Journal Papers

Current Trends and Future Challenges in the Performance Assessment of Adaptive Façade Systems
Energy and Buildings, 179, 165-182
November 2018
By: Attia, S., Bilir, S., Safy, T., Struck, C., Loonen, R.C.G.M., & Goia, F.
Document Number: 10.1016/j.enbuild.2018.09.017

Abstract - During the last decades, a great number of innovative building envelope materials and façade components have been developed. The majority of these technologies promise significant improvements in energy efficiency and occupant's comfort, with products that are easily available in the market. However, it remains a challenge to assess the performance of such facades, leading to difficulties for efficient design, operation, and maintenance. As a consequence, the market adoption of adaptive facades is not realizing its full potential, resulting in missed opportunities for energy savings and improved occupant satisfaction. In this study, the current trends of adaptive facades are investigated, with particular emphasis on their performance assessment. Based on extensive literature review, the gaps in assessment of adaptive facades are determined and a novel object-based façade characterization and classification framework is proposed. Furthermore, a generic stakeholder map and process map are presented to explain current adaptive façade delivery practices. In addition, the findings of interviews and two focus group discussions with experts and specialists are presented to elucidate their expert opinions, leading to a validated framework of key performance indicators. As results of this paper, the gaps related to adaptive façade systems’ assessment are identified with respect to the different actors and stakeholders, and insights and perspectives on current trends and future challenges of adaptive façade system assessment are provided.
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Angle-dependent optical properties of advanced fenestration systems-Finding right balance between model complexity & prediction error
Building Simulation (2018), Online ISSN 1996-8744
August 2018
By: Capperucci, R., Loonen, R.C.G.M., Hensen, J.L.M., Rosemann, A.L.P.
Publisher: Tsinghua University Press
Document Number:

Abstract: Advanced glazing systems with special spectral characteristics or light redirecting behavior are commonly applied to improve building energy efficiency and indoor comfort conditions. The angle-dependent optical properties of such advanced windows can be markedly different from those of ordinary glass. To achieve accurate building performance predictions, it is necessary to represent the physical behavior of advanced window systems at a sufficiently high level of detail in building simulation programs. However, modelers should be aware that overly complex models are also undesirable, because they are costly to develop and input parameters are difficult to obtain. There is little guidance for simulation users to select an appropriate simulation strategy with respect to atypical glazing properties. This paper introduces a new approach for analyzing the influence of angle-dependent glazing properties, taking into account the effect of location and façade orientation. The potential of this method is demonstrated using an innovative switchable glazing system based on liquid crystals. A comparison between measured and derived transmission properties based on normal angle-of-incidence is presented. Results are presented for three European cities at different latitudes and for three different façade orientations. Using this new approach, simulation users can make informed decisions about appropriate modeling strategies for considering angular optical properties in building performance predictions.
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Investigating the potential of a closed-loop dynamic insulation system for opaque building elements
Energy and Buildings 173, 2018, Pages 409-427, ISSN 0378-7788
August 2018
By: Koenders, S.J.M., Loonen, R.C.G.M. & Hensen, J.L.M.
Document Number:

Abstract - The extensive use of thermal insulation in low-energy dwellings makes them susceptible to heat trapping in warmer periods. Construction elements with dynamically adjustable thermal transmittance properties, so-called dynamic insulation systems, can be a promising solution for reducing this overheating problem, while simultaneously lowering the energy consumption for heating. In this paper, the performance of a novel type of closed-loop forced convective dynamic insulation system is investigated. A simulation model to predict the performance of the dynamic insulation is developed in EnergyPlus. First results show that a ninefold higher U-value can be achieved in comparison with the insulating state of the system. Multiple case studies have been analysed to study the behaviour and performance of the system. It was found that the dynamic insulation system can reduce the energy consumption and increase the indoor thermal comfort of a typical residential building, while using less auxiliary energy than comparable passive cooling systems, such as night ventilation. Applying dynamic insulation to a façade construction with a heavyweight interior partition and lightweight exterior partition resulted in the best performance. If a small period of thermal discomfort is allowed, the closed-loop dynamic insulation system can obviate the need for an active cooling system in the climates of Helsinki, Amsterdam and Stuttgart.
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Unglazed Solar Thermal Systems for Building Integration, coupled with District Heating Systems. Conceptual Definition, Cost and Performance Assessment
Journal of Facade Design and Engineering 6(2) 119-131, June 2018, ISSN: 2213-3038
June 2018
By: MUGAGUREN, Mikel Lumbreras; GARAY, Roberto; MARTIN, Koldobika
Document Number:

Abstract - In this paper, the energy performance of a solar thermal (ST) façade system is studied in relation to its connection to a district heating system. This concept allows for the direct use of ST heat in the building, while taking profit from the network for delivery/selling of excess heat and purchase of heat during periods of underproduction. The use of unglazed collectors for low-intrusive architectural interaction in façades is discussed. Studies are carried out on the heat production of the system and its capacity to cope with local demands. Economic studies are carried out in order to balance the investment and operational costs/profits of the system.
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On the development of a façade-integrated solar water storage
Journal of Facade Design and Engineering 6(2) 9-20, June 2018, ISSN: 2213-3038
May 2018
Document Number:

Abstract - The integration of active solar thermal technologies into building envelopes has recently been receiving greater attention, and has been promoted within international projects such as IEA Task 56 and Cost Action 1403. Although the façade integration of solar thermal collectors is a topic that has been debated at length, little attention has been paid to the building integration of solar water storage. The scope of this paper is to highlight the main barriers that are experienced in the development of façade-integrated solar water storage. This activity is a part of the SunRise project that aims to develop a new unitised curtain wall element for tertiary office buildings. The façade element integrates a complete solar thermal system consisting of a solar collector, hot water storage, a radiant panel, and all the required operation components. A mock-up of the solar façade is manufactured to identify practical constructional issues. The thermal behaviour of the tank is analysed through FEM simulations and laboratory tests. Download publication

Experimentation under real performing conditions of a highly integrable unglazed solar collector into a building façade
Energy Procedia, Volume 122, 2017, Pages 775-780, ISSN 1876-6102
September 2017
By: P. Elguezabal, R. Garay, K. Martin
Document Number:

In the current context of moving towards more sustainable construction, advanced façade systems that integrate solar collecting devices represent a commitment with future trends that combine renewable technologies with building skins. This paper describes a real experience when combining a novel unglazed solar collector based on sandwich panel technology, a heat pump and a controller that manages the different operation modes. Installed in the Kubik by Tecnalia testing building in northern Spain, the system has been monitored for several months in 2016, under an energy efficiency scope. The study will present measured values regarding the yield of the collector, performance of the heat pump and general efficiencies.
Keywords: Active envelopes; Prefabricated Sandwich Panels; Unglazed; Integrated Solar Collector; Heating Pump
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Concept, development and thermal characterisation of an unglazed solar thermal collector for facade integration
Dyna, National University of Colombia, Medellín
January 2017
By: Roberto Garay Martinez, Beñat Arregi Goikolea, Paul Bonnamy, Jérôme Lopez
Publisher: Industrial Engineers, Spain,

Despite significant development in the performance and efficiency of solar thermal technology, little consideration has been given to its interaction within building envelopes, aside from mechanical fixing systems. The lack of solutions for the architectural integration of solar collectors and the complexity of their assembly process remain important barriers for the widespread adoption of this technology. An innovative approach is proposed in which solar collectors are not merely integrated into conventional building envelopes, but instead these envelopes are hybridized and activated to house solar thermal systems. This poses the challenge of adapting solar thermal technology to the capacities and limitations of architectural skins. The paper presents results from three ongoing projects. BATISOL and BASSE investigate the development of solar thermal technology so as to fulfil the functional, constructional and formal requirements of building skins. Façade assemblies are turned into active skins by integrating unglazed solar collectors in the place of conventional renders and claddings. RETROKIT explores the usage of renewable energy gains within an alternative environmental control strategy, by direct supply of heated air into the ventilation system. Finally, a discussion is presented on architectural, constructional and thermal performance aspects of these solutions, based on both design assessments and experimental data.
Keywords: Solar collector, Façade integration, Construction, Solar systems, Ventilated façade (in press, article in Spanish)
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Review of current status, requirements and opportunities for building performance simulation of adaptive facade
Review of current status, requirements and opportunities for building performance simulation of adaptive facade
Journal of Building Performance Simulation, 10(2), 205-223;
January 2017 - PDF 0.36MB
By: Roel Loonen, Fabio Favoino, Jan Hensen, Mauro Overend
Document Number:

Adaptive building envelope systems have the potential of reducing greenhouse gas emissions and improving the energy flexibility of buildings, while maintaining high levels of indoor environmental quality. The development of such innovative materials and technologies, as well as their real-world implementation, can be enhanced with the use of building performance simulation (BPS). Performance prediction of adaptive facades can, however, be a challenging task and the information on this topic is scarce and fragmented. The main contribution of this review article is to bring together and analyse the existing information in this field. In the first part, the unique requirements for successful modelling and simulation of adaptive facades are discussed. In the second part, the capabilities of five widely used BPS tools are reviewed, in terms of their ability to model energy and occupant comfort performance of adaptive facades. Finally, it discusses various ongoing trends and research needs in this field.

DALEC – a novel web tool for integrated day- and artificial light and energy calculation
Journal of Building Performance Simulation, 10:3, 344-363
December 2016
By: Matthias Werner, David Geisler-Moroder, Bert Junghans, Oliver Ebert & Wolfgang Feist
Publisher: Taylor & Francis Group
Document Number:

Abstract  -  DALEC is a novel, combined lighting and thermal simulation web tool. This tool allows building designers to evaluate their individual façade concepts in terms of thermal and visual performance and ultimately their impact on overall building energy use. Although easy to use, the software accounts for the complex thermal and light processes in buildings, by way of sophisticated and time-saving pre-calculations. Based on climatic data a calculation of heating, cooling and electric lighting loads can be obtained within a simulation time shorter than one second. The model has been validated by comparison with experimental data and other state-of-the-art software and shows deviations less than 15%. Not only energy demand is considered, but also user behaviour (e.g. glare protection), as well as visual and thermal comfort. This innovative, holistic approach facilitates and accelerates the design of sustainable and energy-efficient building for new, as well as for refurbished buildings.