Urban form and function as building performance parameters

Copyright © 2013 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Building and Environment . Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Building and Environment Vol. 62 (2013), DOI: 10.1016/j.buildenv.2013.01.021The climate in cities differs significantly from those found in the surrounding area. These differences results from modifications of the Earth's surface that alters the disposition of “natural energy balance” at a micro-scale and the concentration of activities that results in anthropogenic emissions that change the composition of the atmosphere. These urban effects have distinctive temporal and spatial properties with different impacts on building energy performance depending on their purpose which are rarely accounted for. This paper examines performance implications of a change-of-use (from office to residential) in the context of the UK government's proposal to encourage regeneration and to meet housing needs. However, the diurnal occupation and activity patterns of these uses are distinct. For office buildings, with daytime occupation, focus is on the diurnal heating cycle driven by solar energy gains to which internal energy sources must be added. For residential buildings occupation and activity are primarily associated with the diurnal cooling period, and lower levels of activity that results in a primary heating need. This paper highlights the link between the timing of the urban climate effects, the urban setting and energy performance in a typical city street, where buildings are currently designed for commercial use. It employs London's current and projected climate to simulate heating and cooling demands. By studying the role of urban form and its implications on the suitability of a buildings function we find that a ‘form first’ approach should be considered in the early design stages over the standard ‘fabric first’ approach

Urban geometry and solar availability on façades and ground of real urban forms: using London as a case study

Availability of solar radiation in the urban environment is determined to a great extent by urban geometry, namely how densely built-up an area is and how the given built volume is distributed spatially within the site. This paper explores relationships between urban geometry and solar availability on building façades and at the pedestrian level, with implications for buildings’ passive potential and outdoor thermal comfort, respectively. The study was based on the morphological and solar analysis of 24 urban forms of London, covering a wide range of built density values found across the city. Two aspects of solar availability were investigated at the neighbourhood scale, through statistical analysis: i) the relationships between urban geometry variables and solar availability indicators in different time periods, and ii) the seasonal solar performance of urban forms’ façades and ground. Apart from the strong, negative effect of density, the analysis revealed that solar availability on ground and façades is significantly affected by urban layout. Mean outdoor distance, site coverage, directionality and complexity were the most influential for the solar performance of open spaces; whilst building façades were mostly affected by complexity, standard deviation of building height and directionality. However, direct solar irradiance on ground and façades was found to be influenced by different variables in January and July, which is attributed to the different solar altitude angles. Related to that, urban forms have been identified that present higher irradiance values in January and lower in June when compared to others. Considering temperate climates, these examples highlight the potential for enhancing the seasonal solar performance of existing and future urban developments. Finally, the seasonal effect on solar availability appears to be much more pronounced for ground with its mean direct irradiance value increasing on average by a factor 15, from January to July, while for façades the increase is only by a factor 2.6

A multi-layer approach for estimating the Energy Use Intensity on an urban scale

Various governments are planning their cities to be climate responsive by reducing the energy consumption and carbon emissions according to different scenarios whilst maintaining good indoor comfort conditions. A robust and reliable tool that can estimate the Energy Use Intensity (EUI) of a city is required. This paper presents a new bottom-up engineering-based multi-layer approach able to analyse the energy performance of existing settlements of every size by retaining as much information as possible about their complexities. The process involves i) creating a 3D model of the urban area, ii) building up templates representing different building characteristics such as functions, the age-band of the buildings and operating schedules, iii) running dynamic thermal simulations and iv) displaying the EUI or total energy demand in the 3D model which can be post-processed for further analysis. This approach offers a flexible simulation process according to various purposes, which is particularly useful in decision-making for urban energy retrofitting or planning for new areas. The hourly high-resolution outcomes would benefit the detailed analysis of energy efficiency strategies in order to achieve carbon reduction. The application of this approach is demonstrated for the case of Yuzhong district in Chongqing municipality, China

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