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Refrigeration and Air Conditioning

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Type: NoteInstitute: Jawaharlal nehru technological university anantapur college of engineering Offline Downloads: 148Views: 3419Uploaded: 11 months ago

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Wang, S.K. and Lavan, Z. “Air-Conditioning and Refrigeration” Mechanical Engineering Handbook Ed. Frank Kreith Boca Raton: CRC Press LLC, 1999 1999 by CRC Press LLC c
Air-Conditioning and Refrigeration Shan K. Wang 9.1 Zalman Lavan Professor Emeritus, Illinois Institute of Technology Introduction ......................................................................9-2 Air-conditioning • Air-Conditioning Systems • AirConditioning Project Development and System Design Individual Consultant 9.2 Psychrometrics ...............................................................9-11 Moist Air • Humidity and Enthalpy • Moist Volume, Density, Specific Heat, and Dew Point • Thermodynamic Wet Bulb Temperature and Wet Bulb Temperature • Psychometric Charts 9.3 Air-Conditioning Processes and Cycles ........................9-18 Air-Conditioning Processes • Space Conditioning, Sensible Cooling, and Sensible Heating Processes • Humidifying and Cooling and Dehumidifying Processes • Air-Conditioning Cycles and Operating Modes 9.4 Refrigerants and Refrigeration Cycles ..........................9-34 Refrigeration and Refrigeration Systems • Refrigerants, Cooling Mediums, and Absorbents • Classification of Refrigerants • Required Properties of Refrigerants • Ideal Single-Stage Vapor Compression Cycle • Coefficient of Performance of Refrigeration Cycle • Subcooling and Superheating • Refrigeration Cycle of Two-Stage Compound Systems with a Flash Cooler • Cascade System Characteristics 9.5 Outdoor Design Conditions and Indoor Design Criteria ...............................................................9-48 Outdoor Design Conditions • Indoor Design Criteria and Thermal Comfort • Indoor Temperature, Relative Humidity, and Air Velocity • Indoor Air Quality and Outdoor Ventilation Air Requirements 9.6 Load Calculations ..........................................................9-54 Space Loads • Moisture Transfer in Building Envelope • Cooling Load Calculation Methodology • Conduction Heat Gains • Internal Heat Gains • Conversion of Heat Gains into Cooling Load by TFM • Heating Load 9.7 Air Handling Units and Packaged Units .......................9-65 Terminals and Air Handling Units • Packaged Units • Coils • Air Filters • Humidifiers 9.8 Refrigeration Components and Evaporative Coolers .......................................................9-76 Refrigeration Compressors • Refrigeration Condensers • Evaporators and Refrigerant Flow Control Devices • Evaporative Coolers © 1999 by CRC Press LLC 9-1
9-2 Section 9 9.9 Water Systems................................................................9-87 Types of Water Systems • Basics • Water Piping • PlantBuilding Loop • Plant-Distribution-Building Loop 9.10 Heating Systems.............................................................9-95 Types of Heating Systems 9.11 Refrigeration Systems ..................................................9-103 Classifications of Refrigeration Systems 9.12 Thermal Storage Systems ............................................9-114 Thermal Storage Systems and Off-Peak Air-Conditioning Systems • Ice-Storage Systems • Chilled-Water Storage Systems 9.13 Air System Basics........................................................9-120 Fan-Duct Systems • System Effect • Modulation of Air Systems • Fan Combinations in Air-Handling Units and Packaged Units • Fan Energy Use • Year-Round Operation and Economizers • Outdoor Ventilation Air Supply 9.14 Absorption Systems .....................................................9-130 Double-Effect Direct-Fired Absorption Chillers • Absorption Cycles, Parallel-, Series-, and Reverse-Parallel Flow 9.15 Air-Conditioning Systems and Selection.....................9-135 Basics in Classification • Individual Systems • Packaged Systems • Central Systems • Air-Conditioning System Selection • Comparison of Various Systems • Subsystems • Energy Conservation Recommendations 9.16 Desiccant Dehumidification and Air-Conditioning ..........................................................9-152 Introduction • Sorbents and Desiccants • Dehumidification • Liquid Spray Tower • Solid Packed Tower • Rotary Desiccant Dehumidifiers • Hybrid Cycles • Solid Desiccant AirConditioning • Conclusions 9.1 Introduction Air-Conditioning Air-conditioning is a process that simultaneously conditions air; distributes it combined with the outdoor air to the conditioned space; and at the same time controls and maintains the required space’s temperature, humidity, air movement, air cleanliness, sound level, and pressure differential within predetermined limits for the health and comfort of the occupants, for product processing, or both. The acronym HVAC&R stands for heating, ventilating, air-conditioning, and refrigerating. The combination of these processes is equivalent to the functions performed by air-conditioning. Because I-P units are widely used in the HVAC&R industry in the U.S., I-P units are used in this chapter. A table for converting I-P units to SI units is available in Appendix X of this handbook. Air-Conditioning Systems An air-conditioning or HVAC&R system consists of components and equipment arranged in sequential order to heat or cool, humidify or dehumidify, clean and purify, attenuate objectionable equipment noise, transport the conditioned outdoor air and recirculate air to the conditioned space, and control and maintain an indoor or enclosed environment at optimum energy use. The types of buildings which the air-conditioning system serves can be classified as: • Institutional buildings, such as hospitals and nursing homes • Commercial buildings, such as offices, stores, and shopping centers © 1999 by CRC Press LLC
Air-Conditioning and Refrigeration 9-3 • Residential buildings, including single-family and multifamily low-rise buildings of three or fewer stories above grade • Manufacturing buildings, which manufacture and store products Types of Air-Conditioning Systems In institutional, commercial, and residential buildings, air-conditioning systems are mainly for the occupants’ health and comfort. They are often called comfort air-conditioning systems. In manufacturing buildings, air-conditioning systems are provided for product processing, or for the health and comfort of workers as well as processing, and are called processing air-conditioning systems. Based on their size, construction, and operating characteristics, air-conditioning systems can be classified as the following. Individual Room or Individual Systems. An individual air-conditioning system normally employs either a single, self-contained, packaged room air conditioner (installed in a window or through a wall) or separate indoor and outdoor units to serve an individual room, as shown in Figure 9.1.1. “Selfcontained, packaged” means factory assembled in one package and ready for use. Room air conditioner Supply outlet Return grille FIGURE 9.1.1 An individual room air-conditioning system. Space-Conditioning Systems or Space Systems. These systems have their air-conditioning—cooling, heating, and filtration—performed predominantly in or above the conditioned space, as shown in Figure 9.1.2. Outdoor air is supplied by a separate outdoor ventilation system. Unitary Packaged Systems or Packaged Systems. These systems are installed with either a single selfcontained, factory-assembled packaged unit (PU) or two split units: an indoor air handler, normally with ductwork, and an outdoor condensing unit with refrigeration compressor(s) and condenser, as shown in Figure 9.1.3. In a packaged system, air is cooled mainly by direct expansion of refrigerant in coils called DX coils and heated by gas furnace, electric heating, or a heat pump effect, which is the reverse of a refrigeration cycle. Central Hydronic or Central Systems. A central system uses chilled water or hot water from a central plant to cool and heat the air at the coils in an air handling unit (AHU) as shown in Figure 9.1.4. For energy transport, the heat capacity of water is about 3400 times greater than that of air. Central systems are built-up systems assembled and installed on the site. Packaged systems are comprised of only air system, refrigeration, heating, and control systems. Both central and space-conditioning systems consist of the following. Air Systems. An air system is also called an air handling system or the air side of an air-conditioning or HVAC&R system. Its function is to condition the air, distribute it, and control the indoor environment according to requirements. The primary equipment in an air system is an AHU or air handler; both of these include fan, coils, filters, dampers, humidifiers (optional), supply and return ductwork, supply outlets and return inlets, and controls. © 1999 by CRC Press LLC

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