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An Executive Summary of Climate & Comfort
Many of today's advances are inspired from observing nature. Close examination of natural systems in order to understand their elements, parts, motives and actions enabled scientists, researchers and engineers to adopt these strategies in their work with small or no modification. The reason why this frame work is beneficial is because nature and its elements can be interpreted as a system that has existed for a long time, this survival is a solid proof of the success of the natural strategies in a natural context. Through critical observation, scientist translation of strategies and correct application, these natural strategies can enhance the man-made environment by improving existing strategies and inspiring for a lot more.
The Science of examining nature to inspire and improve technology is called " Biomimicry ". Inspiring a lot of inventions such as cap parts, swim suits, buildings' building, airplanes, etc.
Keywords : biomimicry, nature, building envelope, birds, feather, double skin facade, roof gardens, heat gain.
Architecture has evolved based on human needs. The first "unaware" introduction of architecture to humanity was simply a cave utilized as a shelter. this perception of space evolved through history and was molded to host human and his various services and needs. This evolution cared on hand in hand with the evolution of science. Today , biomimcry directs a lot of modern technologies and applications thus inflects greatly on building's design and operation.
The objective of this study is to observe a certain behavior in nature & study this behavior and use it as a source of inspiration to improve the overall experience of buildings in terms of their function, comfort and efficiency, enhancing the building's strategies and inspiring for new ones.
A case study will be selected to evaluate the performance of the inspired strategies. the building (or buildings) will be evaluated before and after the installation and application of the strategies through simulation to determine the resulted impact of biomimicry on the building.
This research will depend on observing natural strategies in action, hypothesis will be established based on the understanding gained from the observation. these hypothesis will propose applications and strategies in building design and technology. whose effect will be evaluated through simulation to examine the performance and its feasibility.
Current research and technology has a deep impact on building design and function, strategies are already being applied to enhance the overall building's experience. The inspired strategies will be compared to existing ones to determine feasibility and impact. The strategies will then be applied to an existing building which will be selected as a case study for further study.
One of the most crucial elements of buildings that impacts their environmental foot print is the building's envelope, it is the protector against external elements. If the envelope is designed properly, very little energy is consumed to alter the building's inner environment to suit the users' needs. The building's envelope consists of the roof and the facade were many advances were made in the design and construction of these elements based on technological innovation, improving the efficiency of the building with various forms and functions.
The envelope in a building is very similar to the skin in living creatures. skin is considered the first line of defense against external elements, some creatures have more than just a skin, a second layers of protection sometimes exist to help the skin with some of its functions, like feathers in birds. Feathers most of the times change the way they cluster with their neighbors in response to certain climatic conditions. Some birds look puffed when the weather is cold or hot for their bodies, feathers trap air creating some sort of a thermal buffer to minimize heat gain or loss. Furthermore, they protect the skin from direct exposure to sun light, reducing the overall heat gain of the body. Birds come in different sizes and colors, these colors and forms helps in the process of identification and sometimes in social interactions.
The lessons the can be inspired from this observation are indicated but not limited to the following :
- Heat transfer limitation
- Shading and light penetration control
- Reduction of HVAC usage
Most of the above areas can be achieved utilizing the double skin facade system and roof gardening and insulation, which in buildings' anatomy are similar to the feathers on the birds body.
- Heat transfer limitation.
- Shading and light control.
- Reduction of HVAC usage.
The double skin facade is a building system made of two faces usually parallel to the building's vertical exterior form faces, creating a form of cavity where air can flow. The circulating air can be left to flow naturally or it can be controlled through mechanical means. The double skin facade can be static or adaptive (intelligent) operating in response to the variation of the environment's conditions.
The application of the double skin facade is not new, Saelens (SAELENS, 2002) states that the director of the industrial museum in Brussels, Jean Baptiste Jobard, described something very similar to the current understanding of the double skin facade system back in 1849, while the first reported application of the system was in 1903 in Steiff factory in Giengen, Germany, the design intent was to maximize daylight while taking the cold weather and the strong wind in account. the facade was manufactured primarily using steel , yet due to the success of the idea, additionals were built utilizing the same concept but were constructed out of timber instead to reduce cost.
The system has many configurations in terms of its application and function, individuals and organizations categorized the different type of this system to facilitate identification. One of these systems was devised by The Environmental Engineering Firm of Battle McCarthy in Great Britain, The categorization consisted of 5 parts as the following (Poirazis, 2006) :
Category A: Sealed Inner Skin: subdivided into mechanically ventilated cavity with controlled flue intake versus a ventilated and serviced thermal flue.
Category B: Operable Inner and Outer Skins: subdivided into single story cavity height versus full building cavity height.
Category C: Operable Inner Skin with mechanically ventilated cavity with controlled flue intake.
Category D: Sealed Cavity, either zoned floor by floor or with a full height cavity.
Category E: Acoustic Barrier with either a massive exterior envelope or a lightweight exterior envelope.
The Evolution of this system kept on advancing, where it began to interact with other systems in the building increasing the overall efficiency. Stec & Paasen (Stec, van Paassen , 2004) described different models of interaction between the double skin facades and the HVAC systems, where air could be pre-heated in the cavity of the double skin facade then pumped into the building with reduced or no alternation to the air temperature. Furthermore, adaptive double facades are controlled through building management systems were they operate in accordance with multiple other building systems such as lighting.
The two layers of a double skin facade hosts a cavity that is usually ventilated. The air in summer will flow upwards due to the stack effect. This flow will cool the external layer of the double facade reducing the amount of heat that is radiated towards the inner layer thus reducing the overall heat gain. This technique is similar to what happens to birds when they puff.
Shading and Light Control :
The external facade of the double skin facade is usually the only part of the building's facade that is exposed to direct sun light which would result in heat radiation towards the internal face of the double facade, but since the cavity is ventilated, air will cool the external face of the system reducing the heat gain, rendering the double skin facade as a very efficient shading system. This behavior is similar to the behavior of the feathers on the birds body where they function as a shading system protecting the skin from indirect sun exposure.
HVAC consumes a huge portion of the total energy usage of buildings. This consumption is generally divided into two main parts, energy used to modify air condition and energy used to circulate air. According to the Australian department of industry, air circulation consumes only around 35% of the total energy used to heat or cool a building, which indicated a large consumption rate on the process of changing the condition of the air in terms of heating and cooling.
The rule of the double skin facade is that it minimizes heat gain and heat loss utilizing the strategies discussed earlier, thus reducing the demand of energy by the heaters or chillers, ultimately reducing the building's energy consumption.
Birds have a reduced possibility of being prone to fatigue, heat strokes or freezing due to the availability of feathers which protect the body from temperature changes thus minimizing the body's consumed energy in regulating the body's temperature.
- Heat transfer limitation.
- Shading and light control.
- Reduction of HVAC usage.
A roof garden is a planted space that serves for delight and augmentation, an elevated garden supported by a place or structure (Osmundson, 1999). Roof garden applications started in Iraq, more specifically at the time of the Mesopotamians, where the most well-known example of roof gardens was created, The Hanging Gardens of Babylon, buildings with terraces full of greenery reserved for kings. Roof gardens got more famous in time, Norwegians adopted the application of roof gardens widely in their architecture by covering their roofs with birch bark (broad leaved deciduous hard wood tree) to water proof them, then a layer of twigs then the visible layer of sod (Grass and the soil attached to its roots). Although there was a lot of successful application of this system, real application by architects of this system started in mid 20th century by Le Corbusier and Frank Loyed Wright, taking the application to a whole new level (Donnell-Kilmer, 2012).
Roof gardens can affect both the building and its surroundings. In this study, the focus will be on the benefits that a building would gain, which consist but are not limited to the followings:
- Thermal Insulation.
- Reduction of HVAC usage.
- Create a space of delight for the users and utilize the space of the roof which is usually neglected.
Current applications are divided in two parts, extensive and intensive. Extensive roof garden utilize a thin substrate layer and hosts small plants. Intensive roof gardens utilize thicker substrate layer hosting broader types of plants. General application consists of a planting media, which is the healthy soil where plants can grow, spread over a filter layer usually made of special fabric that would hold the soil in place but will allow the excessive water to find its way to the drainage. Water movement under the roof garden can rely greatly on roof slope, if not available or the angle is not sloped enough, a drainage layer would be required. Protective layer is places on top of the membrane to protect it from the plants' roots.
literature shows that roof gardens have low solar reflectance in comparison to conventional roof treatment systems (white membranes), yet they reduce the average temperature fluctuation dramatically in the same context of the comparison, since conventional membrane get heated up very quickly but the roof gardens don't due to their thermal mass and evap-transpiration process (Andre O. Desjarlais, 2010).
The relationship between the roof gardens and the HVAC loads is pretty straight forward, the roof is usually the main receptionist of direct sun light in a building, making it the largest source of heat gain in terms of building anatomy (not in tall structures). Roof gardens proved to work as a thermal barrier reducing heat gain and loss, resulting in a reduced need to depend on mechanically driven conditioned air.
Case Study :
The case study selection criteria required a common facility that has a wide spread, the reason behind that is to evaluate the response of that facility to the inspired strategies and to attempt to record the users' reaction to such "adaptation". The Selected building is an under construction mixed use low rise tower (G+1) with a mezzanine floor, located in RAK - UAE. See Appendix A.
The architectural style of the building is very similar to the common UAE architecture styles, merely consisting of a domino structural system and CMWs, finished with plaster (stucco) on its exterior with gypsum boards supported by metal studs as interior partitions. The openings are double - glazed.
Andre O. Desjarlais, A.Z.a.J.A.A., 2010. Thermal Performance of Vegetative Roofing Systems. Orlando, Florida: Proceedings of 25th RCI International Convention.
Donnell-Kilmer, N., 2012. Roof Gardens, A Green Solution to Los Angeles' Urban Problems. Senior Comprehensive Project. Occidental College.
Osmundson, T., 1999. Roof Gardens : History, Design and Construction. W. W. Norton & Company.
Poirazis, H., 2006. Double skin facades, A literture review. LUND: Department of Architecture and Built Environment Lund Institute of technology.
SAELENS, D., 2002. Energy Performance Assessments of Single Storey. PhD Thesis. Belgium: Laboratory for Building Physics, Department of Civil Engineering, Catholic University of Leuven.
Stec, van Paassen , 2004. Symbiosis of The Double Skin Facade with The HVAC System. Delft, The Netherlands: ELSEVIER TU Delft, Mechanical Engineering.