group includes yeast and moulds and bacteria.2. #icro$organisms, mainly yeasts and moulds, hich ill gro on fro'en substances don to about $45 0.+elo 75 0 no groth or reproduction of micro$organisms occurs.For each living process there is an optimum temp. at hich the process occurs at the maximum rate. As temp. falls belo the optimum, the rate of living falls off until at lo enough temperatures life ceases. As temperature rises above the optimum, different chemical processes ta(e over from the normal living reactions until at high enough temperature life again ceases . %ptimum temperature varies for each life process, but all lie ithin the range of 75 0 to 1555 0, outside hich life is virtually un(non.Dead animal products.ith dead animal produce, the primary purpose of refrigeration is to delay or prevent the developments of micro$organisms ,moulds, yeast and bacteria- hich live on the produce. 0old storage also retards the slo chemical changes, such as the oxidation of fats, hich hilst not rendering the produce unfit for human consumption do adversely affect flavours.8ead animal products are carried as fro'en cargo belo 75 0.9one of the micro$organisms that cause decay and putrefaction gro and multiply belo this temperature, although some may survive in dormant state to resume groth if temperature is raised subse!uently. Further temperature reduction is re!uired to slo chemical changes that impair flavour. For beef and lamb 155 0 is ade!uate. For por( 16 to 1:5 0. Poultry and fish 175 0 is desirable.Fruits and vegetablesThe living process continues after pic(ing of fruits and vegetables. After pic(ing at immature stage the ripening process continues until it is fully ripe and finally overripe. 0ool storage delays the ripening process. ;econd benefit is delaying of onset of mouldiness as they are li(ely to be attac(ed by moulds. /ence by refrigeration, e (eep it alive and let it ripen sloly. The ater content of fruits and vegetables is 75$nits of )efrigeration 0apacityTonnage %ne Ton of )efrigeration implies latent heat of one tonne of ice or the heat re!uired to convert one tonne of ater to ice. E!uivalent to 16,555 +T>s. %ne +T> is the heat re!uired to raise one pound of ater by one degree Fahrenheit.%ne calorie is the heat re!uired to raise one gram of ater by one degree 0elsius.?oule is the mechanical e!uivalent of heat, or( done hen one a force of one 9eton moves through one metre.%ne ?oule @ A.6 calories0alculate the conversion factor from +T>s to BilocaloriesRefrigerant)efrigeration depends upon a substance called the refrigerant, hich can readily be converted from li!uid into a vapour ,evaporation- and also from a vapour into a li!uid ,condensation- ithin a narro range of pressures. )efrigerants are those fluids, hich are used as or(ing fluids, for example in vapour compression refrigeration systems. These fluids provide refrigeration by undergoing a phase change process in the evaporator. A refrigerant gives up heat by condensing at high temperatures and pressures and absorbs heatby evaporating at lo temperatures and pressures.REFRIGERANTSHalocarbon based Non-Halocarbon basedAeotropic !eotropic"F"s H"F"s HF"sEt#ane based $et#ane based%rimar& Secondar&%ure 'lendedNear Aeotropic A'eotropic )efrigerantsC#ixture of to or more refrigerants ith similar boiling points. .here the change of phase ta(es place at a specific single temperature.exC )$:55D)$:56D )$:52D )$:54. They can be charged as a li!uid or vapour. Eeotropic )efrigerantsC #ixture of to or more refrigerants ith dissimilar boiling points. .here the change of phase ta(es place over a temperature range of over :.:3 degrees 0 ,15 deg F-.exC )$A5AaD A54c.They should be charged as a li!uid. 9ear A'eotropic )efrigerantsC C #ixture of to or more refrigerants ith dissimilar boiling points, but the change of phase ta(es place over a temperature range of less than :.:3 degrees 0 ,15 deg F-. )$A15a.They should be charged as a li!uid. TE#PE)AT>)E FG&8E is the range of temperature over hichchange of phase occurs.&mportant because fractionating of refrigerant occurs especially hen there is a lea(. Also complicates the charging process.Feneration of )efrigerantsFirst Feneration 1725$1. TE> RTenty foot E!uivalent >nitS refers to a unit of volume corresponding to a tenty foot &;% container, hich used to be the standard container. +ut today A5 foot containers of the R/igh0ubeS type dominate the mar(et for ne reefer containers. Their si'e surpasses to TE> and therefore the increase in container traffic exceeds the increase in the number of units at the present time. There are no more than 17,555 containers of the porthole type in operation no and no ne porthole containers are built.About 655 ne container ships and 135,555 TE> ne refrigerated containers ere built annually during the last fe years.Integral refrigerated containerThe integral container ill have an independent refrigeration unit hich enables the container operator to carry cargoes in the temperature range $6:M0 to O6%50. These units are mostly electrically driven and are plugged in to appropriate poer points on shore or onboard ship. 9oadays, a number of units are compact enough to allo for a removable diesel alternator set to be fitted hen the container is travelling on the road, or sited in areas here a suitable 2$phase poer supply is not available.S#ips for t#e carriage of integral containersThe holds of these ships are normally uninsulated. &n order to maintain the hold temperature belo ambient, a very poerful ventilation system is fitted to forard and aft bul(heads ith air inta(es positioned in the vicinity of each container integral unit. Fresh air may be supplied to the holds at tan( top level or through openings in the vicinity of hatches. As soon as the containers are loaded and positioned up to 3 high in guides, the refrigerating units are plugged to the electrical poer supply and those containers having ater cooled condensers are connected to fresh or sea ater cooling systems permanently fitted onboard.The fresh ater is circulated in a closed circuit and cooled by sea ater in heat exchangers, its outlet temperature being A to :M0 higher than the sea ater outlet temperature from the heat exchanger. The fans of air cooled condensers ill not be running. ;ome ships can carry over 355 integral containers under the dec(. Refrigerated container on dec?&ndividual containers ith their on refrigeration plant are connected to the AA5 or 665 I a.c. soc(ets provided on dec(. These containers may be arranged for shipsK systems ith either AA5 or 665 I by provision of a direct connection for a 66%I supply to the self$contained refrigerator and a AA5I connection through a step don transformer.Air cooler fans Fans may be either centrifugal or of the propeller typeD the air circulation systems being based on a pressure re!uirement of about 7= mm ..F. ,ater gauge-. All of the electrical energy of the fan motors is dissipated in the form of heat and has to be removed by the refrigerating plant. Fan output should be variable so that it can be reduced as heat load diminishes. There as no problem ith d.c. motors but ith a.c. either the motors are to speed, or each"ontrolled atmosp#ereFruits and vegetables are actually alive, their cells are metabolising, consuming oxygen and carbohydrate and producing ater vapour, carbon dioxide and heat. Also small amounts of ethylene gas ,06/6- are produced. Therefore it is not enough to "ust refrigerate the cargo, a supply of fresh air must also be provided. "ontrolled atmosp#ere&f insufficient fresh air is supplied, several things can happenC1. Too much carbon dioxide can produce tissue damage, in apples this condition is (non as bron heart6. 9ot enough oxygen can result in anaerobic respiration, in this case the metabolic pathay is incomplete and the final product becomes alcohol resulting in alcoholic fruit2. Too much ater vapour can encourage the development of moulds, rots and fungi. /oever, not enough is "ust as bad as it promotes desiccation of fruit and vegetablesA. Ethylene gas is ripening hormone, very small !uantities building up can promote premature ripening in fruit or degreening in green vegetables "ontrolled atmosp#ere)ate of breathing or respiration can be loered and thus ripening sloed don either by loering the temperature or by reducing the amount of oxygen and increasing the amount of carbon dioxide in the surrounding atmosphere.0ontrolled atmosphere is an inert gas system used to extend the storage life of seasonal perishable products and has been used for many fruits and vegetablesD primarily apples and pears in the past, and no mainly for bananas."ontrolled atmosp#ereTo successfully store fruit for long periods, the natural ripening of the produce has to be delayed ithout affecting the eating !uality. This is achieved by reducing the temperature of the fruit to the loest level possible ithout causing damage through free'ing or lo temperature brea(don. To further delay ripening, the oxygen supply in the space is reduced to levels belo that of the natural atmosphere. This level is belo the level re!uired to support human life."ontrolled atmosp#ereThe precise levels of temperature, oxygen and carbon dioxide re!uired to maximi'e storage life and to minimi'e storage disorders are extremely variable, depending on type of produce, groing conditions and maturity. %ptimum storage conditions can vary from farm to farm and from season to season. %n reefer vessels, oxygen ,56- and carbon dioxide ,0%6- levels and relative humidity ,)/- in controlled atmosphere 'ones ,cargo chambers- can be independently controlled ithin close tolerances, irrespective of type, temperature and volume of cargo carried and the length of the voyage. A typical modern controlled atmosphere marine system ould be expected to have flexibility to control gas levels ithin the folloing rangesC 56C Q 1 7 = 0%6 C5$1:=)/ C A5$sing the Psychrometric 0hart plot the re!uired air conditioning process and estimate ,a- the amount of moisture removed ,b- the heat removed and ,c- the amount of heat added0ooling to 8+T64 )/155=%ver cooling to 8+T1: )/155=/eating to 8+T6: )/:5=;olution,a- the amount of moisture removed V66$15@11.:g of /65J(g of dry airW ,b- the heat removed V,1-$,6-, !cool 77$A5@ A7(?J(g$dry$airW,c- the amount of heat added V,6-$,2-, !heat :5$A5@ 15(?J(g$dry$airW.Air conditioning circuit$arine air conditioning unitT&pes of air conditioning s&stemsAir conditioning systems may be divided into to main classes the central unit type in hich the air is distributed to a group of spaces through ducting and the self$contained type, installed in the space it is to serve.The central unit type is the most idely used, in one or other of a number of alternative systems, characteri'ed by the means provided to meet the varying re!uirements of each of the spaces being conditioned. The systems in general use are as follosC1. Eone control systemD6. 8ouble duct systemD!one control s&stemThe accommodation is divided into 'ones, having different heating re!uirements. ;eparate air heaters for each 'one are provided at the central unit and the temperature of the air leaving the heater is controlled. Air !uantity control in each room served gives individual refinement.The regulation of temperature by individual air !uantity control in this system can give rise to difficulties. For instance, a concerted move to reduce the air volume in a number of cabins ould cause increased air pressure in the ducts, ith a conse!uent increase in air flo and possibly in noise level at other outlets. Double duct s&stem&n this system, to separate ducts, one ith cool dehumified air and the otherith arm humid air. These separate airstreams are mixed "ust before they reach the space to be conditioned. Through dampers that control and balance air, each different space in the ship can be conditioned as needed. The air control in this system is excellent. A single duct air return is used.Double duct systemSAFETD20 $ec#anical #aards30 Electrical #aards40 "#emical #aardsFreon cannot be seen or smeltX Freon is heavier than air so it ill settle and remain at the bottom of the compartments. Freon is extremely harmful if it comes into contact ith the eyes. Freon is suffocating because it displaces air. &f you inhale high concentrations of Freon, it attac(s the nerve system. .hen Freon comes into contact ith hot surfaces and starts to burn, it can give off poisonous gases. Freons, if released into the air, may cause depletion of the %'one Gayer hich contributes to the greenhouse effect. )efrigerants are not to be released into the atmosphere. They must be dran into the condenserJreceiver or into a separate cylinder. #ost refrigerants mix ith oil so oil drained from a refrigeration system must be clearly labelled and disposed of separately. )efrigerants must not be mixed. If &ou start feeling faint or di& as &ou enter a compartment - donEt t#in? t*ice - evacuateFIf a refrigerant lea? occursEvacuate compartment immediately. ;ound alarm and get cre in an up-wind position. &f lea( is in engine room shut don machinery. Turn vessel into ind if still possible. 8o not enter compartment ithout ventilating the compartment. Ientilate compartment. )emember Freon sin(s to the bottom of the compartment and is very hard to remove. Try to force airflo don into the bottom of the compartment to force the Freon upards. )efrigerant pipes are lagged and constantly damp. This means that pipe coatings and surface can deteriorate relatively !uic(ly. 0hec( pipes regularly and ma(e sure the coating is maintained. &nspect +loer )ooms regularly and (eep them clean and dry. %ften, they are neglected areas. &t is a great idea to fit an exhaust fan for the bloer room and start the same and ait for a fe minutes before entering..hen entering compressor rooms, start the exhaust fan and ait for a fe minutes before entering..here flexible hoses are used, only use refrigerant tolerant hoses. Try to avoid using flexible hoses herever possible. #aintain fittings such as valves and gauges in good order. #ar( pipes to sho hat type of refrigerant they have in them. )efrigerants are supplied in metal cylinders hich ill corrode in the salt environment. #a(e sure these are left in dry storage ,preferably ashore-. .hen or(ing on compressor cran(case, for drainingJchanging oil, ensure the cran(case is totally depressurised.)etain a firm grip on the drain plugs and other connections so that they do not fly off uncontrollably. Safe #andling of refrigerants0Ensure that personnel ho handle refrigerants are properly trained in their safe use and handling, and have revieed the #;8; for the refrigerant used. .ear safety goggles and gloves at all times hen handling refrigerants or servicing a refrigeration system. .ear the proper respiratory protection hile or(ing ith refrigerants. 0hec( the #;8; for the proper level of protection re!uired. Proper ventilation or respiratory protection is re!uired for any or( on e!uipment in an enclosed area here a lea( is suspected. Alays ventilate or test the atmosphere of an enclosed area before beginning or(. #any refrigerants hich may be undetectable by human senses are heavier than air and ill replace the oxygen in an enclosed area causing loss of consciousness. &nhaling refrigerants can cause sudden death. &ntentional inhalation of refrigerants to produce intoxication can cause the heart to cease functioning properly and may be fatal. +e certain that the )efrigerant )ecovery 0ylinder being used is the )efillable Type and has the capacity to contain the refrigerant to be added to its contents. )efrigerant cylinders should never be filled over 75= of their capacity ,li!uid expansion may cause the cylinder to burst-. Gabel the cylinder ith the contents using the appropriate colour code0hec( the &.0.0. cylinder stamp to ensure the cylinder is safe. Alays chec( the refrigerant number before charging to avoid mixing refrigerants. Alays chec( for the correct operating pressure of the refrigerant used. >se gauges to monitor the system pressure. Alays charge refrigerant into the lo side of the system to avoid damaging the compressor, or causing the system to rupture. )$414 and )$43A are very irritating to the eyes and lungs. Avoid exposure to these refrigerants. )$414 is slightly flammable and mixed ith the proper proportions of air may form an explosive mixture. Fluorocarbon refrigerants should be treated as toxic gases. &n high concentrations, these vapors have an anesthetic effect, causing stumbling, shortness of breath, irregular or missing pulse, tremors, convulsions, and even death. Ammonia is a respiratory irritant in small concentrations and is a life threatening ha'ard at :,555 parts per million ,ppm-. Ammonia is also flammable at a concentration of 1:5,555$645,555 ppm Alays stand to one side hen operating an ammonia valve. Ammonia can burn and damage the eyes, or cause loss of consciousness. Ammonia lea(s may be detected by their smell, or ith a sulfur candle or sulfur spray vapor. )efrigerant oil in a hermetic compressor is often very acidic causing severe burns. Avoid s(in contact ith this oil. Gi!uid refrigerant on the s(in may free'e the s(in surface causing frostbite. &f contact ith the s(in occurs, ash immediately ith ater, treat any damaged s(in area for frostbite, and see( medical treatment. 9ever cut or drill into an absorption refrigeration mechanism. The high pressure ammonia solutions are dangerous and may cause blindness if the solution contacts your eyes. Ensure that all li!uid refrigerant is removed and the pressure is at 5 psi before disassembling a system. 8o not smo(e, bra'e, or eld hen refrigerant vapors are present. Iapors decompose to phosgene acid vapors and other products hen exposed to an open flame or hot surface. .hen soldering, bra'ing, or elding on refrigeration lines, the lines should be continuously purged ith lo pressure carbon dioxide or nitrogen. Folloing or(, the lines should be pressure tested ith carbon dioxide or nitrogen. &f refrigerant ma(es contact ith the eyes, immediately ash ith mineral oil as this absorbs the refrigerant. Then ash your eyes ith a prepared boric acid solution. &f the refrigerant is ammonia, ash ith ater for at least 1: minutes. ;ee( medical attention as soon as possible. Purged refrigerants must not be released into the atmosphere. Federal la governs their disposal, and they must be collected and disposed of properly. 8o not allo temperatures here refrigerant cylinders are stored to reach 16: degrees F. Temperatures can easily exceed 16: degrees F in your vehicle during hot eather. &nspect refrigerant cylinders regularly. 8o not use the cylinders if they sho signs of rust, distortion, denting, or corrosion. ;tore cylinders secured and upright in an area here they ill not be (noc(ed over or damaged. +eare of valve spindles and other components hich can fly off because of high pressures. Enough fatal accidents have been reported hich have occurred because of personnel coming in direct line of loose flying off parts fitted on pressuri'ed e!uipments.;pecial 9oteC Alays chec( #;8; before handling any refrigerant and follo all safety re!uirements. Exposure to large concentrations of fluorocarbon refrigerants can be fatal. &n high concentrations, these vapors have an anesthetic effect, causing stumbling, shortness of breath, irregular or missing pulse, tremors, convulsions, and even death. Ta(e care and be safe.%recautions *#en *or?ing in Refrigerated SpacesGBeep refrigerated spaces dry and free of ater and condensate accumulation due to cho(ed drains. #oisture inside refrigerated spaces ill reduce the efficiency of refrigeration by accumulating on the evaporator coils asfrost. &t ill also ma(e the floor slippery and can cause accidents due to slips, trips and falls. Ta(e all personal safety precautions not to inhale any refrigerant vapours hich could have possibly lea(ed out into the chamber hich can also cause chemical poisoning of the human system. Refrigerant ,apour under #ig# temperature can liberate %#osgene gasH *#ic# is #ig#l& poisonous. Alays vent refrigerated spaces for sufficient duration before personnel entry. .hen or(ing in refrigerated spaces ith fro'en cargoes, ear protective arm clothing. .hen or(ing in refrigerated spaces ith chilled cargoes, especially fruits, beare of accumulated poc(ets of carbon$di$oxide and ethylene hich could cause an oxygen deficient atmosphere. This is particularly applicable for controlled, regulated and modifiedatmospheres.&t is safer alays for at least to persons to enter and or( in refrigerated spaces at a time. All personnel should be aare of the push button alarms, nearest escape routes and emergency exits from refrigerated spaces. $ec#anical #aardsPersonnel should be aare at all times that refrigeration systems contain li!uids and vapours under pressure. ;uitable precautions must be ta(en hen opening any part of the system to guard against the pressure ha'ard.0ompressors must be operated ithin their design parameters.$ec#anical #aardsPersonnel must not start the compressor until they have ta(en steps to verify thatC1. All guards on coupling, belts drives, and fans are in place, and other personnel are not in positions that might be ha'ardous hen the plant is in operationD6. The compressor discharge stop valve is open.$ec#anical #aards%pening up part of the system ill necessitate the loss of a certain amount of refrigerant to atmosphere. &t is essential that the amount of refrigerant hich escapes is (ept to a minimum and appropriate steps are ta(en to prevent ha'ardous concentrations of refrigerant accumulating. >nder certain conditions, li!uid refrigerant at lo temperature may be present. 0ontact ith this li!uid must be avoided. Electrical #aards+efore carrying out maintenance or repair procedures, persons concerned must ensure that e!uipment is isolated from the electrical supply and tests made to verify that isolation is complete. .henever possible, precautions must be ta(en to prevent the circuit being inadvertently energised i.e. ithdra the mains fuses. "#emical #aards/0F0 and /F0 refrigerants can present a danger to life by excluding air. &nhalation of very high concentrations of the vapour, even for short periods, must be avoided since this maybe dangerous and can produce unconsciousness or prove suddenly fatal due to oxygen deficiency. The refrigerant vapour is heavier than air, and in static or poorly ventilated situations may be slo to disperse. Anyone suffering from the effects of inhalation of the vapour should move or be moved to the open air."#emical #aards0are must be exercised before entering any area here the presence of high vapour concentration is suspected. The vapour ill displace air upards out of cargo chambers, shipsK engine rooms, etc., and tend to collect at dec( level and in pits and trenches.;hould accidental escape of the refrigerant occur indoors, ade!uate fan assisted ventilation must be used to disperse the vapour, preferably by extraction at ground level, before entering the area. .hen any doubt exists it is recommended that breathing apparatus should be orn."#emical #aards/0F0 and /F0 refrigerants are non$flammable, but refrigerant vapour coming into contact ith temperatures of 21:M0and above ,burning cigarettes, gas burners, electrical heating elements, etc.-, ill de$compose to form phosgene, hydrogen fluoride and hydrogen chloride. These compounds have extremely harmful physiological effect on human beings. 9a(ed flame and smo(ing must be prohibited in the presence of refrigerant vapour and refrigerant must be purged from pipes or vessels before carrying out cutting or elding operations."#emical #aardsApproved methods of lea( detection only should be used. &f a halide test lamp is used, remember that the heating or combustion effect ill produce toxic by$products hich could be dangerous if inhaled."#emical #aardsGi!uid refrigerant in contact ith the eyes or s(in ill cause free'ing and in"uries similar to a burn. 0are must be ta(en hen opening pipes or vessels hich may contain li!uid. Thus it is essential hen loosening a connection on any part in hich refrigerant is confined, goggles to be orn to protect the eyes. Ammonia -R:2:.Ammonia is normally considered to be the most dangerous of the primary refrigerants and has inherent material and physiological ha'ards. A limited range of ammoniaJair mixtures ,13 $ 64=- ammonia by volume can be ignited by flame and an explosion may result. Ammonia must not be alloed to come into contact ith iodine, bromine, chlorine, hypochlorite or mercury. There is an explosion ha'ard in each case.Ammonia ,apourGo concentrations may cause only irritation and discomfort./igh concentrations can destroy body tissue. The action is more pronounced on moist tissuesC eyes, nose, breathing passages, and moist areas of the s(in may be burned by high concentrations.Ammonia )i8uid&n this form ammonia can cause severe burning of the s(in and eyes. As the eyes are particularly delicate organs, even small amounts of ammonia can be harmful. The full effects of ammonia on the eyes may not be apparent for 7$15 days but, ultimately, blindness may result.Ammonia#aintenance procedures must not be carried out unless ade!uate ventilation has been provided to avoid ris( of explosion and physiological harm. 9a(ed flames must not be permitted in the area. The pungency of ammonia ill usually arn personnel against remaining in locations here dangerously high concentrations of vapour exist. Personnel must not be permitted to or( ithout earing a gas mas(, even for short periods, in a concentration hich causes any discomfort to the eyes or affects breathing.5peration of refrigeration plantThe refrigerating capacity of any refrigerating plant is at its maximum hen the greatest possible !uantity of refrigerant is evaporated in the evaporator to obtain the re!uired room temperature or to obtain the re!uired brine temperature. The evaporating temperature and hence pressure must be (ept as high as possible consistent ith the temperatures. For a given design this means ensuring that all heat transfer surfaces are (ept clean, so that the temperature difference across them is at its minimum. &t is also essential to ensure that evaporator surfaces are supplied ith li!uid refrigerant at the correct temperature and in the correct condition.The condensing temperature must be (ept as lo as possible so as to (eep the compressor delivery pressure to a minimum. This again means (eeping all heat transfer surfaces clean and ensuring the correct flo of cooling ater or air through the condenser. &t is also important to (eep air out of the systems as, being non$condensable, it ill collect in the condenser vapour space so raising the effective compressor delivery pressure artificially. As per 8altonKs la of partial pressures, the delivery pressure is the sum of that due to the air and that at hich the refrigerant is condensing. Air in the condenser ill be indicated by an excessively high condenser gauge reading in relation to the temperature of the cooling ater or air. Air can be purged out of the top of the condenser, though some refrigerant ill also be lost ith it.The compressor must be maintained in the best possible condition. This means that suction and delivery valves must not lea( and piston clearance must be (ept to a minimum. The correct operation of unloading devices is also important, as the partial operation of these can affect compressor performance. Ialve lea(age or excessive clearance both result in re$expansion of gas from delivery to suction pressure, and hence in reduced pumping capacity.The temperatures at inlet and outlet of each side of the heat exchanger, if fitted, must be correct to ensure correct superheat and sub$cooling temperatures. The refrigerating capacity of a plant is directly proportional to the eight of refrigerant evaporated in the evaporator. This in turn is directly related to the mass of vapour pumped by the compressor. The latter is the sum of the flash gas formed at the expansion valve and the vapour evaporated in the evaporatorD it is therefore important to (eep the flash gas to a minimum.The mass of refrigerant vapour pumped by a given compressor depends directly on the temperature and hence pressure difference beteen the evaporator and the condenser, and this must be (ept to a minimum. Furthermore, the density of the refrigerant vapour varies directly ith the evaporating pressure and hence temperature, and it is therefore important to (eep the evaporating temperature as high as possible in relation to the re!uired load conditions. The sept column of a given compressor at a constant speed is constant, and the volume pumped varies relatively slightly for normal plants, although for a given condensing temperature it drops rapidly at lo evaporating temperatures, i.e. the volumetric efficiency of a compressor is directly related to the pressure ratio beteen the compressor suction and delivery, hich in turn corresponds to the temperature difference beteen the evaporating and condensing temperatures.A rise in condensing temperature has much less effect on the refrigerating capacity than a corresponding drop in evaporating temperatureD both affect the volumetric efficiency, but loering the evaporating temperature also reduces the density of the gas entering the compressor suction. &t is rong, therefore, to assume that a loer evaporating temperature ill improve the refrigerating capacity. .hile heat transfer may be improved in the evaporator, this is much more than counterbalanced by the reduced eight of gas pumped by the compressor, due to its reduced density as ell as to the reduced compressor volumetric efficiency.$AINTENAN"EThe plant ill need a minimum of care and maintenance if it is (eptC1. free of moistureD6. free of impuritiesD2. free of freon lea(sDA. free of frost.Experience has shon that most problems ith marine refrigerating plant involve refrigerant shortage caused by lea(age. &n rooms here fro'en or chilled cargo belo :M0 is carried, it is necessary to (eep evaporators free from frost. 0leaning of filters is also important.&n cases here e!uipment is opened up, neither air nor moisture must enter the refrigeration system, as either ill cause trouble, e.g. in the form of increased condensing pressure. To avoid moisture, filter driers are installed in /0F0J/F0 plants. The drying agent should be changed every time any part of the system is opened. This also applies hen charging ith oil or refrigerant. %il should not be filled from vessels that have not been tightly closed.Drop in oil levelA lea(age$free refrigerating plant does not consume any oil. The oil hich has disappeared from the cran(case or oil separator is alays somehere in the system.5il level drops 8uic?l& at t#e startThis may be due to refrigerant being dissolved in the oil. At evaporation the oil is dran ith the refrigerant into the system. Fill the system ith a small !uantity of oil, as the e"ected oil ill gradually come bac(.5il level drops slo*l&1. the plant is operated at loer evaporating temperature than usual or the refrigerant charge is too smallD6. refrigerant lea(age in the system, by hich the level in the evaporator has become too loD2. condensing temperature is too lo, the minimum condensing temperature should be maintainedDA. the cooling demand is too lo, so the gas velocity becomes too lo in the evaporator and the oil remains in the system.&n those plants ith piston compressors hich have oil separators, the shut$off valve in the oil return line should alays be (ept closed for about 1J6 hour after compressor start in order to avoid the carriage of condensate from the oil separator to the cran(case.'rine specific gravit&&n those cargo refrigerating plants here brine serves as the heat transfer medium, it is of great importance that the correct brine specific gravity for the re!uired cargo temperature is maintained. &f this specific gravity is not chec(ed, functional problems may occur.0alcium 0hloride +rineDail& maintenanceThe daily maintenance for a )66 installation should be completed as follosC1. 0hec( that condensing pressure and evaporating pressure are correct.6. &nspect the compressor unit and chec( that there are no abnormal noises or vibrations.2. 0hec( the oil level.A. 0hec( the tightness of the shaft seal. %il lea(age can be tolerated hereas gas lea(age can not.:. &f an oil separator is installed, chec( that oil is returned to the cran(case, and that the oil return line is armer than the cran(case.)ea? detection)efrigerating plants must be gas$tight to prevent refrigerant lea(age and air entering the lo$pressure side hen under a vacuum. ;ystems hich have been opened to the atmosphere during repairs, must be pressure tested for mechanical strength and lea(s before charging ith refrigerant.%ressure testsPressure tests should be done ith nitrogen. .ater or other fluids must not be used as a test medium. The plantKs compressors must not be used to pressurise the plant. The pressure isgradually increased by pressurising ith nitrogen gas the pressure is e!ual to 1.: times the maximum or(ing pressure of the system. This pressure should be maintained for about 15 minutes.Each "oint must be examined thoroughly for signs of gas bubbles hich indicate a lea(. After sealing any lea(s, pressurise the system again ith the test medium and some refrigerant as a trace gas, and repeat the lea( test using an electronic lea( detector, etc. &t is imperative that all lea(s are found and sealed before the system is charged ith refrigerant, as even the tiniest of lea(s can result in the loss of the hole refrigerant charge.Leak detection equipmentElectronic leak detectorsElectronic lea( detectors are the most sensitive and accurate method of lea( detection. The detector contains an internal pump that dras air into a probe, or tube. &f refrigerant gas is present in the sample, the electrodes in the sensing element generate a current, and an output signal is obtained.Halide lamps/alide lamp is used to locate lea(s of/0F0 refrigerants. This method is based on the colour of a flame that surrounds a gloing copper element. The flame turns blue$green if the air being consumed contains the refrigerant.These lamps should only be used in ell ventilated spaces.Routine inspectionsThe high pressure side of the system may easily be tested for lea(s ith the plant running, but it may be necessary to stop the compressor, and allo the pressure in the lo pressure side to rise sufficiently for lea( test in the lo pressure side. The amount of refrigerant in the system should also be strictly monitored as a drop in level may indicate the presence of a lea(. &n the event of a ma"or lea(, the initial lea( test should be made using the soap bubble method, specially in areas here there are signs of an oil lea(. Dr&ing b& evacuation This method of removing moisture is based on the fact that the boiling point of ater decreases ith falling pressure. &n the course of evacuation, any ater or ice in the plant ill evaporate, and is carried aay by the vacuum pump.1. 0onnect a vacuum pump to the system using a short length of large bore pipe, and open all valves in the system ,expansion valves, solenoid valves, etc., may have to be "ac(ed open-.6. Evacuate the system to a pressure of 3mm /g or less. &f possible, carry out the evacuation at ambient temperatures above 15M0.2. 0lose the line beteen the system and the vacuum pump. The pressure in the system may not rise more than 6mm /g ithin five minutes. A rise of more than 6mm /g indicates the presence of ater, andJor a lea(. .here ater is present, the system ill be colder than its surroundings.A. 0hec( for ater andJor lea(s, carry out any repairs, and repeat the evacuation procedure until the pressure rise is less than 6mm /g. .hen this is achieved the system is free of moisture and non$condensable gases and ready for refrigerant charging."#arging procedures)efrigerating plants should not be overcharged ith refrigerant, as this may overload or damage the compressor.To ensure that the correct amount is added, the refrigerant should be eighed during charging.The li!uid refrigerant is decanted from the refrigerant bottle into the system via a charging valve "ust after, the li!uid receiver."#arging %rocedure1. .eigh refrigerant bottle6. 0onnect refrigerant bottle to charging valve ith flexible charging line.2. 0rac( bottle li!uid valve before tightening line to blo out air. A. 0lose main li!uid line valve and pump don system.:. %pen charging valve and carefully open li!uid valve on refrigerant bottle.3. Gi!uid refrigerant ill flo into the system.4. ;tart compressor.7. 0ontinue charging until re!uired amount of refrigerant has been charged.