We all are experiencing summers which are warmer than before with intolerable heat. The heat has been affecting all realms of human activities, starting from schools, colleges to trade. Discomfort affecting sense of wellbeing negatively also adds on the summer plethora, India being mostly a warm country. Thermal comfort in a body is maintained by the balance between heat gains due to metabolism and heat loss to the environment. A warmer ambience surrounding the body will cause more discomfort. Maintaining thermal comfort through “variations in the indoor environment can be reduced through design and concentration measures. Well planned buildings account for the impacts of the outdoor climate on indoor environment through spatial design, thermal performance of construction materials, and building envelope design and performance. In addition, certain electrical and mechanical systems such as fans, humidifiers, air conditioners are used to further improve indoor thermal environment.” Almost two third of the urban buildings that will exist in 2050 in India is yet to be built hence the demand for cooler environment will also increase rapidly and steadily.
Densification is inevitable as the statistics show that “the number of households in India are estimated to rise from 272 million in 2017 to 386 million in twenty years (MOEFCC, 2019). Unprecedented concentration of building mass without proper climatic design considerations and lifestyle changes are resulting in steeping penetration of air conditioning (40% expected by 2038, MOEFCC, 2019) along with other electro-mechanical cooling devices. Global warming, climate change and micro-climatic heating because of populous urbanism are causing extreme outdoor thermal conditions, which each summer proves now.
Energy, although an essential ingredient in the development of machines and societies could never be imagined to relate to the overall problem in a form, as complex as thermal issues affecting human lives remarked Coad way back in 1982. He also added “the time for disorganized trial and error in the depletion of energy resources must come to an end or our present social system will certainly collapse.” “In residential sector in India alone, it is projected that energy consumption in 2030 will show an increase of 3.5 times to 850 TWh in contrast to that of 2017 data. Most of the energy today is generated from resources extracted from earth and unlike other resources such as aluminium, steel etc., ‘energy resources once used by conversion to thermal energy, not only cannot be recycled but contribute to the imbalance of the system.’ We all are aware that there exists a tremendous scarcity of resources but energy economics and politics revolving around it has reached to blatant state which cannot be ignored. Quoting Coad again “A population with an understanding of the concepts of energy source and conversion, factual limitations, and impact of continued excess would not find it necessary to turn to self-proclaimed leaders … for solution to their inevitable problem, but would, with understanding, naturally develop their own solutions” along with the help of technical knowledge of architects, designers and engineers in the area of energy conservation and thermal comfort of built environment together.
“Considering building envelope optimization as one of the most effective strategies for minimizing energy and cost footprints.” Optimized envelope reduces building energy loads and increases day lighting. It also leads to thermal comfort passively i.e. without use of energy and cost intensive devices such as air conditioning. This further reduces system sizing and optimizes systems resulting in operation loads thus accruing two-fold savings. In a building there are following four primary ways of heat gain through the envelope (1) conduction through roof, (2) conduction through opaque walls, (3) conduction through non-opaque surfaces e.g. glass, and (4) solar radiation through non-opaque surfaces. Now these heat transfer mechanisms are dependent on two criteria (a) spatial characteristics of building which contributes to the amount and nature of incident heat energy and (b) materials which affects the amount of heat energy transferred indoors.
The first and most important in the chain of actions in achieving thermal comfort is spatial design mentioned above. The following important factors could be well corroborated cost effectively at the inception and drawing stage of the building design – (1) orientation, (2) building form, (3) window to wall ratio and (4) shading elements. Sometimes due to various reasons such as limitations of site (size, shape, access etc.), regulations, visibility/ view factors, privacy, existing structures/ trees etc. the desired optimum orientation and building form may not be achieved. However, other strategies can be applied in such scenarios. The second in line is determination and selection of materials and methods of construction based on the building that has been designed and sketched/ drawn.
For example, thermal conductivity of the wall contributing to heat gain can improve by thicker walls, however in today’s dense urban built form and huge value associated with each square feet of liveable floor area, compromising on thicker walls for thermal comfort or energy saving on cooling/heating is a mere luxury. Also the cost of increased material usage and material transportation causing heightened carbon footprint, along with heightened initial project cost along with material storage, handling and labour costs loom in the background. Hence, design of walls alone calls for a deeper scrutiny by the architects, designers, manufacturers and builders. Thermal insulation often plays an important role. Specially with construction in metals such as ACP, where thermal bridge is a concern. However, proper design and simulation can overcome these challenges leading to a satisfactory building design negotiating both thermal aspects (both external and internal), building functions (human activities inside) and aesthetics. It is observed that concrete brick has the highest thermal transmittance plummeted against AAC block which has the lowest.
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In any building wall area sums up to be the largest surface of the envelope and receives the maximum solar radiation hence total conducted heat transfer is very high, same is the case for the roof. Whereas the convection and radiation (through glass) heat gain is high for windows, glass curtain walls etc. Rationalizing various building envelope elements, the following could be inferred. For walls, thermal conductivity with metric R value – U value and thermal mass attributed by specific heat capacity are important indicators for design and selection of materials. For windows and roof, apart from thermal conductivity, solar gains + visible light transmittance and thermal emissivity, respectively, matter most.
Since wall area contributes to a substantial heat transfer considering the building envelope or skin, judicious selection of material is important out of the large array of materials used in building industry today. The façade of the building is not only the face which markets the architecture but plays a key role towards the health of the building. Challenge of striking a good balance between looks and functionality is what a designer is posed with. One of the popular materials used in the commercial and industrial sector is Aluminium Composite Panels (ACP). It is finding a good acceptability in the residential sector too. Known for its versatility, superior durability and other physical characteristics compared to its cost, it is also a promising material in terms of recyclability and sustainability (Selvakumar, James & Thangadurai, 2021). Comparatively newer material in the array being introduced to the market only in 1969, it has gained wide acceptability and use in a very short time and the curve is continuing to steep high.
It can be used for both exteriors and interiors. It manifests great stability for a very high temperature range from -50 to +80oC (Mohaney & Soni, 2018). However, being a metal based walling element, it has a great responsibility towards thermal aspects. Material specifications and methods of construction considering factors of thermal bridge should be critically looked at while selecting brands and fabricators. If need be, thermal insulations must be procured to mitigate any lapse in thermal insulation property. The experiment by Duka et al., in 2022 has shown that different brands of ACP perform differently in terms of thermal properties. A good ACP will act not only as good thermal insulator but also provide air and water tight interior, with superior acoustic barrier. Energy Conservation Building Code (ECBC) published by Bureau of Energy Efficiency, Ministry of Power, Government of India, has specified various aspects of sustainable building including the thermal parameters of elements of buildings for various categories such as use, climatic zones etc. ACP wall units should not be an exception to such standards. Once the ACP is selected it should be analysed and its properties well versed to go for the envelope and skin design for better thermal qualities. To deliberate on this subject, let us take an example of Aludecor ACP Sheets.
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The ventilated façade of Aludecor ACPs is an enclosure system that uses a supporting framework to allow an insulating layer and an outer leaf to be put on top of an inner leaf. The separation gap between the layers allows a current of air to flow between the insulation and the coating, creating a natural ventilation “chimney effect”. This action warms the vented facade in the summer and circulates the air within the chamber, replacing the heated air with cooler air by heat transfer through convection. During the winter, however, the air in the chamber/room is heated but not sufficiently to circulate and replenish itself.
A ventilated facade system offers significant benefits to a building by enhancing thermal efficiency. In hot weather, it reduces heat absorption through partial solar reflection and natural ventilation in the air cavity. In cold conditions, the system retains heat, decreasing reliance on heating. With HVAC systems typically consuming 40% of a building’s electricity, ventilated facades can lead to substantial energy savings, with research indicating a potential reduction of over 30% in energy usage.
The thermal properties of Aludecor is shown in the table below:
Such material along with design aspects, construction techniques (e.g. hollow walls) and aggregating with other materials (e.g. insulation) lead to a superior built environment both externally and internally. Now, for Aludecor the heat transmission coefficient or the U value is above 5.
Read also: Aludecor Systems – The Pioneer of Heat Insulation and Green Building Practices
For calculating the overall U-factor of a wall construction with multiple layers, the U-factors from the wall construction layers must be combined together such that it is 1/Ucombined, where Ucombined is (1/Ulayer1 + 1/Ulayer2). Now the compliance value of opaque external wall assembly has been specified by ECBC for various climate zones of India and for different types of buildings such hotels, schools etc. In order to accommodate the compliance from a thermal conductivity per say. Easy adjustments could be done by the architect/ designer to reach to the desired prescription. For example, an Aludecor ACP wall unit along with an extruded Polystyrene foam insulation will lead to combined U value (1/Ucombined) much lower than permissible maximum value of 0.4 (for hot-humid/ hot-dry/ composite all building type except hotel, business, school as specified), using the stipulated equation/ formula mentioned above. One of the Gold Green rated LEED certified building using Aludecor ACP and such attribution is the Biowwonder non IT environment positive commercial hub of Eastern India, which stands as a live example of superior thermal properties of ACP sheets despite the frown of being a metal based envelope.
Biowonder – Commercial hub, Kolkata
Hence, the architects, designers and engineers play a major role in crafting the “responsible building skin” as I called it which while pleasing people and harnesses a holistic and sustainable development. An energy educated society and responsible building skin is what we need to tackle both the thermal discomfort and unsustainable living today.
References:
- Baker, N. & Steemers, K., 2000, Energy and Environment in Architecture: A Technical Design Guide, E & FN Spon imprint of Taylor & Francis Group, London, ISBN 0419227709.
- Coad, W. J., 1982, Energy Engineering and Management for Building Systems, Van Nostrand Reinhold Company, New York, ISBN 0442254679.
- Rawal, R., Pathak, B. & Shukla, Y., 2022, Climate Smart Building – Training Program on Innovative Construction Technologies & Thermal Comfort in Affordable Housing – Handbook, Center for Advance Research in Building Sceince and Energy, CEPT University, India.
- Mohaney, P. & Soni, G., 2018, Aluminium Composite Panel as a Facade Material, International Journal of Engineering Trends and Technology, Vol 55 (2), Indore, India.
- Duka, E., Beqiraj, E., Molla, X. & Xhexhi, K., 2022, Comparative analyze of thermal and tension strength properties of Alpolic and Durabond aluminum composite panels, Journal of Multidisciplinary Engineering Science and Technology, Vol. 9 (2), Tirana, Albania.
- Selvakumar, M., James, J. D. & Thangadurai, K. R., A Deep Study on Aluminum Composite Panel: Applications, Merits, and Demerits, International Journal of Mechanical Engineering, Vol. 6.
