Spectrophotometric characterization of simple glazings for a modular façade

A large variety of transparent materials is available for uses in buildings façades and all glazing properties must be considered in their choice. Such a selection should be a careful process of evaluation and weighing of tradeoffs. The correct glazing specifications for façades can reduce energy consumption in buildings, because the heat exchange and passage of radiation into the building as light and heat occur through transparent surfaces. Therefore, glazing significantly contributes to the heat transfer between outdoor and indoor spaces, which act directly on daylighting and thermal comfort. This manuscript addresses a spectrophotometric characterization of glazings for the study of components for the design of a modular façade system based on the climate of Portugal. The study focused on results of spectrophotometric measurements of an optical behavior in different solar spectrum intervals (ultraviolet, visible and near infrared), specifically the transmittance of some types of simple glazings. The results show the percentage of transmission to spectrum intervals, which enabled the analysis (OK?) of the efficiency of the glazing regarding daylighting and correlation to the thermal performance. Indications for specifications and adequate uses based on transmission of transparent surfaces have been obtained and complemented the datasheets available from the manufactures.The authors gratefully acknowledge the financial support provided by Erasmus Mundus ISAC – Improving Skills Across Continents for this research.info:eu-repo/semantics/publishedVersio

Energy study of a non-residential and historic building in transient conditions

The purpose of this manuscript is to analyse the interventions of energy retrofit of a non-residential and historic building, through dynamic simulation by the use of the TRNsys code. The study is made up of some steps: - the analysis of the building and utility data, including study of the installed equipment and analysis of energy bills; - the survey of the real operating conditions; - the selection and the evaluation of energy conservation measures; - the identification of interventions of energy retrofit; - TRNsys simulation of the effects of these interventions on the energy behaviour of the building. The present paper aims to present the results of the study, to discuss the expected energy behaviour of the building and to comment on the options for introducing energy conservation technique

The influence of low-temperature surface induction on evacuation, pump-out hole sealing and thermal performance of composite edge-sealed vacuum insulated glazing

Hermeticity of vacuum edge-sealing materials are one of the paramount requirements, specifically, to the evolution of energy-efficient smart windows and solar thermal evacuated flat plate collectors. This study reports the design, construction and performance of high-vacuum glazing fabrication system and vacuum insulated glazing (VIG). Experimental and theoretical investigations for the development of vacuum edgeseal made of Sn-Pb-Zn-Sb-AlTiSiCu composite in the proportion ratio of 56:39:3:1:1 by % (CS-186) are presented. Experimental investigations of the seven constructed VIG samples, each of size 300mm·300mm·4 mm, showed that increasing the hot-plate surface temperatures improved the cavity vacuum pressure whilst expediting the pump-out hole sealing process but also increases temperature induced stresses. Successful pump-out hole sealing process of VIG attained at the hot-plate set point temperature of 50˚C and the approximate cavity pressure of 0.042 Pa was achieved. An experimentally and theoretically validated finite volume model (FVM) was utilised. The centre-of-pane and total thermal transmittance values are calculated to be 0.91 Wm-2K-1 and 1.05 Wm-2K-1, respectively for the VIG. FVM results predicted that by reducing the width of vacuum edge seal and emissivity of coatings the thermal performance of the VIG is improved

Energy simulations of a transparent-insulated office facade retrofit in London, UK

Purpose – Transparent insulation materials (TIMs) have been developed for application to building facades to reduce heating energy demands of a building. The purpose of this research is to investigate the feasibility of TI-applications for high-rise and low rise office buildings in London, UK, to reduce heating energy demands in winter and reduce overheating problems in summer. Design/methodology/approach – The energy performance of these office building models was simulated using an energy simulation package, Environmental Systems Performance-research (ESP-r), for a full calendar year. The simulations were initially performed for the buildings with conventional wall elements, prior to those with TI-systems (TI-walls and TI-glazing) used to replace the conventional wall elements. Surface temperatures of the conventional wall elements and TI-systems, air temperature inside the 20mm wide air gaps in the TI-wall, dry-bulb zone temperature and energy demands required for the office zones were predicted. Findings – Peak temperatures of between 50 and 70°C were predicted for the internal surface of the TI-systems, which clearly demonstrated the large effect of absorption of solar energy flux by the brick wall mass with an absorptivity of 90 percent behind the TIM layer. In the office zones, the magnitude of temperature swings during daytime was reduced, as demonstrated by a 10 to 12 h delay in heat transmission from the external façade to the office zones. Such reduction indicates the overheating problems could be reduced potentially by TI-applications. Originality/value – This research presents the scale and scope of design optimisation of TI-systems with ESP-r simulations, which is a critical process prior to applications to real buildings

Evacuated glazing with tempered glass

The application of tempered glass has made it possible to significantly reduce the support pillar number within evacuated glazing (EG) since tempered glass (T-glass) is four to ten times mechanically stronger than annealed glass (A-glass). The thermal transmittance (U-value) of 0.4 m by 0.4 m double evacuated glazing (DEG) with 4 mm thick T-glass and A-glass panes with emittance of 0.03 were determined to be 0.3 Wm−2K−1 and 0.57 Wm−2K−1, respectively (47.4% improvement) using previously experimentally validated finite volume model. The thermal transmittance (U-value) of 0.4 m by 0.4 m triple evacuated glazing (TEG) with 4 mm thick T-glass and A-glass panes with emittance of 0.03 were determined to be 0.11 Wm−2K−1 and 0.28 Wm−2K−1, respectively (60.7% improvement). The improvement in the U-value of EG with T-glass is due to a reduction in support pillar number, leading to reduction in heat conduction through pillar array. The impact of tempered glass on the thermal transmittance for TEG is greater than that of DEG since radiative heat transfer in TEG is much lower than that in DEG, thus the reduction in heat conduction resulted from the reduction of support pillar number in TEG is much larger than that in DE

Modelling conjugate flow and heat transfer in a ventilated room for indoor thermal comfort assessment

Conjugate natural and forced convection heat transfers in a domestic model room of finite-thickness walls and a heat source have been numerically studied. A 2-D non-ventilated square model room with a heat source is investigated at first for conditions of Prandtl number Pr=0.7 and Grashof number Gr=107. Computational results are compared with already validated numerical predictions and good agreement has been achieved in terms of stream function and temperature distributions. The study continues to consider 3-D ventilated rectangular model room with a finite-thickness wall and a heat source, in order to evaluate flow and heat transfer characteristics. Key physical features such as temperature distributions in both solid wall and indoor air domains, and heat transfer performance have been quantified, analysed and compared. These results provide the correlations among room heating device arrangement, wall thickness effect, indoor thermal comfort level and energy consumption. It was found that the arrangements of heat source and window glazing had significant impact on the temperature field, and further analysis of wall thickness and thermal conductivity variations revealed the level of the comfort temperature within the occupied zone. It was also found that for an average U-value of 0.22 W/m2K, thermal energy loss through a thinner wall of 20 cm thickness is 53% higher and indoor thermal temperature is 4.6 °C lower, compared with those of a thicker wall of 40 cm thickness. The findings would be useful for the built environment thermal engineers in design and optimisation of domestic rooms with a heat source

CFD modelling of double-skin facades with venetian blinds

This paper describes CFD modelling of Double Skin Façades (DSF) with venetian blinds inside the façade cavity. The 2-D modelling work investigates the coupled convective, conductive and radiative heat transfer through the DSF system. The angles of the venetian blind can be adjusted and a series of angles (0, 30, 45, 60 and 80 degrees) has been modelled. The modelling results are compared with the measurements from a section of façade tested within a solar simulator and with predictions from a component based nodal model. Agreement between the three methods is generally good. Discrepancies in the results are generally caused by the simplification of the CFD model resulting less turbulence mixing within the façade cavity. The CFD simulation output suggests that the presence of the venetian blinds has led up to 35 percent enhancement in natural ventilation flow for the façade cavity and 75 percent reduction in heat loads for the internal environment. It was also found that little changes of the convective heat transfer coefficients on the glazing surfaces have been caused by the venetian blinds with different angles

Energy Performance And Long-Term Evaluation Of Internal Thermal Comfort Of An Office Building With Different Kinds Of Glazing Systems And Window Sizes

Although the presence of large window surfaces could be preferable during the heating season when solar gains through the glazed components can overcome heating losses from the same surfaces, during the cooling season more attention has to be paid in order to limit the inlet of solar radiation which causes the increment of cooling load. Generally the optimal tradeoff for energy optimization, as already underlined in a previous paper by the authors, is using low thermal transmittance and high solar factor glazing, even if higher solar transmittance considerably worsens the cooling performance. However, the choice of glazing type and the design of windows on a façade may depend on comfort consideration besides energetic evaluations. Thermal sensation of an individual is mainly related to the whole thermal balance of the human body. Comfort limits can in this case be expressed by two indexes proposed by Fanger in 1970: the Predicted Mean Vote, PMV, and the correlated Predicted Percentage of Dissatisfied, PPD. The PMV depends on four environmental parameters (air temperature, air humidity, air velocity and mean radiant temperature) and two variables connected with human being (physical activity and clothing). The air temperature, the air humidity and the air velocity inside a building are directly under the system control. In contrast, the mean radiant temperature is strongly conditioned by the envelope surface temperature, and in particular, by the presence of glazed surfaces whose insulating performance is lower than the opaque components one. In this paper the study of heating and cooling energy needs of an open-space office with different windows’ characteristics has been carried out controlling the internal comfort conditions with appropriate setpoint of the system. An office module with windows on a single façade, or on opposite façades, oriented towards 3 different orientations has been simulated, varying the glazed area (2 sizes), the glazing systems (4 types) and considering three localities of central and southern Europe. The PMV have been calculated for each hour of occupation of the whole year assuming two season as regards the setpoint conditions and clothing level. Calculations have then been repeated considering also the effect of the diffuse and beam solar radiation through the windows directly reaching the occupants. The evaluation of the long-term comfort conditions (on seasonal basis) has been conducted considering some statistical indicators of distribution (the median, minimum, maximum and the interquartile range) and the energy performance of the different glazing solution have been compared accounting for the comfort one

CFD supported modelling of double skin facades in hot arid climates

Previous simulations predict the possibility of reducing cooling demands in office buildings in hot arid areas if a selective double skin facade is used. The reductions on cooling loads in rooms range between 19%-40% depending on the glazing thermal and visual performance characteristics of the exterior glazing of the double skin façade. However considerable uncertainty exists about the air flow rates and temperatures experienced within the channels of these facades. In this work a CFD model is used to predict these conditions for the case of an air-conditioned building in a hot arid climate. This case uniquely allows a CFD model to be applied to the facade independent of the simulation of the main building and its plant. Results show appreciable flow rates and temperatures generated mainly by buoyancy flow over the outer facade skin

Semi-transparent energy-harvesting solar concentrator windows employing infrared transmission-enhanced glass and large-area microstructured diffractive elements

We report on the study of energy-harvesting performance in medium-size (400 cm2) glass-based semitransparent solar concentrators employing edge-mounted photovoltaic modules. Systems using several different types of glazing system architecture and containing embedded diffractive structures are prepared and characterized. The technological approaches to the rapid manufacture of large-area diffractive elements suitable for use in solar window-type concentrators are described. These elements enable the internal deflection and partial trapping of light inside glass-based concentrator windows. We focus on uncovering the potential of pattern-transfer polymer-based soft lithography for enabling both the improved photon collection probability at solar cell surfaces, and the up-scaling of semitransparent solar window dimensions. Results of photovoltaic characterization of several solar concentrators employing different internal glazing-system structure and diffractive elements produced using different technologies are reported and discussed