R&AC Lecture 34 - Lesson 34 Cooling And Heating...

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Lesson 34 Cooling And Heating Load Calculations - Heat Transfer Through Buildings - Fabric Heat Gain/Loss Version 1 ME, IIT Kharagpur 1
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The specific objectives of this chapter are to: 1. Discuss the general aspects of heat transfer through buildings ( Section 34.1 ) 2. Discuss one-dimensional, steady state heat transfer through homogeneous, non- homogeneous walls, through air spaces and through composite walls of the buildings ( Section 34.2 ) 3. Discuss unsteady heat transfer through opaque walls and roofs ( Section 34.3 ) 4. Discuss one-dimensional, unsteady heat transfer through opaque walls and roofs with suitable initial and boundary conditions ( Section 34.4 ) 5. Describe the analytical method used to solve the 1-D, transient heat transfer problem through building walls and roofs ( Section 34.4.1 ) 6. Briefly discuss the numerical methods used to solve the transient heat transfer problem ( Section 34.4.2 ) 7. Discuss the semi-empirical methods based on Effective Temperature Difference or Cooling Load Temperature Difference, discuss the physical significance of decrement and time lag factors and present typical tables of CLTD for walls and roof ( Section 34.4.3 ) At the end of the chapter, the student should be able to: 1. Calculate the steady heat transfer rates through homogeneous and non- homogeneous walls, through composite walls consisting of a combination of homogeneous and non-homogeneous walls and air spaces 2. Explain the need for considering transient heat transfer through buildings 3. Derive one-dimensional, transient heat conduction equation for building walls and roof and indicate suitable initial and boundary conditions 4. Discuss the general aspects of the analytical, numerical and semi-empirical methods used to solve the transient building heat transfer problem 5. Use the ETD/CLTD methods to estimate heat transfer rate through opaque walls and roof of the buildings 34.1. Introduction: Whenever there is a temperature difference between the conditioned indoor space of a building and outdoor ambient, heat transfer takes place through the building structure (walls, roof, floor etc.). This is known as fabric heat gain or loss, depending upon whether heat transfer is to the building or from the building, respectively. The fabric heat transfer includes sensible heat transfer through all the structural elements of a building, but does not include radiation heat transfer through fenestration. Exact analysis of heat transfer through building structures is very complex, as it has to consider: a) Geometrically complex structure of the walls, roofs etc. consisting of a wide variety of materials with different thermo-physical properties. b) Continuously varying outdoor conditions due to variation in solar radiation, outdoor temperature, wind velocity and direction etc.
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R&AC Lecture 34 - Lesson 34 Cooling And Heating...

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