Natural Ventilation

1. Natural Ventilation Ar. MedhaDeshmukh. Masters in Environmental Architecture

2. Natural ventilation is the intentional flow of outdoor air through an enclosure under the influence of wind and thermal pressures through controllable openings. It can effectively control both temperature and contaminants, particularly in mild climates.

3. Natural Ventilation systems rely on natural driving forces, • Wind • Temperature difference between a building and its environment, • Both work on the principle of air moving from a high pressure to a low pressure zone. • Mixed mode or hybrid ventilation buildings • Natural ventilation systems integrated + mechanical support;

4. It can save substantial amounts of energy. • It may also improve the building’s indoor air quality. • Provide very comfortable and pleasant environments for the occupants. • Two fundamental approaches: • Cross ventilation which uses air-pressure differentials caused by wind • Stack ventilation which uses the increased resilience of air as it warms up.

5. Cross ventilation • Cross ventilation depends on two continuously changing factors: wind availability and wind direction. • Consequently, it is a somewhat unreliable source for providing air flow and thermal comfort.

6. Considerations when designing for cross ventilation: Will work well if the room is up to 5 times the width of the ceiling height. If cross ventilation is not possible placing windows on adjacent walls, at 90 degrees to each other, will work but limit room size to 4.5 m x 4.5 m.

7. Partitions should not obstruct air path.Design spaces so that they are parallel to main ventilation path.

8. In stack ventilation, air movement is created by cool air being drawn into the space low down to replace warmer air that naturally rises as it is warmed and is then exhausted at the top. • Stack ventilation works best in spaces with high ceilings and where cross ventilation is not feasible.

9. Important points • Climate limits the effectiveness of ventilation systems. • The exterior air must be cooler than the interior air. • Thus, making it only possible to reduce the indoor temperature to around 3 degrees HIGHER than the outdoor temperature.

10. Types of Natural Ventilation Openings • Windows : • There are many types of windows. • Windows sliding vertically, sliding horizontally, tilting, swinging. • Doors, monitor openings and skylights. • Roof Ventilators (weather proof air outlet). • Stacks connecting to registers. • Specially designed inlet or outlet openings. Natural Ventilation

11. Natural Ventilation Rules • Buildings and ventilating equipment should not usually be oriented for a particular wind direction. • Inlet openings should not be obstructed by buildings , trees, signboards, or indoor partitions. • For temperature difference to produce a motive force, there must be vertical distance between openings; vertical distance should be as great as possible. • Openings in the vicinity of the neutral pressure level are least effective for ventilation. • Openings with areas much larger than calculated are sometimes. • The openings should be accessible to and operable by occupants. Natural Ventilation

12. THIRD YEAR B. ARCH. • Building Services & Sciences II • Paper 100 Sessional 100 Total 200 Course Outline: 1. Natural Ventilation (passive.) - Factors affecting comfort conditions. - Functions, requirements, mechanism and design factors.