Anybody who has lived on the uppermost floor of any building in the Australia or other parts of the world with similar climate may have experienced discomfort that results from higher temperatures especially during the summer seasons. Majority of the buildings in Australia are built using concrete with flat configurations of tar roofings.These surfaces normally absorb the incident radiations that are directed to the building. The ceiling that is hot will continue to heat the available space hence making these places unbearably hot during the day as well as night in the entire season of winter. ( Tong et al 2014).
In the recent years, these places have undergone improved level of urbanization especially in the developed countries like Singapore,Indonasia and Malaysia. This increased process of urbanization has been as a result of the increased population in those areas. The intensity of the urban heat island commonly known as UHI has also increased. This affect is characterized by the increase in the consumption of the energy especially the issue of cooling and this is just a primary concern.
Objectives
The studies that have been carried out by the Building and Construction authority clearly showed that the structures in the Singapore areas that are also the world fourth leading center of finance takes up to 57% of the entire consumption of electricity. Also the study showed that the total house hold consumption of the energy in the whole country was on the increase from 6514GWh that was in the year 2009 to almost 6560GWh in the year 2011.The economic statistics of the country has also been shown to be on the increase from every year by at least 15%.The increased consumption rate was possible owing to the fact the much of the energy is derived from the fossils fuels.
The effects or impacts of roofs on the energy consumption has been overlooked more oftenly.This particular impact can be as well significant if properly utilized. In seasons such as winter, damages on the roof insulation can results into escape of heat. In summer seasons, heat that is gained through the roof increases loading on the cooling systems. In order to address these problems effectively, several options of low energy roofing systems have been utilized in various section of the world including Australia. Three of these options include; Convectional strategy, Radiant strategy and reflective strategy.
The results indicated the increased trend in the demand of electricity. The areas of the residence consumed at least 20% of the total supply. It was also found that at least 21% of this supply is used in the areas of the air conditioning and also 2% to facilitate or power the mechanical fans. These figures have been on the increase and this has been a clear indication that Malaysians rely majorly on the conditioned air sources in order to maintain comfortable working environment.
Figure 1; Convective strategy of roofing system extracted from (Sauna Takebayashi and Moriyama 2012)
The study of the tropical architecture indicated that most of the Malaysia structures are constructed using building materials including clay, bamboo and also wood. These materials have been facing rejection in the new cities that have considered construction using other materials like shiny metals, glass and also concrete. The close analysis of the environment and survival conditions indicated that very comfortable structures in Malaysia suffered from the effects of high temperatures.
There has been need to control this high temperature so that the global warming consequences are brought to control as well. It has been found that the majority of the cooling demands on the energy in the tropical areas are dependent on the roofing materials. The system of the roofing represents almost over 70% of the total heat gained. This was the example that was used in the Malaysia construction. The distribution of the materials were very rational with concrete being 20% and clay being 2.5%.These materials allow for the transmission of solar radiation that actually induces the effect known as (Sauna Takebayashi and Moriyama 2012).
The Sauna effects creates environment that is very uncomfortable. One of the approaches that assist in the maintenance of the right temperature is the strategy of passive cooling. This particular strategy involves the use of a controller whose primary function is to limit the total effect of the heat that has been gained. The control effect is that the interior temperatures are far much below the temperatures of the surrounding. In general terms this practice implies passive design that is achieved through the natural means( Miranville et al 2012).
These natural mean include conduction, radiation and also convection. The passive cooling system does not completely eliminate the use of other mechanical means like fan but it assist in the improvement of the installed structures. Most of the studies have shown that enhanced means of cooling is through the use of hybrid system. The passive system of cooling normally consists of the measures that are considered preventive against the effects of overheating in the interior of the buildings.
The most commonly used approaches in the area reduce the heat gains and also the temperatures that are within the building. In order to have all these strategies work effectively and also to prevent the entry of the excess heat in the building, there are two factors that are required. The first requirement is a heat sink that has temperature below the interior air (Medina 2012). All these activities use the earth as the source of cooling( Lee and Lim 2016).Installation cost is approximately $4500.
This strategy is meant to slow down the heat transfer into the building. The studies have estimated over 60% of the area in the urban set up covered by the roofs and also covered by the pavements. These figures are on the rise considering that the world’s population tend to concentrate in the urban centres.The estimation is that by the year 2040,
Figure 2; reflective roofing system extracted from Celsius (Ko?ny et al 2012).
Characteristics of the relative approach
the figure will hit to over 70%.This will be reflected in the general characteristics of the UHI.The heat Island intensity has been on the rise to almost 10 degrees Celsius. Effects of the development of the urban are affected by the quality of the environment in Singapore. The available reports have indicated that the surface of the air temperature is very high almost 50 degrees Celsius (Ko?ny et al 2012).
This is a design concept that focuses on the reduction of the effect of the heat gain on the roofs of the building especially on the sunny days. The design constitutes single or many layers of different materials. The properties of the physical structures are given major attention in these cases. The property considered is whether cool or not. They’re very many reasons that are put forward to support the cool roofs. They promote the indoor thermal or temperature of the spaces without having air conditioning.Secondly,they1 extend the service life of any roof through reduction of the roof operating temperatures. There is also aspect of energy reduction in the consumption units( Gaither et al 2016).
Considering that most of the light that is derived from the sun is normally visible, the idea of the reflective roof works with the surface properties. The reflector is normally targeting the invisible electromagnetic radiation. These will include both short waves and also long waves. They form the best emitter of radiations opposed to the black heat that will absorb large amount of heat. It is interesting to note that a reflective roof under such similar environmental conditions will clearly maintain the temperature to about 28 degrees Celsius( Asadi, Hassan and Beheshti 2013).
The properties of the material have been considered key factors. These factors included solar reflectance. The solar reflectance is also known as albedo. This particular feature focuses on the reflection of the solar energy especially after it has come into contact with the materials of the surface. The other key factor of the material response was thermal emittance.This particular feature focuses on the radiant remittance of heat of a specific object that is in the form of thermal radiation or just infrared (Ferrari et al.2016).
The construction and installation need a mechanism that is improved to facilitate the movement of heat from the hot place to the sink. The above requirement is achievable through use of environmental sinks of the heat. These environmental heat are divided into four main cartegories.The transfer of heat by convection is vacillated by the ambient air. There is transfer of heat by long heat radiation in the atmosphere using very long radiation. There is transfer of heat by evaporation that takes place in the outside and inside the fabric of the building (Rodriguez et al .2014). The installation cost is approximately $5400.
Radiant Low Energy Roofing system.
It involves the removal of the unwanted heat from the structure. This particular technique is based on the fact that any material or object at a particular temperature above 0K will definitely emit some forms of electromagnetic radiations (Klement, 2012). This is a viable mechanism that needs to be used considering that more than half of the heat transfer takes place through thermal radiation. In the concept of radiation, heat will normally flow from the warmer region to the cooler region. The radiant exchange process has very little impacts on temperatures as opposed to the natural convection( Arumugam et al. 2015).
Figure 3; radiant roofing system extracted from (Ferrari et al.2016).
Characteristics of the radioactive approach
In the general analysis, net radiation flux is created whenever two different surfaces with different temperatures face each other. There will be repetition of the processes until the equilibrium state is achieved. In addition, there will be response from the other surface in case the other surface becomes cooler. The heat sink exchange operation is based on the temperature difference between the conditions of the sky and also the component of the building. In practice, the conditions of the sky plays Avery significant role that affects the radioactive cooling strategy since air humidy,cloud covers among others like pollution reduces the strategy performance.
Most of the known radiant cooling systems can operate both during the day and during the night. This is because the approach has the best view of the dome of the sky hence the radiator is very effective. As compared to the conventional methods, radiant cooling systems appear to save on the cost.
However this system has a shortcoming that comes from the accumulation of the dust on the roofs and this definitely reduces the solar reflectance capacity. The reflectance capacity will keep reducing as time progresses. Also the radiant method has got very minimal effects on the air temperature hence will require a strategy for improvement.
Heat transfers are achieved through conduction beneath the surfaces of the soil. Each of the building has utilized different ways in the various systems. The heat rejection into these heat sinks are normally achieved through other methods considered natural done. These natural means of temperature are normally boosted using mechanical methods that are use of power fans or just pumps. There has been grouping of the common passive cooling system into comfort ventilation, radiant cooling, cooling through evaporation means, and nocturnal cooling through ventilations. The installation of this roofing system utilizes materials whose properties serve the requirement of the building conditions. The installation cost of the entire system is approximately $5830.
Conclusion
Implementation of receptive and also radioactive approaches in the system of the roofing will definitely enhance the environmental sinks. This will also facilitate heat dissipation. The result of this impact is to minimize the effect of the penetration of heat as well as reducing the gains through lighting and appliances. The efficiency of these structures depends on the type of the building, the patterns of the occupancy, boundaries of the climate which is subject to air temperatures, velocity and direction of the wind and also relative humidity.
The effective understanding of the characteristics of the building will always help to improve the heat rejection from the buildings by natural means. It is important to note that when improper selection is done on the technique, unpleasant indoor environment will be created. The limitation in the evaluation tools and also insufficient information will be a draw back to the designer. In the set up like those of Malaysia, there was no objection in relation to modifications of the roofs so as to reduce the need for air conditioning. This was a clear indication that the respondent has been willing to adopt the new cooling strategies for their buildings (Algarni and Nutter 2015).
References
Algarni, S. and Nutter, D., 2015. Influence of dust accumulation on building roof thermal performance and radiant heat gain in hot-dry climates. Energy and Buildings, 104, pp.181-190.
Arumugam, R.S., Garg, V., Ram, V.V. and Bhatia, A., 2015. Optimizing roof insulation for roofs with high albedo coating and radiant barriers in India. Journal of Building Engineering, 2, pp.52-58.
Asadi, S., Hassan, M.M. and Beheshti, A., 2013. Performance evaluation of an attic radiant barrier system using three-dimensional transient finite element method. Journal of Building Physics, 36(3), pp.247-264.
Ferrari, C., Libbra, A., Cernuschi, F.M., De Maria, L., Marchionna, S., Barozzi, M., Siligardi, C. and Muscio, A., 2016. A composite cool colored tile for sloped roofs with high ‘equivalent’solar reflectance. Energy and Buildings, 114, pp.221-226.
Gaither, G., Toyota Motor Engineering and Manufacturing North America Inc, 2018. Fluid turbine systems for harnessing light radiant energy, thermal energy and kinetic energy in vehicles and methods of operating thereof. U.S. Patent Application 10/017,053.
Klement, M.R., 2012. Radiant baffle/collector for roof construction and retrofit. U.S. Patent 8,137,170.
Ko?ny, J., Biswas, K., Miller, W. and Kriner, S., 2012. Field thermal performance of naturally ventilated solar roof with PCM heat sink. Solar Energy, 86(9), pp.2504-2514.
Lee, S.W. and Lim, C.H., 2016. Reflective thermal insulation systems in building: A review on radiant barrier and reflective insulation. Renewable and Sustainable Energy Reviews, 65, pp.643-661.
Medina, M.A., 2012. A Comprehensive Review of Radiant Barrier Research Including Laboratory and Field Experiments. ASHRAE Transactions, 118(1).
Miranville, F., Fakra, A.H., Guichard, S., Boyer, H., Praene, J.P. and Bigot, D., 2012. Evaluation of the thermal resistance of a roof-mounted multi-reflective radiant barrier for tropical and humid conditions: Experimental study from field measurements. Energy and Buildings, 48, pp.79-90.
Rodriguez-Ubinas, E., Montero, C., Porteros, M., Vega, S., Navarro, I., Castillo-Cagigal, M., Matallanas, E. and Gutiérrez, A., 2014. Passive design strategies and performance of Net Energy Plus Houses. Energy and buildings, 83, pp.10-22.
Takebayashi, H. and Moriyama, M., 2012. Relationships between the properties of an urban street canyon and its radiant environment: Introduction of appropriate urban heat island mitigation technologies. Solar Energy, 86(9), pp.2255-2262.
Tong, S., Li, H., Zingre, K.T., Wan, M.P., Chang, V.W.C., Wong, S.K., Toh, W.B.T. and Lee, I.Y.L., 2014. Thermal performance of concrete-based roofs in tropical climate. Energy and Buildings, 76, pp.392-401.
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