1,721,112 research outputs found
Soiling of building envelope surfaces and its effect on solar reflectance - Part III: Interlaboratory study of an accelerated aging method for roofing materials
No full textA laboratory method to simulate natural exposure of roofing materials has been reported in a companion article. In the current article, we describe the results of an international, nine-participant interlaboratory study (ILS) conducted in accordance with ASTM Standard E691-09 to establish the precision and reproducibility of this protocol. The accelerated soiling and weathering method was applied four times by each laboratory to replicate coupons of 12 products representing a wide variety of roofing categories (single-ply membrane, factory-applied coating (on metal), bare metal, field-applied coating, asphalt shingle, modified-bitumen cap sheet, clay tile, and concrete tile). Participants reported initial and laboratory-aged values of solar reflectance and thermal emittance. Measured solar reflectances were consistent within and across eight of the nine participating laboratories. Measured thermal emittances reported by six participants exhibited comparable consistency. For solar reflectance, the accelerated aging method is both repeatable and reproducible within an acceptable range of standard deviations: the repeatability standard deviation sr ranged from 0.008 to 0.015 (relative standard deviation of 1.2-2.1%) and the reproducibility standard deviation sR ranged from 0.022 to 0.036 (relative standard deviation of 3.2-5.8%). The ILS confirmed that the accelerated aging method can be reproduced by multiple independent laboratories with acceptable precision. This study supports the adoption of the accelerated aging practice to speed the evaluation and performance rating of new cool roofing materials
Long term self-cleaning and photocatalytic performance of anatase added mortars exposed to the urban environment
No full textBuilding envelope materials containing titanium dioxide have been proposed to exploit their photoactivated depolluting and self-cleaning potential, but a full appraisal of their durability and long-term performance is still missing. This study reports a two-year campaign of natural exposure in Milano, Italy, of photoactive and non-photoactive fiber-reinforced mortars, analyzing the evolution of lightness, solar reflectance, porosity and photoactivity. After aging, photoactive samples showed limited color variation. The photocatalytic activity of TiO2 containing samples, characterized with dye degradation tests, was minimal after aging. Then, after alternated cycles of UV-Vis irradiation and rinsing, almost 70% of the initial photocatalytic efficiency was recovered. © 2015 Published by Elsevier Ltd
On the solar reflectance angular dependence of opaque construction materials and impact on the energy balance of building components
No full textThe solar reflectance of the surfaces is a property that varies according to spectral and angular distribution of the incident solar radiation which in turn depends on orientation and latitude. In this paper, an optical characterization was conducted on some typical opaque building materials, generally used as roof covers: shingles, membranes, bricks and tiles. The measurements were carried out through an experimental factory equipped with a large integrating sphere which allows to measure the spectral reflectance at different incidence angles of the light beam on the sample. Thus it was possible to create a function that linked reflectance values with the incidence angle. The results obtained were included within a dynamic software in order to optimize the calculation of solar gains in the energy balance of a building
Natural aging of cool walls: Impact on solar reflectance, sensitivity to thermal shocks and building energy needs
No full textWall finishes with high solar reflectance and thermal emittance, commonly known as cool walls, can reduce the exterior surface temperatures of façades, and consequently the building cooling energy needs and power demand, and lower the sensitivity to degradation. Aging, though, may affect their performance. To investigate this risk, we exposed for four years in Milan, Italy, two series of façade finish coats, white and beige, facing north and south, in vertical and vertical-sheltered position, and we measured their solar spectral reflectance and thermal emittance before and after aging. The solar reflectance of the white finish coats drops from 0.75 to 0.55 in four years, and from 0.46 to 0.38 for the beige coats, while the thermal emittance is unchanged. Then, for a typical residential building with white walls, we computed that the cooling energy needs increase with walls aging by 5% and 11%, respectively, with or without exterior wall insulation. The exterior surface temperature is increased even by 6 °C, and the number of sudden surface temperature variations in one hour is boosted. Finally, the moisture content in the external layers is reduced, showing the impact on the heat and mass balance because of the uncertainty in solar absorption due to aging. © 2017 Elsevier B.V
Transparent multilayer ETFE panels for building envelope: Thermal transmittance evaluation and assessment of optical and solar performance decay due to soiling
No full textThis paper is divided in two sections. The first section present the measurement and evaluation of soiling effects of spectral light and solar transmittance decay of Ethylene Tetrafluoroethylene Copolymer (ETFE) membranes after three and six months of exposure in Milano city outdoor urban conditions, with different tilt and orientation. The obtained values where use to compute thermal and solar properties of a multilayer ETFE panel. The second section presents the results of an experimental campaign for measuring thermal transmittance of a non-pneumatic and non-cushion shape double layer ETFE sample panel realized with two membranes parallel to each other and tensioned on a frame. The thermal transmittance measurement reflects ISO 9869 measurement approach combined with the use of a thermographic camera to evaluate surface temperatures over the sample panel
Optical properties and influence of reflective coatings on the energy demand and thermal comfort in dwellings at Mediterranean latitudes
No full textClimatic conditions affect shape, colour, geometry and lay-out of buildings. The vernacular Mediterranean architecture was characterised, among other passive techniques, by light colours to minimise solar gains through the opaque components of the building envelope. Actual building design and construction often forget such old bioclimatic approaches, delegating the comfort conditions to artificial systems. The energy consumption increase in the residential sector witnesses this problem, due to the high penetration of air conditioning systems. Ancient concepts, merged with innovative technologies, are hence necessary today. Reflective coatings can reduce the cooling loads with an effective solar control on the building envelope. Photometric analyses were carried out the measure the optical properties of a sustainable light coloured cool paint. Dynamic energy simulations were run for different Mediterranean localities (Rome, Palermo, Seville, Athens, Tripoli), buildings geometry (stand alone and row house), different thermo-physical properties of the opaque envelope (solar reflectance, U-value, thermal capacity) and of the whole building (natural ventilation rates and shading of glazing systems). The influence of reflective materials was assessed respect to the cooling and overall energy demand. The same simulations were repeated considering not cooled dwellings and the related thermal comfort conditions
Experimental Characterization and Energy Performances of Multiple Glazing Units with Integrated Shading Devices
No full textModern architecture is characterized by the use of large glazed surfaces. New technologies ensure thermal insulation by multiple glazing units so that, maintaining good solar gains, highly glazed buildings can achieve good energy performance during the heating season. More complicated is the management of the energy performance during the cooling season due to high permeability to solar radiation. External shading devices are a suitable solution but they are often neglected for functional and aesthetic reasons. Solar protection devices can be, however, introduced in the air gap of multiple glazing units, providing solar protection without interfering with the building envelope. Solar and thermal properties of several solution of glazing units with in-gap shading devices were measured with advanced experimental set-up, to be compared with conventional systems. Numerical analyses were also performed to estimate the impact of this technology on the energy performance of office buildings. © 2017 The Authors. Published by Elsevier Ltd
A Novel Methodology to Optimize Visual Comfort and Energy Performance for Transparent Adaptive Façades
No full textTransparent adaptive façade components are designed to improve either visual comfort aspects or the energy performance of a building. Focusing only on one domain implies drawbacks that negatively influence the performance of the component itself. This paper hence presents a novel multiobjective methodology aimed at determining the most viable trade-off between energy performance and comfort issues for active components. This multi-objective optimization strategy was applied to a thermochromic glazing (TCG), i.e. a passive transparent façade component whose thermo-optical properties vary in response to its thermo chromic layer temperature. As one of the key elements of the methodology, the influence of TCG hysteresis on visual comfort and energy performance was taken into account. The hysteresis of the TCG in an enclosed office was determined for 3 different climates and for five hysteresis widths. The results obtained show that, for all the cases analyzed, the hysteresis influence on the overall energy performance is negligible, whilst it can significantly affect visual comfort, both in terms of workplane horizontal illuminance and perceived glare. İ 2018 IEEE
Metal mesh as shading devices and thermal response of an office building: Parametric analysis
No full textWindows are the most important part of the building façade to control solar gains, thermal losses and visual comfort. Office buildings usually have medium-high WWR (window to wall ratio value) and high internal gains (due to users, lighting and appliances). For this reason, they require a good balance between thermal and visible performances of transparent façades and shading control strategies to avoid overheating, optimizing daylighting aspects. A sensitivity analysis was assessed to evaluate primary energy use for heating, lighting and cooling for conventional Italian single office units equipped with static metal mesh shading devices with different geometries and openness factor values. Different location (Milan, Palermo), orientation (south and west) and WWR (33% and 100%) were analyzed. Hence shading devices alternatives as venetian blinds and sun control windows are proposed as a comparison. © 2015 The Authors
The daylighting contribution in the electric lighting energy uses: EN standard and alternative method comparison
No full textThe standard EN 15193: 2007. Energy performance of Buildings. Energy requirements for lighting includes a comprehensive method, which takes into account the daylighting contribution in the calculation procedure. Such contribution is obtained through several approximations. An alternative approach is developed, where the daylighting contribution is based on the availability of outdoor illuminance data and an explicit procedure. The methods are tested on a standard office building, whose lighting requirements are calculated for different visual tasks, observation positions and climatic zones. The results show discrepancies among the methods and address the need of a more accurate estimation of the lighting energy service. © 2015 The Authors
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