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•Window-to-wall ratio (WWR) that minimizes total energy use in four European climates.•Integrated thermal-lighting simulations on a low-energy office building.•Most optimal WWR values ...in the range of 0.30–0.45 – but not for south-facing façades.•With best façade technologies, moderate impact of WWR on energy performance.
This paper deals with the search for the optimal window-to-wall ratio (WWR) in different European climates in relation to an office building characterized by best-available technologies for building envelope components and installations. The optimal WWR value is the one that minimizes, on an annual basis, the sum of the energy use for heating, cooling and lighting.
By means of integrated thermal and lighting simulations, the optimal WWR for each of the main orientations was found in four different locations, covering the mid-latitude region (35° to 60° N), from temperate to continental climates. Moreover, the robustness of the results was also tested by means of sensitivity analyses against the efficiency of the building equipment, the efficacy of the artificial lighting and the compactness of the building.
The results indicate that although there is an optimal WWR in each climate and orientation, most of the ideal values can be found in a relatively narrow range (0.30<WWR<0.45). Only south-oriented façades in very cold or very warm climates require WWR values outside this range. The total energy use may increase in the range of 5–25% when the worst WWR configuration is adopted, compared to when the optimal WWR is used.
► Integrated thermal-daylighting simulations on a low energy building are performed. ► Optimal WWR of the façade that minimizes the total energy demand is searched. ► Optimal WWR are found in the ...range 35–45%, regardless the orientation, in a temperate oceanic climate. ► If state-of-the-art technologies are used, WWR does not play a crucial role (maximum influence: 11%). ► The optimal configurations are tested against different building geometries and HVAC efficiencies.
The building enclosure plays a relevant role in the management of the energy flows in buildings and in the exploitation of solar energy at a building scale. An optimized configuration of the façade can contribute to reduce the total energy demand of the building.
Traditionally, the search for the optimal façade configuration is obtained by analyzing the heating demand and/or the cooling demand only, while the implication of the façade configuration on artificial lighting energy demand is often not addressed.
A comprehensive approach (i.e. including heating, cooling and artificial lighting energy demand) is instead necessary to reduce the total energy need of the building and the optimization of the façade configuration becomes no longer straightforward, because non-linear relationships are often disclosed.
The paper presents a methodology and the results of the search for the optimal transparent percentage in a façade module for low energy office buildings. The investigation is carried out in a temperate oceanic climate, on the four main orientations, on three versions of the office building and with different HVAC system’s efficiency. The results show that, regardless of the orientations and of the façade area of the building, the optimal configuration is achieved when the transparent percentage is between 35% and 45% of the total façade module area. The highest difference between the optimal configuration and the worst one occurs in the north-exposed façade, while the south-exposed façade is the one that shows the smallest difference between the optimal and the worst configuration.
The adoption of Phase Change Materials （PCMs） in glazing systems was proposed to increase the heat capacity of the fenestration, being some PCMs partialty transparent to visible radiation. The aim of ...the PCM glazing concept was to let （part） of the visible spectrum of the solar radiation enter the indoor environment, providing daylighting, while absorbing （the largest part of） the infrared radiation. In this paper, the influence of the PCM glazing configuration is investigated by means of numerical simulations carried out with a validated numerical model. Various triple glazing configurations, where one of the two cavities is fitled with a PCM, are simulated, and PCM melting temperatures are investigated. The investigation is carried out in a humid subtropical climate （Cfa according to K6ppen climate classifi-cation）, and ＂typical days＂ for each season are used. The results show that the position of the PCM layer （inside the outer or the inner cavity） has a retevant influence on the thermo-physical behaviour of the PCM glazing system. PCM glazing systems （especially those with the PCM layer inside the outermost cavity） can be beneficial in terms of thermal comfort. The assessment of the energy performance and efficiency is insteadmore complex and sometimes controversial. All the configurations are able to reduce the solar glain during the daytime, but sometimes the behaviour of the PCM glazing is tess efficient than the reference one.
Building envelopes can play a crucial role in building improvement efficiency, and the adoption of Phase Change Materials (PCMs), coupled with transparent elements, may: (i) allow a better control of ...the heat flows from/to the outdoor environment, (ii) increase the exploitation of solar energy at a building scale and (iii) modulate light transmission in order to prevent glare effects. Starting from a literature review, focused on experimental works, this research identifies the main possible integrations of PCMs in transparent/translucent building envelope components (in glazing, in shutters and in multilayer façade system) in order to draw a global picture of the potential and limitations of these technologies. Transparent envelopes with PCMs have been classified from the simplest “zero” technology, which integrates the PCM in a double glass unit (DGU), to more complex solutions—with a different number of glass cavities (triple glazed unit TGU), different positions of the PCM layer (internal/external shutter), and in combination with other materials (TIM, aerogel, prismatic solar reflector, PCM curtain controlled by an electric pump). The results of the analysis have been summarised in a Strengths, Weakness, Opportunities and Threats (SWOT) analysis table to underline the strengths and weaknesses of transparent building envelope components with PCMs, and to indicate opportunities and threats for future research and building applications.
Diffuse Ceiling Ventilation (DCV) is a promising concept to address internal air quality and thermal comfort requirements in contemporary buildings. Sound-absorbing perforated ceiling panels are ...common in office rooms and can be used as air diffusers without modifications. The optimization of such systems is not a trivial procedure, and numerical simulation can represent an important tool to carry out this task. Today, most of the numerical studies on DCV are performed using porous medium models and focus on the general system performance rather than on the optimization of the diffuser design. In previous studies, a CFD model was used to optimize the size and distribution of the ceiling perforation. In the study presented in this paper, the results of simulations conducted on a full-scale three-dimensional domain and the performance comparison between a continuous and non-continuous perforation distribution are given. The results show that the non-continuous diffuser design does not disturb the internal comfort and does not introduce a negative effect in the system performance. The different configurations lead to a different air distribution in the room, but in both cases, the velocity magnitude is always well below values leading to draft discomfort.
Double skin facades (DSF) are an interesting and important architectural element in buildings as they are visually very attractive and can, at the same time, lead to better performance than single ...skin facades. DSFs need to be properly designed and operated, or their potential benefits might vanish. For this reason, the physical processes occurring in a DSF should be well understood and predicted. However, they are highly dynamic and in constant interaction with each other, and they depend on the geometric, thermo-physical, optical and aerodynamic characteristics of the different DSF elements. This literature review reports experimental and numerical studies of DSFs that investigate and assess the cause-effect link between constructional features and the thermophysical phenomena occurring in the systems. These studies are analyzed to better understand the current knowledge available to design both naturally and mechanically ventilated DSFs. The review shows that it is possible to understand simple links between families of constructional properties and performance, but only when one parameter at a time is analyzed. General trends can be defined, such as that the optical properties and especially shading (when present) properties are driving factors for both mechanically ventilated and naturally ventilated DSF, while other features seem to be less relevant (at least alone) to determine the behaviour of these systems. However, the complex interaction between more than one constructional feature is seldom investigated, if not completely explored, and this leaves a relatively large knowledge gap to support the optimal design and operation of DSF systems.
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•We investigate how constructional features affect the behaviour of double skin façades (DSFs).•We review nearly 70 scientific articles and organize systematically the current knowledge.•Mechanically and naturally ventilated DSF show similar patterns when it comes important features.•Interaction with solar radiation (especially shading devices) is the most influential property.•Complex interactions between more than one parameter at a time are mostly unexplored.
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•We analyzed the main design of experiments (DOE) and their applications in building physics.•We compared how 31 different DOE characterized the thermal performance of a double skin ...facade.•Some designs allowed a good characterization (e.g., CCD and some Taguchi arrays) while others failed.•The extent of the nonlinearity played a crucial role in selecting the optimal design(s).•We developed a general set of guidelines for selecting the optimal DOE.
Although a general set of guidelines and procedures for performing the design of experiments (DOE) exists, the literature lacks a recommended course of action for finding and selecting the optimal design of experiments among a large range of possible designs. This research tries to fill this gap by comprehensively testing more than thirty different DOEs through nearly half a million simulated experimental runs. The performance of various DOEs in the characterization of the thermal behaviour of a double skin façade (DSF) is assessed by comparing the outcomes of the different designs and using the full factorial design (FFD) as the ground truth. Besides the finding for the specific case study used in this investigation, this research allowed us to obtain some broad conclusions on the behaviour of different DOEs, which are summarized and translated into recommendations and a general decision tree chart for selecting the suitable DOE(s). The outcomes of this study help researchers and designers to apply DOEs that consider the extent of nonlinearity and interaction of factors in the investigated process in order to select the most successful and the most efficient designs for the specific process characterization.
This paper systematically investigates and quantifies the interplay between mechanical ventilation rate and operation of venetian blinds in determining the performance of a single-story double skin ...façade. The investigation covers both the supply-air mode and the outdoor air curtain mode of a mechanically ventilated double skin façade. For this experimental study, a full-scale mock-up of a single-story double skin façade was installed in a climate simulator facility and exposed to a series of steady-state regime conditions under two representative cases of temperature gradient and solar irradiance replicating the summer, and the mid-season/winter case. The study results showed the relative weights of the different variables in leading the behavior of the façade. They provided evidence that the control of the performance of a double skin façade may change with the seasons, and that airflow rates and venetian blinds can play different roles depending on the boundary conditions and target performance. Venetian blinds were far more dominant than the mechanical ventilation rate in controlling the net heat transfer in the tested summer conditions, while the opposite was seen for the dynamic insulation efficiency. In mid-season/winter conditions, while operating the façade in a supply-air operation mode, the mechanical ventilation rate was the dominant variable in controlling the net heat transfer. Recommendations for the operation of the double skin façade were also developed as a result of this study. Low and moderate ventilation rates (up to 100 m3h−1 per linear meter of façade) were found suitable to deliver enough fresh air with good preheating efficiency while provide adequate control over the net heat transfer. Higher airflow rates, even in summer peak conditions, were not found to be particularly effective in reducing the solar gain through a façade operated in an outdoor air curtain mode when the interior skin was realized with an insulated glazed unit.
The two-fold aim of this study was to compare and reflect on the impact of different experimental designs on the characterization of a complex façade system, and to understand the role of ...constructional elements and boundary conditions on the thermal and fluid dynamic behavior of a double-skin facade (DSF), focusing on the controllability of these phenomena during the operation of the DSF.
We employed and compared four experimental designs capable of assessing factors’ interactions and non-linear behaviors typical of dynamic façades. Experimental data were obtained using a full-scale DSF mock-up, installed in a climate simulator, which was operated in outdoor air curtain mode under boundary conditions typical of the summer season. Similarities and differences between characterizations obtained through different experimental designs enabled us to analyse the impact of different experimental designs and to identify the features that affect the DSF’s performance.
The results demonstrated that the design of experiments methodology could be successfully employed to study the behavior of complex facades. Using more than one experimental design allowed us to obtain a robust picture of the behavior of a naturally ventilated façade. Relevant factors and interactions were also identified and linked to phenomena that determine how the DSF behaves under typical summer conditions.
•We propose a framework to classify occupant centric data.•The classification is based on theory of physiological and psychological processes.•The framework highlights the relations between different ...types of occupant centric data.•Information attributes for each occupant centric data are made explicit.•A deeper analysis of the classification can stimulate research in comfort theories.
New and pervasive information and communication technologies have made it possible to capture a large range of continuous data from, or close to, each individual building occupant. These occupant-centric data streams may include subjective votes, evaluations, complaints, control actions, physiological measurements such as heart rate or pupil size, physical measurements of skin temperature or local draft and air temperature measurements, and much more. Currently, considerable resources are put into studies that focus on the development and potential uses of such systems, while the origin and nature of the collected information which is embedded in the data is poorly investigated. In this paper, we propose a taxonomy for the classification of occupant-centric data streams, developed through the application of established theories and categories in environmental and market psychology. The proposed framework organises five data source categories and links them to four levels of physiological and cognitive processes, making an explicit connection between data and embedded information attributes. The framework, originally developed to classify continuous occupant centric data in the domain of indoor climate, can also bring insights that might help explain known gaps and challenges in different models and theories that aim at predicting individual satisfaction with indoor climate conditions.
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