R&AC Lecture 33 - Lesson 33 Cooling And Heating...

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Lesson 33 Cooling And Heating Load Calculations -Solar Radiation Through Fenestration - Ventilation And Infiltration Version 1 ME, IIT Kharagpur 1
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The specific objectives of this lesson are to discuss: 1. Need for fenestration in buildings and effects of fenestration on air conditioning systems ( Section 33.1 ) 2. Estimation of heat transfer rate into buildings through fenestration, concepts of Solar Heat Gain Factor (SHGF) and Shading Coefficient ( Section 33.2 ) 3. Effect of external shading, calculation of shaded area of fenestrations, estimation of heat transfer rate through windows with overhangs ( Section 33.3 ) 4. Need for ventilation and recommended ventilation rates ( Section 33.4 ) 5. Infiltration and causes for infiltration ( Section 33.5 ) 6. Estimation of heat transfer rate due to infiltration and ventilation ( Section 33.6 ) At the end of the lecture, the student should be able to: 1. Define fenestration and explain the need for fenestration and its effect on air conditioning 2. Calculate heat transfer rate due to fenestration using SHGF tables and shading coefficients 3. Calculate the dimensions of shadow cast on windows with overhangs and estimate the heat transfer rate through shaded windows 4. Explain the need for ventilation and select suitable ventilation rates 5. Define infiltration and explain the causes for infiltration 6. Calculate the heat transfer rates due to infiltration and ventilation 33.1. Solar radiation through fenestration: Fenestration refers to any glazed (transparent) apertures in a building, such as glass doors, windows, skylights etc. Fenestration is required in a building as it provides: a) Daylight, heat and outside air b) Visual communication to the outside world c) Aesthetics, and d) Escape route in case of fires in low-rise buildings Version 1 ME, IIT Kharagpur 2
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Because of their transparency, fenestrations transmit solar radiation into the building. Heat transfer through transparent surfaces is distinctly different from heat transfer through opaque surfaces. When solar radiation is incident on an opaque building wall, a part of it is absorbed while the remaining part is reflected back. As will be shown later, only a fraction of the radiation absorbed by the opaque surface is transferred to the interiors of the building. However, in case of transparent surfaces, a major portion of the solar radiation is transmitted directly to the interiors of the building, while the remaining small fraction is absorbed and/or reflected back. Thus the fenestration or glazed surfaces contribute a major part of cooling load of a building. The energy transfer due to fenestration depends on the characteristics of the surface and its orientation, weather and solar radiation conditions. A careful design of fenestration can reduce the building energy consumption considerably.
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R&AC Lecture 33 - Lesson 33 Cooling And Heating...

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