Ventilation - Air movement

This is a lesson for ventilation study in a built environment.

1. Ventilation Air movement

2. This lecture is about Fundamentals of building ventilation Natural Ventilation Wind patterns Openings Building strategies

3. Why is it necessary to ventilate? Air for breathing Adult man has frequency of breathing typically 16 times per minute –8 l/min. Respiration

4. Why is it necessary to ventilate? Indoor environment in a room has to meet level suitable for people and theirs activity. In an industrial building ventilation requirements may relate also to industrial processes. In an agricultural building all focus aims to animals. Ventilation is one of systems keeping habitable environment.

5. Information about wind patterns and prevailing wind direction Functions of ventilation Three distinctly different functions Supply of fresh air Convective cooling Physiological cooling Achieved by - air movement Ventilation In Architectural terms, Ventilation is the intentional introduction of outdoor air into a space and is mainly used to control indoor air quality by diluting and displacing indoor pollutants; it can also be used for purposes of thermal comfort or dehumidification.

6. SUPPLY OF FRESH AIR - Air movement around building Wind is generated by pressure differences – so an air flow through the building is result of pressure difference between two sides. 1. The air flow around a building Development of positive pressure on windward side and negative pressure on leeward side of the building Side elevation plan

7. Air stream separation at the face of building Reverse flow behind tall block Air flow grid iron pattern Air flow checkboard pattern Air movement around building

8. Air movement around building Form of the buildings, specially in terms of high rise building should be carefully planned to help the air movement in the surroundings

9. 30 St Mary Axe, informally known as The Gherkin , is a commercial skyscraper in London's primary financial district. It was completed in December 2003 and opened in April 2004.[10] With 41 floors, it is 180 metres (591 ft) tall.

10. Air movement inside the building – opening positions

11. Air movement inside the building – opening positions

12. Cross ventilation Lack of cross ventilation Effect of opening positions Pressure built up at inlet Air flow in a two storey building Position of openings Air movement inside the building – opening positions

13. Air movement inside the building

14. Size of the openings The largest air velocity will be obtained through a small inlet opening with large outlet. This is partly due to the total force acting on the small area forcing air through opening at high pressure and partly due to venturi effect. When the wind direction is not constant and when air flow through whole space is required , the large inlet opening will be proffered Controls of openings Effect of sashes Effect of louvers Effect of canopies Effect of Venetian blinds Air movement in and around building

15. Wind Angle at 75 ˚ A study done in a residential building for understanding the effect of wind angles

16. Wind Angle at 0 ˚ Wind Angle at 30 ˚

17. CONVECTIVE COOLING – Stack effect The driving force for the stack effect The stack effect relies on thermal forces, set up by the density difference (caused by the temperature difference)between the indoor and outdoor air and change in temperature due to height.)

18. Convective cooling – Stack effect

19. Various techniques for ventilation

20. The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. Venturi effect To increase speed of air to reduce temperature.

21. when the air flow is channeled and restricted, the pressure rises and the velocity increases. This is called the venturi effect By using these principles and understanding how air moves and acts similar to a fluid, like water, we can visualize wind patterns on different sites and in different conditions. Venturi effect Vegetation creating the venturi effect

22. A local wind created by acceleration of the airflow through a gap, constriction, or channel Changing the direction by diverting. A strong, low-level wind through channel between two structures Lack of cross ventilation

23. Humidity control Wind scoop – in hot and dry climate humidification is necessary which can be associated with evaporative cooling Functions of wind scoop controlled air supply Filtering out sand and dust evaporative cooling. humidification

24. Various techniques for ventilation

25. Open jet wind stimulator On basis of experiments following factors can be isolated which affect the indoor flow - Orientation - size of openings - Cross ventilation - controls of openings - Position of openings Experiments to check ventilation in models

26. Closed Wind tunnel