By
Kayode Samuel. O
Arc/05/5617
Department of Architecture
Federal University of Technology, Akure
In Partial Fulfilment of the course
Applied Climatology (Arc 810)
Course Lecturer:Prof. Ogunsote, O.O.
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1.0 Introduction
2.0 What is the greenhouse effect?
2.1 What Causes the Green House Effect?
2.2 How Do Humans Contribute to the Greenhouse Effect?
2.3 Impacts of the greenhouse effect
3.0 Implication of Greenhouse Effect for design of Residential Buildings in Hot and Humid
Climate
3.1 What makes a Climate Hot and Humid?
3.2 Residential design responses to greenhouse effect
4.0 Conclusion
1.0 Introduction
The greenhouse effect refers to circumstances where the short wavelengths of visible light from the sun pass through a transparent medium and are absorbed, but the longer wavelengths of the infrared re-radiation from the heated objects are unable to pass through that medium. The trapping of the long wavelength radiation leads to more heating and a
higher resultant temperature.
Besides the heating of an automobile by sunlight through the windshield and the namesake example of heating the greenhouse by sunlight passing through sealed, transparent windows, the greenhouse effect has been widely used to describe the trapping of excess heat by the rising concentration of carbon dioxide in the atmosphere.(www.weatherstreet.com,2010)
An issue of major concern is the possible effect of the burning of fossil fuels and other contributors to the increase of carbon dioxide in the atmosphere. The action of carbon dioxide and other greenhouse gases in trapping infrared radiation is called the greenhouse effect .
Those gas molecules in the Earth's atmosphere with three or more atoms are called
"greenhouse gases" because they can capture outgoing infrared energy from the Earth, thereby warming the planet. The greenhouse gases include water vapour with three atoms
(H
2
O), ozone (O
3
), carbon dioxide (CO
2
), and methane (CH
4
).Also, trace quantities of chlorofluoro-carbons (CFC's) can have a disproportionately large effect. (www.about.com,2011)
The potential consequences greenhouse effects in terms of loss of snow cover , sea level rise , change in weather patterns . On the other hand, proposed measures to reduce human contributions to greenhouse gases can also have great consequences.
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The greenhouse effect was discovered by Joseph Fourier in 1824, first reliably experimented on by John Tyndall in 1858, and first reported quantitatively by Svante Arrhenius in 1896.
If an ideal thermally conductive blackbody was the same distance from the Sun as the Earth is, it would have a temperature of about 5.3 °C. However, since the Earth reflects about 30%
(or 28%) of the incoming sunlight, the planet's effective temperature (the temperature of a blackbody that would emit the same amount of radiation) is about −18 or −19 °C, about 33°C below the actual surface temperature of about 14 °C or 15 °C. The mechanism that produces this difference between the actual surface temperature and the effective temperature is due to the atmosphere and is known as the greenhouse effect .
There are two meanings of the term "greenhouse effect". There is a "natural" greenhouse effect that keeps the Earth's climate warm and habitable. There is also the "man-made" greenhouse effect, which is the enhancement of Earth's natural greenhouse effect by the addition of greenhouse gases from the burning of fossil fuels which are mainly petroleum, coal and natural gas.( www.physicalgeography.net)
In order to understand how the greenhouse effect operates, we need to first understand
"infrared radiation". Greenhouse gases trap some of the infrared radiation that escapes from the Earth, making the Earth warmer that it would otherwise be. You can think of greenhouse gases as sort of a "blanket" for infrared radiation-- it keeps the lower layers of the atmosphere warmer, and the upper layers colder, than if the greenhouse gases were not there.
About 80-90% of the Earth's natural greenhouse effect is due to water vapour, a strong greenhouse gas. The remainder is due to carbon dioxide, methane, and a few other minor gases.
The greenhouse effect is a naturally occurring process that aids in heating the Earth's surface and atmosphere. It results from the fact that certain atmospheric gases, such as carbon dioxide, water vapour , and methane, are able to change the energy balance of the planet by absorbing long wave radiation emitted from the Earth's surface. Without the greenhouse effect life on this planet would probably not exist as the average temperature of the Earth would be a chilly -18° Celsius, rather than the present 15° Celsius. As energy from the Sun passes through the atmosphere a number of things take place. A portion of the energy (26% globally) is reflected or scattered back to space by clouds and other atmospheric particles.
About 19% of the energy available is absorbed by clouds, gases (like ozone), and particles in the atmosphere. Of the remaining 55% of the solar energy passing through the Earth's
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atmosphere, 4% is reflected from the surface back to space. On average, about 51% of the
Sun's radiation reaches the surface. This energy is then used in a number of processes, including the heating of the ground surface; the melting of ice and snow and the evaporation of water; and plant photosynthesis. (www.physicalgeography.net)
The heating of the ground by sunlight causes the Earth's surface to become a radiator of energy in the longwave band (sometimes called infrared radiation). This emission of energy is generally directed to space .However; only a small portion of this energy actually makes it back to space.
Life on earth depends on energy from the sun. About 30 percent of the sunlight that beams toward Earth is deflected by the outer atmosphere and scattered back into space. The rest reaches the planet's surface and is reflected upward again as a type of slow-moving energy called infrared radiation. The heat caused by infrared radiation is absorbed by "greenhouse gases" such as water vapor, carbon dioxide, ozone and methane, which slows its escape from the atmosphere. Although greenhouse gases make up only about 1 percent of the Earth's atmosphere, they regulate our climate by trapping heat and holding it in a kind of warm-air blanket that surrounds the planet.
This phenomenon is what scientists call the "greenhouse effect." Without it, scientists estimate that the average temperature on Earth would be colder by approximately 30 degrees
Celsius (54 degrees Fahrenheit), far too cold to sustain our current ecosystem.
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Table1: Gases involved in the Greenhouse Effect: past and present concentration and sources
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Source: www.physicalgeography.net,2011
While the greenhouse effect is an essential environmental prerequisite for life on Earth, there really can be too much of a good thing.
The problems begin when human activities distort and accelerate the natural process by creating more greenhouse gases in the atmosphere than are necessary to warm the planet to an ideal temperature.




Burning natural gas, coal and oil -including gasoline for automobile engines-raises the level of carbon dioxide in the atmosphere.
Some farming practices and land-use changes increase the levels of methane and nitrous oxide.
Many factories produce long-lasting industrial gases that do not occur naturally, yet contribute significantly to the enhanced greenhouse effect and "global warming" that is currently under way.
Deforestation also contributes to global warming. Trees use carbon dioxide and give off oxygen in its place, which helps to create the optimal balance of gases in the atmosphere.
As more forests are logged for timber or cut down to make way for farming, however, there are fewer trees to perform this critical function.
 Population growth is another factor in global warming, because as more people use fossil fuels for heat, transportation and manufacturing the level of greenhouse gases continues to increase.
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
Climate
The average temperature will almost certainly further increase (1 to 6°C in 100 years). Dry and extremely warm and hot climate will be more frequent; Heavy rainfalls may also increase in frequency.

Water
River discharge is has increase considerably due to more extreme temperatures and precipitation events.

Nature
The rate at which the temperature rises will probably be too high to enable many species to adapt or migrate. Several plant and animal species are threatened with extinction in the earth.

Economic losses
The agricultural and tourism sectors is undergoing changes that could be both positive and negative from an economic point of view. There are signs that agricultural damage risks
(water logging, droughts and insects) are increasing.

Public health
Temperature rise caused by climate change may have a direct negative influence on human health.
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Hot and humid climates occur in a belt extending roughly 15° either side of the equator.There is very little seasonal variation, other than the amount of rain, which is high throughout the year, and the incidence of gusty winds and electric storms. Mean maximum Dry Bulb
Temperature is between 27 and 32°C. Night minimum varies between 21 and 27°. Relative
Humidity is usually high at around 75%,but may vary between 55 and 100%.Sky conditions are fairly cloudy throughout the year, although luminance can vary considerably. Solar radiation is partly reflected and partly scattered by cloud and the high humidity. The latter also reduces outgoing radiation.
Wind velocities are generally low. Vegetation grows quickly, and the high humidity encourages mould, algae and rusting. Mosquitoes, usually malarial, and other insects abound.
Table 2:Climatic data for akure for the year 2010.
June
July
Aug
Sept
Oct
Months
Jan
Feb
Mar
Apr
May
Nov
Dec
Min.
Temp.(°C)
22
23
23
23
23
22
22
21
22
22
22
22
Max.Temp.(°C
)
32
33
33
32
31
29
28
28
28
30
31
32
Temp.
(°C)
27 -
28 -
Sea Temp
(°C)
28 -
28 -
27 -
26 -
25 -
24.5 -
25 -
26 -
27 -
27 -
Precipitatio n (mm)
40
57
100
115
215
336
150
59
214
222
77
41
Sun
Hrs/Day R -H (%)
5.9
6.7
83
81
6.4
6.2
5.6
80
81
85
3
3.1
4
3
4.9
88
88
86
88
88
85
83
Source:metrology department,Federal University of Technology,Akure.
6.6
6.6
Wind Spd
3
3
3
3
3
4
3
3
4
3
3
3
From the table, one will notice an incessant rise in the level of sunshine hours of more than 5hours occupying eight months of the year. This gives an indication of the greenhouse effects which will normally cause the overheated hours to rise and consequently changes in climate.
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8
7
6
5
4
3
2
1
0
3
4
1
2
5
6
7
8
9
1 2 3 4 5 6 7 8 9 10 11 12
months fig 1:showing the heated up hours
These are principally temperature, humidity, precipitation, sky condition, solar radiation, and intensity and direction of winds.

Temperature:
Temperature is usually expressed as a monthly mean, but average monthly maximum and minimum values may be preferable. Mean maximum Dry Bulb Temperature for Hot and
Humid climate is between 27 and 32°C. Night minimum varies between 21 and 27°C.

Humidity:
Humudity is the amount of water vapour present in the air. The amount of moisture the air can hold varies with temperature. Usually the indicator used is relative humidity, which is the ratio of the actual moisture present to the amount of moisture the air is capable of holding at the same temperature, expressed as a percentage. Relative Humidity is established by the use of the wet and dry bulb hygrometer. This consists of two mercury thermometers side by side.
The first measures the air (dry bulb) temperature (Dry Bulb Temperature). The second bulb is covered by a wick which is kept wet. As moisture evaporating gives a cooling effect, the wet bulb temperature (Wet Bulb Temperature) will be less than Dry Bulb Temperature.
Evaporation is faster in dry air, producing a more pronounced difference between Wet Bulb
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Temperature and Dry Bulb Temperature, or wet bulb depression. Relative Humidity for Hot
Humid climate is usually high at around 75%, but may vary between 55 and 100%.

Precipitation :
Precipitation includes rain, hail and dew, is measured in mm/time units, using a rain gauge.
Data are collated in a form which indicates the pattern of dry and wet seasons. Also Useful are 'ever recorded' maxima and minima, and maxima in any 24 hr period, which will provide degrees of deviation from average, and prediction factors for flooding. Building designers also need to know the probability of intense periods of rain being associated with strong winds, in order to predict the degree of exposure to driving rain.

Sky condition:
Sky condition is usually indicated in terms of the degree and frequency of cloud cover, and may be used in calculations of luminance of daylight factors for building interiors, and also for decisions on shading devices.

Wind Velocity:
Wind velocity is measured with anemometers, using propeller type blades or cups. Direction is recorded by a wind vane. These can be recorded on paper or by computerised A/D systems.
Values (usually meters/second) are taken at (or calculated to) a height of 10 meters in flat open country. Directions are usually grouped into 8 or 16 categories, corresponding to the 8 cardinal or semi-cardinal compass points, and the 8 tertiary points. Wind charts or roses are used to plot the force, percentage frequency and direction of winds for any given location.
As of a result of the greenhouse effects and more of the heat from the sun is been exposed on the planet earth, there is the need to consider some special requirements when designing for hot and humid climate taking the various climate indicators into play. Such designs should be guided by the principles that will enhance and facilitate easy flow of air throughout the building and give enough room for cross ventilation and provide maximum surface surface area for night cooling.
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
Design and Construction:
Since the dry bulb temperature is between 27
0
C and 32
0
C during the day then as a result of the high heat up of the green gases, hence the design should be done in such a manner that the building depth is minimized hence employing lightweight (low mass) construction to enhance and facilitate cross ventilation during this heated up hours. The design should be such a one that gives room for free interpenetration of spaces and well use of space combination.

Walls:
Maximize external wall areas especially the south and north wall. Plans with one room depth are ideal to encourage movement of breezes through the building (cross ventilation) and minimize west facing walls so as to reduce heat gain. Ceiling fans should be used where required.

Orientation:
Site should be exposed to breeze and provide for shading all year for exposure to breezes.

Consider creating sleep out spaces:
In designing for hot and humid climate, special consideration should be made for sleep out places probably during the day when the interior temperature is unbearable. Provision of balconies, terrace, and verandas more on the north-south elevations will create a cool shade for good body comfort during the day.

Use light coloured roof and wall materials.
These light colours have high reflectance ratio and would be able to reflect heat easily without losing its properties. Light coloured roofs will reflect direct radiance of the sun.

Consider high or suspended ceilings of absorbent properties:
This give room for circulation of hot air that are not been reflected by the roofing material and such heat is been trapped within the enclosed air area or better still absorbed by some special made ceiling materials which can absorb heat without losing its properties and roof trusses should be constructed in such a way that enhances roof space ventilation.
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
Consider the Use of Green Shades
Since the temperature range of such a climate is between 27 0 C-32 0 C the day, provision should be made for green shading of the site. This can be plan from the outset of the design process. Trees that can shade properly during this heated periods should be left on site during the clearing process and in a cases where there is need to plant trees with broad leaves that will facilitate adequate shading, then it should be inculcated in the design in such a way that they will act as shading device during the day and at night facilitate cool and fresh breeze penetration.
Plate1: showing the use trees as green shades, Lagos

Step-up building appropriate to permit airflow across Level of floors.
Since air temperature flows with levels, a good interplay of levels in a building in hot and humid climate region will enhance cross ventilation appropriate since the incoming cool air at the windward direction will flow in a level-like manner hence minimizing much suction formed in some parts of the building. Also, this will place the building in a good level of cross ventilation since air temperature flows best at different levels of openings.
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In conclusion, the greenhouse effect causes the atmosphere to trap more heat energy at the
Earth's surface and within the atmosphere by absorbing and re-emitting longwave energy.
The activities of humans have directly or indirectly caused the concentration of the major greenhouse gases to increase and thus an increase in sunshine hours and rise in temperature and consequently increase in degree of rainfall thus giving major implications specially in designing for the hot and humid zones the need such as considering the heated up hours to shade against and the spread hours to protect against heavy rainfall by using the foregoing elements to make a residential environment comfortable for human habitation and green in nature.
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
Martin Clark & BA GradDip T.P
( 1993) Designing for Climate .

Olgyay, V. (1963). Design With Climate - Bioclimatic Approach To Architectural
Regionalism .Princeton University Press, Princeton, New Jersey.
 www.about.com
 http://www.physicalgeography.net/fundamentals/7h.html
 www.WeatherStreet.com
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