The Impact of External Shading and Windows’ Glazing and Frame on Thermal Performance of Residential House in Abu-Dhabi

The amount of solar heat gain and thermal transmittance of the glazing and its setback properties are the main factors that can be calculated. External Shading devices contribute a lot in solar radiation penetration and reflectance. The present study aim is to determine the ideal design in dealing with solar radiation and heat gain through windows system, in order to improve building energy consumption. This target will be achieved through examining and analyzing different fenestration system design parameters of residential villa in Abu Dhabi with the help of computer simulation (IES VE2012). Windows’ system properties and shading devices performance can have a great impact on the building annual energy consumption, peak load of mechanical cooling system, and CO2 emissions. The present study shows that around 6% reduction in the houses annual energy consumption could be achieved. So, this study will help the designers and stakeholders to identify simple and effective factors in improving buildings’ energy consumption and thermal comfort. Keywords: solar heat gain, external shading devices, window setback 1. INTRODUCTION: Sustainable development needs have set one of the bottom lines of Abu-Dhabi vision, the capital of the UAE. Construction industry was prioritized in this vision due to the huge expanding and developments that have been carried on in the area. Construction and buildings industry are the cause of energy’s massive demands in the area as residential buildings’ energy consumption contributes around 45% of UAE’s energy consumption. Therefore, reducing energy consumption during buildings’ life cycle contributes the most in CO2 emissions reduction. The present study significance is to enhance existing buildings’ performance and at the same time improve regulators and buildings designers’ ability to adopt energy efficient practices. Passive design strategies’ effectiveness is to be analyzed and evaluated in terms of energy saving. Windows’ system is one of the significant factors of buildings’ thermal performance because of its direct relation to solar radiation and heat gain. The amount of solar radiation and heat transmittance through transparent façade elements determine indoor thermal and visual conditions and thus energy demands. Significant impact has been stated in many articles, dealing with buildings envelope characteristics and their relation to air-conditioning system demands and energy consumption. Al Shaali (2013) found out that triple glazing improves house energy consumption by 3% only, when compared to double glazing in house in UAE. Amin & Abu-Hijleh (2012) study of Dubai villa glazing assessment showed that the change from double low-e into triple low-e impact on cooling load as 5% less. Sinha & Kutnar (2012) study stated that PVC frames showed better performance than Aluminum frames, thermally as well as SB13 Dubai _ Paper 9 environmentally. Chi-Ming & Yao-Hong (2011) finding is; Box shading had the maximum reduction effect, more than horizontal and vertical shades. Many other studies stated that the use of an appropriate ? window glass reduced the annual energy consumption the most, followed by the shading devices (Wong & Istiadji, 2004; Chi-Ming & Yao-Hong, 2011; Lai & Wang, 2011). Another study conducted on residential buildings in Al-Ain, UAE found that window area and glazing system provide a considerable amount of energy savings? , while SDs provide a limited reduction in terms of energy use (Radhi, 2009). On the contrary, Ebrahimpour & Maerefat (2010) found that using of the most appropriate overhang or side fin is more useful ,for any direction of window, than the advanced glazing windows. This is related to the fact that SDs’ working prenciple is solar radiation penetration prevention while windows system works on two prenciples; solar radiation and heat conductivity reduction, based on low-e and U-value properties. This study will contribute to the international Passive House programme and help to differentiate Passive Houses from traditional construction. 2. METHODOLOGY: Series of simulations by an energy analysis program, IES VE, adopted in Kim et al. (2011), Bojic (2006), Yu et al. (2008), El Sherif (2012), and Ayyad (2011) studies. The last study stated that IES VE simulation program has the ability to integrate valid weather data, having a friendly user interface, and the flexibility to perform different types of simulations. This computer simulation software will be used to model a case study house design at first, then different case scenarios will be applied to study their impacts on solar heat gain, cooling loads, and energy consumption. This software has different modules that can perform different calculations for the same model but with specific data inputs. An existing three-bedroom villa in Abu-Dhabi has been chosen as a case study. The villa’s land area is 330m, ground floor area is 155m, and first floor area is 100m. The external walls are basically lightweight concrete blocks with external rendering and internal dense plaster. Total thermal transmittance; U-value, is 0.75 W/m.K, while roof’s U-value is 0.4 W/m.K. Windows’ glazing is double clear glass with aluminum frame. Windows net thermal transmittance is 3.4 W/m.K, solar heat gain coefficient (SHGC) is 70% and light transmittance ratio is 100%. No external shading devices applied to the current house design. It is worth mentioning that the Passive House according to the Germans standards should have: Triple glazing with two low-e coatings, “Warm Edge” spacers between the panes of glass, and Super-insulated frames. • Modeling Steps: Weather data file of Abu Dhabi city (latitude: 24.43◦N, longitude: 54.65◦E) assigned (inputted) before simulation process has started. Annual solar radiation and shading calculations of the whole building run by Sun Cast module and this is basically depends on Abu Dhabi’s sun path throughout the year. Thermal conditions inputs have been set through building template manager as follows: domestic family occupancy profile assigned for cooling system and people internal load. The assigned profile working hours during the week days are different from the weekends, Figure 1 and 2 illustrate each of them respectively. Optimal occupancy profiles proposed assuming energy saving in residents’ practices. SB13 Dubai _ Paper 9 Figure 1: Domestic occupancy profile during weekdays (IES VE2012) Figure 2: Domestic occupancy profile during weekends (IES VE2012) Design temperature for cooling set point is 23C while no heating system considered due to the climatic conditions in the area. Relative humidity control kept between 30% and 70%. Air change rate profile follows cooling profile with minimum flow rate of 3.0 l/s.m. Infiltration gain set on continuously with external air maximum air flow 0.1 ACH. Internal gains were basically related to two factors; people (5 persons (sensible gain: 90 W/person, latent heat: 60 W/person)), and electrical lighting (fluorescent lighting with domestic lighting profile shown in Figure 3 (sensible gain: 15 W/m)). SB13 Dubai _ Paper 9 Figure 3: Domestic lighting profile (IES VE2012) The next step was to assign construction materials as per the existing building based on the data collected from the project main contractor. Apache-sim is a dynamic simulation calculates cooling load in the process of energy analysis and this was the reference scenario outputs. Using the same inputs, FlucsDL module used to examine the base case daylight performance using CIE standard overcast sky and medium quality setting in order to consider SDs applications’ impact on the assigned scenarios. • Assigned Scenarios: Building envelope characteristics, internal loads, interior lighting, ventilating, air conditioning, and occupancy profiles, in addition to weather data, are all unchanged throughout the simulation process. Windows shading condition, glazing and frame materials are the only varying parameters. Horizontal, vertical, and combination of them with two different projections; 30cm and 60cm, are the scenarios assigned in terms of shading devices design and their impact on thermal and daylight performance, in addition to energy consumption changes. Also, shading devices applied for south, east, and west facing windows based on aesthetical, technical, and functional aspects. As for windows’ system scenarios, double clear, triple clear, double low-e, and triple low-e glazing with two different frame materials; Aluminum and PVC, are examined in terms of solar heat gain, cooling loads and energy consumption variations. 3. RESULTS AND DISCUSSION: Reference scenario or existing case annual energy consumption is 84MWh with cooling sensible load of 104.5MWh and solar heat gain of 22.8MWh. Windows’ system in the reference scenario is basically; double-clear glazing with Aluminum frame and no shading devices applied. • Windows’ System Scenarios: SB13 Dubai _ Paper 9 Windows’ system is basically the number of glass panes, type of glass, and frame material. Window to wall ratio (WWR) of house’s ground floor is not the same as for the first floor, but the average WWR of the whole house is taken 16%. Window to floor ratio (WFR) is constant in both floors’ area; 28%. Not all house’s rooms have the same opening area but these parameters kept as per the existing case study design; reference scenario. The same thing applied to openings distribution on different façade’s orientation. East facing windows area is more than 50% of total windows area of the house. Table 1 presents examined scenarios in terms of windows glazing and frame material. Glazing types proposed are different configurations between double and triple panes, clear and low emissivity (Low-e) glass. As for frames, only Aluminum and PVC materials proposed. These scenarios proposals are based on the mostly used and available materials in the market, thus most of construction professionals and stakeholders are familiar with these sys