Ventilation Flashcards
Why do we need to ventilate buildings?
- To dilute odours.
- To remove pollutants.
- To control moisture levels.
- To cool the building and it’s occupants.
How is natural ventilation affected?
- Building form (size/shape) plays a key role in enabling natural ventilation.
- Natural ventilation is achieved by:
Wind
Stack effect
- Therefore, natural ventilation relies on variable external conditions.
What are the different types of ventilation openings?
- Windows
- Doors
- Roof ventilators
- Solar chimney
- Stack
What needs to be considered when choosing natural ventilation openings?
- Overheating
- Function of the building
- Health and Safety
What are the different types of ventilation?
- Infiltration
- Natural ventilation
What is infiltration?
- The uncontrolled exchange of air through openings in the envelope of a building - such as cracks or joints.
- Infiltration contributes to ventilation but should be minimised and not relied upon.
What is natural ventilation?
- The movement of air through purpose-provided openings in the building fabric.
- This is due to wind, or pressures created by differences in temperature between the interior and exterior of the building.
What are the effects of wind pressure?
- Wind flowing around a building produces ares of positive and negative pressures.
- The wind velocity typically increases with height above the ground.
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What is the pressure coefficient?
- Wind creates pressure differences across a building, which is the driving force of air flow.
- The pressure coefficient describes the relativity of these two pressures.
What is the equation for pressure coefficient?
What is the equation for velocity pressure?
What is the equation for cross ventilation (ventilation rate) due to the wind?
What is single sided ventilation?
- Single sided ventilation is a result of a single opening, or a series of openings which are in the same facade of the building.
- Single sided ventilation is much less effective than cross ventilation.
What is the equation for single-sided ventilation (ventilation rate) due to the wind?
What are the design considerations for wind driven ventilation?
- Average wind velocity
- Prevailing wind directions
- Local terrain
- Draughts leading to occupant discomfort
- Noise
- Heat loss
What is the equation for indoor/outdoor density?
Air density decreases with an increasing absolute temperature.
What is stack (buoyancy) ventilation?
- Stack ventilation is driven by internal and external temperature differences.
- It occurs between openings at different heights.
How can we visualise the stack effect?
What is the equation for pressure differences between indoors and outdoors?
What is the equation for cross ventilation (ventilation rate) due to the stack effect?
What is the equation for single-sided ventilation (ventilation rate) due to the stack effect?
What is presssure testing?
What is the equation for total air-flow?
What is the equation for air changes per hour?
q = total air-flow (m3/s)
