HEAT FLOW THROUGH BUILDINGS IN NIGERIA
Course Title: APPLIED CLIMATOLOGY
BY
OLABIWONNU ABIMIBOLA OLADUNNI
ARC/05/5628
Department of Architecture.
School of Post Graduate Studies,
The Federal University of Technology Akure, Ondo State.
Course Mentor: Prof. Ogunsote
AUGUST, 2011
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TABLE OF CONTENTS
1.0
INTRODUCTION
1.1
HEAT FLOW
1.1.1 CONDUCTION
1.1.2 CONVECTION
1.1.3 RADIATION
1.2
SOURCES OF HEAT FLOW IN BUILDINGS
1.2.1 SOLAR RADIATION THROUGH WINDOWS
1.2.2 ANY LEAKAGE FROM THE BUILDING ELEMENTS
1.2.3 VENTILATION AND CROSS VENTILATION
1.2.4 OBJECTS IN THE BUILDING ENVELOPE OTHER THAN WINDOWS
1.2.5 HEAT GENERATION
1.3
SOLAR HEAT GAIN
1.3.1 SOLAR GAIN THROUGH BUILDING
1.3.2 SOLAR GAIN THROUGH THE USE OF MATERIALS
1.4
THERMAL DESIGN
1.4.1 THERMAL ENERGY
1.4.2 THERMAL INSULATION
1.4.3 NIGERIAL CLIMATIC ZONES
1.5
ENERGY EFFICIENT BUILDINGS
1.5.1 GREENHOUSE EFFECT
1.5.2 AIR FLOW
RECOMMENDATION
CONCLUSION
REFERENCES
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1.0
INTRODUCTION
Heat flow is an inevitable consequence of contact between objects of differing
temperature. In order to maintain acceptable temperatures in buildings, there will be various
uses of large proportions of global energy consumption. When buildings are well insulated, it
is more energy-efficient and it provides more uniform temperatures throughout the spaces
both internally and externally. There is less temperature gradient both vertically and
horizontally from exterior walls, ceilings and windows to the interior walls, thus producing a
more comfortable occupant environment when outside temperatures are extremely cold or
hot.
In Nigeria, different climatic zones have affected the flow of heat through buildings.
Nigeria is a country located in West Africa and shares land borders with the Republic of
Benin in the west, Chad and Cameroon in the east, and Niger in the north. Its coast in the
south lies on the Gulf of Guinea on the Atlantic Ocean. Also, the three largest and most
influential ethnic groups in the country are the Hausa, Igbo and Yoruba and they also affect
the building types in their respective location as a result of their culture, traditional religion
and weather condition.
1.3
HEAT FLOW
Heat is the energy of molecular activity (Ashrae 1971) .It is present in all matter and it
moves naturally from warmer part to cooler part or objects or spaces. It is a form of energy
measured in joules (J). Heat is transferred from a high temperature zone towards a low
temperature zone via three different modes of heat transfer. In view of this, heat energy
(thermal energy) is transferred when different parts of a substance are at different
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temperatures. It is transferred from an area of higher temperature to one at a lower
temperature.
Heat transfer is made up of these media in Nigeria.
(a) By convection and radiation from the hot air and surrounding surfaces to the wall surface
in buildings.
(b) By conduction through the wall in an enclosure.
(c) By convection and radiation from the wall surface to the cold air and surrounding surfaces
1.3.1
CONDUCTION
This is the transfer of heat through a material i.e. it is transferred directly in and through
the substance. Heat loss or gain through conduction results from the transfer of heat directly
through the materials of the building envelope (Evans 1980). If the outside temperature is
greater than the inside temperature, there is heat gain from outside the building. Conduction
can also occur through heat lost or gained through our windows, walls and roofs, some
building materials which are poor or good conductors of heat or any two contacting objects
can allow heat transfer to occur. Furthermore, conduction depends on molecular activity and
requires the presence of matter.
Figure 1- Example of conduction is heat transfer through wall.
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1.3.2
CONVECTION
This is the transfer of heat from particle to particle. It is the transfer of heat by the
movement of fluids such as air or water. Convention is of two type’s namely natural and
forced convention. It is natural type if it occurs without the use of mechanical means e.g.
naturally hot air rises and cool air sinks while forced convection is referred to the use of fans
or pumps to move a fluid or air and the heat contained in it e.g. forced-air furnaces mostly in
bathrooms in the homes.
1.3.3
RADIATION
This is energy transmitted directly through space. It requires a line of sight connection
between the objects without requiring matters in transmission. All objects radiate energy or
heat, which heats all cooler objects around it. Solar radiation passes through space to heat and
light objects that it strikes. For example, a person in a room with cold windows will radiate
heat to the windows and that person will feel cool even if the air in the room is warm, if the
window is covered, the sight connection is broken and that person will no longer feel cool.
1.4
SOURCES OF HEAT FLOW IN BUILDINGS
The two most important sources of heat flow are heat from the sun and air movement.
Heat from the sun creates passive solar design and air movement with different climatic zones
and various temperature in Nigeria. The natural tendency of heat is to move from warmer
objects or spaces to cooler objects or spaces. The heat flow through buildings is from:

Solar radiation through windows.

Any leakage from the building materials
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
Ventilation and cross ventilation

Objects in the building envelop other than windows

Generation of heat from animal or human bodies or through their activities such as
washing clothes or cooking.
1.5
SOLAR HEAT GAIN
The solar heat gain is the sum of the transmitted radiation and the portion of the
absorbed radiation that flows inward. Several measures can be adopted to reduce solar
radiation in buildings such as external and internal shading devices, proper building design
and planning; use of natural vegetation such as tall trees can also reduce solar heat gains.
Moreover, window areas can be reduced and buildings can be orientated so that there is less
window area facing directly south, west and east depending on the climatic zone of the area..
Solar heat gain can either be through the building (fenestration or openings) or through
the use of building materials e.g. glass
1.5.1
SOLAR GAIN THROUGH BUILDING
According to Ashrae (1971), Solar gain in buildings can be achieved through the use of
fenestration. Fenestration is refers to any glared aperture in the building envelope. Purposes of
fenestration in buildings are to satisfy human needs of visual communication with the outside world,
admit solar radiation to provide supplement daylight and heat, and enhance the exterior and interior
appearance of a building.
Fenestration affects building on thermal heat transfer, solar heat gains, air leakage and day
lighting. The net effect depends on:
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(a) the characteristics and orientation of the fenestration,
(b) the weather and solar radiation conditions, and
(c) the operation of the building thermal system.
1.5.2
SOLAR GAIN THROUGH THE USE OF MATERIALS
In order to provide satisfactory visual effects, better solar heat control and thermal
insulation, various types of glass have been produced. Glass is a reflective material and those
widely used in most Nigeria buildings are as follows:
1.6

Clear Plate or Sheet Glasses

Tinted Heat Absorbing Glasses

Reflective Coated Glasses

Insulating Glasses
THERMAL DESIGN
Heat transmission and absorption by building materials is affected by the absorptivity,
the conductivity and thermal capacity of the materials. The following are some terms
commonly used in describing heat flow through buildings.
Thermal conductivity: Thermal conductivity of a material is the rate of heat flow through a
unit area of unit thickness of the material for a unit temperature across a material. It is also
known as K- value and it is measured in W/m deg C.
Thermal Conductance: Thermal conductance (C) is the thermal transmission through unit
area of a slab of material, or of a structure, divided by the temperature difference between the
hot and cold faces in steady state conditions. It is measured in W/m 2 deg C.
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Thermal Resistivity: Thermal resistivity is the reciprocal of thermal conductivity. The unit is
Km/W.
Thermal Resistance: Thermal resistance (R) is the reciprocal of thermal conductance. It is a
measure of the resistance to heat transmission across a material, or a structure. The unit is
Km2/W.
Surface Conductance: Surface conductance is the rate of transfer of heat to or from unit area
of a surface in contact with a fluid due to convection and radiation per unit difference in
temperature between the surface and the neighboring fluid.
Surface resistance: it is the resistance offered to heat flow by the surface of a body, as
different from the resistance offered by the body itself. The unit is Km2/W.
1.4.1 THERMAL ENERGY
1.4.2 THERMAL INSULATION
Thermal insulation is the reduction of the effects of the various processes of heat transfer
between objects in thermal contact. It provides a means of maintaining gradient of
temperature, thereby insulating object till the heat flow is reduced or thermal radiation is
reflected rather than absorbed. If two faces of a wall are exposed to different but steady
temperature conditions, a temperature gradient is established across the thickness of the wall:
(a) The temperature gradient is linear between the two surfaces for a homogenous wall.
(b) The slope of temperature gradient is proportional to the resistances of individual layers for
a composite structure.
Moreover, thermal insulation has minimal recurring expense.. Many forms of thermal
insulation also reduce noise and vibration, both coming from the outside and from other
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rooms inside a building, thus producing a more comfortable environment. In addition, there
are factors resisting the airspaces. The thermal resistance of airspaces depends mainly on the
following factors:
(a) Thickness of the airspace: Resistance of airspace increases with the thickness up to a
maximum at about 20 mm.
(b) Surface emissivity: In Nigeria buildings, commonly used building materials have a high
emissivity and radiation which account for about two-thirds of the heat transfer through an
airspace with high emissivity surfaces. Therefore, lining the airspace with low emissivity
material such as aluminum foil increases the thermal resistance by reducing radiation.
(c) Direction of heat flow: A horizontal airspace offers higher resistance to downward than to
upward heat flow, because downward convection is small.
(d) Ventilation: Airspace ventilation provides an additional heat flow path which decreases
the effective airspace resistance.
1.4.3 NIGERIAL CLIMATIC ZONES
Nigeria Climates includes;
HOT DRY CLIMATES
These climates are characterized by a high diurnal temperature range and low humidity
with discomfort caused by either high or low temperatures. The design of walls and roofs
should therefore moderate temperature fluctuation (Ogunsote, 1988).
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WARM HUMID CLIMATES
These climates are characterized by a low diurnal temperature range, high humidity and
generally high temperatures. Comfort is in this areas of Nigeria is achieved by mostly
ventilation and by restricting the flow of heat into the building.
COLD CLIMATES
Cold climates are distinguished by low air temperatures. The design of walls and roofs
in this area should prevent loss of heat. The preservation of heat is achieved through high
insulation and auxiliary heating in severe cases and the insulation provided must prevent
condensation on the internal surfaces. (Ogunsote, 1988).
COMPOSITE CLIMATES
Composite climates are characterized by alternating hot dry, cold dry and warm humid
seasons. The design of roofs and walls depends on the relative duration of the seasons.
1.7
ENERGY EFFICIENT BUILDINGS
Heat gains from the sun can lead to increases in internal temperatures beyond the limits
of comfort. It is therefore necessary to determine the amount of solar radiation in every part of
the country having knowing the climatic zones the area falls under. The solar radiation that is
transmitted into buildings through; windows, walls, roof, floor and by admitting external air
into the building must be checked and planned before design and construction.. The basic
reason people live in houses is to be more comfortable and safe than they would be outdoors
and houses even buffer their inhabitants from weather extremes and keep them safe from
animals, human or otherwise.
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Unfortunately, architects and home designers often created homes of beauty in the past,
houses that are not energy efficient to make inhabitants comfortable. Now that utility bills and
climate change have entered the green equation, design principles must adjust to include both
beauty and energy efficiency.
Moreover, comfort is not determined by temperature alone. Comfort depends on
individual perception of things in his or her environment. Other than heat, there are other
factors that affect comfort in Nigeria which are humidity and air movement.
Also, control of air movement is essential to build an energy-efficient, healthy,
comfortable, and sustainable home through;
1.7.1

Temperature of surrounding surfaces

Activity levels of people

Individual perceptions of comfort
GREENHOUSE EFFECT
Glass allows short-wave solar radiation get into an interior space. This radiation is
absorbed by the interior of the building. The interior then radiates long-wave, thermal
radiation. Glass is opaque (not transparent) to this long wave radiation. Thus energy is trapped
in the building and the indoor air temperature rises. This is known as the green effect
The diagram below show the ways in which heat energy is lost from a typical house.
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The losses can be reduced in several ways by
a)
Loft insulation uses materials that trap air in tiny spaces. Air is a poor conductor, so less
heat escapes through the roof
b)
Double-glazed windows have two layers of glass. Between the layers, air is trapped.
This reduces heat loss by conduction and convection
c)
Cavity wall insulation traps air between two layers of bricks to reduce heat loss through
the walls
d)
Draught excluders around windows and doors, stop warm air escaping, and cold air
from getting into the house
e)
Carpets also help to prevent draughts; they reduce heat loss by convection. They also
trap air, reducing heat loss by conduction
1.7.2
AIR FLOW
Air flow is also one of the most important methods of heat transfer, making the control
of air flow is an important control of temperature in green homes. Air flow occurs only when
there is a difference between pressures. Air will flow from a region of high pressure to one of
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low pressure--the bigger the difference, the faster the flow. The negative and positive pressure
differences of air in homes control its flow. Air movement carries with it humidity, heat,
pollutants, and sound. Controlling airflow across the enclosure, between zones, and from the
distribution system to hollow partitions is necessary to build a high-performance, green home
and prevent infiltration and ex-filtration.
Common air leaks in buildings can take three forms:
Orifice Air Flow: Air flow where the air entry point and exit point are in a linear pathway;
such as a crack between a window frame and the window opening.
Diffuse Air Flow: The passage of air through porous building materials such as fiberglass or
uncoated concrete blocks.
Channel Air Flow: Air passing through openings in the building envelope where the air entry
and exit points are not in a linear pathway. This often gives the air adequate time to cool
below its dew point and deposit moisture in the building envelope. Channel flow is typically
found at the interface of dissimilar materials and is probably the most common and serious of
all air leaks.
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RECOMMENDATION
Heat flow through buildings can be minimized by reducing the energy consumed in the
building through

Switching lights off

Using low energy bulbs

Lagging heating pipes and hot water tanks

Keeping internal doors closed and

Reducing the setting on central heating thermostats by a degree

Introduce and design more green buildings
CONCLUSION
Architecture which is the philosophy of human habitation into void or spaces has been
solving problems related to buildings or structures and the environment .It has started to
control heat flow with as little energy expense as possible by an important aspect of designing
green buildings. Although controlling heat flow through buildings is somehow complicated in
Nigeria because of her different climatic zones, there has been works going on this aspect to
saves energy and make the space conducive for the users.
Furthermore, green buildings are seen to help the economy by reducing the impact of
different homes on the environment. It allows strong health of the users, impact durability of
the materials, and productivity of different element in the society. Therefore, heat control is
crucial to green building and it requires effective air barriers, solar radiation control, proper
insulation, control of heat generated internally and control of thermal bridging, among others.
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REFERENCES
Evans, M. (1980). Housing, Climate and Comfort. The Architecture Press, London.
Szokolay, S.V. (1975). Solar Energy and building. The Architectural Press, London. John
Wiley and Sons.
Ashrae, (1971). Applications of Solar energy for heating and cooling of buildings.
Ed Richard, C. J and Benjamin Y.H. ASHRAE, New York.
Ogunsote, O.O. (1988). Introduction to building climatology, Department of Architecture,
Faculty of Environmental Design, Ahmadu Bello University, Zaria, Nigeria.
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