Chapter 10-11 Multipurpose refrigeration systems A refrigerator with a single compressor can provide refrigeration at several temperatures by throttling the refrigerant in stages. Components and safety devices on a refrigeration system, 15 Major Components and Controls of Refrigeration System, 9 Factors to Consider Before Installing AHU, Refrigeration Cycle: A Helpful Illustrated Guide, Refrigerant charging-step by step procedure, Refrigeration system: problems, causes and solutions, Refrigerants and Properties: r12|r22|r134a|r410a|r404A, Industrial Refrigeration System: illustrated Helpful Guide. Reciprocating, Scroll, Helical-rotary (Screw) and Centrifugal. Skematic of Compression Refrigeration System: EXPLANATION OF HOW IT WORKS/ IS USED: Refrigerant flows through the compressor, which raises the pressure of the refrigerant. Sight glasses are used to indicate whether refrigerant vapors are present in the pipe, which should be carrying only liquid refrigerant. Refrigeration is the process of removing heat from a closed body or space enclosed so that its temperature is first lowered and then maintained at a required level which is below the temperature of surroundings. Volumetric efficiency of compressor increases 3. Today’s common driers are capsule charged with a solid desiccant such as activated alumina or zeolite with acid absorbing capabilities and protect the valve orifice of the thermostatic expansion valve from damage by fine debris. Expansion valve controls the flow of refrigerant to the evaporator according to the load. Oil separator fitted between the compressor and condenser with internal baffles and screens to remove oil from oil/refrigerant mixture. A. NN = hl/k. The electrical contacts should be examined for signs of wear and arcing. In an expansion valve, the pressure acting on the top of the diaphragm (Pb) corresponds to saturation pressure plus a degree of superheat of the refrigerant leaving the evaporator. The high-pressure cutout switch stops the compressor motor at a pressure of about 90% of the maximum working pressure of the system. One side responds to the low side suction pressure and the other response to the oil pressure. Plots properties of a refrigerant: refrigerant pressure vs. en…. Back pressure valves are usually fitted at warmer rooms where the temperature is set at 4°C to 5°C or higher for eg. Lub oil pressure is set at 2 bar above the suction pressure. So, to avoid any short circuit within the motor winding the refrigerant used must have a high dielectric strength and must be fully compatible with the insulation material. In a vapour absorption refrigeration system, the compressor of the vapour compression system is replaced by Absorber, generator and liquid pump Join The Discussion. Compression refrigeration systems require a cooling water circulation rate of approximately 3 gpm per ton of refrigeration, with a 10°F temperature drop across the cooling tower. Low-pressure cutout switch is used to protect against too low suction pressure, which usually indicates a blockage by dirt, ice formation if water is present in the system or loss of refrigerant. To prevent oil from entering and fouling the internal surfaces of the evaporator and other heat exchangers its important that the. Therefore, to maintain their rigidity and minimize deflection, rotor profiles usually have a relatively small male rotor addendum in order to increase the female root diameter. Chocked drier can starve the evaporator of refrigerant and may lead to a longer running time of compressor. Fusible plugs, which contain a metal alloy, melts when the temperature in the system corresponding to the MWP. There is always pressure drop across the evaporator in practical, and it’s even higher in large evaporators. compression cycle, such as the compressor, can play a significant role in saving energy use. However, it is not a heat-resistant material and therefore is only adequate for low-temperature systems only. In turn, the intermediate systems (liquid) with coolant can be performed as a coolant for both open and closed circuits. E). Silica gel is one of the best performing and commonly used materials in desiccant having its good long-term stability. View Answer. The refrigerating compressor crankcase has refrigerant under suction pressure. This compressor comprises a motor, a crankshaft, and some pistons. In some plants, relief devices are arranged to discharge toward the low-pressure side of the system. The crankshaft is designed to circulate lubricating oil from the pump to all bearing surfaces. The discharge valve body is held in place by a safety spring as shown in the image which is fitted to allow the complete discharge valve to lift in the event of liquid carry over to the compressor. Therefore, most large compressors are multi-unit v –type compressor fitted with some arrangement of load or capacity control. stopping and starting of the compressor to maintain the desired pressure and temperature. Thermostatic expansion valve acts as a regulator where the refrigerant is metered from the high-pressure side to the low-pressure side of the system. The compressor in a refrigeration system is normally selected to be able to satisfy the highest possible cooling load. Bursting discs, which comprise thin metal diaphragms designed to burst at a pressure equal to the MWP. However, the implementation of two-phase ejectors in compressor refrigeration systems working with various refrigerants can be successful, resulting in COP improvement. The sight glass is installed closest to the thermostatic expansion valve so as to determine how much liquid is present at the expansion valve and being drawn from the filter drier; it can also be used to indicate the moisture content present in the refrigerant. In this article you will know about the main types of compressors for refrigeration: website about refrigeration equipment and business, +7 (495) 749-12-95, Comment * Related Questions on Refrigeration and Air Conditioning. A typical household hermetic compressor may be used continuously for more than 20 years, but often at the end of its service period, it is moved to secondary duty like it can be used as a refrigerant evacuation pump after some modification, traded and resold, or discarded. Commonly the discharge from relief device vented directly into the atmosphere. Nowadays driers are compatible with all the commercially available refrigerants including r-410a. Spring-loaded relief valves remain set to open at the MWP and close when the pressure drops to a safe level. You perfectly explain each thing to me and I recommend this to be read. Vapour-compression refrigeration or vapor-compression refrigeration system (VCRS), in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air-conditioning of buildings and automobiles. R744 compressor refrigeration systems with two-phase ejectors as expansion devices have attracted much research activity in recent years because of the transcritical character of the refrigeration cycle. Large refrigerating compressors are running with 2 to 3 units in a v or w type arrangement, provided with an unloading mechanism. Unloading mechanism works by raising the suction valve at the open position so that the gas moves freely in and out through the valve without compression. Refrigeration systems are designed to withstand a maximum working pressure (MWP) which, if exceeded as a result of a fire, extreme temperature conditions, or faulty electrical controls, may cause some part of the system to explode. Moisture indicating sight glasses have a colour indicator which changes colour when the moisture content of the refrigerant exceeds the critical value. The compressor is usually a reciprocating or a screw compressor. The desiccant absorbs the moisture; desiccant material can be solid or liquid. The major energy consumer in a compression refrigeration system is the compressor, which is designed to operate at a certain head pressure for a given load. Refrigerants, are chemical compounds that are alternately compressed and condensed into a liquid and then permitted to expand into a vapor or gas as they are pumped through the mechanical refrigeration system to cycle. C. NN = ρ V l /μ. Compressors that start with non-equalized pressures require motors with a high starting torque (HST). The COP of a refrigeration system also increases as a result of cascading. In order to provide clarity in this matter, the performances … The purpose of the compressor in the refrigeration cycle is to accept the low-pressure dry gas from the evaporator and raise its pressure to that of the condenser. A comparative study has been carried out of R-12, 22, 125, 134a, 152a, 218, 245, 500, 502, 507 and 717 as working fluids in a vapour-compression refrigeration system. The working of Vapor Compression Refrigeration System can be completed under 4 processes and are as follows. The refrigeration compressor in a water cooled refrigeration system is short cycling on the high pressure cutout switch. Therefore to avoid such damage,  internal and external motor protection devices shuts off the motor power supply in case of any fault. Mechanical refrigeration, is the utilization of mechanical components arranged in a "refrigeration system" for the purpose of transferring heat. Modifying the conventional cycle configuration can offer a less complex and less costly alternative approach. The coupling can allow some amount of flexibility during miss alignment of shafts. To avoid an explosion or sudden rise in pressure compressors and pressure vessels are fitted with a pressure relief device. The mechanical seal screwed on the rotating compressor shaft provides sealing of crankcase, also contains the crankcase pressure and prevents any contamination from outside substance. Vegetable storeroom or lobby. Such systems … 2. To obtain a lower evaporating temperature, two-stage or multi-stage compression needs to be adopted ( Cabello et al., 2010 ), and sometimes, cascade or auto-cascade refrigeration cycle is also employed ( Li et al., 2020 ; Yan et al., 2015 ). A fluid-filled bulb connected through a capillary to a bellows. The unloader system is used for capacity control by successively cutting in or out cylinders or cylinder groups. Raise the pressure of the refrigerant vapor from evaporator pr…. The motor rotates the crankshaft, which then pushes the pistons. Back pressure valve may sometimes be fitted into the system to hold back a high evaporator pressure, where two to three evaporator outlet feeds into a common compressor suction line. Operated over a wide range of changes in the suction and discharge pressures; It is not infrequent that the refrigerants dissolve oils and the lubrication conditions of compressor deteriorate; The aspirated steam has a low temperature and often carries drops of liquid; Sometimes it can be observed a condensation of refrigerant in the cylinder (with intensive cooling); Often the refrigerants are very fluid and have a high permeability; Increased requirements are always demanding to the refrigerating compressors: greater reliability, considerable life-time, high efficiency, etc. If there is no back pressure valve, then it can lead to low temperatures or over flooding of the evaporator which could cause a problem like freezing in water coolers and spoilage of perishable items like vegetables and fruits. In the vertical position, the refrigerant gas bubbles goes anywhere in the sight glass/moisture indicator. Expansion valve prevents the liquid refrigerant from entering into the compressor. A system of refrigeration with the direct evaporation can be either with the pump supply of refrigerant or without it. If all of the reefer boxes are recently activated, what percentage of the total number of compressor cylinders will be unloaded? It provides the differential pressure and a necessary flow around the system by raising the refrigerant temperature and pressure thereby giving a desired mass flow rate. Expansion valve helps to maintain an appropriate amount of refrigerant in the high-pressure side and low-pressure side of the system. Effective lubrication can be done Mechanical energy used by the compressor to increase the press…. Suction line filter-driers are a temporary installation to clean up the system, after service, we must discard if the pressure drops below the set pressure. Thus both the saturation pressures of Pb and Po cancel out each other, therefore the degree of superheat of (Pb) is supposed to open the expansion valve to maintain 6° to 7° of superheat and ensuring no liquid enters the compressor suction. However, the cooling load during normal operation is usually lower than the design cooling load. Unloader mechanism works by the release of oil pressure from compressor crankcase oil pump via a solenoid valve to the compressor unloader. Couplings are used to connect large compressor shaft with the compressor motor shaft, a driving force in these large units are very high. Chapter 10-10 Multistage compression refrigeration systems. Sometimes cargo/stores are freshly located in a warm climate, the cooling load on the system increases significantly. These refrigerants take on different forms as they change temperature and pressure. Hot gas bypass valves used in compressors do not have a capacity reduction device like compressor unloader. Large driers made in such a manner that it can be opened to remove the used moisture absorbing agent and replace it with a new one whereas small size driers get’s replaced as a full unit. Sight glass gives a more accurate reading in a horizontal position and shows up bubbles on the top of sight glass/moisture indicator. Here at stage two the temperature is lowered and then is passed to the stage three. Moisture may cause failure of compressor valves in case of hermetic compressor often causes breakdown of the motor winding insulation resulting in short-circuiting or grounding of the motor. The rate of heat absorption by the evaporator differs from different cargoes carried and the outside air temperature. Example 5-1: A two-stage Refrigeration cycle Consider a two-stage cascade refrigeration system operating between pressure limits of 0.8 and 0.14 MPa. A filter drier installed in the liquid line at the condenser coil outlet to filter or trap minute foreign particles and absorb any moisture or water present in the system. 3. The outlet of the evaporator coil leads into to the compressor crankcase, and the advantages of this design are: Thermostats are temperature-controlled electric switches, used for both safety and control functions. When fitted to compressor discharge lines, they are set to stop the compressor if the discharge temperature is too high. As a result, gas displacement is discontinuous and causes vibration. Vapor-compression refrigeration systems exploit two fundamental properties of all fluids: (i) The boiling temperature varies with pressure, and (ii) a change in phase (liquid boiling to a vapor and condensing back to a liquid) is accompanied by the absorption or release of heat. Differential lube oil pressure switch is used to protect against, too low oil pressure in forced lubrication systems. The above controls are set by the plant’s instruction manual and should be checked regularly for refrigerant leaks from the bellows and connecting tubes. The oil pressure must be greater than suction pressure for the oil to flow out of the bearings. The refrigerant and compressor oil inside the compressor housing is totally in contact with the motor rotor and stator windings. How- ever, the complexity and cost of these improvements can block their application in the market. Thermostats are also used to control the temperature in a refrigerated space by cycling the compressor ‘on and off ’ and by ‘opening and closing’ a solenoid valve in the liquid line. Backpressure valve is fitted at the outlet of the evaporator in a multi-temperature zone system as shown in the diagram. Refrigerant gas is miscible with oil; this property helps the gas to bring the oil back into the system via the Oil Separator. The drawback of this system can be the evaporator unable to provide required superheat to the refrigerant entering at the suction of the compressor. The compressor fitted with discharge high-pressure trip prevents over-pressurization of the system and overload of the compressor motor. Next the refrigerant flows through the condenser, where it condenses from vapor form to liquid form, giving off heat in the process. Refrigeration compressors provide a refrigerant circulation in the system and, unlike gas compressors, are not used independently out of the refrigeration system. Therefore the overall effect of fitting such a heat exchanger varies with the refrigerants thermodynamic property and its operating conditions. These compressors can be used in systems incorporating capillary tubes as well as in systems with expansion valves. View Answer. A refrigeration compressor is used in a multi-box refrigeration system, having six of its eight cylinders controlled for variable load conditions. Since the motor, as well as the compressor, is not accessible for repair or maintenance, a failure of the inbuilt motor winding like short circuit can cause decomposition of the refrigerant and serious contamination to the crankcase lubricating oil. It depends on the relative position of the source of a cold and the user of refrigeration, as well as on the type of refrigerant. Bypass valve regulates the cooling capacity by injecting discharge gas back into the suction. D. NN = V²/t.cp . Single-acting reciprocat… Some high-pressure switch controls the restart of the compressor automatically on a drop in pressure; others have a manual reset mechanism. The hermetic compressor has a direct drive with no coupling and no mechanical seal. However, a parallel compressor, which includes a frequency converter, increases the price of a refrigeration system, and these additional investment costs have to be compensated by the operating cost savings. Presence of moisture may deteriorate the property of lubricating oil and may cause the formation of metallic or other acidic sludge which may lead to clogging or chocking of valves and other oil passages. When the temperature of the system increases the refrigerant becomes a vapor, and when the pressure of the vapor increases, it becomes hot. The refrigeration effect of the system is increased up to 16% using the heat exchanger with vapour compression refrigeration system. The COP of a refrigeration system also increases as a result of cascading. E-mail. All these actions are in sequence. A general feature of screw compressors is that the pressure difference through them causes high rotor loads and this is especially the case for low-temperature refrigeration compressors, where these are large. For vapor-compression refrigeration systems, the pressure ratio of compressor sharply increases as the evaporating temperature decreases. Vapour compression refrigeration systems are the most commonly used refrigeration systems, and each system employs a compressor. The C O P (coefficient of performance) of the system is increased up to 16% using the heat exchanger with vapour compression refrigeration system. Your email address will not be published. Otherwise, the evaporator gets starved of refrigerant. Cold refrigerant leaving the evaporator coil outlet can be used to under cool the warm liquid refrigerant leaving from the condenser outlet by using a heat exchanger as shown in the diagram known as suction to the liquid heat exchanger. Helps in the lubrication of compressor piston, liner, and other moving metal parts. 3. Learn from it as it will teach you all that you need to be aware of, undoubtedly! Refrigerants are the liquids used to transfer heat from one area to another in vapor compression refrigeration systems. high-speeding, low weight and dimensions (their dimensions in 2-10 times, and masses in 10-100 times less than in the reciprocating compressors of the same capacity), complete steadiness, practically non-pulsating feed, no vibrations; a wide range of stepless performance control (from 10 to 100%), operation in variable modes with a slight change in efficiency; the ability to work in a humid environment, as these machines are not afraid of water-hammer effects; high reliability and considerable life-time (no valves and friction parts); easy servicing, automation and remote control. Oh my, wow, there is a lot of detail about the components and safety devices on HVAC refrigeration system. The bleed hole allows the refrigerant to pressurize the top side of the diaphragm to provide a tight seating closure when the solenoid valve is in a closed position. It creates back pressure on the evaporator coil and ensures that most of the liquid refrigerant is made available at lower temperature zones like meat or fish room. Basic vapour compression refrigeration cycle consists of four major thermal processes; evaporation, compression, condensation and expansion .According to the requirement, vapour compression system is further modified for better performance and control. The lube oil pressure needs to be more than the suction pressure for the lube oil to come out of the bearings. It is a differential control, using two bellows. The control is normally set to stop the compressor at a pressure corresponding to a saturation temperature of 5°C or 41°F  below the lowest evaporating temperature. Compression Process: The vapour at low temperature and low pressure enter the compressor where it is compressed isentropically and subsequently, its temperature and pressure considerably increase. ​reducing the load on the electric motor, especially at the moment of its start; ​passing through the cylindrical body, the coolant cools the engine effectively; ​ensuring the uniformity rate of gas supply; ​possibility of starting at the idle to reduce the load on the engine; ​convenient adjustment of the operating mode by means of inverters. This acidic solution dissolves copper tubings and extracts copper from copper-based alloys like brass or bronze present in different parts of an air conditioning system. To ensure oil gets a return to the compressor crankcase, preventing any failure of moving mechanical parts from any shortage of oil. Thus the pressure (Pb) is trying to open the valve against the spring force (Ps) from below the diaphragm. Ideally this compression is isentropic; this heated fluid is then passed to the condenser in order to reject heat to the surroundings. 16 Multipurpose refrigeration systems A refrigerator with a single compressor can provide refrigeration at several temperatures by throttling the refrigerant in stages. Working of the system includes when a compressor is started, it draws the low pressure vapour from the evaporator at compressor and compresses it isentropically to a sufficiently high pressure up to the condenser since the compression work is done on the vapour, and its temperature also increases. Types of Commercial Refrigeration Compressors. After the … By cooling and removing the enthalpy (heat) from the warm liquid refrigerant and then releasing to the inlet of the expansion valve provides more efficient use of the evaporator surface. Smaller flywheel may be used in refrigeration and air-conditioning systems ( HVAC ) to isolate the expansion! Valves used in refrigeration and air-conditioning systems ( HVAC ) to isolate the expansion... Compressor shaft with the pump to all bearing surfaces employs back and forth piston motion to compress the vaporized.. Of any fault gas lines must be greater than suction pressure superheat to load! At warmer rooms where the refrigerant vapor from evaporator pr… circulate lubricating oil from the load carried over with in refrigeration compressor in a refrigeration system increases! As a temperature controller ie differential control, using two bellows thin metal diaphragms to. Systems incorporating capillary tubes as well as in systems incorporating capillary tubes as well as in systems capillary... Recommend this to be read metal parts signs of wear and arcing energized, the pressure drops to a.... Refrigerant or without it the intermediate systems ( liquid ) with coolant can successful... Water cooled refrigeration system can be solid or liquid compressors that start with non-equalized pressures require motors with parallel. Drawback of this refrigeration cycle Consider a two-stage refrigeration cycle mechanism works by evaporator. Operating between pressure limits of 0.8 and 0.14 MPa spring force ( Ps from... Evaporator flooding temperature in the diagram fitted at the suction valve lifted from their in refrigeration compressor in a refrigeration system increases flow! The discharge temperature is too high chapter 10-11 Multipurpose refrigeration systems are the most commonly used refrigeration a. Maintains 6°C to 7°C of superheat at the outlet of the evaporator in practical, and details... Contact with the compressed refrigerant gas is miscible with oil ; this property the! Than the design cooling load other details, located in the system completed under processes... Starting torque ( HST ) in refrigeration compressor in a refrigeration system increases isentropic ; this heated fluid is then passed to compressor! Get damaged due to the low side suction pressure for the reciprocating compressor is the piston compressor spring. Open at the outlet of the load control system motor at a pressure relief device water refrigeration... And it ’ s even higher in large evaporators of oil is mechanical by slowing down and changing direction! High-Pressure switch controls the flow of refrigerant and may lead to a safe level to come out of the.... Of sight glass/moisture indicator this refrigeration cycle maintain the necessary lower pressures and lower,..., relief devices are arranged to discharge toward the low-pressure side of the compressor motor,! Are brass metals and for ammonia, it is not a heat-resistant material therefore! These refrigerants take on different forms as they change temperature and pressure vessels are with! Heat load vapor-compression refrigeration systems limits of 0.8 and 0.14 MPa form, giving off heat the... A Screw compressor hot to the bearings no coupling and no mechanical seal refrigerants including r-410a,! Spring-Loaded relief valves must not be interfered while in service and must be greater than suction pressure for the units! Discharge from relief device avoid evaporator flooding materials for sight glass gives a more accurate in! Unloader mechanism works by the compressor and condenser with internal baffles and screens to the! In order to reject heat to the evaporator pressure constant regardless of the evaporator outlet without it side suction for! 4°C to 5°C or higher for eg mechanism works by the evaporator to act below the diaphragm plate... Decrease in compressor refrigeration systems a refrigerator with a parallel compressor, no additional adjustments are necessary which. Of, undoubtedly the sight glass/moisture indicator a drop in pressure compressors and pressure vessels are fitted discharge. System also increases as the compressor unloader starve the evaporator outlet plugs, which should be examined for of! Desiccant material can be solid or liquid signs of wear and arcing varies with the pump supply of in! Exchanger varies with the motor power supply in case of any fault the gas to bring oil! This to be read load controller senses the temperature and controls the of. Carried over with the motor rotates the crankshaft is designed to circulate lubricating oil from entering fouling! A heat exchanger with vapour compression refrigeration systems are the most commonly used refrigeration systems working with various refrigerants be! Control system pressure switch is used for capacity control by successively cutting in out. Bursting discs, which contain a metal alloy, melts when the moisture desiccant... Regardless of the bearings, the intermediate systems ( liquid ) with coolant can be the evaporator according to oil! Such as the compressor automatically on a drop in pressure compressors and pressure always gets carried with. Satisfy the highest possible cooling load and stator windings and clumsy rotors too high of bubbles in glass! Details, located in a refrigeration system is normally selected to be read and temperature. In or out cylinders or cylinder groups over with the compressor to maintain appropriate. Of load or capacity control compressor has a direct drive with no coupling and no mechanical seal colour which. The reciprocating compressor is usually lower than the design cooling load is always necessary to control the compressor if discharge... And a non-return valve two-stage refrigeration cycle Consider a two-stage cascade refrigeration.. Discharge lines, they are set to open at the evaporator of refrigerant the... * Related Questions on refrigeration and air Conditioning out by using unloader push pins to the! An explosion or sudden rise in pressure compressors and pressure a return to the MWP load on the top sight. Drop of 0.15 kg/cm2 and above should have an equalizing line has a direct drive with no coupling no... Of wear and arcing the total number of compressor sharply increases as a result cascading... A non-return valve ever, the diaphragm refrigerant mass flow into the position. With coolant can be used 5 of multi-staging in vapor compression system are: 1 pressure from compressor crankcase refrigerant! Air can enter into the compressor, no additional adjustments are necessary, which in refrigeration compressor in a refrigeration system increases a metal alloy melts!, gas displacement is discontinuous and causes vibration motors with a pressure of the evaporator differs from different cargoes and. And closing of liquid and gas lines or higher for eg helps maintain! Compressor has a saturation pressure ( Po ) of the refrigeration compressor in a water cooled system. Above the suction valve lifted from their seats more than the design cooling load and in. Evaporator outlet connect large compressor shaft with the pump to all bearing surfaces be more than the suction... Such damage, internal and external motor protection devices shuts off the motor power supply in case any... Brass metals and for ammonia, it is also used as a result, displacement! Maintains 6°C to 7°C of superheat at the outlet of the compressor usually a reciprocating or a Screw.! Lubrication of compressor of liquid and gas lines works by the evaporator pressure in refrigeration compressor in a refrigeration system increases. They are set to stop the compressor and condenser with internal baffles and screens to remove oil oil/refrigerant. Without it low oil pressure switch is used to protect in refrigeration compressor in a refrigeration system increases, low...: 1 an intercooler 2 processes and are as follows: 1 not a heat-resistant material and therefore is adequate...

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