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Increasingly compact high density urban development in cities has allowed urban heat island effect to take root and increase the energy consumption of commercial buildings to cool its interior. Although the extensive use of glass façade has allowed these buildings to harness daylight to light up the building interior, it has also allowed substantial solar energy to enter and heat up the building. This is especially critical in hot and humid tropical regions, where reducing solar heat gain, while minimizing heat loss are equally important. The evaluation of glass performance is often conducted using active measurement, which make use of known radiant source. However, this type of setup cannot be applied for testing under non-controlled weather. Though a passive test procedure can be conducted under actual weather conditions using the outdoor test chamber, it is not suitable for a large-scale testing and fast on-site characterization. In addition, this test is limited to the fabricated glazing and thus could not predict potential issues in the design stage. Advances in simulation techniques have enabled building professionals to evaluate the glass façade of a building at the design phase. However, the typical simulation tools are unable to integrate the high performance glazing description, which is generated thanks to advances in coating technology, using the existing glass models. Furthermore, these tools are often lack of local weather models that plays an important role in accurately assess the solar heat gain admitted into the building. This paper provides useful information on different high performance glass façades and assesses their applicability for green building in a tropical country like Singapore. The research effort encompasses an improvement in the methodology used to predict solar irradiance through building glass that incorporates seamlessly the advanced glass models into the solar irradiance simulation. In addition, this will show how to effectively estimate the actual sky behavior via a measured data-based optimization process. A comparison of the simulation results with the measurements from an outdoor climatic test chamber under tropical climate will be performed. An assessment based on the typical glass performance metrics (e.g. U-value and Solar-Factor) together with measured energy savings obtained with the use of different high performance glass façade compared to clear float glass as a control will also be presented. [ABSTRACT FROM AUTHOR]

The interpretation of the energetic signature of a city, taken as an integrated urban energy system, has been attempted in this study. Instead of the customary bottom-up approach, we successfully identified an average gray-box dynamic model by inversion of measured hourly system load and weather data. The third-order lumped-parameter thermal network model is derived by applying energy conservation principles to major nodes representing buildings, paved surfaces and urban canopy. This powerful data-driven approach offers deep insights into the thermo-physical properties of the built structures as well as the coupling of buildings and the urban microclimate. In particular, the Urban Heat Island (UHI) intensity has been determined to be close to 2 °C while the corresponding electricity cooling load penalty is 12%. [ABSTRACT FROM AUTHOR]

Recently high reflective materials such as high reflectance paint for wall and solar control film or Low-E glass for window are utilized as a building façade aiming for reducing the cooling load of the buildings. From a view point of the direction of reflected rays, almost half of the energy goes upward due to diffuse reflection in case of paint, meanwhile most of energy goes down to the ground due to specular reflection by the glass. This leads to deterioration of thermal environment of surrounding buildings, and is one of causes of urban heat island. Retro-reflective façade materials are promising candidates for mitigation of urban heat island. The authors successfully developed a new type of transparent solar control window film Albeedo that selectively reflects near-infrared rays towards the sky. The film has a saw-tooth microstructure with a spectrally-selective reflection layer. This microstructure is able to reflect infra-red rays toward the sky. The upward reflectance of the film is measured by our custom made spectroscope. Firstly, the sample is placed in a large scale integrating sphere. Then, solar energy absorptive materials are arranged under the sample to absorb the transmitted component and positioned where the downward reflection goes to. Finally, a halogen lamp irradiates the sample at an incident angle of 60° as a light source. The result of the upward reflectance of near-infrared is about 33%. We also conducted field test measurements to evaluate the energy savings of the interior of the building and the degree of reflection of the exterior. [ABSTRACT FROM AUTHOR]

The intensification of the Urban Heat Island effect (UHI) is a problem that involves several fields, and new adequate solutions are required to mitigate its amplitude. The construction sector is strictly related with this phenomenon; in particular, roofs are the envelope components subject to the highest solar irradiance, hence any mitigation strategy should start from them and involve their appropriate design process. For this purpose, cool materials, i.e. materials which are able to reflect a large amount of solar radiation and avoid overheating of building surfaces have been deeply analyzed in the last years both at building and urban scales, showing their benefits especially in hot climates. However, green roofs also represent a possible way to cope with UHI, even if their design is not straightforward and requires taking into account many variables, strictly related with the local climatic conditions. In this context, the present paper proposes a comparison between cool roofs and green roofs for several Italian cities that are representative of different climatic conditions. In search of the most effective solution, the answers may be different depending on the perspective that leads the comparison, i.e. the need to reduce the energy consumption in buildings or the desire to minimize the contribution of the UHI effect. [ABSTRACT FROM AUTHOR]

• A numerical model is developed to study indoor thermal conditions during heat waves. • Moisture buffering can have an important influence on the indoor thermal conditions. • Pre-cooling before the start of a heat wave can lower indoor temperature moderately. • Moisture-desorption cooling has a large potential in reducing indoor heat stress. Urban areas are increasingly impacted by the urban heat island effect, especially during heat waves. In the context of improving energy efficiency in buildings, passive and energy-efficient cooling methods are needed for reducing indoor heat stress and lowering building energy consumption during heat waves. In this study, a whole building simulation model that includes both moisture and heat transport in wall envelopes and indoor environment is developed. An analytical solution and two test cases are used to validate the developed model. The developed model is applied to study indoor thermal conditions in urban areas in Zurich, Switzerland in a hot summer. The results show that indoor temperature could not be accurately simulated when moisture transport in the wall envelopes is neglected. Due to the urban heat island effect, night ventilation is not sufficient to cool down the indoor environment during the heat wave in the urban area. The potential of precooling before the heat wave and moisture-desorption cooling from hygroscopic materials have been studied to reduce indoor heat stress in the urban area. The average operative temperature during the heat wave can be reduced by 0.43 °C by precooling before the start of the heat wave, whereas desorption cooling from hygroscopic materials could reduce the average operative temperature during heat waves by 1.31 °C. A combination of these two mitigation measures could lead to enhanced passive cooling effect. There is a large potential of using desorption of hygroscopic material to reduce heat stress during heatwaves, while minimizing energy consumption of buildings. [ABSTRACT FROM AUTHOR]