PasteCHAPTER ONE
Introduction
1.0 Introduction
A roof is the covering on the uppermost part of a building. A roof protects the building and its contents from the effects of weather, and the invasion of animals. Structures that require roofs range from a letter box to a cathedral or stadium, dwellings being the most numerous. In most countries a roof protects primarily against rain and sun shine. Depending upon the nature of the building, the roof protect against heat, sunlight, cold, snow and wind. Other types of structures, for example, a garden conservatory, might use roofing that protects against cold, wind and rain but admits light. The characteristics of a roof are dependent upon the purpose of the building that it covers. Whitney et al (1901)
According to Castleton et al. (2010), a green roof is a layered system comprising of a waterproofing membrane, growing medium and the vegetation layer itself. Green roofs often also include a root barrier layer, drainage layer and, where the climate necessitates; an irrigation system. A green roof offers a building and its surrounding environment many benefits. These include storm water management, improved water run-off quality, improved urban air quality, extension of roof life and a reduction of the urban heat island effect. Other benefits also include enhanced architectural interest and biodiversity .There are two main classifications of green roofs; extensive and intensive. Extensive green roofs have a thin substrate layer with low level planting, typically sedum or lawn, and can be very lightweight in structure. Intensive green roofs have a deeper substrate layer to allow deeper rooting plants such as shrubs and trees to survive.
As a result of man's activities on earth, a lot of changes do occur in our landscape. Some of the activities includes infrastructural developments such as buildings, roads and others which replaces vegetation with impervious surfaces. These surfaces absorb solar radiation during the day and give its out at night making indoors uncomfortable to live in.
Ghana is right now at the point of rapid urbanization causing people to migrate from all over the country towards the major cities of Accra and Kumasi. Kumasi is thus at the threshold of rapid urbanization as the City's growth rate of 5.47 % as compared to the nation's 2.5% and Accra 3.5% (Ghana Statistical Service ,2012). is higher than both the national and regional figures. This could lead to rapid depletion of its resources such as green spaces for infrastructural development. The most evident problems that face Kumasi are deforestation, desertification and heavy pollution, which negatively affect the quality of life of the city's dwellers.( Kumasi Metropolitan Assembly ,2010).
Kumasi, the second largest city in Ghana is within the HFZ (high forest zone) of the country. In 2000, Kumasi had a population of 1,170,270 people, reflecting an inter-censal growth rate of 5.4% between 1984 and 2000. (Ghana Statistical Service ,2012). The population is projected to be 2,443,737 in 2014 based on the annual growth rate of 5.4% between 2010 and 2014. Due to its fast physical and demographic growth, Kumasi now extends beyond the administrative boundaries of the KMA into the neighboring districts. ( Kumasi Metropolitan Assembly ,2010).
The city was endowed with natural landscape, especially urban trees, to become an excellent example of an ecological city in Africa. (Quagraine, V. K. ,2011). Unfortunately, like a typical African city, the green spaces of the Kumasi Metropolis are being depleted at a faster rate. The city of Kumasi is suffering from a rapid decline in its green spaces (Collins Adjei Mensah,2014) due to uncontrolled urbanization. Studies show that the green spaces in Kumasi, once the Garden City of West Africa, have been depleted remaining only a small fraction which together with other open spaces constitute about 10.7 percent of the total land area of Kumasi.( Amoako et al,2011)
In the building sector, the increased use of air-conditioners, inefficient curtain walls and sliding windows, and the lack of sustainable design principles, especially in residential buildings have contributed to the present energy situation (Koranteng, 2010). In addition, as the roof act as a barrier between the sun and the building, care should be taken in constructing the roof to ensure thermal comfort in the space and avoid the usage of mechanical ventilators such as air conditions and fans which cannot be supported in developing countries like Ghana.
Energy is the bedrock for the success of very nation and leads to the improvement in the quality of life of people. Given that by 2020 almost 70% of the world population will be living in cities, 60% will be energy poor (Serageldim and Brown, 1995). Thus for the next decade, thousands of megawatts of new electrical capacity have to be added. Der-Petrossian (1999) indicated that developing countries may avoid spending $ 1.7 trillion on oil refineries, coal mines and new power plants by spending for the next 30 years $ 10 billion annually to improve energy efficiency and conservation. Another estimate by the US Office of Technology Assessment shows that developing countries have the potential to half their electricity production if energy is used more effectively and introduction of other technologies such as the use of green roofs to cool buildings.
The above study into green roof construction is worth looking into over a longer period of time in order to assess and validate thermal comfort and the eventual implication on energy performance of residential buildings.
1.1 The Research Problem
The city(Kumasi) was endowed with natural landscape, especially urban trees, to become an excellent example of an ecological city in Africa. (Quagraine et al 2011). Unfortunately, like a typical African city, the green spaces of the Kumasi Metropolis are being depleted at a faster rate. The city of Kumasi is suffering from a rapid decline in its green spaces( Collins Adjei Mensah, 2014) due to uncontrolled urbanization. Studies show that the green spaces in Kumasi, once the Garden City of West Africa, have been depleted remaining only a small fraction which together with other open spaces constitute about 10.7 percent of the total land area of Kumasi. (Amoako et al,2011).It therefore becomes necessary that a technology such as the use of green roofs be employed to replace the amount of green spaces we destroy during building on the roof top.
Koranteng (2010) expressed that in the building sector, the increased use of air-conditioners, inefficient curtain walls and sliding windows, and the lack of sustainable design principles, especially in office buildings have contributed to the energy situation. In Ghana, the growth in demand for energy is amongst other factors caused by the numerous air-conditioned commercial buildings being constructed especially in the metropolitan areas of Accra and Kumasi. Occupants' behaviour in these high-rise office buildings have always been to abate thermal discomfort .These behaviours have an eventual effect on energy. However the exact effect is insufficiently investigated into especially in developing countries like Ghana.
The increase of utilities tariff, late 2013 with electricity being the most affected up to almost 100%, it has becomes critical that the issues of power consumption should be looked at. According to Ghana Grid Company Limited(GRIDCo), demand for electricity in Ghana have increased to all-time high of 12.38 percent in 2013, growing from the 2012 peak of 1728.9 Megawatts(MW) to 1942.9 MW at the close of the year. They further indicated that demand for electricity is growing and current projections indicated that the country's requirement for electricity would hit 2,764.2 MW in 2015.
1.2 Research Aim
The aim of the research is to use simulation-based explorations to advance efforts towards a reduction of energy usage through the usage of green roofs whiles enhancing thermal comfort for occupants in residential buildings in Ghana.
1.3 Research Questions
The study would address the following questions.
' How can urban temperature and relative humidity patterns be determined?
' What effect does green roof have on indoor climate?
' What effect does green roof have on the reduction of the urban heat island effect?
' How can the cost benefits and acceptability of green roofs be establish in Ghana?
' Which design options would be energy efficient for residential buildings?
1.4 Research Objectives
The following objectives have been formulated for the study based on the research questions above:
' To determine urban temperature and relative humidity patterns over the past 37 years in Kumasi .
' To access the effect green roofs have on indoor climate.
' To assess the cost benefit and acceptability of green roofs in Kumasi, Ghana.
' To assess the effect of green roofs on urban heat island.
' To determine the best design options for thermal performance towards the reduction of energy for cooling residential buildings.
1.5 Significance of Research
The importance of the study is summarized in the following areas:
' The study will be of interest to prospective house owners as thermal discomfort would be reduced.
' The use of green roofs in Ghana would show the potential in contributing positively to the energy situation in Ghana which in recent times has failed to meet demand.
' The study would also be a guide to roofing sheets manufacturers to meet the demands of prospective house owners.
' To serve as the bases for the choice of roofing material and the design of roofs for professionals such as Architects, Engineers, Quantity Surveyors and so on.
1.6 Scope of the Research
The research is geographically conducted within Kumasi, the Ashanti Regional Capital. Parametric simulation analysis is used as a means of comparing the thermal performance of test cells with design parameters as options so as to find the perfect scenario that will efficiently reduce thermal discomfort by the introduction of green roofs and in the long term reduce energy consumption in residential houses.
1.7 Methods and Data
1.71 Methods
Nine test cell scale models is created at the Department of Horticulture to assist in investigating the benefits of green roofs on thermal performance of buildings in Kumasi.
One of the models is replicated 6 time and incorporated with a green roof but first 3 of the replication of the green roof vegetation would be Portulaca grandiflora(Portulacaceae) whilst the other 3 would be Setcreasea pallida.The other model is a precoated 0.4mm aluzin brick red roofing sheets which is replicated 3 times . The model is to a scale of 1:100 and a size of 1m x 1m meters.
The nine models consist of a typical Ghanaian building materials such as sandcrete blocks,concrete,wood,paint,sand and a vegetation.
The plants for the green roof would consist of a ground cover called Portulaca grandiflora(Portulacaceae) and Setcreasea pallida. Portulaca is a low prostrate creeping plant with terele leaves about .15m high. This plant is not fussy about the soil and thrives well on even poor soil and is propagation by division.(Norman,1971). Setcreasea pallida a native of Mexico, it is a prostrate plant, about 0.3m (12 inches) high, with oblong-oval leaves up to 15cm (6 inches) long and 4cm (1'' inches) across. The stems and leaves are purple. It produces violet flowers which are open in the morning and close in the late afternoon. Grows best in direct sun. Can also grow under semi-shade, but it has the tendency to turn towards the sun. Suitable as a bedding and a pot plant. Propagated by stem cuttings. Quick growing.. (Source: Norman, 1971)
Sandy Loam soil is used as a media for the plants. A sample is taken to the Soil Science laboratory for characterisation of the soil. No amendments such as poultry waste is added to the Sandy loam as the plants selected can even strive in poor soil.
The composition and character of green-roof vegetation depend on many factors. To a large extent, substrate depth dictates vegetation diversity and the range of possible species. Shallow substrate depths between 2 and 5 cm have more rapid rates of desiccation and are more subject to fluctuations in temperature, but can support simple sedum-moss communities.
For the purpose of my reserach,Substrate depths of 15-20 cm is used as it can support more diverse mixtures of grasses, geophytes, alpines, and drought-tolerant herbaceous perennials, but are also more hospitable for undesirable weeds which is controlled.(Oberndorfer et al. 2007).The plants are propagated by division and watering is done at least 3 to 6 weeks until the plants establishes and more often during the dry season . Once the plant is established during the raining season, no watering is required. Maintenance ,irrigation and treatment is carried out when necessary.
Mean Temperature and Relative humidity would be collected from the Metrological Agency for Kumasi and statistical tools such as Excel and a mathematical model is used to find the temperature and relative humidity trend for kumasi.
The whole life cycle cost analysis(WLCC) and benefit assessment is use to determine the cost benefits of green roofs in Kumasi. Life cycle cost is an economic method for evaluating project investment alternatives over a selected period of time. It is particularly suited to determining whether the higher initial cost of an investment is justified by reductions in future costs e.g., operating, maintenance, repair or replacement costs.( Green Roofs for Healthy Cities)
Parameters such as :
1. the Present Value (PV) of the entire stream of cash flows;
2. the Internal Rate of Return (IRR) on the investment; and
3. the simple payback period, is used to calculate the whole life cycle cost.
1.72 Components of Green Roofs
The main components of the green roof is consist of four layers: growing medium, drainage and filter, root protection barrier, and waterproofing membrane. Figure 3 illustrates a typical cross section of a green roof containing these major layers ( Jiayin 2006).Below is figure 1 showing the components of the green roof.
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