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Natural Ventilation - Coggle Diagram

- - - - Wind velocity
      - Turbulence
      - Flow pattern
    - - Building exposure
      - Orientation
    - - Flow direction through building
      - Ventilation intensity
- - - - air moves into the buildings
    - - air moves out of the buildings
  - - - Type of openings
        
        doors
        
        windows
        
        vents
      - Depends on
        
        dimensions
        
        geometry
      - Airflow rate
        
        usually assumed as turbulent (for well-defined opening, such as vent)
        
        area of opening that useful for calculating airflow rate is Net openable area (A)
        
        Discharge Coefficient (Cd)
        
        depends on
        
        opening geometry
        
        direction of approaching flow (wind)
        
        value
        
        0.61-0.65 (for a flat plate orifice in which the air stream is directed at right angles to the opening)
    - - appears at each joint in the building envelope
      - increasing level of airtighness
        
        to incorporate the impact of air infiltration
      - For very narrow cracks with relatively long flow paths (found in mortar and between tight fitting components) is dominated by the effects of viscosity
      - Airflow rate
        
        usually assumed as laminar (for less well-defined opening, such as infiltration)
        
        flow rate is proportional to the pressure difference
        
        Flow coefficient (C) is related to the size of the opening
        
        Flow exponent (n)
        
        related to characterize flow regime
        
        varies in value between 0.5 (fully turbulent) to 1.0 (fully laminar)
- - - - Surface of terrain roughness
      - Thermal nature of the atmosphere (thermal stability)
  - - - on the upwind surface
    - - at sharp edges of the building
      - the wake region on the leeward face
    - - less than 30 degree
        
        negative pressures are on both faces
      - more than 30 degree
        
        positive pressures are on the leading face
    - - net positive pressure on both upwind faces
      - as flow veers towards a particular side, the remaining face will undergo a transition from positive to negative pressure
        
        transition occurs is dependent on the side ratio of the building
    - - wind will directly affect the ceiling pressure distribution
- - - - influenced by
        
        roughness of the underlying terrain
        
        height above ground
  - - - onsite data is rarely available
      - data usually taken from the nearest
        climatological station
    - - difference between measurement height and building
        height
      - intervening terrain roughness
  - - - because wind pressure is very sensitive to the wind velocity
- - - - creating vertical pressure difference
      - When the internal air temperature > outside air mass
        
        air enters in the lower part of the building
        
        air escapes at a higher level
      - When the internal air temperature < outside air mass
        
        air enters at a higher level
        
        air escapes in the lower part of the building
    - - airflow derived from the imbalances in pressure distribution caused by internal/external temperature difference