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One of the most important properties of a glazing system is the solar heat gain coefficient (SHGC, or g-value) which quantifies the passive solar thermal gains. There are several standardized numerical methods of determining a window's g-value. However, the methods do not consider the glazing systems in real boundary conditions, and usually are subjected to assumptions and empirical parameters regarding the thermal/optical behavior of the system, and the rate of ventilation of the gap between the glazing unit and the shading device which would result in under- or over-estimation of the results. For this reason, several experimental methods for investigating the g-value of windows have been developed to be used either alone or as a supplementary method for the validation purpose. This review aims to analyze the main experimental methods for assessing the g-value of windows that have been published as international standards or as scientific papers while taking into consideration the condition of experiment (laboratory or in-situ) and the part of the window which was tested (the glazing part or the entire window). The methods reviewed here include standardized numerical methods based on spectrophotometric measurements, solar calorimetric methods, non-calorimetric and in-situ methods. This review set out to give insights into the procedure, the necessary equipment units, the advantages and disadvantages, new possibilities, and the gaps associated with each method. At the end the authors proposed an approach for comparing the reviewed methods more precisely and confidently, and for investigating the reliability of in-situ methods. [ABSTRACT FROM AUTHOR]

Abstract: This paper analyses the transient heat transfer across multi-layer floors subjected to multiple heat sources. The formulation that is proposed to solve this problem uses analytical expressions handling both conduction and convection phenomena. The Green''s functions (analytical expressions) for the layered formation are established by imposing the continuity of temperatures and heat fluxes at the medium interfaces between the various layers. The heat field inside a layer is obtained by adding the contribution of the direct heat incident field, generated as in an unbounded medium, to the heat produced by a set of virtual surface heat sources, that take into account the presence of the interfaces. The technique used to deal with the unsteady state conditions consists of first computing the solution in the frequency domain and then applying (fast) inverse Fourier transforms into space-time. [Copyright &y& Elsevier]

The Boundary Element Method (BEM) is used to compare the steady-state heat and moisture diffusion behaviour across double brick walls provided by two different models: in the first one, the brick wall is assumed to be composed of a set of homogeneous layers bonded together, which is the model frequently used to predict internal condensation; in the second model, the geometrical modelling and hygrothermal properties of the individual bricks are taken into account.The BEM is implemented allowing the use of multi boundaries, which permits the full discretization of the brick cavities.Three different construction solutions are analysed. In the first, the double-brick wall is assumed not to be thermally insulated; in the second, the space between the two layers of bricks is filled with thermal insulation material; in the third solution, both the space between the brick layers and the holes of the inner brick layer are filled with thermal insulating material. [Copyright &y& Elsevier]

The influence of the curvature radius of curved walls on the condensation patterns across a single panel homogeneous wall is analysed under steady-state conditions. Condensation is defined according to the Glaser approach, which is a practical tool in building design, recommended by the DIN 4108 and prEN ISO 13788 standards. This methodology uses an iterative process, which requires the resolution of temperature equilibrium and several vapour pressure equilibrium problems. Each of these potential problems is solved using the Boundary Element Method (BEM). The iterative process is first implemented and validated by applying it to the definition of condensation patterns across a hollow cylinder, for which the solution is calculated analytically. The BEM is then applied to the curved wall models, identifying the zones where condensation occurs and quantifying the amount of liquid water generated. [Copyright &y& Elsevier]

A key factor for achieving nearly-zero energy buildings is to reduce their energy demand using highly efficient thermal insulation materials, such as vacuum insulation panels (VIPs). Currently, the high investment cost of VIPs is hindering the technology penetrating the building market. However, their high thermal performance coupled with reduced thicknesses can lead to economic benefits associated with space savings, significantly changing the economic standing of VIPs. This study presents a comprehensive life cycle cost (LCC) analysis of the application of VIPs in external thermal insulation composite systems (ETICS) in office building façades performed from the landlord perspective. The proposed LCC methodology, based on the EU cost-optimal regulation, allows for comparing the cost-effectiveness of VIPs with conventional insulation materials, taking full account of the additional rental income due to space savings. Energy calculations are performed based on transient heat transfer. The study takes into account varying parameters, such as location, cost of materials, insulation thickness, and rental prices, among others. The results demonstrate that VIPs can be economically viable, in particular in cities where office full-leasing rental prices are high. The range of VIP and rental prices that make their use in buildings cost-effective are identified. For example, it is shown that for rental costs higher than 350 €/(m2.y) VIP can be cost-effective for a current market price of 3000 €/m3, when local climate demands for thermal transmittance bellow 0.19 W/(m2.K). This analysis is useful for VIP manufacturers, project owners and landlords that may be looking for competitive insulation products. • Global costs for a vacuum panel system are compared with conventional insulation. • A methodology for life cycle cost analysis, including rental costs, is used. • Energy balance is determined with transient calculations for a unit area of wall. • The influence of changing several technical and economic parameters is discussed. • VIPs can be found to be cost-effective for buildings in high rent locations. [ABSTRACT FROM AUTHOR]

There is an increasing need for energy-efficient windows; however, these windows can have high embodied impacts and can be costly. This has not been thoroughly analyzed and the literature has mainly focused on the operational performance of windows. It is important to wisely select optimal windows that minimize energy consumption, costs, and environmental impacts throughout their life cycle, considering the influence of window orientation and climate data. This article presents an integrated cost and environmental life-cycle assessment (LCA) of window solutions, combining alternative glazing and framing options. Optimal window solutions were selected using a Pareto bi-objective optimization (costs vs. environmental impacts) for three different European climate regions, considering various window orientations. The influence of each window component (glazing and framing), as well as window properties (thermal transmittance and solar factor) on the overall environmental and cost life-cycle impacts was studied. Pareto optimal window solutions for warm climates highlight low solar factor windows, while for cold climates they highlight low thermal transmittance value. The glazing is the component with the greatest influence on the total environmental impacts (mainly operational). The impacts depend to a very great extent on the thermal transmittance values and solar factors. The life-cycle cost analysis shows that the initial investment in the windows has a high impact on the overall cost, even when a lifespan of 30 years is considered. This article provides insights into and recommendations for the design of windows by addressing different climatic conditions and window orientations. • Trade-offs between environmental impacts and costs of windows are presented. • The influence of climate and orientation on window performance is investigated. • West-facing windows have higher impacts due to the larger energy needs. • In warm climates, low solar factor contributes significantly to reduce impacts. • Window thermal transmittance is key to reduce impacts in cold climates. [ABSTRACT FROM AUTHOR]

The global market trend for Vacuum Insulation Panels (VIPs) is projecting a significant increase in their uptake in the construction sector. This is mainly due to the uniquely high-performance properties of the ultra-thin insulation materials. This uptake, however, can potentially be hindered by the VIPs' higher cost and environmental impacts when compared with conventional insulation materials. This paper, for the first time, presents a detailed evaluation of the environmental impact of the most common type of VIPs currently used in different applications with a focus on alternating the core material as the main contributing component to their footprint. Pyrogenic silica, glass fibre, expanded polystyrene, aerogel and a silica/sawdust hybrid core were analysed from cradle to gate. The study, on a comparative basis, demonstrates the sensitivity of the various environmental impact categories to the internal vacuum pressure and the subsequent thermal conductivity values. The results show a lower environmental impact for glass fibre and low density expanded polystyrene compared to the other alternatives. Pyrogenic silica, the most common core material, had the highest environmental impact out of the core materials considered. The higher environmental impacts of pyrogenic silica suggest that measures such as the recycling of the core material alongside the deployment of eco-friendlier manufacturing techniques should be considered if the material is to compete environmentally with the other alternative materials. Image 1 • Environmental impact of different VIP core materials was compared for the first time. • Cradle to gate approach has been adopted for the analyses in accordance with EN15804. • Sensitivity analyses conducted for internal vacuum pressure and core material EPDs. • Pyrogenic silica had the highest environmental impact of the core materials studied. • Glass fibre had the lowest environmental impact for vacuum pressures lower than 10Pa. [ABSTRACT FROM AUTHOR]

Green roofs are increasingly being used to improve the energy balance and stormwater management of buildings. This work examines the thermal behaviour, water drainage and vegetation growth of two green roof systems: a conventional system containing extruded polystyrene and polyethylene, and an alternative cork-based system. In the new system, an eco-friendly expanded cork layer is used to provide thermal resistance and water storage capacity in a more sustainable way, as cork is a natural material. This material can also be used as an uncoated finishing layer for architectural purposes. The main goal of this work was to see if the new system is reliable in real environmental conditions and to compare its behaviour to that of the conventional system for a full year. This work presents the results of a fully functioning prototype built in Portugal with a technical substrate 10 cm thick and planted with a variety of vegetation. The reference and proposed systems were installed side by side and monitored under spring, summer, autumn and winter conditions. The thermal insulation and the water drainage and storage capacity provided by the cork-based green roof were found to be similar to those of the reference solution, with the expanded cork layer showing a more marked temperature delay and a more effective management of rainfall events under dry conditions. Additionally, it was found that the growth and health of plants in the cork-based green roof were comparable to those of the reference solution, indicating the good performance of the cork system. • An innovative cork-based green roof system was compared with a conventional solution. • Thermal, drainage and vegetation behaviour were assessed under real conditions. • More pronounced temperature delays were exhibited by the cork-based system. • The cork-based system was more effective at managing the drainage of the first rainfall event. • Vegetation development was similar for the two green roofs compared here. [ABSTRACT FROM AUTHOR]

Green roof technology is increasingly being used to improve the energy and environmental performance of buildings. However, the description of the thermal behaviour of green roofs is very complex since it depends on several variables and relies on intricate phenomena. In this work the authors characterize a green roof system that replaces the conventional drainage and water storage polyethylene membranes with insulation cork boards (ICB). To enable the experimental characterization of this system, a double walk-in bioclimatic chamber was designed and built to recreate indoor and outdoor environmental conditions. Winter and summer environments with steady and unsteady conditions in both dry and wet states were simulated. Thermocouples and heat flux sensors were used to collect data over time from the different layers of the green roof prototypes. Measurements were first performed on a concrete slab insulated with ICB to assess the contribution of the latter to the thermal performance of the system. The effect on the heat transfer was further evaluated for systems of increasing complexity, containing first a substrate layer and then vegetation. It was noted that the substrate and vegetation layers improved the thermal insulation, and reduced heat fluxes and the thermal amplitude within the system. The vegetation layer was found to be of key importance to the overall performance of the green roof. It was also found that ICB and the substrate layers lose part of their insulation capacity when the system was wetted, although it was fully restored in the ICB layer within a few hours. • Green roof system using insulation cork boards (ICB) in the water storage layer. • Use of bioclimatic chambers that recreate environmental conditions. • Winter and summer environment conditions in both dry and wet states assessed. • ICB provides high insulation; substrate and vegetation both improve thermal delay. • After wetting, the ICB layer recovers its thermal insulation performance faster. [ABSTRACT FROM AUTHOR]