Passive cooling of a building

1. PASSIVE COOLING

2. Passive cooling is a building
design approach that focuses on
heat gain control and heat
dissipation in a building in order to
improve the indoor thermal comfort
with low or no energy
consumption.

3. Approach
1. Heat Prevention
2. Modulation and Heat Dissipation

4. Heat Prevention
To provide protection and/or prevention of
external and internal heat gains.
Techniques
• Microclimate and site design
• Solar control
• Building form and layout
• Thermal Insulation

5. 1. Microclimate and Site Design
The passive design depends very much on local
climate and site characteristics.
Factors
Local climate (sun, wind)
Site characteristics (type of terrain and landscape ie., plain,
hilly, plateau)
These two factors influence selection of suitable
cooling strategy, building design and location.

6. 2. Solar Control (Shading)
A properly designed shading system can
effectively contribute to minimizing the solar
heat gains. Shading both transparent and opaque
surfaces of the building envelope will minimize
the amount of solar radiation that induces
overheating in both indoor spaces and building’s
structure. By shading the building structure, the
heat gain captured through the windows and
envelope will be reduced.

7. • Over hangs
• Awnings
• Light colored building material and paints
• Deciduous trees

10. 3.Building Form and Layout/Orientation
The form refers to surface/volume ratio of the
building.

11. The orientation is the positioning of building in
relation to sun.

12. 4. Thermal Insulation
Insulation in the building’s envelope will
decrease the amount of heat transferred by
radiation through the facades. This principle
applies both to the opaque (walls and roof) and
transparent surfaces (windows) of the envelope.
Since roofs could be a larger contributor to the
interior heat load, especially in lighter
constructions (e.g. building and workshops with
roof made out of metal structures), providing
thermal insulation can effectively decrease heat
transfer from the roof.

14. Modulation and Heat Dissipation
This technique makes use of heat sinks which
store and remove internal heat gain.
Examples
Night sky, Earth soil, Building mass
There are two types of modulation and heat dissipation.
• Thermal Mass
• Natural cooling

15. 1. Thermal Mass
These materials store the heat during day and re-
radiate it to space at night. Concrete, brick is a
good example of thermal mass.
In summer, the re-radiated heat can be removed
through ventilation at night and vice versa for
winter.

17. 2. Natural cooling
Natural cooling refers to the use of ventilation or
natural heat sinks for heat dissipation from
indoor spaces. Natural cooling can be separated
into five categories different categories:
• Ventilation
• Night flushing
• Radiative cooling
• Evaporative cooling
• Earth coupling

18. Ventilation
Ventilation as a natural cooling strategy uses
physical properties of air to remove heat or
provide cooling to occupants.
Types
Cross ventilation
Stack ventilation

19. Cross Ventilation
It relies on wind to pass through the building for
the purpose of cooling the occupants. Cross
ventilation requires openings on two sides of
the space, called the inlet and outlet. The sizing
and placement of the ventilation inlets and
outlets will determine the direction and velocity
of cross ventilation through the building.
Generally, an equal (or greater) area of outlet
openings must also be provided to provide
adequate cross ventilation.

21. Stack Ventilation
It is the upward movement of air through
openings in a building fabric due to thermal
buoyancy and/or negative pressure generated by
the wind over the roof.

22. Night Flushing
The building thermal mass (concrete, brick)
absorbs solar heat during day and re-radiate the
same at night. The ventilation (winds) removes
the heat and make building cool.
The technique is mostly suitable in areas where
there is large difference in daily max and min
temperature.

24. Radiative Cooling
All objects constantly emit and absorb radiant
energy. An object will cool by radiation if the net
flow is outward, which is the case during the
night. At night, there is a net flow to the sky.
Since the roof provides the greatest surface
visible to the night sky, designing the roof to act
as a radiator is an effective strategy.

26. Evaporative Cooling
It is the evaporative process of water to cool the incoming
air while simultaneously increasing the relative humidity.
A saturated filter is placed at the supply inlet so the
natural process of evaporation can cool the supply air.
Apart from the energy to drive the fans, water is the only
other resource required to provide conditioning to indoor
spaces. The effectiveness of evaporative cooling is largely
dependent on the humidity of the outside air; dryer air
produces more cooling. A study found that evaporative
cooling reduced inside air temperature by 9.6 °C
compared to outdoor temperature. An innovative passive
system uses evaporating water to cool the roof so that
major portion of solar heat does not come inside

28. Earth Coupling
Earth coupling uses the moderate and consistent
temperature of the soil to act as a heat sink to
cool a building through conduction. This passive
cooling strategy is most effective when earth
temperatures are cooler than ambient air
temperature, such as in hot climates.
• Direct coupling
• Indirect coupling

29. Direct coupling or earth sheltering occurs when
a building uses earth as a buffer for the walls.
The earth acts as a heat sink and can effectively
mitigate temperature extremes. Earth sheltering
improves the performance of building envelopes
by reducing heat losses and also reduces heat
gains by limiting infiltration.

31. Indirect coupling means that a building is
coupled with the earth by means of earth ducts.
An earth duct is a buried tube that acts as avenue
for supply air to travel through before entering
the building. The supply air is cooled by
conductive heat transfer between the tubes and
surrounding soil. Therefore, earth ducts will not
perform well as a source of cooling unless the
soil temperature is lower than the desired room
air temperature.