• Energy Research

Abstract Calculating the air change rates inside naturally ventilated buildings is essential for many applications including indoor temperature calculation. The air change per hour (ACH) at a particular time step and ambient conditions (wind speed, direction, temperature, etc.) is usually calculated via sophisticated simulators, e.g., CFD. However, having a mathematical model describing the relationship between ACH (output variable) and other ambient conditions (input variables), rather than mere simulated numbers, is very important for several reasons: understanding the nature of this relationship and its dominating variables; calculating the indoor temperature at arbitrary time steps; and saving the enormous simulation time when simulating long spans. In this article, a novel approach from pattern recognition literature is introduced to model ACH. A Classification and Regression Tree (CART) was designed from 180 CFD simulated values of ACH, along with their experimentally measured ambient conditions. The RMS error between the ACH values predicted by CART and those simulated by CFD is calculated using cross validation and found to be very acceptable (0.78 and 1.48) h−1 for two different rooms. The model revealed that the ambient temperature is not predictive and hence was dropped from the final model. Designed CART was then fed to TRNSYS 17 as an equation where variables defined as algebraic functions to produce an hourly output for ACH and calculate the indoor temperature along the summer season. The absolute deviance error between the indoor temperatures simulated by TRNSYS and those measured experimentally is as low as (0.3 and 0.4) °C for the two rooms respectively.

Abstract Despite the global call for a paradigm shift towards new environmentally conscious urban planning, little has changed in practice, especially in hot climatic regions. This paper helps bridge this gap by introducing an automated parametric workflow for performance driven urban design. The methodology was tested here in the climatic and urban Mediterranean context consists of a parametric typological analysis, automated through Grasshopper with a total of 1920 iterations. For each iteration the performative effects of both building (i.e. typology, window to wall ratio and glazing properties) and urban design parameters (i.e. distance between buildings, floor area ratio and the orientation) were evaluated for residential and office building uses. The performance metrics - monthly/hourly energy load match and spatial daylight autonomy - were calculated using Energyplus and Radiance, respectively, and recorded for each iteration. The main results indicate substantial performative differences between typologies under different design and density scenarios; the correlation between the shape factor and the energy load match index as well as the benefits of the courtyard typology in terms of energy balance, with its challenging daylight performance, were established. These results demonstrate the potential of this workflow to highlight the design trade-offs between form and environmental performance considerations by designers and thus provide a new way to bridge the performative gap between buildings and their urban surroundings. Its application should help designers and policy makers contextualize nearly zero energy block concepts as well as define new criteria and goals.

Due to climate change, emission balancing is a relevant tool to quantify the environmental impact of a building system. The electrification of energy production at a national level, as well as energy supply at a building level, shifts the focus to the emission factor (EF) of the electricity grid. Currently, static EFs are used for calculating the emission balance. However, the electricity grid already shows fluctuations in power generation and EF due to renewable energies. The paper reviews recent literature outlining the research gap and presents the development of a simulation setup and concept, in which the emission balance of the building operation changes, using dynamic EFs that map fluctuations at an hourly resolution. In the first step, we simulate the thermal building and radiance performance. The data are than used in a second step to conduct a system simulation, which analyzes the effects of the dynamic EFs. The results show that the dynamic balance approach for different building system variants deviates considerably from the static approach. By comparing different concepts for the loading strategy, the predictive strategy outperforms a common control strategy, when considering the energy prices and/or the emissions. This is especially true for systems with inert storage units, where charging times significantly influence the balance, as well as for systems with PV integration. This paper outlines the potential of the EFs-optimized control increases when evaluating a potential scenario for the year 2040, factoring in increased seasonal and daily fluctuations in electricity generation.

The main aim of this paper is a multi-objective evaluation of electrochromic (EC) glazing with consideration of operational and embodied energy including the impact of switchable glazing on visual and thermal comfort. Different criteria were evaluated for the refurbishment of a prototypical 30 m2 office room in Mannheim, Germany. The room prototype was assumed as lightweight and heavyweight construction, where refurbishment strategies such as the addition of thermal insulation and the exchange of windows were investigated. For the window exchange, EC-glazing was compared to a high-performance glazing with solar coating. The EC-glazing was automated via a rule-based (incident radiation) and a penalty-based (multi-objective prediction) control strategy. Regarding operational energy, the EC-glazing performed slightly better than the glazing with solar coating. However, the results showed that the high amount of embodied energy in EC-glazings could not be justified by the rather small savings of the operational energy. On the other hand, with the penalty-based control, the EC-glazing improved visual comfort significantly in comparison to the static glazing with solar coating. The decision to replace the original glazing with an EC-glazing as opposed to a glazing with solar coating would have to be based on the improvement of occupants’ comfort, due to an unjustifiable increase of embodied energy and marginal savings of operational energy.

Abstract With the rise of awareness of health and well-being in cities, urban environmental analysis should expand from energy performance to new environmental quality-based considerations. The limited potential to annually evaluate outdoor thermal comfort, predominant among these considerations, has restricted the exploration of the interrelations between urban morphology and annual energy performance. This study aims to bridge this gap by capitalizing on the new capabilities of Eddy3D – a Grasshopper plugin which enables effective calculations of hourly microclimatic wind factors via OpenFOAM which in turn are used to generate annual outdoor thermal comfort plots. Using this method, a parametric study was conducted for different typology and density scenarios in three different hot climatic contexts in Israel. The automated analytical workflow evaluated a total of 60 design iterations for their energy balance, outdoor thermal comfort autonomy (OTCA) and self-shading levels using the shade index. The high correlation found here between the annual shade index and the OTCA, across all climatic contexts, shows the potential of the shade index to serve as an effective indicator, in these contexts, for comparative or optimization outdoor comfort studies. Further results are both the superiority of the courtyard typology in both energy and outdoor comfort studies, and the contrasting impact of higher density on the annual energy balance (lower performance) and outdoor thermal comfort (higher performance) in hot climates. The annual plots of both the energy balance and OTCA reveal various seasonal and monthly trends in the three different climatic zones which can lead to localized and seasonal urban design strategies.

Cooling demands of commercial buildings present a relevant challenge for a sustainable future. They account for over half of the overall energy needs for the operation of an average office building in warm climates, and this situation is expected to become more pressing due to increasing temperatures in cities worldwide. To tackle this issue, it is widely agreed that the application of passive strategies should be the first step in the design of energy efficient buildings, only using active equipment if it is truly necessary. Nonetheless, there is still further need for information regarding the potential limits derived from their application.This paper explores the effectiveness of selected passive cooling strategies in commercial buildings from warm climates, defining performance ranges based on the assessment of multiple scenarios and climate contexts. This task was conducted through the statistical analysis of results from documented research experiences, to define overall ranges and boundary conditions; and through software simulation of selected parameters to isolate their impact under a controlled experimental setup. General findings showed that the mere application of passive strategies is not enough to guarantee relevant savings. Their effectiveness was conditioned to both the harshness of a given climate and different building parameters. Specific recommendations were also discussed for the selected passive strategies considered in the evaluation.

Small-scale systems and integrated concepts are currently being explored to promote the widespread application of solar cooling technologies in buildings. This article seeks to expand application possibilities by exploring the feasibility of solar cooling integrated façades, as decentralized self-sufficient cooling modules on different warm regions. The climate feasibility of solar electric and solar thermal concepts is evaluated based on solar availability and local cooling demands to be met by current technical possibilities. Numerical calculations are employed for the evaluation, considering statistical climate data; cooling demands per orientation from several simulated scenarios; and state-of-the-art efficiency values of solar cooling technologies, from the specialized literature. The main results show that, in general, warm-dry climates and east/west orientations are better suited for solar cooling façade applications, compared to humid regions and north/south orientations. Results from the base scenario show promising potential for solar thermal technologies, reaching a theoretical solar fraction of 100% in several cases. Application possibilities expand when higher solar array area and lower tilt angle on panels are considered, but these imply aesthetical and constructional constraints for façade design. Finally, recommendations are drafted considering prospects for the exploration of suitable technologies for each location, and façade design considerations for the optimization of the solar input per orientation.

What is an adequate school building nowadays and which amount of technology does it need? How high is the indoor comfort in terms of thermal, visual, hygienic, and acoustical comfort? Are there technical aspects that stand out to other solutions? How do users feel and act in the buildings? For this purpose, the Chair compared, in total, twelve selected modern, older, and renovated school buildings from different building age groups. For the comparison, it was essential to intensively analyze each of the twelve schools. This included visiting the schools, talking with the participating architects, specialist planners, builders, and school managers, procuring and analyzing planning documents and, where available, publications and reports, performing simulations and measurements in the classrooms, and surveying the buildings’ users. The predominant energy demand in schools is the energy expenditure for heating and cooling the air, especially for heating the air in the winter. Nevertheless, it turns out that from a purely energy-focused perspective, mechanical ventilation cannot be justified. It is also evident that transmission heat losses play a negligible role in school construction, which is why the “passive house” as a goal for renovations must be called into question.