THERMAL COMFORT BY ADEEBA AFREEN

UNIT -1
-THEORY OF HEAT FLOW
-THERMAL COMFORT
-BODY HEAT BALANCE
-UNITS OF HEAT ENERGY
-PERIODIC HEAT FLOW
-THERMAL PERFORMANCE OF BUILDING ELEMENTS
-THERMAL PROPERTIES OF MATERIALS
PRESENTATION BY ADEEBA AFREEN-B.DES-S.M.E @ BONFIRE INSTITUTE OF DESIGN

-THEORY OF HEAT FLOW
•CONDUCTION – heat transfer through direct contact with cool surfaces.
For example, as we step on a cool surface our body heat quickly starts
moving from our body to the stone material.
•CONVECTION – movement of active warm air molecules to cooler
areas.
For example, when air moves pass our body it observes its energy/heat.
•RADIATION – heat radiates to cooler surfaces without any physical
contact.

-THERMAL COMFORT is the condition of mind that expresses
satisfaction with the thermal environment.
•Thermal comfort defines not only our well-being but our
physical and intellectual performance.
•There are many factors that effect human thermal comfort,
such as
-Air temperature,
-Temperature of surfaces,
-Humidity, and
-Air movement.
All of the above may be grouped under "environmental
variables".
•"Personal" variables such as clothing insulation value ["clo"
value] and the metabolism rate ["met" value] are also
important components.

metabolic rate is the amount of energy expended by a person in a given time
period - usually daily. In periods of inactivity, the metabolic rate is known as the
basal metabolic rate (BMR). At rest, the BMR is low compared to when the body is
undergoing activities like exercise.
-BODY HEAT BALANCE

-BODY HEAT BALANCE
•A temperature around 37°C is required for our
body in order to feel comfortable and in addition
to perform all the necessary functions in the best
way.
• If this temperature drops or rises, the body
immediately reacts doing what is needed to
maintain its temperature.
•In cold environments for example, the body
generates heat by movement (shivering).
• On the other hand in too hot environments,
cooling of the surface of the skin is achieved by
evaporation.
• In general, there is a constant effort to keep the
temperature of the body at the acceptable levels,
which involves the continuous cooperation of the
body with its environment.
•This is what we call metabolic rates.
•What is more important is that this metabolic rate
is associated with the activity that a person is
doing at a specific time (physical activity). When
the physical activity increases the heat produced
by the body increases as well. As a result the
perception of hot and cold is affected as well.
If the ambient temperature drops,
the body first allows the extremities
to cool in order to protect the
functions of the brain, heart and
other vital organs.

-BODY HEAT BALANCE
The body’s heat balance can be expressed as
M ± R ± Cv ± Cd - E = ΔS
where M = metabolic rate
Cv = convection
R = net radiation
Cd = conduction
E = evaporation heat loss
ΔS = change in heat stored

The joule is a derived unit of energy.
It is equal to the energy transferred to (or
work done on) an object when a force of
one newton acts on that object in the
direction of its motion through a distance
of one metre (1 newton metre or N⋅m).
A newton is the force required to give a
mass of 1 kilogram (1 kg) an acceleration
of 1 meter per second per second (1
m/s2). It is abbreviated as N

-PERIODIC HEAT FLOW
In nature the variation of climatic conditions produces a non- steady state. Diurnal
variations produce an approximately repetitive 24-hour cycle of increasing and
decreasing temperatures. The effect of this on a building is that in the hot period heat
flows from the outdoors into the building, where some of it is stored, and at night during
the cool period the heat flow is reversed: from the building to the outside. As this cycle
is repetitive, it is described as periodic heat flow.
The diurnal variations of external and internal temperatures is a periodic cycle. In the
morning, as the outdoor temperature increases, heat starts entering the outer surface of
the wall. Each particle in the wall will absorb a certain amount of heat for every degree
rise in temperature, depending on the specific heat of the wall material. Heat to the next
particle will only be transmitted after the temperature of the first particle is increased.
Thus the corresponding increase in the internal temperature will be delayed.
The outdoor temperature reaches its peak and starts decreasing, before the inner
surface temperature has reached the same level. From this moment the heat stored in
the wall will be dissipated partly to the outside and only partly to the inside. As the out
door air cools, an increasing proportion of this stored heat flows outwards, and when
the wall temperature falls below the indoor temperature the direction of the heat flow is
completely reversed.

-THERMAL PERFORMANCE OF BUILDING
ELEMENTS i.e BUILDING ENVELOPE
•The building envelope is the physical separator
between the interior and the exterior
environments of a building.
•The physical components of the envelope
include the floors, roofs, walls and openings
(doors and window)
•The thermal performance of the building
envelope can make a significant contribution to
reducing the overall building energy usage.
•It serves as the outer shell to help maintain the
indoor environment (together with the
mechanical conditioning systems)

•One of the key elements of modern building
envelopes is the integration of design and window
strategies to bring daylight into a building's interior
without heat and glare.
•Other key elements of the building envelope that
affect thermal performance include shading
elements, air tightness, wall and roof insulation and
roof reflectance.

Of the total solar radiation incident on the outer surface of the wall, a
part of it is reflected to the environment.
The remaining part is absorbed by the wall and converted into heat
energy.
A part of the heat is again lost to the environment through convection
and radiation from the wall’s outer surface.
The remaining part is conducted into the wall; where it is partly stored ,
thereby raising the wall temperature , while the rest reaches the room’s
interior surface.
The inner surface transfers heat by convection and radiation to the room
air, raising its temperature.
Additionally, mutual radiation exchanges between the inner surfaces of
the building also occur (for example, between walls, or between a wall
and roof).Such heat transfer processes affect the indoor temperature of
a room and consequently, the thermal comfort experienced by its
occupants.
Insulation in walls and ceiling spaces can affect the amount of heat
entering or leaving your home. The level of insulation required will vary
depending on what roofing and walling materials you choose.

WINDOWS AND DOORS: Well-positioned windows and doors
allow you to take advantage of the naturally cooling effects of
summer breezes.
• Louvers can also be good for promoting air movement on hot
days.
•One way to improve a window's energy efficiency is to increase
its insulation ability by making it from two or more panes of glass,
separated by either a vacuum (as in a thermos bottle) or an inert
gas that conducts less heat than air does, like argon or krypton.
•Some high performance windows are called "low emissivity
windows" or "low-e windows", referring to the low emission of
infrared radiation (heat) due to low-e coatings on the glass.
•Advanced high performance windows can reduce energy losses
to nearly zero, achieving energy savings.

SKYLIGHTS can introduce daylight in poorly oriented sections of a building,
unwanted heat transfer may be hard to control but energy that is saved by
reducing artificial lighting is often more than the energy required for operating
HVAC systems to maintain thermal comfort.

-THERMAL PROPERTIES OF MATERIALS
•Most homes have their wall
cavities filled with some kind of
insulation.
•There are many different materials
used for insulation.
•Homes built in climates which
experience extreme heat and/or
cold should be fitted with insulation
that does not transfer energy.
•Examples of insulating materials
are wool and polyester.

-THERMAL PROPERTIES OF MATERIALS - CONCRETE SLAB
• In older buildings, concrete slabs were cast directly on the ground and would drain
heat from a room.
•In modern construction, concrete slabs are usually cast above a layer of insulation
such as expanded polystyrene, and the slab may contain underfloor heating pipes.
•However, there are still uses of an uninsulated slab, typically in outbuildings which are
not heated or cooled to room temperature.
•In those cases, casting the slab directly onto a rocky substrate will maintain the slab at
or near the temperature of the substrate throughout the year, and can prevent both
freezing and overheating.
• It is a disadvantage where the rooms are heated intermittently and require a quick
response, as the concrete takes time to warm up, causing a delay in warming the
building.
•But it is an advantage in climates with large daily temperature swings, where the slab
acts as a regulator, keeping the building cool by day and warm by night.

-THERMAL PROPERTIES OF MATERIALS - GLASS

UNIT -2
-WIND CONTROL
https://buildingscience.com/documents/digests/bsd-014-air-flow-control-in-buildings
https://www.youtube.com/watch?v=gAMPJyOY34s
https://www.youtube.com/watch?v=H8SgVi5_4qg

•The control of air flow is important for several
reasons:
1.To control moisture damage
water vapour in the air can be deposited within the
envelope by condensation and cause serious health,
durability, and performance problems.
2.To reduce the use of energy.
3.To ensure occupant’s comfort and health.
cold drafts and the excessively dry wintertime air that
results from excessive air leakage directly affect human
comfort, wind-cooled portions of the interior of the
enclosure promote condensation which supports
biological growth which in turn affects indoor air
quality.
Mould around a windowsill

For air flow to occur, there must be both:
1. A pressure difference between two points, and
2. A continuous flow path or opening connecting
the points.

There are three primary mechanisms which generate the pressure differences required for
air flow within and through buildings.
1.wind
2.stack effect or bouyancy
Stack effect pressures are generated by differences in air density with temperature, i.e. hot
air rises and cold air sinks.
3.mechanical air handling equipment and appliances.
Fans and blowers cause the movement of air within buildings and through enclosures. If
more air is exhausted from a building than is supplied, a net negative pressure is generated
and vice versa. In design, one should aim for almost no mechanically-induced air pressure
across the enclosure. This is achieved by balancing systems so that the same amount of air
is supplied as is exhausted. In some case pressurization can be used to control airflow
direction.
Since, it is widely
acknowledged that a
perfectly airtight air barrier
system is unlikely to be
achieved in practise, it is
also desirable to control the
air pressure differences
driving the flow.

UNIT -3-SOLAR
-INTRODUCTION TO PASSIVE SOLAR HEATING AND COOLING
-DIRECT SOLAR RADIATION
-CONVECTIVE COOLING
-CONDUCTIVE COOLING
-EVAPORATIVE COOLING

-INTRODUCTION TO PASSIVE SOLAR HEATING AND COOLING
In passive solar building design, windows, walls, and floors are made to
collect, store, reflect, and distribute solar energy in the form of heat in the
winter and reject solar heat in the summer. This is called passive solar design
because, unlike active solar heating systems, it does not involve the use of
mechanical and electrical devices.
•The key to design a passive solar building is to best take advantage of the
local climate performing an accurate site analysis.
• Elements to be considered include window placement and size, and glazing
type, thermal insulation, thermal mass, and shading.
•Passive solar design techniques can be applied most easily to new buildings,
but existing buildings can be modified.

PASSIVE SOLAR COOLING

-DIRECT SOLAR RADIATION

-CONVECTIVE COOLING is the mechanism where heat is transferred from the hot
device by the flow of the fluid surrounding the object. The fluid can either be air,
which is most common, or another suitable liquid.
There are two types of convectional cooling,
namely
1.Natural convection cooling - the air surrounding
the object transfers the heat away from the
object and does not use any fans or blowers.
2. Forced air convection cooling - This is used in
designs where the enclosures or environment do
not offer an effective natural cooling performance,
in high power applications, and other areas where
natural cooling is not effective.
other areas where natural cooling is not effective.
The forced air convectional cooling uses a cooling
fan to blow and direct air towards the electronic
components. Most power supply units have built-
in fans that provide the require forced-air
convectional cooling.

-CONDUCTION COOLING: This is defined as the transfer of heat from one hot part to
another cooler part by direct contact.
-EVAPORATIVE COOLING: reduction in temperature resulting from the evaporation of a
liquid, which removes latent heat from the surface from which evaporation takes place.
This process is employed in industrial and domestic cooling systems, and is also the
physical basis of sweating.
https://www.youtube.com/watch?v=vLfWnX0ahtc
https://www.youtube.com/watch?v=m3PxzQwVOyo
https://www.youtube.com/watch?v=NiPLJEFRBnM

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