R&AC Lecture 39 - Lesson 39 Space Air Distribution...

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Lesson 39 Space Air Distribution Version 1 ME, IIT Kharagpur 1
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The specific objectives of this chapter are to: 1. Requirements of a proper air distribution system, definition of Air Distribution Performance Index and Space Diffusion Effectiveness Factor ( Section 39.1 ) 2. Design of air distribution systems, buoyancy effects and deflection of air jets ( Section 39.2 ) 3. Behaviour of free-stream jets, definitions of drop, throw, spread and entrainment ratio ( Section 39.3 ) 4. Behaviour of circular jets ( Section 39.4 ) 5. Behaviour of rectangular jets ( Section 39.5 ) 6. Characteristics of different types of air distribution devices, such as grilles, registers, ceiling diffusers, slotted diffusers etc. ( Section 39.6 ) 7. Return air inlets ( Section 39.7 ) 8. Airflow pattern inside conditioned spaces using different types of air distribution devices ( Section 39.8 ) 9. Stratified mixing flow ( Section 39.9 ) 10. Cold air distribution ( Section 39.10 ) 11. Displacement flow ( Section 39.11 ) 12. Spot cooling/heating ( Section 39.12 ) 13. Selection criteria for supply air inlets ( Section 39.13 ) At the end of the chapter, the student should be able to: 1. Explain the importance of proper air distribution in conditioned space and define ADPI and SDEF 2. List the factors to be considered in the design of air distribution devices and explain buoyancy effects and deflection of air jets 3. Estimate throw, drop, spread and entrainment ratio of circular and rectangular, isothermal free jets 4. List different types of supply air outlet devices and their characteristics 5. Draw the airflow patterns for ceiling, sidewall and slotted diffusers 6. Explain stratified mixing flow, displacement flow, cold air distribution and spot cooling and heating 7. List the criteria for selection of supply air outlets. 39.1. Introduction After the required amount of supply air is transmitted to the conditioned space, it is essential to distribute the air properly within the conditioned space. Thus it is important to design suitable air distribution system, which satisfies the following requirements: a) Create a proper combination of temperature, humidity and air motion in the occupied zone. The occupied zone is defined as all the space in the conditioned zone that is from the floor to a height of 1.8 m and about 30 cms from the walls. In the occupied zone, the maximum variation in temperature should be less than 1 ο C and the air velocity should be in the range of 0.15 m/s to 0.36 m/s. Version 1 ME, IIT Kharagpur 2
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b) To avoid draft in the occupied zone. Draft is defined as the localized feeling of cooling or warmth. Draft is measured above or below the controlled room condition of 24.4 ο C and an air velocity of 0.15 m/s at the center of the room. The effective draft temperature (EDT) for comfort is given by: EDT (DBT 24.4) 0.1276(V 0.15) =−− (39.1) where DBT is the local dry bulb temperature (in o C) and V is the local velocity (m/s).
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R&AC Lecture 39 - Lesson 39 Space Air Distribution...

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