Architectural Flows and Ventilation

Question 1

What is ventilation?

Answer 1

The supply and removal of air to and from a space in a building.
Can be natural or mechanical.

Question 2

Why ventilate?

Answer 2

1. Oxygen - for respiration and combustion
2. Dilute pollutants & improve air quality - Body odour, carbon dioxide etc.
3. Thermal comfort

Question 3

What are isolated spaces and how to ventilate them?

Answer 3

Isolated spaces are separate in terms of airflow from other parts of the building.
Can be ventilated by single-sided or cross-flow ventilation.

Question 4

What are connected spaces and how to ventilate them?

Answer 4

Form a single cell - flow through any opening depends on flow through other openings.
Ventilated using and atrium or tower (solar chimney)

Question 5

Advantages of natural ventilation

Answer 5

1. Zero running costs
2. Lower capital and maintenance costs compared to MV
3. Lower greenhouse gas emissions.
4. Does not require space for plant room and duct work.
5. Lower incidences of SBS

Question 6

Disadvantages of Natural Ventilation

Answer 6

1. Difficult to design & errors difficult to correct
2. Airflow rates are variable
3. Less control over the internal thermal environment
4. Impose restriction son building layout.
5. Winter heat loss.
6. Noise ingress and security

Question 7

What is adventitious air leakage?

Answer 7

Leakage through cracks and small openings less than 10mm. Occurs in joints between building envelope and windows, doors, wall ducting etc.

Question 8

What are the 5 steps of the design process?

Answer 8

1. Feasibility
2. Ventilation Strategy
3. Envelope Design
4. Internal Environment
5. Commissioning

Question 9

How to increase flow rates in a natural ventilation design?

Answer 9

1. Increase opening sizes
2. Increase spacing between openings to increase pressure gradient driving flow.
3. Optimise shape and character of opening e.g. review opening mechanism, remove blinds/shutters.

Question 10

What factors effect Cp?

Answer 10

Depends on the shape of the building and the direction of wind. Also the geometry of the opening and any coverings.

Question 11

How does a solar chimney drive ventilation in a building?

Answer 11

Material and surface selected to absorbs heat from the sun - warms the surrounding air.
Warm air rises, through convection, and leaves the room. Conservation of mass means that air is in drawn into the room through other orifices.
Chimney at top of room to support natural buoyancy driven ventilation.
Above neutral pressure level so pressure inside space is higher than pressure outside - drives flow.