Natural ventilation relies on wind and temperature differences to flow fresh air through a building without mechanical systems. It is best suited for open plan layouts and areas with minimal noise pollution. The benefits include energy savings, reduced environmental impact, and robustness. To be effective, natural ventilation must be planned early in the design process with a team approach to meet the client's objectives. Equations are provided to calculate airflow based on factors like opening area, wind velocity, and indoor/outdoor temperature difference. Considerations like inlet/outlet placement and sizing are also discussed.

1. DT018
Stephen Agunbiade
Rory Conlon
Paul Derwin
Paul Dunne

2. What is Natural Ventilation?
A system that relies on natural sources such
as wind and temperature difference between a
building and its environment in order to flow
fresh air through a building

3. Most Suited
 Open plan Layouts
 Areas of minimised noise pollution and
external air
Not Suited
 Buildings containing small spaces
 Buildings that need a consists air temperature

4. What are the benefits of a Natural
ventilation system?
 Energy Savings
 Reduce environmental impact
 Robustness

5. In order to work effectively you must
 Plan at the earliest stage of design
 Team approach
 Work out the clients desired objectives

6. Q=C * A * V
Q = Air flow
C = Effectiveness factor 0.5-0.6 for openings
perpendicular to wind direction and 0.25-0.35 for
openings diagonal to wind direction.
A = Area of opening ft2
V = Wind velocity ft./min.
Ref: “Natural Ventilation in non-domestic buildings” CIBSE guide.

7. Q= 60 K A √ G * H (TI – TO)/TI
Q= Airflow cfm.
K= discharge coefficient of an opening 0.6
A= Area of opening ft.2
G= Gravitational constant 32.2 ft./s2
TI = Indoor temperature
TO= Outdoor temperature
Ref: “Natural Ventilation in non-domestic buildings” CIBSE guide.

8.  When both forces combine without
obstructions resulting air flow, is not equal to
the two flows estimated separately.
 Wind velocity and direction, outdoor
temperature and indoor distribution cannot be
predicted with certainty.
 When the two flows are equal the actual flow is
30%greater than the flow caused by either the
wind or stack effect.

9.  Openings must be accessible so occupants can
operate them manually.
 Openings in areas of neutral pressure are not
desirable.
 For temperature difference to produce a motive
force its important of maximum vertical
distances between openings.
 Inlets should not be obstructed by buildings,
trees externally and walls internally.
 Openings of larger areas than calculated are
more desirable.