Search

Highlights • The U-value impact on the thermal performance of residential buildings was analyzed. • 192000 buildings were randomly generated and evaluated using dynamic simulation. • Six geometry-based indexes were correlated with the buildings performance. • Higher U-values can decrease energy consumption in lower latitudes. • Higher and wider U-value intervals increase the geometric freedom for lower latitudes. Abstract Contrarily to what happens in northern European countries, buildings in the Mediterranean region are prone to overheating. Consequently, it is important to better understand the role that the thermal transmittance of the building envelope elements has on air-conditioning consumptions. This paper analyzes the effect of different U -values on building design in the Mediterranean area. 192 000 residential buildings were randomly generated for sixteen distinct locations and the energy consumption was assessed for each. It was found that in northern Mediterranean locations, as U -values decreased, energy consumption also decreased. However, in warmer climates, low thermal transmittances tended to significantly increase energy consumption. Hence, the lower the latitude, the higher the U -values should be, in order to prevent increasing the cooling demands. Additionally, geometry-based indexes were correlated with the building's energy performance. For high U -values, it was found that bigger buildings worsen the energy performance and larger windows tended to improve it. For low U -values, bigger north-facing windows were beneficial. There is an adequate interval of values for which the geometry has a lower impact, which is wider and higher for lower latitudes, thus meaning that not only does the building performance improve but architects are also freer to explore alternative designs. [ABSTRACT FROM AUTHOR]

Highlights • The U -value impact on the thermal performance of residential buildings was analyzed. • 96,000 buildings were randomly generated and evaluated using dynamic simulation. • Six geometry-based indexes were correlated with the buildings performance. • Low U -values can increase energy consumption in warm and moderate climates. • Adequate U -values allow designers to explore new building forms and window designs. Abstract European countries impose regulations for low thermal transmittance envelopes to improve the buildings' energy efficiency. However, in scientific literature, evidences are surfacing that such low U -values are affecting the validity of traditional design guidelines. The purpose of this paper is to analyze the implications of lowering the envelope U -values. To achieve this, 96,000 residential buildings were generated, with random geometries and U -values, and their energy consumption evaluated for eight European locations. The buildings were grouped according to the envelope elements' thermal transmittance and the results statistically analyzed. For each group, six geometry-based indexes were correlated with the energy performance. As U -values decrease, the performance variation amplitude was found to reduce, making the geometry less important. However, in warm/moderate climates, low U -values tend to actually increase the energy consumption and also rise the performance variation, meaning that geometry regains importance. In this case, instead of helping reducing the heating demands, solar exposed windows and compact geometries raise the energy consumption. It is concluded that, for each climate location, there is an ideal U -value range for which the energy demand is low and the geometry effect becomes less significant, thus freeing designers to further explore building forms and window designs. [ABSTRACT FROM AUTHOR]

This paper presents a study on the application of lightweight steel framed (LSF) construction systems in hot climate. A generative design method created 6010 houses, with random geometry and random roof and exterior wall types with different insulation levels, and EnergyPlus was used to evaluate the energy consumption for air-conditioning of each building. The main goals were to determine which geometric variables correlate with the energy performance, and to provide some guidelines to foster efficient LSF buildings in hot climates. By correlating six geometry-based indexes with the energy consumption for each construction element type group, it was verified that roofs do not show significant correlation, while exterior walls presented weak to moderate positive correlation with the building volume, very weak to weak negative correlation with the relative compactness, no correlation with the shape coefficient, moderate to strong negative correlation with the window-to-floor, window-to-wall, and window-to-exterior surface ratios. The results also show that buildings with larger windows and greater level of insulation have better energy performance. No significant difference of energy performance was found between different LSF construction systems with equivalent thermal resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Heat convection models have several limitations in dynamic simulation. • Different models produce significantly different energy performances. • Wind direction is not adequately considered in EnergyPlus. • The models show spikes and steps in a building's 360° orientation curve. • New convection models are needed to improve precision and reliability. Wind plays an essential role in the heat convection on building outside surfaces. In EnergyPlus, a dynamic simulation program, heat convection models present several limitations reported by the scientific community. However, this communication reveals and discusses some implications that highlight the importance of developing more accurate models. The current models are first analyzed to identify what are the pitfalls considering the influence of wind direction on the thermal performance of the building walls. Then, a discussion is made on why their implications are important and, lastly, it is suggested how wind direction-driven studies and new models can overcome this issue. Concluding, this communication calls for efforts from the scientific community to research and develop more accurate models for wind-driven surface convection. [ABSTRACT FROM AUTHOR]

Efficient ventilation is an effective method for reducing thermal loads inside buildings, thus decreasing cooling energy consumption. This is especially relevant in warmer climates. Therefore, it is important to better understand the role that different ventilation parameters play on air-conditioning consumptions. This study analyzes the effect of three different ventilation parameters – air flow rate, minimum indoor temperature and indoor-outdoor temperature difference – on the energy performance of buildings in the Mediterranean region. A set of 500 residential building geometries was randomly generated and the energy consumption for different combinations of ventilation parameters was assessed in sixteen distinct locations. Results suggested that the ventilation specifications that minimize air-conditioning energy consumption fall within similar values for all the evaluated locations: ventilation rates of at least 10 air changes per hour, a minimum indoor temperature for ventilation slightly below the building's cooling setpoint, and a low indoor-to-outdoor temperature difference. It was also found that, in lower latitudes, the buildings' energy performance tended to become similar, thus reducing the impact of their geometry and orientation. These results may help building practitioners to infer the most adequate ventilation strategies to implement, since this study is not limited to specific ventilation methods. • The ventilation impact on energy performance of residential buildings was analyzed. • 500 buildings were randomly generated and evaluated using dynamic simulation. • Similar ventilation specifications can be used for all the evaluated locations. • Ventilation rates of at least 10 ACH show to be the most adequate. • In lower latitudes, geometry and orientation are less impacting on energy performance. [ABSTRACT FROM AUTHOR]

• Datasets of low and high thermal mass with random U -values are compared. • Low thermal mass buildings have lower and wider range of ideal U -values. • High thermal mass buildings demand more cooling energy. • Buildings with high thermal mass consume lesser heating energy in warmer climates. • Thermal mass impacts differently the energy consumption along the U -value scale. High thermal mass construction is commonly used to reduce cooling energy consumption during the summer period as a passive design strategy in the Mediterranean region. Although being a generalized design practice, the benefit to the building performance is not fully consensual within the scientific community. This work explores the influence of thermal transmittance on the energy efficiency of buildings with different thermal mass levels. Hence, a statistical comparison of the buildings' annual energy consumption for air-conditioning is carried out based on two synthetic datasets with high and low thermal mass and varying thermal transmittance for opaque and transparent elements. In addition to climate location, the results demonstrate that thermal transmittance has varying impact on the contribution of thermal mass. The locations presenting such behavior were Marseille (−0.99% to +3.89%), Istanbul (−0.73% to +4.21%), Valencia (−1.31% to +4.97%), Algiers (−2.32% to +3.81%), Malaga (−3.95% to +6.21%), Casablanca (−5.66% to +6.96%), and Tel Aviv (−1.81% to +5.44%). These findings demonstrate that the influence of thermal mass is more complex than previously thought and levels should be chosen in relation with the thermal transmittance value. [ABSTRACT FROM AUTHOR]

This paper critically reviews the role of performance-based generative design in fast prototyping of buildings, describes the methodology of an automated generative layout design to produce complete building solutions, and presents a case study of multi-story buildings in urban context. The proposed approach evolves the building design solutions by interacting with the city 3D geometry and evaluates the energy consumption for air-conditioning. The building designs take into consideration urban geometric constraints and objectives, such as alignment with surrounding buildings, urban lot area, and relative and absolute position of the generated elements. During the evaluation process, the urban context is considered for casting shadows and reflecting solar radiation. The case study consists of six alternative 15-story buildings located in the city of São Paulo (Brazil), having commercial areas on the ground floor and two apartments per story on the remaining floors. The results show that, despite having similar apartments in every story, the urban context has a relevant impact on the buildings' energy performance. The difference between the apartments' best and worst energy performing stories ranges from 9% to 12% (ignoring the outlier story located in the first level), depending on the building solution. The results also show that the most energy efficient apartments' story is not located in the top or bottom floors, but rather at an intermediate level. • Urban context is added to an automatic floor plan generation procedure. • Alternative 15-story buildings are generated with residential and commercial spaces. • Energy consumption for air-conditioning is evaluated for every apartment. • Shadows and reflections from surroundings are evaluated during dynamic simulation. • Stories' energy performance vary from 9% to 12% despite having similar geometry. [ABSTRACT FROM AUTHOR]

Strong convergence problems may arise during the dynamic simulation of the phase transitions of adsorption systems subjected to larger and/or random fluctuations of the boundary conditions, which do not follow the conventional cycle sequence (e.g., adsorptive thermal storage systems). This sequence could even be reversed at some instants and its stages not completed. Such convergence problems preclude solving those phase transitions, and thus the successful dynamic simulation of the adsorption systems. A set of numerical procedures for solving those problems is proposed, consisting of a small group of new conditions to be added to the conventional numerical algorithms. Its successful use is demonstrated in the dynamic simulation of a thermal energy storage system provided with an adsorption module, modeled in two distinct but coupled platforms (TRNSYS and MATLAB), for which the convergence difficulties are identified and described. Results indicate successful convergence by applying the proposed methodology, in contrast with the original algorithm, attesting for its capability to overcome the convergence problems that occur during the system's dynamic simulation. This set of numerical recipes can be adapted for other systems' algorithms, or to serve as a basis for its successful dynamic simulation, thus showing a promising and enlarged range of use. [ABSTRACT FROM AUTHOR]