passive cooling done on building

2.  PASSIVE COOLING
What is Passive Cooling?
What’s the purpose of Passive Cooling?
Some techniques of Passive Cooling
oSHADING
oVENTILATIONS AND COOLING
☺Natural Ventilation
☺Stack Ventilation
☺Cross Ventilation
☺Thermal Comfort
☺Night Ventilation

3. OTHER TECHNIQUES:
☺Evaporative Cooling
☺Desiccant Cooling
☺Time Lag Cooling
☺Earth Cooling

4. Passive House
- refers to the
rigorous, voluntary, Passivhaus standard
for energy efficiency in a building, reducing
its ecological footprint.
Ecological Footprint
- The ecological footprint is a measure of human
demand on the Earth's ecosystems.
Conduction
- The transfer of energy, such as heat or an
electric charge, through a substance.

5.  Convection
- The act or process of conveying;
transmission.
 Radiation
- is energy that comes from a source
and travels through some material or
through space.

7.  Passive Cooling
- Passive cooling refers to technologies or design features
used to cool buildings without power consumption, such
as those technologies discussed in the Passive
house project.
 The term "passive" implies that energy-consuming
mechanical components like pumps and fans are not
used.
 Passive cooling building design attempts to integrate
principles of physics into the building exterior envelope
to:
Slow heat transfer into a building. This involves an
understanding of the mechanisms of heat
transfer: heat conduction, convective heat
transfer, and thermal radiation (primarily from the
sun).
Remove unwanted heat from a building. In mild
climates with cool dry nights this can be done
with ventilating. In hot humid climates with
uncomfortable warm / humid nights, ventilation is
counterproductive, and some type of solar air
conditioning may be cost effective.

8.  Provides indoor comfort
 Low maintenance
 Zero/ Low energy consumption
 Low running cost
 Promotes healthy environment
☺Saves the Earth

9.  SHADING
 Shading a building from solar radiation can be
achieved in many ways.
Buildings can be orientated to take
advantage of winter sun (longer in the East
/ West dimension), while shading walls and
windows from direct hot summer sun. This
can be achieved by designing location-
specific wide eaves or overhangs above
the Equator-side vertical windows (South
side in the Northern hemisphere, North side
in the Southern hemisphere).

11.  VENTILATION
› The mechanical system or equipment used
to circulate air or to replace stale air with
fresh air.
Ventilation in buildings has three main
purposes:
1. To maintain a minimum air quality
2. To remove heat (or other pollutant)
3. To provide perceptible air movement to enhance
thermal comfort

12. Natural Ventilation
oStack Ventilation
oCross Ventilation
oNight Ventilation

13.  Stack ventilation is where air is driven
through the building by vertical pressure
differences developed by thermal
buoyancy. The warm air inside the building
is less dense than cooler air outside, and
thus will try to escape from openings high
up in the building envelope; cooler denser
air will enter openings lower down. The
process will continue if the air entering the
building is continuously heated, typically by
casual or solar gains.

15.  The most effective application of this
natural law (stack effect) is a "thermal
chimney," a solar-exposed enclosure tall
enough to generate maximum air flow
and massive enough to retain heat and
power the system into the evening hours.

17.  Stack ventilation, can operate when no
wind pressure is available. A building can
be designed to induce its own
ventilation by duplicating the
temperature stratifications that are the
source of wind itself.
 It must be born in mind that the stack
effect can only take place when the
average temperature in the stack is
greater than the outside air.

18.  Typically the stack effect is quite weak, and therefore
openings and ducts must be large, to minimize
resistance.
 The pressure difference within the stack varies with
height resulting in diminishing air flows from spaces
opening on to the stack, as their height above ground
floor increases.
 In tall spaces (multi-room height) the temperature of the
air may be hotter in the upper zone. This is referred to
as stratification. For a given average temperature, this
means that there is a cooler zone at the bottom, which
is good news if this is the only occupied space. However
it means that rooms facing the upper zone may
experience unwanted heat gains, as well as reduced
stack effect due to their smaller stack height.

19.  Due to the weakness of the driving
pressures generated by thermal
buoyancy, openings have to be large and
unobstructed. This means that they will
readily transmit noise. Noise attenuating
techniques, often used in ductwork of
mechanical systems, involve labyrinthine
pathways, lined with acoustic absorber. This
principle can be applied here but has to be
on a large scale in order to cause a
minimum flow resistance.

20.  Wind-induced ventilation uses pressures
generated on the building by the
wind, to drive air through openings in the
building. It is most commonly realised as
cross-ventilation, where air enters on one
side of the building, and leaves on the
opposite side, but can also drive single
sided ventilation, and vertical ventilation
flows.

22.  Wind speed and direction is very variable.
Openings must be controllable to cover the
wide range of required ventilation rates
and the wide range of wind speeds.
 As with stack ventilation, the internal flow
path inside the building must be
considered.
 For cross-ventilation, bear in mind that the
leeward space will have air that has picked
up heat or pollution from the windward
space. This may limit the depth of plan for
cross-ventilation.

23.  As with stack ventilation, the requirement
for large openings may present problems
with noise control. Also, the need to
provide flow paths within the building
may conflict with acoustic separation
beteen internal spaces. However, the
provision of by-pass ducts can help
reduce this.

24.  the condition of mind that expresses
satisfaction with the thermal environment
and is assessed by subjective evaluation.

25.  Night ventilation is the use of the cold night air
to cool down the structure of a building so
that it can absorb heat gains in the daytime.
This reduces the daytime temperature rise.
 An overheating prevention strategy which uses
little or no fossil energy, and together with other
passive strategies such as natural ventilation
and shading , can avoid the use of air-
conditioning. This saves energy (and CO2
emissions), and once set-up would require
lower maintenance than mechanical systems.

27.  EVAPORATIVE COOLING
› Swamp coolers, fountain courts, and atrium
pools are all applications of evaporative
cooling, a particularly powerful technique in
climates of low relative humidity. When a
body of water is placed in a hot and
relatively dry space, the water evaporates
into the air and increases humidity.

29.  System combines induced ventilation to
bring air from underground over an
activated charcoal desiccant and cool
the interior with dry air. As the air warms
and exits high on the south wall, it passes
over the saturated desiccant plate,
spurring the evaporative process

31.  The principle is that the transmission of
heat through mass—stone, concrete,
adobe-—is both delayed and
attenuated over time. Depending on the
material and the thickness of a massive
wall, the delay can stretch from two to
12 hours, and the greater the lag the
greater the attenuation of heat
transmitted.

32.  Another method for taking advantage of
Mother Earth is to pre-condition air by
running it through subterranean cool
pipes before it enters the building, or by
storing it in a below-grade rock storage
chamber before use