Applied... · Web viewThe aim of design with climate is to maintain comfort within buildings....
Transcript of Applied... · Web viewThe aim of design with climate is to maintain comfort within buildings....
A TERM PAPER
ON
THERMAL PROPERTIES OF POPULAR BUILDING MATERIALS IN NIGERIA
BY
ASHIRU MONSURU OLATUNDE
(ARC/05/5596)
COURSE- ARC 810
(APPLIED CLIMATOLOGY)
MENTOR: PROF. OGUNSOTE, O.O.
SEPTEMBER, 2011
1
TABLE OF CONTENT
TITLE PAGE NUMBER
1.0 INTRODUCTION 1
2.0 POPULAR BUILDING MATERIALS IN NIGERIA 2
2.1 CONCRETE 2
2.2 LATERITE 2
2.3 STONE 3
2.3.1 REQUIREMENTS OF GOOD BUILDING STONES 3
2.4 TIMBER 4
2.5 METALS 6
2.6 PLASTICS 7
2.7 GLASS 7
3.0 THERMAL PROPERTIES OF BUILDING MATERIALS IN NIGERIA 8
3.1 ABSORPTIVITY 8
3.2 SPECIFIC HEAT 9
3.3 THERMAL CONDUCTIVITY 9
3.3.1 CONDUCTANCE VS CONDUCTIVITY 10
3.4 DIFFUSIVITY 12
3.5 THERMAL DIFFUSIVITY 12
3.6 THERMAL MASS 13
REFERENCES 15
2
LIST OF FIGURE
Figure 1: Thermal diffusivity measurement apparatus. 13
LIST OF TABLES
Table 1: Selected Nigerian timber species and their uses in building construction 5
Table 2: Thermal Properties of Building Material at Room Temperature 8
Table 3: Building Materials And Their Thermal Conductivity For Dry (Indoor) And Wet
(Outdoor) Conditions. 10
3
1.0 INTRODUCTION
The aim of design with climate is to maintain comfort within buildings. Thermal design
of buildings for thermal comfort requires an understanding of the basic thermal properties of
building materials. Komolafe (1988) opine that Climatic factors do not affect people's comfort
alone, they can also impair the safety of buildings and lead to building damage and premature
fatigue of building materials. Heat transmission and absorption by building materials is affected
by the absorptivity, the conductivity and thermal capacity of the materials. These properties of
materials determine the characteristics of wall and roof elements and therefore the way they will
modify the thermal environment. In tropical region for instance, with reference to Nigeria,
materials like zinc, aluminum and asbestos are commonly used in form of sheets for roofing in
modern building constructions, but these materials have a high ability to conduct heat (solar
radiation) into the interior space of a building, a situation that causes discomfort in indoor space
in dry season.
The heat flow through any building material is dependent on the thermal properties of the
material (Akpabio et al., 2001). It can therefore be deduced that the heat generated indoor
depends solely on the rate of heat conducted through the building materials used for the
construction. Materials used in walls, floor and other sun-exposed parts of the house should have
adequate thermal storage or reflectance, that is, thermal properties able to respond to the needs of
the climate where the building is located. Hence, the problem is not only what is readily
available and economically affordable to the people, but also what is thermally desirable and
efficient.
4
2.0 POPULAR BUILDING MATERIALS IN NIGERIA
Building material is any material which is used for a construction purpose. Many
naturally occurring substances, such as clay, sand, wood and rocks, even twigs and leaves have
been used to construct buildings. The popular building materials in Nigeria are laterite, stone,
concrete, timber, metal, plastics, bamboo, and glass.
2.1 CONCRETE
Concrete is a composite building material made from the combination of aggregate and a
binder such as cement. The most common form of concrete is Portland cement concrete, which
consists of mineral aggregate (generally gravel and sand), portland cement and water in
predetermined proportions. After mixing, the cement hydrates and eventually hardens into a
stone-like material. When used in the generic sense, this is the material referred to by the term
concrete. Additional materials called admixture may be added to influence the properties of
concrete. Concrete as building material is very good in compression (Fullerton, 1979)
2.2 LATERITE
Laterite is a porous soil ranging from soft earthly material to hard rock. It ranges in
colour from white to dark red, depending on the amount of iron in the soil. Laterite is found in
areas of high temperatures with high rainfall and well defined rainy season (Fadamiro and
Ogunsemi, 1996). Products of laterite include brick, compressed laterite blocks, tiles, pipes,
sanitary wares, etc. It has the following properties.
Laterite hardens on drying (e.g. sundried block)
At a very high temperature, it melts and when it cools, it produces a very hard, semi-
vitrified building material.
5
2.3 STONE
Stone is a natural resource available in most parts of the world often with low cost of
extraction and is generally usable without further processing other than cutting and simple
dressing.
2.3.1 REQUIREMENTS OF GOOD BUILDING STONES
The following are the requirements of good building stones:
(i) Strength: The stone should be able to resist the load coming on it. Ordinarily this is not of
primary concern since all stones are having good strength. However in case of large structure, it
may be necessary to check the strength.
(ii) Durability: Stones selected should be capable of resisting adverse effects of natural forces
like wind, rain and heat.
(iii) Hardness: The stone used in floors and pavements should be able to resist abrasive forces
caused by movement of men and materials over them.
(iv) Toughness: Building stones should be tough enough to sustain stresses developed due to
vibrations. The vibrations may be due to the machinery mounted over them or due to the loads
moving over them. The stone aggregates used in the road constructions should be tough.
(v) Specific Gravity: Heavier variety of stones should be used for the construction of dams,
retaining walls, docks and harbours. The specific gravity of good building stone is between 2.4
and 2.8.
(vi) Porosity and Absorption: Building stone should not be porous. If it is porous rain water
enters into the pour and reacts with stone and crumbles it. In higher altitudes, the freezing of
water in pores takes place and it results into the disintegration of the stone.
6
(vii) Dressing: Giving required shape to the stone is called dressing. It should be easy to dress so
that the cost of dressing is reduced. However the care should be taken so that, this is not be at the
cost of the required strength and the durability.
(viii) Appearance: In case of the stones to be used for face works, where appearance is a
primary requirement, its colour and ability to receive polish is an important factor.
2.4 TIMBER
The wood that is suitable for building or other construction purposes is called timber.
When sawn into various market forms like beams, battens and planks, etc., it is called converted
timber. Timber and other wood products have, for ages, remained one of the major structural
materials for building construction worldwide due to their renewable nature, availability in
various sizes, shapes and colours, affordability, relatively high fatigue resistance and specific
strength, ease of joining, durability, and aesthetic appeal (Goldstein, 1999). Also, un-serviceable
wooden building components are re-cyclable either for their structural properties, e.g., reused
permanently as framing or temporarily as form-work, or for their heat content as fuel.
Timber is a material that provides much better thermal insulation than the metals or
concrete; it has higher ratios of strength and stiffness to weight than the other major materials; it
is relatively easy to work and to join requiring only simple tools; and in certain circumstances it
has high durability (Keenan and Tejada, 1984). In Nigeria, the major area of structural utilization
of wood is in roof construction, with the building industry alone consuming about 80% of the
country’s estimated 20 million cubic meters of annual lumber production (Alade and Lucas,
1982, Lucas and Olorunnisola, 2002).
7
Table 1: Selected Nigerian timber species and their uses in building construction
Building Component Recommended Timber Species
Carcassing Afara (Terminalia superba),), Albizia (Albizia spp.), Alstonia (Alstoniaboonei), Celtis (Celtis spp.), Dahoma (Piptadeniastrum africanum), Danta(Nesogordonia papaverifera), Ilomba (Pycnanthus angolensis), Iroko(Milecia excelsa), Obeche (Triplochiton scleroxylon)
Door and window frames(external)
Agba (Gossweilerodendron balsamiferum), Albizia (Albizia spp.), Apa(Afzelia africana), Danta (Nesogordonia papaverifera), Gedu Nohor(Entandrophragma angolense), Iroko (milecia excelsa), Lagos Mahogany(Khaya ivorensis), Opepe (Nauclea diderricchii)
Doors and windows – Solid Afara- white (Terninalia superba), Apa (Afzelia africana), Black Afara(Terninalia ivorensis), Gedu Nohor (Entandrophragma angolense), Iroko(milecia excelsa), Lagos Mahogany (Khaya ivorensis), Mansonia(Mansonia altissima), Sapelewood (Entandrophragma cylindricum), Utile(Entandrophragma utile)
Flooring and decking Agba (Gossweilerodendron balsamiferum), Albizia (Albizia spp.), Danta(Nesogordonia), Iroko (milecia excelsa), Omu (Entandrophragmacandolei) (Opepe (Nauclea diderricchii), Sapelewood (Entandrophragmacylindricum)
Shingles and battens Abura (Mitragyna stipulosa), Black Afara (Terninalia ivorensis), GeduNohor (Entandrophragma angolense), Mangrove
(Rhizophora racemosa)
Sills and thresholds Dahoma (Piptadeniastrum africanum), Iroko (milecia excelsa), Opepe(Nauclea diderricchii)
Stair Treads Guarea (Guarea spp.), Mahogany (Khaya spp.), Sapelewood(Entandrophragma cylindricum)
(Entandrophragma cylindricum) Abura (Mitragyna stipulosa), Afara (Terminalia
8
Roof rafters and purlins superba), Agba(Gossweilerodendron balsamiferum), Albizia (Albizia spp.), Danta(Nesogordonia papaverifera), Iroko (milecia excelsa), Obeche(Triplochiton scleroxylon), Opepe (Nauclea diderricchii), Sapelewood(Entandrophragma cylindricum)
Source: (Okigbo, 1964)
2.5 METALS
Recognition of metals is based on two headings, namely ferrous and non-ferrous metals.
Ferrous metals are produced from iron ore, cast iron, wrought iron and steel while ferrous metals
include aluminium, copper, zinc, bronze and brass. Metal sheets for roofing are quite effective
in warm, humid climates, for these materials can be at the same time reflective and impermeable.
They are also highly conductive, and they cool down as quickly as they heat up (Gut and
Ackerknecht 2005). In Nigeria, materials like zinc, aluminum and asbestos are commonly used
in form of sheets for roofing in modern building constructions, but these materials have a high
ability to conduct heat (solar radiation) into the interior space of a building, a situation that
causes discomfort in indoor space in dry season (Akpabio et al., 2001).
Aluminium is leading the way into the future of the construction industry. The great
growth in the use of aluminum metal indicates its versatility. It has a unique combination of
useful properties: lightness, good thermal and electrical conductivity, high reflectivity,
malleability, resistance to corrosion, and excellent tensile strength in alloyed form (Komolafe,
1988).
9
2.6 PLASTICS
The term plastics cover a range of synthetic or semi-synthetic organic condensation or
polymerization products that can be molded. The two major types of plastic are thermoplastics
and thermosetting resins (thermosets). Plastics vary immensely in heat tolerance, hardness, and
resiliency.
2.7 GLASS
Glass is used in building mainly as flat glass and for products such as lences, glass fibres
and foamed (cellular) glass (Fadamiro and Ogunsemi, 1996). Glass has the following properties.
I. Appearance: Glass is transparent and more or less colourless.
II. Strength properties: Glass in building is required to resist loads including wind
loads, impact by persons and animals and sometimes thermal and other stresses.
III. Thermal insulation: Although glass is dense and is a good conductor of heat, its
surface resistance is high so that doubling the thickness almost halves the heat lost
through a single plane, the optimum gap being about 20mm.
10
3.0 THERMAL PROPERTIES OF BUILDING MATERIALS IN NIGERIA
The basic properties that indicate the thermal behavior of building materials are:
absorptivity, density (p), specific heat (cm), and thermal conductivity (k).
Table 2: Thermal Properties of Building Material at Room Temperature
Material Thermal Conductivity(W/m degree K) @~300 K
Specific Heat(J/kg degree K)
Density(kg/m3)
Brick 0.7 840 1600Concrete – cast dense 1.4 840 2100Concrete – cast light 0.4 1000 1200Granite 1.7-3.9 820 2600Glass (window) 0.8 880 2700Hardwoods (oak) 0.16 1250 720Softwoods (pine) 0.12 1350 510Polyvinyl chloride 0.12-0.25 1250 1400Paper 0.04 1300 930Acoustic Tile 0.06 1340 290Particle board (low density)
0.08 1300 590
Particle board (high density)
0.17 1300 1000
Fiberglass 0.04 700 150Expanded polystyrene 0.03 1200 50
Source: (Incropera, 1990)
3.1 ABSORPTIVITY
Absorptivity is the property of a surface which determines what proportion of incident
radiation it absorbs. It is the property of a material which determines radiant exchange of a
surface with its environment. It is the main factor in determining the temperature response to
short-wave (solar) radiation, and is dependent largely by color.
11
3.2 SPECIFIC HEAT
Specific heat of a substance is the amount of heat energy required to raise the temperature
of a unit mass of the substance by one degree Celsius. Specific heat describes a material's ability
to store heat energy. It is measured in J/kg degree C (ASHRAE, 2005).
3.3 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 difference across the material. It is also known as
the K-value and is measured in W/m degree C. Good insulators have lower thermal
conductivities (ASHRAE, 1977).Thermal conductivity as a material property will not differ with
the dimensions of the material, but it is dependent on the temperature, the density and the
moisture content of the material (CLEAR website). Generally light materials are better insulators
than heavy materials, because light materials often contain air enclosures. Dry still air has a very
low conductivity. A layer of air will not always be a good insulator though, because heat is easily
transferred by radiation and convection.
When a material, for instance insulating material, becomes wet, the air enclosures fill
with water and, because water is a better conductor than air, the conductivity of the material
increases. That is why it is very important to install insulation materials when they are dry and
take care that they remain dry.
The process of conduction and radiation often generate heat experience in interior spaces via the
roof and walls. The radiation transport is strongly dependent on temperature and particularly
significant at high temperatures. The convention can be negligible for small pore sizes (Akpabio
12
et al., 2001). The temperature variation with thickness of a solid material determines if a material
is suitable as heat insulator or conductor. The actual heat transmission by conduction depends on
the bonding between molecules (Collieu and Powney, 1977).
3.3.1 CONDUCTANCE VS CONDUCTIVITY
Conductivity (k) is a material property and means its ability to conduct heat through its
internal structure. Conductance on the other hand is an object property and depends on both its
material and thickness. Conductance equals conductivity multiplied by thickness, in units of
W/m²K. As conductivity is the reciprocal of resistivity, the total resistance of a material can
therefore be given as its total thickness divided by total conductivity (CLEAR website).
Table 3: Building Materials And Their Thermal Conductivity For Dry (Indoor) And Wet (Outdoor) Conditions.
Group Material Specific mass (kg/m3)
Thermal conductivity (W/mK)Dry Wet
Metal Aluminium 2800 204 204Copper 9000 372 372Lead 12225 35 35Steel, Iron 7800 52 52Zinc 7200 110 110
Natural stone Basalt, Granite 3000 3.5 3.5Bluestone, Marble 2700 2.5 2.5Sandstone 2600 1.6 1.6
Masonry Brick 1600-1900 0.6-0.7 0.9-1.2Sand-lime brick 1900 0.9 1.4 1000-1400 0.5-0.7
Concrete Gravel concrete 2300-2500 2.0 2.0Light concrete 1600-1900 0.7-0.9 1.2-1.4 1000-1300 0.35-0.5 0.5-0.8 300-700 0.12-0.23 Pumice powder concrete 1000-1400 0.35-0.5 0.5-0.95
700-1000 0.23-0.35 Isolation concrete 300-700 0.12-0.23
13
Cellular concrete 1000-1300 0.35-0.5 0.7-1.2 400-700 0.17-0.23 Slag concrete 1600-1900 0.45-0.70 0.7-1.0 1000-1300 0.23-0.30 0.35-0.5
Inorganic Asbestos cement 1600-1900 0.35-0.7 0.9-1.2Gypsum board 800-1400 0.23-0.45 Gypsum cardboard 900 0.20 Glass 2500 0.8 0.8Foam glass 150 0.04 Rock wool 35-200 0.04 Tiles 2000 1.2 1.2
Plasters Cement 1900 0.9 1.5Lime 1600 0.7 0.8Gypsum 1300 0.5 0.8
Organic Cork (expanded) 100-200 0.04-0.0045 Linoleum 1200 0.17 Rubber 1200-1500 0.17-0.3 Fibre board 200-400 0.08-0.12 0.09-0.17
Wood Hardwood 800 0.17 0.23Softwood 550 0.14 0.17Plywood 700 0.17 0.23Hard-board 1000 0.3 Soft-board 300 0.08 Chipboard 500-1000 0.1-0.3 Wood chipboard 350-700 0.1-0.2
Synthetics Polyester (GPV) 1200 0.17 Polyethene, Polypropene 930 0.17
Polyvinyl chloride 1400 0.17 Synthetic foam
Polystyrene foam, exp. (PS) 10-40 0.035
Ditto, extruded 30-40 0.03 Polyurethane foam (PUR) 30-150 0.025-0.035
Phenol acid hard foam 25-200 0.035
PVC-foam 20-50 0.035 Cavity isolation
Cavity wall isolation 20-100 0.05
Bituminous materials
Asphalt 2100 0.7 Bitumen 1050 0.2
Water Water 1000 0.58 Ice 900 2.2 Snow, fresh 80-200 0.1-0.2 Snow, old 200-800 0.5-1.8
14
Air Air 1.2 0.023 Soil Woodland soil 1450 0.8
Clay with sand 1780 0.9 Damp sandy soil 1700 2.0 Soil (dry) 1600 0.3
Floor covering Floor tiles 2000 1.5 Parquet 800 0.17-0.27 Nylon felt carpet 0.05 Carpet (with foam rubber) 0.09
Cork 200 0.06-0.07 Wool 400 0.07
Source: Comfortable Low Energy Architecture website
3.4 DIFFUSIVITY
Diffusivity is the measure of how fast heat travels through a material, and is a function of
the conductivity divided by the product of the density and specific heat (units: area/time). The
time lag between outside and inside peak temperatures is a function of the thickness of the
material divided by the square root of the diffusivity.
3.5 THERMAL DIFFUSIVITY
The principle of thermal diffusivity is to generate a signal on one face of a material and
examine the response on the other face (Meukam, P. 2004).
15
Fig. 1: Thermal diffusivity measurement apparatus.
Source: (Meukam P., 2004)
Materials used in walls, floor and other sun-exposed parts of the house should have
adequate thermal storage or reflectance, that is, thermal properties able to respond to the needs of
the climate where the building is located. Hence, the principle of thermal mass.
3.6 THERMAL MASS
Thermal mass is a property that enables building materials to absorb, store, and later
release significant amounts of heat. Buildings constructed of concrete and masonry have a
unique energy-saving advantage because of their inherent thermal mass (EUSFHVEW, 2001).
These materials absorb energy slowly and hold it for much longer periods of time than do less
massive materials. This delays and reduces heat transfer through a thermal mass building
component, leading to the following results.
1. There are fewer spikes in the heating and cooling requirements, since mass slows the
response time and moderates indoor temperature fluctuations.
16
2. A massive building uses less energy than a similar low mass building due to the reduced
heat transfer through the massive elements (EUSFHVEW, 2001).
The thermal mass of concrete has the following benefits and characteristics:
Delays peak loads
Reduces peak loads
Reduces total loads in many climates and locations
Works best in commercial building applications
Works well in residential applications
Works best when mass is exposed on the inside surface
17
REFERENCES
Akpabio, L.E, Ekpe, S.D, Etuk, S.E, and Essien, K.E (2001): Thermal Properties of Oil and
Raffia Palm Fibrers, Global J.Pure Appl. Sci., 7(3): 575-578.
Alade, G.A. and Lucas, E.B. (1982): Timber connector: a major contributor to structural
failure in wooden components in Nigeria. Paper presented at the 36th annual
meeting of the Forest Products Research Society, mechanical fastening session,
New Orleans, U.S.A., June 24, 1982. 22 pp.
ASHRAE Handbook of Fundamentals, 1977.
ASHRAE Handbook of Fundamentals, 2005.
Comfortable Low Energy Architecture website:
(http://www.learn.londonmet.ac.uk/packages/clear/index.html )
Collieu, A.M.B and Powney, D.J (1977): The Mechanical and Thermal Properties of
Materials. London: Edward Arnold. p. 283.
Energy Use of Single-Family Houses with Various Exterior Walls, “EUSFHVEW” (2001).
Fullerton, R.L. (1979): “Building Construction In Warm Climates (vol. 1)” Oxford University
Press, London.
Goldstein, E.W. (1999): Timber construction for Architects and Builders. McGraw-Hill, New
York, USA.
Gut, P. and Dieter, A. (2005): Climate Responsive Building. St. Gallen, Switzerland:
24 SKAT [Swiss Centre for Development Cooperation in Technology and
Management].
18
Incropera, F., De Witt, D. (1990): Introduction to Heat Transfer, 2nd Edition, John Wiley and
Sons
Keenan, F.J. and Tejada, M (1984) : Tropical Timber for Building Materials in the Andean
Group Countries of South America
Komolafe, L. K. (1988): "Influence of Climate on Building Design and Thermal Performance
Assessment of Some Construction Materials" in Ten Years of Building and Road
Research. Edited by G. N. Omange, NBRRI, Lagos. pp 95-108.
Lucas, E.B. and Olorunnisola, A.O. (2002): Wood processing and utilization in Nigeria: the
present situation and future prospects in: Ajav, E.A., Raji, A.O., and Ewemoje,
T.A. (Eds) Agricultural Engineering in Nigeria: 30 Years of University of Ibadan
Experience, Published by the Department of Agricultural Engineering, University
of Ibadan, Nigeria. pp. 98-109.
Meukam, P. (2004): Construction and Building Materials.
19