The document discusses heat transfer and thermal comfort in buildings. It defines thermal comfort and explains the factors that affect it, including air temperature, mean radiant temperature, air velocity, humidity, clothing, and activity level. It also describes the three main modes of heat transfer: conduction, convection, and radiation. Finally, it provides examples of passive strategies that can be used to improve thermal comfort, such as building orientation, shading devices, thermal mass, ventilation, insulation, and green roofs.

1. HEAT TRANSFER IN BUILDINGS
ENERGY CONSCIOUS
ARCHITECTURE
SUBMITTED TO-
AR. SHUBHAM SINGH
ASSIGNMENT - 3
SUBMITTED BY – SHAHEEN PARVEEN
B.ARCH 5TH YEAR ‘A’

2. 2
WHAT IS THERMAL COMFORT?
Thermal comfort is “the state of mind that
expresses satisfaction within the thermal
environment” and generally assessed subjectively
(ASHRAE, 2004).
Human thermal comfort cannot be expressed in
degrees
and can’t be defined by an average range of
temperatures.
It is a very personal experience and a function of many
criteria, which differs from person to person in the

3. A lack of thermal comfort makes us feel stressed, annoyed and
distracted if it is too cold and it can make us feel sleepy, tired, and
lacking concentration if it is too hot.
The need for thermal comfort is as follows:
 Thermal Comfort Increases Productivity and Performance.
 Provides insulation from harsh outside weather conditions.
 Provide better radiant and ambient temperature within the envelope
of the building.
 Reduces high energy demands and conserve extra energy for future
use.
 Promote sustainability to the design and surrounding environment.
NEED FOR THERMAL COMFORT-

4. TRANSFER OF HEAT IN BUILDING
ENVELOPE
Mode of Transfer of Heat
What affects the Thermal indoor environment?
• The heat exchange between the human body and its environment occurs mainly
in
three ways
• Conduction
• Convection
• Radiation
Thermal indoor environment is affected by both
internal and external sources.

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Conduction
Conduction is the diffusion of internal heat within a body as a result of
a temperature difference across it.
This is particularly important in buildings where there may be
a temperature difference between the inside and outside of a building,
such as in a heated building during winter. Conduction is one of the
main potential heat transfer mechanisms by which the
internal heating or cooling can be lost to the outside, resulting in
high operating costs, high carbon emissions and occupant discomfort.
For building materials it is sometimes thought that conductivity is
expressed by the U-Value, however, U-values are the reciprocal of the
sum of the thermal resistances of a body plus its inside and outside
surface thermal resistances. Conductivity is more accurately
expressed by a material's R-Value, which is the reciprocal of
its thermal resistance and does not include a surface component.
See U-Value for more information.
Conduction can be inhibited by insulating materials which have a
high thermal resistance and so help reduce heat transfer between the

6. 6
Convection
Convection is the movement of a fluid, such as the air, by
advection and diffusion. This is a very important mechanism in the
design of buildings, where air movement is necessary to: Moderate
internal temperatures. Reduce the accumulation of moisture,
odours and other gases that can build up during occupied
periods.Improve the comfort of occupants.
Convection is also a heat transfer mechanism, resulting from the
movement of air of different temperatures.Air movement in
buildings can be 'forced' (for example driven by fans), or 'natural'
resulting from pressure differences from one part of a building to
another. Natural air movement can be either wind driven, or
buoyancy driven.
Fluids can also be used to transfer heat within a building by 'mass
transfer', for example by the flow of a refrigerant, chilled water or
hot water around a building to provide heating or cooling

7. 7
Radiation
The difference in the total amount of radiation emitted and absorbed by a body at any given moment may result in a net heat
transfer which will produce a change in the temperature of that body.The range of terrestrial temperatures experienced within the
built environment is relatively small, and relative to the temperature of the sun this range is 'cold' and so radiating at a 'long'
wavelength compared to the sun. This anomaly allows us to categorise thermal radiation as short-wave solar radiation and
terrestrial or long wave infra-red radiation. Surfaces in the built environment will tend to absorb solar radiation and emit long wave
infra-red radiation. This difference also produces effects such as the greenhouse effect. The atmosphere is relatively transparent to
solar radiation, this means it allows sunlight to enter the atmosphere and heat the Earth's surface. These surfaces then re-radiate
that heat as long-wave infra-red radiation, which greenhouse gases tend to absorb rather than transmit. The result is that the long-
wave infra-red radiation is 'trapped' and heat accumulates in the atmosphere causing a warming process.
The thermal optical properties of a material are a function of three basic parameters; transmittance, reflectance, and absorptance
(or emissivity) , describing the ratio of the transmitted, radiated or absorbed radiation to the incident radiation. These properties
vary depending on the wavelength and angle of the incident radiation.

8. 8
HUMAN BODY PERCEPTION TOWARDS
THERMAL COMFORT
Heat Mechanism And Human
Body Perception Towards
Thermal Comfort

9. 9
FACTORS AND INDICES AFFECTING
THERMAL COMFORT
Environmental
Parameters/Factors
• Air Temperature
• Mean Radiant Temperature
• Air Velocity
• Humidity
Personal Parameters/Factors
• Clothing Level
• Physical Activity

10. 10
FACTORS AND INDICES AFFECTING
THERMAL COMFORT
Air
Temperature
It can easily be influenced with passive and mechanical heating and cooling.
Mean
Radiant
Temperature
It allows defining the operative temperature which is the most essential component
of thermal comfort.
Air Velocity Quantifies the speed and direction of the air movements in the room. Rapid air
velocity fluctuations might result in draught complaints.
Humidity The moisture content of the air. Too high or too low humidity levels may
induce discomfort.
Clothing Level The amount of insulation added to the human body. Higher clothing levels will
reduce the heat lost through the skin and lower the environment´s temperature
perceived as comfortable.
Physical Activity The amount of heat produced by the human body and therefore also in the
perception of a hot or cold environment.

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FACTORS AND INDICES AFFECTING
THERMAL COMFORT
Derived Parameters For Measuring Thermal Comfort
• Mean Radiant temperature: The mean radiant temperature
representation of how human beings experience radiation.
• Operative temperature: Operative temperature is defined as a uniform temperature of a
radiantly black enclosure in which an occupant would exchange the same amount of heat
by radiation plus convection as in the actual non-uniform environment. Numerically it is
close to the average of indoor dry bulbs and MRT.
• Effective temperature: Combination of 50% relative humidity with the operative
temperature that causes the same sensible plus latent heat exchanges as in the actual
environment.
It is an experimentally determined index of the various combinations of dry-bulb
temperature, humidity, radiant conditions (MRT), and air movement.

12. 12
Appropriate orientation of the building
• Daylight penetration and fenestration design
have
implications on heat gain/loss through the building
envelope.
• Careful orientation of fenestration can help achieve
thermal and visual comfort
• Daylight harvesting from the north and south
facade should be maximized with proper
orientation of the
PASSIVE STRATEGIES FOR THERMAL COMFORT

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Shading Devices
• Reduce heat gain and cooling
energy use of the building.
• To prevent summer overheating and
glare, a good shading device
strategy should be used with glazed
openings.
• Well designed sun shading devices
will help keep the building cool and
comfortable
PASSIVE STRATEGIES FOR THERMAL COMFORT

14. 14
PASSIVE STRATEGIES FOR THERMAL COMFORT
• Exterior shading devices can be
provided in a variety of materials and
designs, sunshades, awnings,
louvers, bamboo screens, jaali, and
green cover through vines.
• These can be implemented with
minimal cost implications and have
the most favorable cost-benefit
relation with respect to thermal
comfort.

15. 'Thermal mass' describes a material's capacity to absorb, store and release heat.
A common analogy is thermal mass as a kind of thermal battery.
• When heat is applied (to a limit) by radiation or warmer adjoining air, the battery
charges up until which time it becomes fully charged.
• It discharges when heat starts to flow out as the adjoining air space becomes relatively
cooler.
PASSIVE STRATEGIES FOR THERMAL COMFORT

16. • Denser thermal mass materials are more effective passive solar materials.
Thus, denser the material the better it stores and releases heat.
• Integrate thermal mass with an efficient passive solar design, by considering
the placement of added mass.
• Do not substitute thermal mass for insulation. It should be used in conjunction
with
insulation.
PASSIVE STRATEGIES FOR THERMAL COMFORT

17. PASSIVE STRATEGIES FOR THERMAL COMFORT

18.  Layout facilitates hot
air exhaust using
stairwell.
 Airflow
and
facilitation
natural
ventilation.
 Use of trees to limit
sun path.
 High thermal
mass
materials in
envelope.
PASSIVE STRATEGIES FOR THERMAL COMFORT

19. PASSIVE STRATEGIES FOR THERMAL COMFORT

20. ● Green roofs.
● Louvre and shading devices.
● Insulation
● Low energy cooling
techniques.
● Wind catchment and
ventilation.
● Double glazed glass.
● High solar reflective surface.
PASSIVE STRATEGIES FOR THERMAL COMFORT

21. Internal Sun Shading Devices
By the name, internal shading devices are incorporated within a building’s interior. They basically comprise of
some forms of material covering the glare coming in from the window openings. They function in various ways;
some are brightly coloured and reflect solar rays back outwards of the building while some are even designed to
absorb the solar rays. They are flexible and administered time to time based on the wish of the occupants of the
building. They include drapes, venetian blinds, louvers, curtains, shutters etc.
1. Venetian Blinds
The venetian blind is a common used kind of window blind consisting of numerous
horizontal slats that are pivoted to be able to control the amount of solar rays
passing through. This shading system can be likened to that of the louvres but the
horizontal layers are on a multiplied scale. Venetian blinds add aesthetic value to
the interior and are also functional. Adjusting the tilting angle of the blinds
efficiently controls the amount of light entering the interior spaces. Depending on
the angle, heat and light rays are either reflected away from the building or
transmitted into the interiors. In cases where the occupants would like a total view
of the outdoors and wouldn’t want their line of vision to be hindered by the
venetian blinds, draw cords are provided. These draw cords help to completely
raise the venetian blinds into a compacted collapsed position where the venetian
blinds pose no threat to the line of vision of the occupants to the outdoors. They
are finished with various patterns and colours that usually have high reflectance
values.

22. Internal Sun Shading Devices
2. Louvres
Louvres are usually used in door and window types. Louvres by definition
have a set of angled slats at regular intervals, which screen the amount of
light, heat and air passing through into the interior spaces. They can either
be flexible or fixed.
When flexible or operable, they are engineered to be able to rotate
through an approximately 180-degree axis. If the occupant chooses not to
totally reflect the light outwards of the building, the louvres can be angled
in a way that the light rays are bouncing of its usually reflective material
into the interior space. When installed at fixed angles, the louvres are
engineered to reflect outwards the higher and hotter sun rays and let the
lower and less warm sun rays into the interior spaces.
Aluminium alloys are the most commonly used materials for making sun
louvres. For longevity and durability of these materials, the alloys are
usually powdered, coated or even painted. These tweaks to its
appearance also enhance its aesthetic effects on the building’s general

23. Internal Sun Shading Devices
3. Roller Shades
This system is a little similar to the venetian blinds. They are also called
‘roller blinds’ or ‘roll-down shades’. This system is highly operable by the
occupants. The roller shades are engineered to fit into the window frame
and are just like an extra layer of material entering the interior space. Roller
shades are created in a very wide variety of materials, weaves or fabrics.
The most common roller shades types are made of completely opaque
materials are usually put in place to darken rooms and attain maximum
privacy. They act as insulators on small scale, block solar rays entering the
interiors and also help to trap air sometimes.

24. External Sun Shading Devices
a) Horizontal Sun Shading Devices
Horizontal shading devices exist mostly in form of roof eaves and overhangs, canopies, balconies and horizontal
shelves and so on. They are best suited to the longer southern and northern building elevations.
I. Projecting Horizontal Shelves and Balconies
This is a commonly used method of shading northern and southern building
faces. They are of little or no value on any other orientation. Horizontal shelves
must be considered at the initial stages of the design and built into the
building’s structure, by reason of this; they are limited to new construction. For
effectiveness, they should be a lot wider than the windows. As usual, they are
installed at levels above that of the windows. Shelves are installed along the
whole span of the northern or southern faces if the windows are in close
proximity to each other. Projected horizontal shelves on a building. As for the
balconies; they usually produce the same effect as in the case of the
horizontal shelves. They provide considerable shading even when they are not
facing a northerly or southerly direction. Balconies help provide additional
value as they can be utilized as spaces, aesthetic components and as
ambiance features.

25. External Sun Shading Devices
II. Awnings
Awnings are downwardly projected building elements made out of canvas
sheets or other building materials attached to buildings’ exterior walls serving
as covering for windows and other openings. Usually made up of canvas,
polyestered fabric, or sometimes cotton. They are usually designed to be
retractable. (D. R. Wulfinghoff, 1999) Awnings are usually supported by
smaller lighter structures of wood, aluminium or steel, which are also
attached to the buildings exterior walls. These support structures are either
space frames, planar frames or even truss systems at times. When the use of
fabric awnings does not seem practicable, louvred aluminium awning systems
are commonly used. Awnings should be designed to be larger than the
window spaces, to prevent excessive amount of heat gain from the sides.

26. External Sun Shading Devices
III. Overhangs And Roof Eaves
Overhangs are very widely used shading devices. By definition, they are
usually horizontal projections from the roofs or exterior walls above windows,
doors and other openings. They can support vegetation, solid and are
sometimes louvred even employ all these forms at the same time. Most
scholars classify roof eaves as a type of overhang and some don’t. (Crosbie,
1997) states that fixed overhangs are the most durable but also the least
flexible and efficient. When designing in passive solar building designs, eaves
can get extended to even two metres. Asides helping in achieving thermal
comfort, they help to reduce below-grade moisture problems and protecting
the wall paints or finishes.

27. External Sun Shading Devices
IV. Recessed and Inset Windows
When inset windows are employed, it is the entire exterior walling
that acts as a shading device. This is a very rigid and non-flexible
system. Apparently, to use this system, a designer must have put it
into consideration from the initial stages of the design. Unlike other
rational methods of actually trying to minimize solar heat gain, the
use of recessed and inset windows is most times for the aesthetic
satisfaction. It is even considered a waste of utilizable space and is
very expensive to be designed. It also drastically reduces amount of
natural day lighting received by the building’s interior. Although, when
this system is properly thought about and designed, it can be one of
the most effective sun shading systems.

28. External Sun Shading Devices
b) Vertical Sun Shading Devices
I. Fins
Fins are vertical sun shading devices placed on openings of a
building. They are used to shade building surfaces and interiors from
the sun’s intense solar rays. as wisdom should demand, they are
usually placed on the parts of the building facing the eastern and
western direction for effective functioning. Depending on the type,
these fins can be adjusted to tilt at different angles at different times
in the day. The effectiveness of these fins also depends on their
depth. The farther away the depth of the fin is from the building, the
greater the shadow it casts hence, increasing its shading effect. Like
all other sun shading devices, they also add an aesthetic effect to
the buildings general outlook.

29. External Sun Shading Devices
c) Egg-crate Sun Shading Devices
Like earlier stated, these egg-crate sun shading devices are invented
when both horizontal and vertical shading devices are implored at
the same time intertwined with each other on the same building.
They can look like blocks, grills, and sometimes, depending on the
designer’s creativity, they can take the form of decorative patterns
like circles and different sizes depending also on the designer’s
specifications. Similar to the fins, with knowledge of the sun path in
that region and the building’s orientation, they are usually placed on
the parts of the building facing the east and western directions. The
egg-crate sun shading devices might add the most aesthetic values
to buildings when considered; they are the least flexible of shading
devices. They are also expensive and have several complications in
installation; this then discourages their extensive in residential
buildings.

30. External Sun Shading Devices
d) Vegetative/Natural Sun Shading Devices
Natural shading devices are the last types to be looked at. They
actually perform quite a number of functions when they are put in
place. Unlike every other shading device earlier mentioned, the use
of vegetation (trees and shrubs) as shading devices aids the whole
ventilation process as they create and exchange of gases. These
same trees provide shading for both the openings on the buildings
and even the buildings’ exterior surfaces. How effective these trees
are with shading depends on the kinds of trees planted. Trees with
thicker foliage will obviously provide more effective shading effects
than those with foliage not as thick. In selecting these trees, special
characteristics based on seasonal variations for these trees must
also be considered. Maintenance plans must also be made, as
these trees will most definitely shed their leaves from time to time.

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