Search

This paper is a contribution towards the link between urban microclimate and building energy modelling using the Town Energy Balance model TEB as a new component embedded into the non-stationary building energy model TRNSYS. A number of comparative features between TEB and TRNSYS motivated this work, which includes commensurate time processing speed, similarity in describing the building facets, comparable inputs and simulation time scope, and the versatile modular architecture of TRNSYS. The paper describes the parameter tabs, inputs and outputs of TEB-Type 201, which offers (i) a user-friendly graphical interface, (ii) short time for data pre-processing with consistency check of inputs, (iii) versatility in selecting and storing outputs in small-sized files and (iv) easy installation. Besides illustrating the capabilities and practicality of this new component, an extensive sensitivity analysis highlights in a hierarchical form the main decisive urban and building parameters responsible in the formation of urban canopy heat or cool islands. The anthropogenic heat, the canyon geometry (aspect ratio, roof plan density) as well as the thermo-physical and radiative properties of the building envelope (thermal insulation, thermal inertia, albedo, emissivity) considered individually or in combination with each other appear to have clear effects on the formation of a microclimate in-canyon on the one hand, and in the magnitude and frequency of canopy heat or cool island episodes at daily and monthly basis on the other hand. The warming of canyon air is heavily influenced by the combination of high urban density (deep canyons and high plan density), high level of anthropogenic heat and weak thermal insulation. Low emissivity, no or low anthropogenic heat, better thermal insulation and low thermal mass favour the cooling of the canyon. These findings reveal the decisiveness of urban and building design choices on the outdoor thermal environment and hence on the energy demand for heating and cooling indoors. As outlook, the paper also notes the necessity of a synchronised coupling of urban canopy and building energy models. [ABSTRACT FROM AUTHOR]

Among several urban design parameters, the height-to-width ratio (H/W) and orientation are important parameters strongly affecting thermal conditions in cities. This paper quantifies changes in thermal comfort due to typical urban canyon configurations in Campinas, Brazil, and presents urban guidelines concerning H/W ratios and green spaces to adapt urban climate change. The study focuses on thermal comfort issues of humans in urban areas and performs evaluation in terms of physiologically equivalent temperature (PET), based on long-term data. Meteorological data of air temperature, relative humidity, wind speed and solar radiation over a 7-year period (2003-2010) were used. A 3D street canyon model was designed with RayMan Pro software to simulate the influence of urban configuration on urban thermal climate. The following configurations and setups were used. The model canyon was 500 m in length, with widths 9, 21, and 44 m. Its height varied in steps of 2.5 m, from 5 to 40 m. The canyon could be rotated in steps of 15°. The results show that urban design parameters such as width, height, and orientation modify thermal conditions within street canyons. A northeast-southwest orientation can reduce PET during daytime more than other scenarios. Forestry management and green areas are recommended to promote shade on pedestrian areas and on façades, and to improve bioclimate thermal stress, in particular for H/W ratio less than 0.5. The method and results can be applied by architects and urban planners interested in developing responsive guidelines for urban climate issues. [ABSTRACT FROM AUTHOR]

The paper focuses on the absorption of shortwave radiation in an urban street canyon. To test the effective albedo of the canyon an analytic solution of the multiple reflection problem is applied. The infinitesimally long canyon is divided into slices and a matrix of view factors for the slices is defined. Incoming shortwave radiation includes direct and diffuse parts and shadowing effects are included in the analysis. The model is validated against Aida’s (1982) scale model data and measurements in a real canyon. The results demonstrate a rapid decrease of the effective albedo as the canyon aspect ratio (its height to width, H/ W) are increased. It is also shown that diurnal changes of the effective albedo can be very complex depending on the particular combination of H/ W ratio, surface reflectivity and canyon orientation. [ABSTRACT FROM AUTHOR]

Based upon a 'human-centred approach', combinations of existing and new methodologies were applied to determine how Ankara's morphological characteristics influenced the magnitude/frequency of Cold Stress (CS) and Heat Stress (HS) to detect/quantify seasonal and yearly human thermal stress frequency. To quantify these conditions upon the human biometeorological system, the Physiologically Equivalent Temperature (PET) was utilised by processing climatic variables from Ankara's Meteorological Station (AMS). In situ assessments of human thermophysiological thresholds were undertaken within characteristic existing/future Urban Canyon Cases (UCCs), with a further stipulation of three interior Reference Points (RPs). Indoor PET values were moreover calculated within a stereotypical vulnerable residential dwelling. Seasonal frequencies revealed that winter PET values frequently ranged between 0.0 and − 19.9 °C, with corresponding summer values frequently ranging between 35.1 and 46.0 °C. Accounting for Ankara's urban morphology, yearly frequency of No Thermal Stress remained at ~ 48%, CS remained at ~ 26%, and HS ~ 28%. HS varied the most between the eight evaluated Aspect Ratios (ARs). It reduced by up to 7.1% (114 min) within the Centre (RPC) area of UCCs with an orientation of 90°. Out of twelve orientations, the highest HS frequency took place between 105 and 135°. Including in UCC3.50, the frequency of HS almost always remained above 72% (2592 min). [ABSTRACT FROM AUTHOR]

Two radiative transfer models are presented that simplify calculations of street canyon spectral irradiances with minimum data input requirements, allowing better assessment of urban exposures than can be provided by standard unobstructed radiation measurements alone. Fast calculations improve the computational performance of radiation models, when numerous repetitions are required in time and location. The core of the models is the calculation of the spectral diffuse-to-global ratios (DGR) from an unobstructed global spectral measurement. The models are based on, and have been tested against, outcomes of the SMARTS2 algorithm (i.e. Simple Model of the Atmospheric Radiative Transfer of Sunshine). The modelled DGRs can then be used to partition global spectral irradiance values into their direct and diffuse components for different solar zenith angles. Finally, the effects of canyon obstructions can be evaluated independently on the direct and diffuse components, which are then recombined to give the total canyon irradiance. The first model allows ozone and aerosol inputs, while the second provides a further simplification, restricted to average ozone and aerosol contents but specifically designed for faster calculations. To assess the effect of obstructions and validate the calculations, a set of experiments with simulated obstructions (simulated canyons) were performed. The greatest source of uncertainty in the simplified calculations is in the treatment of diffuse radiation. The measurement-model agreement is therefore dependent on the region of the sky obscured and ranges from <5 % at all wavelengths to 20-40 % (wavelength dependent) when diffuse sky only is visible from the canyon. [ABSTRACT FROM AUTHOR]

summary¶the existence and character of an intra-urban thermal breeze (iutb) in the city centre of göteborg, sweden was examined. the study was carried out in a 10 ha open area covered with gravel, asphalt and grass, surrounded by narrow street canyons. measurements included an array of fixed wind and temperature sensors and smoke in the open area; temperature of the surrounding neighbourhood from mobile thermal mapping and fixed temperature sensors; standard climate measurements from four automatic weather stations in and around göteborg. the results based on sixteen field surveys performed between december 1998 and march 2000 showed that the open urban area might generate a special type of iutb under certain conditions. the iutb was shown to be a rare nocturnal winter phenomenon developing during clear and calm weather conditions, with snow covered ground, strong ground based inversions and high stability (rib > 1). the most important driving forces for the generation of an iutb were large intra-urban horizontal air temperature differences and strong atmospheric stability which led to decoupling of the canopy layer atmosphere from wind flow aloft. in order to estimate the physical principles underlying an iutb of this type a simple 1.5-dimensional model was devised. results indicated that the horizontal intra-urban air temperature difference recorded in göteborg was enough to develop an iutb. [ABSTRACT FROM AUTHOR]