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Air Conditioning Clinic Refrigeration Cycle One of the Fundamental Series TRG-TRC003-EN ...
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NO POST AGE NECESSARY IF MAILED IN THE UNITED ST A TES BUSINES S REPL Y MAIL FIRST -CLAS S MAIL PERMIT NO. 11 LA CROS SE, WI POST AGE WILL BE P AID BY ADDRESSEE THE TRANE COMP ANY Attn: Applications Engineering 3600 P ammel Creek Road La Crosse WI 54601-9985 NO POST AGE NECESSARY IF MAILED IN THE UNITED ST A TES BUSINES S REPL Y MAIL FIRST -CLAS S ...
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P erforation 5.5” from bottom/top P erforation 0.75” from edge Comment Card We want to ensure that our educational materials meet your ever -changing resource development needs. Please take a moment to comment on the effectiveness of this Air Conditioning Clinic. Refrigeration Cycle Level of detail (circle one) T oo basic Just right T oo diffic ...
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Refrigeration Cycle One of the Fundamental Series A publication of The T rane Company— W orldwide Applied Systems Group ...
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Preface © 1999 American Standard Inc. All rights reserved TRG-TRC003-EN ii The T rane Company believes that it is incumbent on manufacturers to serve the industry by regularly disseminating information gathered through laboratory research, testing programs, and field experience. The T rane Air Conditioning Clinic series is one means of knowledge s ...
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TRG-TRC003-EN iii Contents period one Heat and Refrigeration ....................................... 1 What is Heat? ......................................................... 2 Principles of Heat Transfer ...................................... 4 period two Refrigerants ............................................................ 9 Change of Phase . ...
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iv TRG-TRC003-EN ...
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TRG-TRC003-EN 1 notes period one Heat and Refrigeration Before discussing the refrigeration system, we need to understand the terms heat and refrigeration. The term refrigeration is commonly associated with something cold. A household refrigerator , for example, keeps food cold. It accomplishes this task by removing heat from the food. Therefore, r ...
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2 TRG-TRC003-EN notes period one Heat and Refrigeration What is Heat? Heat is a form of energy . Every object on earth contains heat energy in both quantity and intensity . Heat intensity is measured by its temperature, commonly in either degrees Fahrenheit (°F) or degrees Celsius (°C). If all heat were removed from an object, the temperature of ...
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TRG-TRC003-EN 3 period one Heat and Refrigeration notes These two different masses of water contain the same quantity of heat, yet the temperature of the water on the left is higher . Why? The water on the left contains more heat per unit of mass than the water on the right. In other words, the heat energy within the water on the left is more conce ...
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Trane TRG-TRC003-EN - page 11
4 TRG-TRC003-EN notes period one Heat and Refrigeration Principles of Heat T ransfer Air -conditioning and refrigeration systems use the principles of heat transfer to produce cooling and heating. The three principles discussed in this clinic are: ■ Heat energy cannot be destroyed; it can only be transferred to another substance ■ Heat energy f ...
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TRG-TRC003-EN 5 period one Heat and Refrigeration notes substance. This is commonly referred to as the principle of “conservation of energy .” Ice cubes are typically placed in a beverage to cool it before it is served. As heat is transferred from the beverage to the ice, the temperature of the beverage is lowered. The heat removed from the bev ...
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6 TRG-TRC003-EN notes period one Heat and Refrigeration The third principle is that heat is transferred from one substance to another by one of three basic processes: conduction, convection, and radiation. The device shown is a baseboard convector that is commonly used for heating a space. It can be used to demonstrate all three processes of transf ...
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Trane TRG-TRC003-EN - page 14
TRG-TRC003-EN 7 period one Heat and Refrigeration notes In refrigeration, as in heating, emphasis is placed on the rate of heat transfer , that is, the quantity of heat that flows from one substance to another within a given period of time. This rate of heat flow is commonly expressed in terms of Btu/hr—the quantity of heat, in Btus, that flows f ...
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8 TRG-TRC003-EN notes period one Heat and Refrigeration In the English system of units, there is a larger and more convenient measure of the rate of heat flow . It is called a ton of refrigeration . One ton of refrigeration produces the same cooling effect as the melting of 2000 lb of ice over a 24-hour period. When 1 lb of ice melts, it absorbs 14 ...
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TRG-TRC003-EN 9 notes In this period we will discuss refrigerants, the substances used to absorb and transfer heat for the purpose of cooling. Ice can be used to preserve food. Because heat flows from a higher temperature substance to a lower temperature substance, ice can be used in a frozen display case to absorb heat from the relatively warm foo ...
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10 TRG-TRC003-EN notes period two Refrigerants Pure ice, however , does have an important disadvantage. It absorbs heat and melts at 32 °F [0 °C]. Ice cream, for example, melts at a temperature lower than 32 °F [0 °C]. In the same frozen display case, ice cannot keep the ice cream frozen because ice melts at a higher temperature than ice cream. ...
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TRG-TRC003-EN 11 period two Refrigerants notes Finally , Refrigerant-22 (R-22) is a chemical used in many refrigeration systems. If, hypothetically , an open container of liquid R-22 were placed in the frozen display case, when exposed to atmospheric pressure, it would absorb heat and boil violently at -41.4 °F [-40.8 °C]. This is a hypothetical ...
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Trane TRG-TRC003-EN - page 19
12 TRG-TRC003-EN notes period two Refrigerants Change of Phase This question is best answered by examining the effects of heat transfer on water . Consider 1 lb of 60 °F water . By adding or subtracting 1 Btu of heat energy , the water temperature is raised or lowered by 1 °F . Similarly , by adding or subtracting 1 kcal (4.2 kJ) of heat energy t ...
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TRG-TRC003-EN 13 period two Refrigerants notes In fact, 970.3 Btu must be added to 1 lb of 212 °F water to completely transform it to 1 lb of steam at the same temperature. Similarly , 244.5.3 kcal (1023 kJ) must be added to 1 kg of 100 °C water to completely transform it to 1 kg of steam at the same temperature. Conversely , when 1 lb of 212 °F ...
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14 TRG-TRC003-EN notes period two Refrigerants The quantity of heat that must be added to the water in order for it to evaporate cannot be sensed by an ordinary thermometer . This is because both the water and steam remain at the same temperature during this phase change. This kind of heat is called latent heat, which is dormant or concealed heat e ...
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TRG-TRC003-EN 15 period two Refrigerants notes have different capacities for absorbing heat. This capacity is a property of the substance called specific heat. Suppose equal quantities of two different liquids, $ and % , both at room temperature, are heated. The gas burners are lighted and adjusted so that each is burning exactly the same quantity ...
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16 TRG-TRC003-EN notes period two Refrigerants Modern Refrigerants Refrigerants are substances that are used to absorb and transport heat for the purpose of cooling. When selecting a refrigerant to use for a given application, in addition to these heat transfer properties the manufacturer considers efficiency , operating pressures, compatibility wi ...
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TRG-TRC003-EN 17 notes period three Refrigeration Cycle The frozen display case example used in the last period demonstrates that, at a given pressure, refrigerants absorb heat and change phase at a fixed temperature. It also shows how these refrigerants are “consumed” in the cooling process, either melting into a liquid or evaporating into a v ...
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18 TRG-TRC003-EN notes period three Refrigeration Cycle liquid refrigerant to the coil so that all the refrigerant evaporates before it reaches the end of the coil. One disadvantage of this system is that after the liquid refrigerant passes through the coil and collects in the drum as a vapor , it cannot be reused. The cost and environmental impact ...
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Trane TRG-TRC003-EN - page 26
TRG-TRC003-EN 19 period three Refrigeration Cycle notes The liquid refrigerant absorbed heat from the air while it was inside the evaporator , and was transformed into a vapor in the process of doing useful cooling. Earlier in this clinic, we demonstrated that if the heat is then removed from this vapor , it will transform (condense) back to its or ...
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Trane TRG-TRC003-EN - page 27
20 TRG-TRC003-EN notes period three Refrigeration Cycle At higher pressures, refrigerant boils and condenses at higher temperatures. This can be explained by examining the properties of water . At atmospheric pressure (14.7 psia [0.10 MPa]), water boils and evaporates at 212 °F [100 °C]. When pressure is increased, however , water does not boil u ...
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TRG-TRC003-EN 21 period three Refrigeration Cycle notes increase the pressure of the resulting refrigerant vapor to 280 psia [1.93 MPa]. This increase in pressure raises the temperature at which the vapor would condense back into liquid to 121.5 °F [49.7 °C]. In order to condense the refrigerant vapor at this higher temperature, a substance at a ...
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22 TRG-TRC003-EN notes period three Refrigeration Cycle Basic Refrigeration System This diagram illustrates a basic vapor -compression refrigeration system that contains the described components. First, notice that this is a closed system. The individual components are connected by refrigerant piping. The suction line connects the evaporator to the ...
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Trane TRG-TRC003-EN - page 30
TRG-TRC003-EN 23 period three Refrigeration Cycle notes At the inlet to the evaporator , the refrigerant exists as a cool, low-pressure mixture of liquid and vapor . In this example, the evaporator is a finned-tube coil used to cool air . Other types of evaporators are used to cool water . The relatively warm air flows across this finned-tube arran ...
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24 TRG-TRC003-EN notes period three Refrigeration Cycle The condenser is a heat exchanger used to reject the heat of the refrigerant to another medium. The example shown is an air -cooled condenser that rejects heat to the ambient air . Other types of condensers are used to reject heat to water . The hot, high-pressure refrigerant vapor ( & ) f ...
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TRG-TRC003-EN 25 period three Refrigeration Cycle notes The high-pressure liquid refrigerant ( ' ) flows through the expansion device, causing a large pressure drop. This pressure drop reduces the refrigerant pressure, and, therefore, its temperature, to that of the evaporator . At the lower pressure, the temperature of the refrigerant is high ...
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Trane TRG-TRC003-EN - page 33
26 TRG-TRC003-EN notes period four Pressure–Enthalpy Chart During this period we will again analyze the basic vapor -compression refrigeration cycle. However , this time we will use a graphic tool called the pressure–enthalpy chart. The pressure–enthalpy (P- h ) chart plots the properties of a refrigerant— refrigerant pressure on the vertic ...
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TRG-TRC003-EN 27 period four Pressure–Enthalpy Chart notes envelope, the refrigerant exists as a mixture of liquid and vapor . If the enthalpy of the refrigerant lies to the right of the envelope, the vapor is superheated . Similarly , if the enthalpy of the refrigerant lies to the left of the envelope, the liquid is subcooled . Lines of constant ...
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Trane TRG-TRC003-EN - page 35
28 TRG-TRC003-EN notes period four Pressure–Enthalpy Chart The distance between the edges of the envelope indicates the quantity of heat required to transform saturated liquid into saturated vapor at a given pressure. This is called the heat of vaporization . For example, B represents the enthalpy of saturated liquid water at 14.7 psia [0.10 MPa] ...
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TRG-TRC003-EN 29 period four Pressure–Enthalpy Chart notes At the inlet to the evaporator , the refrigerant is at a pressure of 85 psia [0.59 MPa] and a temperature of 41.2 °F [5.1 °C], and is a mixture of liquid and vapor (mostly liquid). This cool, low-pressure refrigerant enters the evaporator ( $ ) where it absorbs heat from the relatively ...
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Trane TRG-TRC003-EN - page 37
30 TRG-TRC003-EN notes period four Pressure–Enthalpy Chart The compressor draws in the superheated refrigerant vapor ( & ) and compresses it to a pressure and temperature ( ' ) high enough that it can reject heat to another fluid. As the volume of the refrigerant is reduced by the compressor , its pressure is increased. Additionally , th ...
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TRG-TRC003-EN 31 period four Pressure–Enthalpy Chart notes temperature is 121.5 °F [49.7 °C]. The refrigerant vapor leaving the compressor is therefore 70 °F [38.9 °C] above its saturation temperature. This hot, high-pressure refrigerant vapor then travels to the condenser . Inside of the condenser , heat is transferred from the hot, high-pre ...
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Trane TRG-TRC003-EN - page 39
32 TRG-TRC003-EN notes period four Pressure–Enthalpy Chart The primary purpose of the expansion device is to drop the pressure of the liquid refrigerant to equal the evaporator pressure. At this lower pressure, the refrigerant is now inside the saturation envelope where it exists as a mixture of liquid and vapor . The high-pressure liquid refrige ...
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TRG-TRC003-EN 33 period four Pressure–Enthalpy Chart notes The temperature of the refrigerant entering the expansion device ( * ) is 110 °F [43.3 °C] and its pressure is 280 psia [1.93 MPa]. (The refrigerant condensed at 121.5 °F [49.7 °C] and was subcooled to 110 °F [43.3 °C].) The enthalpy of the refrigerant at this condition is 42.4 Btu/ ...
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34 TRG-TRC003-EN notes period four Pressure–Enthalpy Chart This cool mixture of liquid and vapor refrigerant leaving the expansion device then enters the evaporator ( $ ) to repeat the cycle. The vapor -compression refrigeration cycle has successfully recovered the refrigerant that boiled in the evaporator and converted it back into a cool liquid ...
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Trane TRG-TRC003-EN - page 42
TRG-TRC003-EN 35 notes W e will now review the main concepts that were covered in this clinic reagrding the vapor -compression refrigeration cycle. Period One introduced the concept of heat and how it is transferred from one substance to another . Recall that heat is a form of energy and can vary in both quantity and intensity (temperature). Heat e ...
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Trane TRG-TRC003-EN - page 43
36 TRG-TRC003-EN notes period five Review Period T wo discussed refrigerants and how they are used in the process of removing and transporting heat. Remember that refrigerants absorb significant amounts of heat when they change phase (e.g., from a liquid to a vapor). Chemical refrigerants commonly evaporate at low temperatures when exposed to atmos ...
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TRG-TRC003-EN 37 period five Review notes Refrigerant enters the evaporator as a cool, low-pressure mixture of liquid and vapor . It absorbs heat—from the relatively warm air or water to be cooled—and boils. The cool, low-pressure vapor is then pumped from the evaporator by the compressor . This increases the pressure and temperature of the ref ...
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38 TRG-TRC003-EN notes period five Review For more information, refer to the following references: ■ T rane Air Conditioning Manual ■ T rane Reciprocating Refrigeration Manual ■ ASHRAE Handbook – Fundamentals ■ ASHRAE Handbook – Refrigeration ■ ASHRAE Handbook – Systems and Equipment Visit the ASHRAE Bookstore at www .ashrae.org. Fo ...
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TRG-TRC003-EN 39 Questions for Period 1 1 Heat intensity is measured in terms of its __________? 2 Heat quantity is measured with units of __________? 3 Heat always flows from a substance of ________ (higher , lower) temperature to a substance of ________ (higher , lower) temperature. 4 What are the three basic processes by which heat is transferre ...
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40 TRG-TRC003-EN Quiz 10 What is the state of the refrigerant when it enters the compressor? 11 What is the state of the refrigerant when it enters the expansion device? Questions for Period 4 12 What is enthalpy? 13 Using the pressure–enthalpy chart in Figure 59, identify the components of the vapor -compression refrigeration cycle: a $ to % b & ...
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TRG-TRC003-EN 41 Quiz 14 Referring to Figure 60 and given the following conditions, A - 44.5 °F , 90 psia, 41.6 Btu/lb [6.9 °C, 0.62 MPa, 96.8 kJ/kg] B - 44.5 °F , 90 psia, 108.5 Btu/lb [6.9 °C, 0.62 MPa, 252.4 kJ/kg] C - 54.5 °F , 90 psia, 110.3 Btu/lb [12.5 °C, 0.62 MPa, 256.6 kJ/kg] D - 190 °F , 280 psia, 128.4 Btu/lb [87.8 °C, 1.93 MPa, ...
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42 TRG-TRC003-EN 1 T emperature or degrees Fahrenheit [degrees Celsius] 2 British Thermal Unit (Btu) [kilocalorie (kcal) or kiloJoule (kJ)] 3 Higher to lower 4 Conduction, convection, and radiation 5 Boiling the water requires more energy–970.3 Btu/lb [244.5 kJ/kg]. Raising the temperature of the water from 50 °F [10 °C] to 200 °F [93.3 °C] r ...
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TRG-TRC003-EN 43 Answers 14 a 10 °F [5.6 °C] (temperature rise from % to & ) b 14 °F [7.8 °C] (temperature drop from ) to * ) c 68.7 Btu/lb [159.8 kJ/kg] (enthalpy difference between $ and & ) d 22% refrigerant vapor % of Refrigerant Vapor at A Enthalpy at A Enthalpy at H – Enthalpy at B Enthalpy at H – ? ...
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44 TRG-TRC003-EN ASHRAE American Society of Heating, Refrigerating and Air -Conditioning Engineers British Thermal Unit (Btu) A measure of heat quantity , defined as the quantity of heat energy required to change the temperature of 1 lb of water by 1 °F . compressor A mechanical device in the refrigeration system used to increase the pressure and ...
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Trane TRG-TRC003-EN - page 52
TRG-TRC003-EN 45 Glossary radiation The process transferring heat by means of electromagnetic waves emitted due to the temperature difference between two objects. refrigerant A substance used to absorb and transport heat for the purpose of cooling. refrigeration effect The change in enthalpy that occurs inside the evaporator a refrigeration cycle t ...
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The T rane Company Worldwide Applied Systems Group 3600 Pammel Creek Road La Crosse, WI 54601-7599 www .trane.com An American Standard Company Literature Order Number TRG-TRC003-EN File Number E/A V -FND-TRG-TRC003-1299-EN Supersedes 2803-1-1079 Stocking Location Inland-La Crosse Since The T rane Company has a policy of continuous product improveme ...
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