Topic 6 Natural Ventilation

Question 1

Necessity of ventilation

Answer 1

1. Provide oxygen for the proper functioning of the human body
2. Provide air movement for human comfort
3. Keep carbon dioxide concentration at an acceptable level
4. Dilute contaminants and toxic gases
5. Dilute odour
6. Remove bacteria
7. Remove excessive or unwanted heat
8. Remove moisture

Question 2

What is air pressure difference

Answer 2

Caused by wind movement over and around the building. Sometimes referred to as natural ventilation by induction

Question 3

What is stack effect

Answer 3

Caused by natural convection of warm air rising within building

Question 4

Natural ventilation by air pressure difference

Answer 4

1. Wind causes positive air pressure to move from windward side to negative air pressure on the leeward side
2. Openings on windward side will serve as inlets and those on leeward side will serve as outlets.
3. Inlets and outlets should be as large as possible

Question 5

Stack effect

Answer 5

1. Stack effect is created by the difference in temperature between air inside and outside of a building. The warmer (less dense) air inside is displaced by the cooler (denser) air from the outside.

Question 6

What is the minimum size of opening for both rooms and multi-story car parks

Answer 6

5% and 15% respectively

Question 7

Advantages of natural ventilation

Answer 7

1. No running cost as it does not require energy
2. Provides fresh air that improves air quality
3. No maintenance or breakdown problems compared to mechanical ventilation
4. Supports “green building” design concept and environmental sustainability

Question 8

Disadvantages of natural ventilation

Answer 8

1. No filtering of incoming air as compared to mechanical ventilation
2. Uncertain and unpredictable as it depends on external weather conditions
3. Degree of control and extent of ventilation is limited
4. Not effective when the difference in temperature between the indoor and outdoor air is small