Existing Buildings in Hot Arid Climates
Excessive use in hot and arid regions such as the United Arab Emirates (UAE) for mechanical cooling systems to achieve thermal comfort led to exaggerated consumption of energy and sometimes a poor quality of the indoor air because of insufficient ventilation, poor daylight distribution and health issues of building occupants. As a result, the focus of this study is on how to reduce energy consumption in existing fully glazed buildings by applying climate responsiveness in the design of the facade. This is accomplished by integrating the double-skin façade (DSF) and Phase-change materials (PCMs) into the buildings in the UAE for indoor thermal comfort and energy savings. The study emphasizes the importance of the PCMs application in the built environment and reduces the demand for indoor thermal comfort of air conditioning. It also offers new ideas about incorporating PCM into the building envelope and its effect on indoor visual and thermal quality.
2. RESPONSIVE FACADE DESIGN
The building envelopes play an indispensable role in the building's energy demand because they are the first barrier between the indoor thermal comfort zone and the harsh exterior climate. Specially, the U value can be up to 4.8 W/m2K of single glazing, which is substantially greater than the values for construction materials that are recommended.  Even if the U value for glazing has decreased by using double glazing and triple glazing, but still heat is considerably transmitted inner spaces. Numerous studies are being carried out to optimize energy consumption, including insulation and thermal mass, ventilated facades , façade albedo , opaque multi-layer facades  , building-integrated photovoltaics (BIPV), and modular building facades . Double-skin façade (DSF) with responsive kinetic facade . PCMs (phase-change materials), etc. Even though the UAE's energy consumption per capita is among the highest in the world, the PCMs have received the least attention. This study provides a solution to this issue and builds on a responsive DSF integrated with PCMs, which can adapt to various weather to provide internal thermal comfort as in fig 1.
3. DESIGN GUIDELINE TOWARD ADAPTIVE FAÇADE:
3.1. Double-Skin Façade (DSF) In Hot Climates
A main factor that regulates the ventilation rate and the heat maintained in the DSF is the cavity depth. The ideal cavity depth for the building's cooling load is located is between at least 100–120 cm. For this research, a cavity depth of 100 cm is introduced and is modeled as fully ventilated naturally see Fig 2.
3.2. Phase Change Materials (PCM) Selection
The PCMs selection criteria for adaptive facades are influenced by many factors, including cost-effectiveness, conductivity stable cycle, low volume change, non-flammable, and non-toxic. As shown in Table 1, salt hydrate is an adequate choice in hot climates.
3.3. Restrictions for Design
The designer would then consider several obstacles such as climate, geography, building use, and building components to make an appropriate design decision.
3.3.1. Analyzing Weather Data
All data about the case study: (Student Hub Building - Ajman University, UAE), which follows the international system, has several issues that are discussed in the introduction and more details are in the reference paper .
So, Figure 3 depicts weather data for this study expressed by the use of the Climate Consultant software, such as solar irradiation, mean and average maximum temperatures and wind speed are gathered using the Climate Consultant software to help in selecting proper design decisions in Fig4 .
3.3.2. Simulation of Energy
For the case study, preliminary energy calculations were conducted using various PCMs and glazing ratios. To gain an understanding of how different PCMs types, and the ratio between PCM and glazing in the envelope can affect the building's total energy demands(additional electricity, heating, and air conditioning) as Fig 5.
3.3.3. Parameters of Design
In particular, the case study uses various types of PCMs façade to examine distinct patterns using simple geometries. The ratios between glazing and PCM are different for each of these varieties.
The design is concerned with experimenting with basic geometries and the potential of integrating façade modules with different melting temperatures and different PCM to glazing per panel ratios. That results in a more viable façade design that can be easily built and adapts to different climate conditions.
3.3.4. Digital and Environmental Simulations
The façade design is evaluated through a series of numeric calculations, simulations, and physical tests. The PCMs façade panels are constructed with different transparency levels, different PCM quantities, and different melting temperatures to make physical measurements that show the thermal and the optical behavior of the PCMs (flux of heat, thermal cycle duration, changes in visual properties as a result of solar irradiation and air temperature).
Overheating should be overcome in hot-arid countries like the UAE. In addition, the façade should be able to respond to different weather conditions. Thus, the integration between DSF and PCMs by using different melting temperatures would contribute to the daytime stability and the solar heat can be saved by PCMs. In addition, the thickness of PCMs can change based on wind speed, air temperature, and solar irradiation.
So, the application of DSF integrated with PCMs, as demonstrated in this report, saves up to 80%. of total energy demands.
However, several studies in this field show a major reduction in temperature variations and achieve the desired level of thermal comfort. Despite these results, only a few of researches focus on the use of PCMs in the DSF system as a way to improve the visual and thermal comfort of a building's indoor environment. The combination of these impacts results in annual cooling demand reductions for the entire building.
To summarize, this study will provide recommendations to architects who need to incorporate a facade system based on the use of DSF and PCMs, by addressing all of the key properties of PCMs that should be considered in order to develop facade strategies that will improve energy performance and thermal comfort in the indoor space of existing buildings in the hot arid environment.
LAMIAA MOSTAFA MOSTAFAABD-RABO
I have always been very interested in architecture and interior design. Through my academic work as a lecturer and professionally as an architect / interior designer, my thoughts are crystallized on the advanced design approach in the rapid progress of advanced technological environmental approaches. So, in my studies on technological and advanced construction methods, I move on to improve my knowledge of building energy performance assessment, emphasizing the interrelationships between building structure, building envelope and building technology by merging between CAD and BIM software in order to achieve human comfort in the building. In addition, I have developed a general interest in the sustainable built environment and the impact of buildings on our natural environment, taking into account climatic conditions.
MAHMOUD Z. ALTEMMAMY
Through my work in architecture field academically as a lecturer and professionally as a senior architect, my thoughts are crystallized about the advanced approach of architecture design within the rapid progress of advanced technological and computational processes. In addition, recently, my concerns increase about the future built Environment's techniques, practices and theories of design through a coordination between fields of engineering, robotics, digital manufacturing, material science, morphology and ecological systems.
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