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HEAT FLOW THROUGH A TYPICAL WALL IN AKURE

By

Adeyinka Adeniran Progress (ARC/06/8483)

Department of Architecture, Federal University of Technology, Akure-Nigeria

Email: was_nig@yahoo.com

For

ARC 810: Applied Climatology

Course lecturer

Ogunsote, O. O.

Federal University of Technology, Akure

Email: profogunsote@gmail.com; Web sites: sdngnet.com, sdecng.net, archnetng.org

ABSTRACT

This paper assesses heat flow through a typical wall in Akure. Heat flow through sandcrete block

wall is a combined conduction, convection and radiation heat transfer. It shows that the

resistance of the block itself depends on the temperature difference between the external and

internal parts. Each wall layer has its own conductance, and this we identify to vary the rate of

heat transfer through sandcrete block walls.

The objectives used in this research work are; to identify built walls in Akure, particularly the

materials for wall construction and sandcrete-block wall was chosen for case study. The paper

examines also, heat flow through block wall with illustrations. It submits that heat flow through

wall depends on the thermal quantities of the wall layers and according to the K-Value, U-

Factor and the R-Value. In conclusion, it identifies conductive heat transfer in the solid of the

block, convective heat transfer in the air of the cavities and radiative heat transfer between the

internal surfaces of the cavity as the mechanism of heat flow in block walls.

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Keywords: K-value, R-value, U-Factor, Adobe laterite bricks, metal wall, timber wall, bamboo

wall, canopy wall , Sandcrete block wall, cavities, solid of the block, conductive heat transfer,

convective heat, Radiative heat transfer.

1. INTRODUCTION

Building materials no matter the section of construction they belong to, they either gain or loss

heat from or to the environment respectively. The total heat gained by a building must be lost in

order to maintain a thermal balance (Ogunsote, 1991). The heat energy gained will not remain on

surfaces or totally trapped within an internal layer without attempting to flow through by several

transformative mechanisms. In this paper, we are assessing heat flow through a typical wall in

Akure, and Sandcrete block was chosen for case study. The mechanisms of heat flow in block

walls are majorly convection, conduction and radiation. Traditionally in Nigeria, sandcrete

blocks are available in two categories; the six inches and the nine inches thick blocks with two

internal cavities, of which heat transfer can depend upon, see plate 1 and 2 of appendix 1.

2. THERMAL QUANTITIES

First of all, let us define Heat as a form of energy measured in Joules (J).

Every wall material have a Specific Heat, which is the amount of heat energy necessary to cause

unit temperature increase of a unit mass of the substance, it is measured in J/kg deg C (Ogunsote,

1991).

The Thermal capacity of the material is the amount of heat required to raise the temperature of

the body by one unit. It is measured in J/deg C. the 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 difference

across the material. It is (known as the K-value and) measured in W/m deg C (Ogunsote, 1991).

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The Thermal Conductance is the rate of heat flow through a unit area of a body when the

temperature difference between the two surfaces is one degree Celsius. It is also known as the U-

value (thermal transmittance) and is measured in W/m2 deg C (Ogunsote, 1991).

The thermal resistance is the reciprocal of thermal conductance known as the R-value. Block

walls used in Akure are partially hollow. Over the face of the wall, there are significant areas that

are solid and hollow, and each area has a different thermal transmittance.

U-Factor can further be defined as the rate of steady-state heat flow. It is the amount of heat in

Btu (British thermal units) that flows each hour through one square foot, when there is a one

degree temperature difference between the inside air and outside air. The heat flow can be in

either direction, as heat will flow from the warmer side to the cooler side (Taylor et al, 2005).

Each layer of a building wall has its own conductance, or rate of heat transfer. The conductance

for an individual layer is like the U-Factor, and it has the same units. The difference is that it is

only for a single element or layer.

3. WALL CONSTRUCTION IN AKURE

Akure being the capital city of Ondo-State Nigeria is a developed city as far as Ondo-State

standard is concern. Laterite wall, timber wall, bamboo wall, sandcrete block wall, etc are some

of the noticeable building materials traditionally used for wall construction in the coastal and

forest climatic zones of the country, particularly in the Yoruba speaking communities. But

laterite, timber, and bamboo walls are not so common here in Akure. Perhaps, it is as a resulting

of social esteem or their availability. If you go round town, you can still find adobe laterite brick,

metal, timber, bamboo, canopy, sandcrete block walls in their proportion being use for wall

construction, see appendix 2. This segment of the paper tries to look at the choice building

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material for wall construction in Akure, to be presented for assessment towards the aim of this

paper.

Block Walls

Sandcrete block is the most prevalent building material used for wall construction in Nigeria.

Most buildings are enclosed in this plastered and painted hollow cement-sand mixture, see plate

4, appendix 2. When laid in course to appropriate bonding, plastered and finished, each layer has

its own conductance, or rate of heat transfer. The heat flow is also dependent on the thickness of

block, either nine inches or six inches block as shown in appendix 1.

The heat transfer processes include conductive heat transfer in the solid of the block, convective

heat transfer in the air of the cavities and radiative heat transfer between the internal surfaces of

the cavity (Concrete Masonry Association of California and Nevada, 2006). The wall we are

considering in this paper is a sandcrete block wall. This is because it has a predominant use in

the city and is worth examined under this research work.

4. RESEARCH METHODOLOGY

The aim of the research is to assess the heat flow through a typical wall in Akure.

The objectives used to appraise and to compose this paper are:

to identify built walls in Akure, particularly the materials for wall construction, and

of heat flow through block wall.

Data Collection

The data used for the research was collected from various sampled field work at Alaba layout,

Federal University of Technology, Akure south gate, in Akure-Nigeria. This data of the samples

taking in this area is similar to any other of the same likeness in the city comparatively. The

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literature review was based on library, Internet searches and personal observations noticeable

and assumed of the matter.

Scope of research

The scope of this research work as been limited to assessment of heat flow in block walls in

Akure. It does not entail practical measurement of any form or the use of any special instrument

for investigation neither does it involves the use of mathematical models for analysis. Careful

steps were taking to study the types of walls in Akure and quantities were used to justify the

assumptions by library researches.

Definition of thermal quantities.

The thermal quantities were defined based on the definitions given by Ogunsote, in chapter five

of his book “Introduction to Building Climatology”. Other necessary quantities were also from

material studied as referenced.

5. HEAT FLOW THROUGH BLOCK WALL

5.1.Thermal Quantities of block wall

The U-Factor

The U-Factor includes the conductance of every element of the building wall, including the

interior and exterior surfaces of the block walls. The surface conductance quantify the rate at

which heat is transferred between the surface of the block wall and the surrounding environment

(Taylor et al, 2005).

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The dynamic heat storage properties of the Block walls alter the thermal behavior of the wall,

and the U-Factor becomes less accurate as a predictor of heat flow rates. Figure 1 illustrates the

rate of steady heat flow through block wall.

The R-Values

The R-Value are also used to describe steady-state heat flow, but in a slightly different way. The

R-Value is the thermal resistance to heat flow. A larger R-Value has greater thermal resistance, or

more insulating ability, than a smaller R-Value. The big advantage of R-Values is that they can

be added together. The total R-Values of a block wall is the sum of the R-Values of each of the

layers. The layers should include the wall plaster and the wall finishes and weatherproofing

elements like paints. The U-Factor is the inverse of the total R-Value (CMACN, 2006).

The R-Value is widely recognized in the building industry and is used to describe insulation

effectiveness. The insulation R-Value is not the total R-Value of the wall, however. It only

describes the thermal resistance of the insulation material. The R-Value of the entire wall

assembly can be significantly lower when metal framing penetrates the insulation (Hassid, 2011).

EXTERIOR INTERIOR

Heat Typical block wall

in Akure

Figure 1: diagram illustrating heat flow through a typical wall in Akure.

Source: researcher.

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5.2.Heat Flow Mechanism in Sandcrete Block Wall

Convection: this refers to heat loss or gain through the air in the cavity of the block wall cause by

the tendency of any heated surface. The amount of heat that will flow through a cavity block wall

is significantly lower than that of a mass of block. Of course, air is not a perfect insulator, some

amount of heat flows through by convection. As the heated surface is heating up the air molecule

in the cavity are charged also. Hence, if the as illustrated in figure 2.

Conduction: do not confuse convection for conduction. When metal frames or conductors

penetrate the wall, there is high tendency of heat transfer by conduction through the wall

molecules. Similarly, a block wall is not a perfect insulator, we expect some amount of heat

energy to flow through the blocks, plaster and finishes depending on their R-Value which is the

thermal resistance to heat flow.

Hollow of block wall contains heated air.

Heated surface

Heat

AKURE HOT & HUMID

EXTERIOR

INTERIOR OF AKURE

HOUSES

air

Unheated surface

Wall plaster & finishes

Block binding mortar

Sandcrete block

Figure 2: shows heat flow through a typical block wall section: the heated wall

absorbs and transfer heat into the less heated interior.

Source: researcher.

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Radiation: this refers to the heat emitted that takes place when the trapped heat is equally emitted

as longwise radiation into the less heated interior. Radiative heat transfer can be between the

internal surfaces of the cavity.

6. CONCLUSION AND RECOMMENDATIONS

The assessment of heat-flow through a typical wall in Akure has been examined in clear terms

using block-wall as case-study. It involves the use of thermal quantities for appraisal and

ascertained that heat flow through building wall operates under different heat levels. Outdoor

heat flows through respective layers of the wall according to the K-Value, U- Factor and the R-

Value. In conclusion, it identifies conductive heat transfer in the solid of the block, convective

heat transfer in the air of the cavities and radiative heat transfer between the internal surfaces of

the cavity.

7. REFERENCES

Concrete Masonry Association of California and Nevada (2006). Steady-State Heat Flow.

Retrieved from www.CMACN.com

InspectAPedia (2011). How to Measure & Correct Unwanted Building Heat. Retrieved from

www.InspectAPedia.com

Ogunsote O. O. (1991). Introduction to Building Climatology-a basic cause for architectural

students. Ahmadu Bello University press limited, Zaria, Nigeria.

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S. Hassid & E. Levinsky (2011). Heat Transfer in Block Walls; Environmental & Water

Resources Engineering Department Technion - Israel Institute of Technology, Haifa

32000 – Israel. PDF.

Taylor, P. Fuller, R. &Luther, M. (2005). Study of heat flow through a rammed earth wall

building. Kevan Publisher Faculty of Design, Architecture and Building, University of

Technology, N.S.W. Retrieved from http://hdl.handle.net/10536/DRO/DU:30009690

8. APPENDIXES

8.1.APPENDIX 1: sandcrete blocks

Plate 1: 6 inches block for wall construction.

Source: researchers field survey.

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8.2. APPENDIX 2: types of walls in Akure

Plate 2: 9 inches block for wall construction.

Source: researchers field survey.

Plate 3: bamboo, for bamboo wall construction.

Source: researchers field survey.

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Plate 4: timber wall construction.

Source: researchers field survey.

Plate 5: sandcrete block wall construction

Source: researchers field survey

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Plate 6: metal wall construction.

Source: researchers field survey.

Plate 7: canopy used for wall construction (tent structure).

Source: researchers field survey.

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Plate 8: Adobe laterite bricks used for brick wall construction.

Source: researchers field survey.