Comprehensive Performance Metrics for Complex Fenestration Systems Using a Relative Approach

Buildings account for over 40% of the energy consumption in the United States, nearly 40% of which is attributed to lighting. The selection of a fenestration system for a building is a critical decision as it offsets electric lighting use as well as impacts energy performance through heating and cooling systems. Further, the fenestration system contributes to both occupant comfort and ambiance of the space. Complex Fenestration Systems (CFS) address these factors with a variety of innovative technologies but the language to describe, discuss, and compare them does not exist. Existing traditional metrics for fenestration systems are unable to reveal the benefits that characterize complex fenestration systems because they are rigid, do not reflect annual performance, and were developed for a different purpose. The framework presented in this research offers a solution to this problem by using an annual climate-based methodology to provide a comprehensive evaluation of a system by incorporating three of the most relevant performance aspects: energy efficiency, occupant visual comfort, and ability to view through. Three metrics, the Relative Energy Impact (REI), the Extent of Comfortable Daylight (ECD), and the View Through Potential (VTP), were derived from these three criteria to express, in relative terms, a façade’s contribution to building energy use, comfortable daylight conditions, and the degree of transparency, respectively. Several practical matters were considered when developing a policy-relevant set of metrics, including both ease of calculation for manufacturers and usability for consumers. As such, the calculation methodology evolved from its initial proposal into a simplified approach, analytical where possible, and into a label-like concept for visual representation. These metrics are intended to exist as a mechanism by which manufacturers can evaluate and compare façade systems, provide high-level intuition of relative performance for designers and contractors, and enable the balance of performance objectives based on user preference. Ultimately, the creation of this comprehensive language is intended to stimulate innovation in fenestration systems and encourage their use in both new and retrofit building applications.

Practical and Policy-Relevant Performance Metrics for Complex Fenestration Systems

Marilyne Andersen

The selection of a fenestration system for a building is critical, as it impacts energy performance, occupant comfort, and ambiance of a space. Complex Fenestration Systems (CFS) address these criteria using a wide variety of novel technologies but are difficult to define or be characterized. Existing metrics for fenestration systems are unable to reveal the dynamics or degree of variety over climate conditions or time of year that define CFS because they rely on a single and arbitrarily-defined set of environmental conditions to calculate. Although the optical characteristics of a CFS can be predicted using its Bi-Directional Transmission Distribution Function (BTDF) – a mathematical dataset that describes the angular distribution of light flux as it passes through a material – this information is too abstract to be meaningful to the building industry. A set of metrics that uses the BTDF in an intuitive way could allow the performance and physical characteristics of these technologies to become more accessible, ultimately allowing the various benefits of daylighting to be realized. The proposed approach offers a solution to this problem by using an annual climate-based methodology to provide a comprehensive evaluation of a system by incorporating three of the most relevant performance aspects: energy efficiency, occupant visual comfort, and ability to view through. Three metrics, the Relative Energy Impact (REI), the Extent of Comfortable Daylight (ECD), and the View Through Potential (VTP), were derived from these three criteria to express, in relative terms, a façade’s contribution to building energy use, the fraction of time and space for which it achieves comfortable daylight conditions, and the degree of transparency as it relates to an occupant’s view through the façade, respectively. These metrics are intended to exist as a mechanism by which manufacturers can evaluate and compare façade systems, provide high-level intuition of relative performance for designers and contractors, and enable the balance of performance objectives based on user preference. In order to successfully implement these metrics, a simple and repeatable calculation process was identified first through a series of sensitivity analyses compromising on relevance or accuracy, and then by defining input conditions that are able to reduce calculation or simulation time substantially. Using both approaches, each of these metrics was further and applied to five sample façades that cover a broad range of Complex Fenestration System types, including a validation study for the VTP metric. A visual representation of this information in a condensed format was then investigated so as to allow straightforward comparisons amongst systems and a synthetic understanding of their performance. A graphical, label-like structure could indeed provide an initial suggestion for the use of these metrics in the rating and standard-setting environments.

2012

Velux Lab: innovation between art and science

Arianna Brambilla

Veluxlab is the first Italian Nearly Zero Energy Building. It is placed in Bovisa Campus of Politecnico di Milano and it represents a study case of high energy efficiency building, integrating in the future scenario required by the European Directive 2010/31/UE. VELUXlab was born as a Mediterranean Model Home for VELUX, called Atika, designed by J.A. Cantalejo and R.A.Ronda from ACXT/IDOM studio. It personified the prototype of energy efficiency building for the Mediterranean Region and it is the result of an important architectural and performance retrofit. The renovation was led by Atelier2 with the supervision of Professor Imperadori and Professor Motta from Politecnico di Milano.The collaboration between Politecnico di Milano and VELUX Italia gave the opportunity of create a new lab, a sort of test building, where it is possible to develop the experimental research on going in the University. In this way VELUXlab became itself matter of research on the energy efficiency and sustainability in the building sector. The use of innovative solutions and materials for the envelope coupled with an advanced technological system, makes representing the first Italian nearly Zero Energy Building in a University Campus. Furthermore, thanks to its energetic performance and to the integration of renewable source, it is the first built Active House in Italy (www.activehouse.info). VELUXlab is, therefore, an example of smart and sustainable re-use of an existing structure as well as a model of energy efficient building and a prototype for the new generation home, bringing forward future experimentations and implementation in the sector. It is the profitable collaboration between Politecnico and construction companies that allows to innovate, test and research sustainability and efficiency. The west wing of the building and the conditioning system are equipped with a revolutionary wireless sensors network (WSN), designed by the DEI Department of Politecnico di Milano (Prof. Cugola, Ing. Sivieri), that allows a constantly monitoring of the real performance of the envelope - indoor comfort system. The real time results are broadcasted on the University intranet, elaborated by a remote server and then made available on-line. Thanks to this streaming it is possible to understand the real performance of VELUXlab in the first year of measurement. This data portray the ordinary operational situation, including the internal strains given by the users; it is easy to understand that the building itself is a prototype, conceived as an active and dynamic laboratory. In order to make easier the data interpretation and management, the Design Department (Prof. Bordegoni), is been studying an innovative and more intuitive way to visualize the sensors data, with the implementation of the graphic interface in an augmented reality platform. It is easy to understand that VELUXlab offers continuously incentives and opportunities for testing and experimenting innovative solutions and ideas, giving the chance to continue research and studies.

2013

Active façades : life cycle environmental impacts and savings of photovoltaic power plants integrated into the building envelope

Gianluca Cattaneo, Angela Clua Longas

Aim and approach used Increased energy supply from photovoltaics is a main priority in the “Energy Strategy 2050”. Within the joint research project "Next generation photovoltaics" funded by the Swiss National Science Foundation, we analysed different options for the enhanced integration of photovoltaic technologies into the envelope of Swiss buildings (BIPV). The PV modules for building integration are using novel monolithic silicon heterojunction organometallic perovskite tandem cells (SHJ-PSC) with adaptions to improve the visual acceptance. In a joint effort of product developers, architects and scientists, this project aimed at providing pathways for the wide-scale use of BIPV façade solutions, and developing integrated designs based on emerging high-efficiency module technologies to improve the visual aspect and acceptance of PV systems installed in Switzerland. These so-called active façades incorporating BIPV modules to generate electricity can provide a significant contribution to the energy transition away from fossil and nuclear fuels. We compared the environmental impacts of different façade construction systems with and without SHJ-PSC BIPV modules with improved visual design, using a prospective life cycle assessment with a time horizon of 2025. The comparison includes a conventional brick and roughcast façade, a timber frame façade, and the Advanced Active Façade (AAF), which integrates SHJ-PSC BIPV modules in a low embodied impact façade substructure. In addition, we compared the environmental impacts caused by the construction of the above described façades with the environmental impacts saved due to the electricity produced by BIPV modules incorporated into the AAF. 2. Scientific innovation and relevance Our research focuses on the combined expertise of life cycle thinking, PV module development and façade design. The major scientific innovations are: 1) the prospective life cycle assessment of novel monolithic silicon heterojunction organometallic perovskite tandem cells (SHJ-PSC); 2) the comparison of different façade construction systems and their environmental impacts; 3) the quantification of the saved environmental impacts arising from the electricity generated by the active façade; and 4) the visual adjustments of PV modules to improve their acceptance. The main advantage of integrating PV into building façades is the large available area, which can be limited on rooftops. In order to reach the market penetration for PV required for the energy transition, PV modules must be integrated into façades as well as into rooftops. 3. Results and conclusions An equilibrium must be achieved among different technical and aesthetic issues when integrating energy generation systems into the building envelope, especially into the façade for its public condition and exposure. Based on these prerequisites, the research team has developed the AAF which combines passive and active energy design strategies while meeting contemporary architectural requirements. This façade design is based on low-embodied-energy construction principles, it is defined by a non-loadbearing wood-panel substructure and it integrates a double layer of natural insulation: cellulose and wood-fibre. In addition, its design incorporates an opaque SHJ-PSC BIPV façade-cladding following contemporary façade design trends. (Figure 1). The use of photovoltaic modules integrated into the façade cladding or roof will increase the environmental impact of the building envelope, compared to using conventional construction materials. The environmental impacts of the AAF using PV modules are two to four times higher compared to a conventional façade. The PV modules cause the highest share of greenhouse gas emissions of the AAF with about 375 kg CO2-eq per square meter (see Figure 2). The additional materials required to build the AAF including exterior panels, insulation and other materials cause about 75 kg CO2-eq per square meter of façade. The brick and timber frame façades cause greenhouse gas emissions around 200 and 100 kg CO2-eq, respectively. If the greenhouse gas emissions caused by the PV module is excluded this will result in a reduction between 25 and 125 kg CO2-eq per square meter of façade. However, the environmental impacts of the AAF are significantly reduced if the whole life cycle is considered due to the PV electricity produced by the building. Therefore, we calculated the saved greenhouse gas emissions due to the electricity produced by the advanced active façade and fed to the European electricity grid using the greenhouse gas emissions caused by the current European electricity mix as reference. These calculated savings due to the electricity produced by the BIPV are about 4 times higher than the impacts of the advanced active façade. Incorporating BIPV panels into building’s façades will cause net savings of about 1700 kg CO2-eq per square meter over the whole life cycle of BIPV façades, while simultaneously saving up to 125 kg CO2-eq per square meter of façade for the reduced material demand to build the façade (see Figure 3). We performed this analysis for 16 different environmental impacts according to the recommended midpoints by the Joint Research Council of the European Commission. The results were comparable to greenhouse gas emissions with the net saved environmental impacts being many times higher for all the environmental impacts analysed except mineral resource use caused by the indium used in the novel SHJ-PSC tandem module (see Figure 4). To conclude, the use of PV modules in AAF can reduce the greenhouse gas emissions per square meter of façade between 25 and 60 % if the production of the PV module and its produced electricity are excluded. If the production and life cycle of the PV modules are included into the analysis the AAF will cause net greenhouse gas savings up to four times higher than the production of the AAF itself. The results for environmental impacts other than greenhouse gases were similar except for mineral resource depletion. Overall, the building integration of photovoltaic modules as AAF will reduce the environmental impacts of the building while simultaneously providing a visually appealing building envelope.

2019