R&AC Lecture 37 - Lesson 37 Transmission Of Air In...

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Lesson 37 Transmission Of Air In Air Conditioning Ducts Version 1 ME, IIT Kharagpur 1
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The specific objectives of this chapter are to: 1. Describe an Air Handling Unit (AHU) and its functions ( Section 37.1 ) 2. Discuss the need for studying transmission aspects of air in air conditioning ( Section 37.2 ) 3. Discuss airflow through air conditioning ducts, Bernoulli and modified Bernoulli equations, Static, dynamic, datum and total head, Fan Total Pressure (FTP) and power input to fan ( Section 37.3 ) 4. Discuss estimation of pressure loss through air conditioning ducts ( Section 37.4 ) 5. Estimation of frictional pressure drop of circular and rectangular ducts using friction charts and equations ( Section 37.4 ) 6. Estimation of dynamic pressure drop in various types of fittings ( Section 37.5 ) 7. Static regain ( Section 37.6 ) At the end of the lecture, the student should be able to: 1. Apply Bernoulli equation and modified Bernoulli equation to air conditioning ducts and estimate various pressure heads, pressure loss, FTP and fan power input 2. Estimate frictional pressure drops through circular and non-circular ducts using friction charts and equations 3. Estimate dynamic pressure drop through various fittings used in air conditioning ducts using tables, charts and equations 4. Define static regain and calculate static regain factor for various types of duct enlargements 37.1. Introduction: In air conditioning systems that use air as the fluid in the thermal distribution system, it is essential to design the Air Handling Unit (AHU) properly. The primary function of an AHU is to transmit processed air from the air conditioning plant to the conditioned space and distribute it properly within the conditioned space. A typical AHU consists of: 1. A duct system that includes a supply air duct, return air duct, cooling and/or heating coils, humidifiers/dehumidifiers, air filters and dampers 2. An air distribution system comprising various types of outlets for supply air and inlets for return air Version 1 ME, IIT Kharagpur 2
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3. Supply and return air fans which provide the necessary energy to move the air throughout the system 37.2. Transmission of air: In an AHU, air is transmitted through various ducts and other components with the help of fans. Since the fan motor consumes a large amount of power, and the duct system occupies considerable building space, the design of air transmission system is an important step in the complete design of air conditioning systems. In the end the success of any air conditioning system depends on the design of individual components as well as a good matching between them under all conditions. In order to design the system for transmission of air, it is important to understand the fundamentals of fluid (air) flow through ducts. These aspects have been dealt with to some extent in Chapter 6 on Fundamentals of Fluid Flow. 37.3. Flow of air through ducts:
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This note was uploaded on 02/29/2012 for the course CHEMICAL 302 taught by Professor Nptel during the Spring '12 term at Birla Institute of Technology & Science.

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R&AC Lecture 37 - Lesson 37 Transmission Of Air In...

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