Chapter 01 - Refrigeration Principles.ppt

March 31, 2018 | Author: LaminTun | Category: Air Conditioning, Refrigerator, Refrigeration, Evaporation, Electromechanical Engineering


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Student CD forCommercial Refrigeration for A/C Technicians Chapter 1 Refrigeration Principles Chapter 1 Overview • • • • Temperature ranges of refrigeration Refrigeration cycle Relate refrigeration to air conditioning Relationship between a refrigerant’s pressure and its temperature • Newer refrigerants used in commercial refrigeration systems • Relationship between the 4 basic components of a refrigeration system Copyright 2006 Thomson Delmar Learning 2 . Common Space & Product Temperatures • • • • • Air Conditioning = 24° C High temperature refrigeration = 12°C Medium temperature refrigeration = 2°C Low temperature refrigeration = -23°C Extra low temperature refrigeration = -32°C Copyright 2006 Thomson Delmar Learning 3 . . but . Condenses as heat is rejected 3. . • Refrigerant: 1. Then the vapor superheats after all refrigerant has evaporated Copyright 2006 Thomson Delmar Learning 4 . Temperatures drop as discharge gas cools 2. . but .Simple A/C System • A compressor + two tanks + metering device is used to illustrate a simple A/C system: – High pressure stays the same. . Sub-cools before entering the TEV – Low pressure stays the same. • Refrigerant: 1. Temperatures rise as liquid vaporizes and absorbs heat in the evaporator 2. Simple A/C System AMBIENT AIR 95o 165o 278 psig 175o 69 psig 60o RETURN AIR 75o 50o 40o 125o 125o 115o 40o 105o Copyright 2006 Thomson Delmar Learning 40o 5 . Simple Medium Temperature Refrigeration System • Compare the previous A/C system illustration to the following refrigeration system: – Are the high side pressures and temperatures of both systems different? Why or why not? – Are the low side pressures and temperatures of the two systems different? Why or why not? Copyright 2006 Thomson Delmar Learning 6 . Simple Medium Temperature Refrigeration System AMBIENT AIR 95o 165o 278 psig 175o 49 psig 45o RETURN AIR 35o 35o 25o 125o 125o 115o 25o 105o Copyright 2006 Thomson Delmar Learning 25o 7 . “Standard” A/C System with fixed metering device The following slide is an example of what happens to refrigerant in an A/C system: • Compressor discharges hot gas • Gas condenses to liquid. absorbing heat • Returns to the compressor Copyright 2006 Thomson Delmar Learning 8 . releasing heat • Metering device lowers pressure • Refrigerant vaporizes. Standard A/C System R-22 69 psig 278 psig 175º 60º 40º 125º CONDENSER 125º EVAPORATOR 115º 40º 50º AMBIENT AIR 95o Copyright 2006 Thomson Delmar Learning RETURN AIR 75o 9 . Standard A/C System R-22 Total Superheat 20° 69 psig 278 psig Super Heated Vapor 175º 60º 40º 125º Evaporation Starts CONDENSER Condensing Starts EVAPORATOR 125º Fully Evaporated Fully Condensed Liquid Sub-Cooled Liquid 115º Coil Superheat 10° AMBIENT AIR 95o Copyright 2006 Thomson Delmar Learning 40º 50º RETURN AIR 75o 10 . Commercial Refrigeration System with a TEV metering device Comparing A/C to Refrigeration systems: • Same ambient. same high side pressures and temperatures • Lower space temperature. low side pressures and temperatures are lower than those on the A/C system Copyright 2006 Thomson Delmar Learning 11 . Typical Walk-In Refrigerator (R22) 50 psig 280 psig 175º 45º 125º 25º TEV CONDENSER 125º EVAPORATOR 115º 25º 35º AMBIENT AIR 95o Copyright 2006 Thomson Delmar Learning BOX TEMPERATURE 35 12 . Total Superheat 20° 50 psig Typical Walk-In Refrigerator (R22) 280 psig Super Heated Vapor 175º 45º 25º 125º TEV Evaporation Starts CONDENSER Condensing Starts EVAPORATOR 125º Fully Evaporated Fully Condensed Liquid Sub-Cooled Liquid 115º 25º Coil Superheat 10° AMBIENT AIR 95o Copyright 2006 Thomson Delmar Learning 35º BOX TEMPERATURE 35 13 . 134a Reach-in freezers – R404A Note: after 2010.Current refrigerants used in most new refrigeration systems • • • • • Walk-in refrigerators – R22 and R404A Walk. manufacturers will not be allowed to produce equipment with R22 • Note: R404A must be charged in a liquid state Copyright 2006 Thomson Delmar Learning 14 .in freezers – R404A Reach-in refrigerators – R22. R404A. Condenser • Rejects heat from the refrigerant as vapor condenses Copyright 2006 Thomson Delmar Learning 15 . Evaporator • Absorbs heat as refrigerant evaporates 3. Compressor • Increases the refrigerant temperature above the ambient temperature 4. Metering device • Lowers the refrigerant temperature below the space temperature 2.The Four Basic Components of a Refrigeration System 1. Basic Components and Piping Discharge Line Compressor Suction Line Condenser Metering Device Liquid Line Evaporator Copyright 2006 Thomson Delmar Learning 16 . Refrigeration System “Baseball Diamond” • The 4 components can be illustrated in the shape of a baseball diamond • Half the system is high pressure • Half the system is low pressure Copyright 2006 Thomson Delmar Learning 17 . Basic Components Metering Device “Baseball Diamond” Li qu i Lo Evaporator Su ct io n w Si igh deH d Li n e e d i S Li ne h c is D ge r a ne i L Condenser Compressor Copyright 2006 Thomson Delmar Learning 18 . Copyright 2006 Thomson Delmar Learning 19 .
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