The shadows in a city disclose its energy flow
Researchers at the Universidad Politécnica de Madrid’s Facultad de Informática (UPM, Spain) have created "shadow models" and software that calculates the amount of solar radiation that reaches streets and buildings in high resolution. According to the results published in the Research Journal of Chemistry and Environment, these shadow models could help to optimise the energy consumption of cities.
"Solar radiation that falls on a certain point in the city varies depending on the time of day, the weather conditions, the pollution level and other variables," explains Roberto San José, lecturer at the Universidad Politécnica de Madrid (UPM). "What we have done is to calculate radiation using supercomputers that simulate the vast amount of data involved in the entire atmospheric process," he adds.
The method involves throwing up to 100,000 rays of light from any position for just a few seconds and verifying the point of collision upon reaching obstacles. Calculations are so complex that it took the powerful machines at Madrid’s Supercomputing and Visualization Centre (CEsViMa-UPM) and the Mare Nostrum supercomputer at the Barcelona Supercomputing Centre 72 hours to get just 6 seconds of light and shadow evolution for an area of Madrid, Spain.
The study, which was published in the Research Journal of Chemistry and Environment, is based on global meteorological data provided by the USA's National Centre for Atmospheric Research. Information applying to Europe and Spain was taken from this data before homing in on a more local level. The starting point of the whole process is an open source of geophysical research, called EULAG.
The researchers have devised two mathematical "shadow" models. The first model supplies data to the second. One model shows highly detailed 3D images of the behaviour of radiation, whereas the other reveals the energy exchange occurring in a selected area. Urban morphology plays a crucial role in the energy balance.
As San José explains, "At a certain time of day, rays of light collide, depending on the urban layout, with the tarmac, the pavement and other buildings. They are then successively reflected until they create different degrees of shadow on the surface."
The team has implemented their two models in an IT tool named SHAMO (SHAdow MOdel). This software is capable of quantifying shadows and solar radiation in any city. It analyses cubic areas with a base of 1 km x 1 km and a height of 400 m at a resolution of 4 m.
City energy optimisation
"The results are a useful tool for sustainability and energy optimisation in cities from both an architectural (a shaded building requires more internal heating than a building in the sun) and urban planning point of view. In this respect, results can be used to harmonise artificial and natural energy consumption”, states San José.
By way of an example, "The heating is often turned on during the day and off at the night, but it might, in some cases, be better the other way round. For instance, sometimes the amount of solar radiation that reaches a building is enough to keep in the warmth that has accumulated from the heating being on during the night."
This study is part of the European BRIDGE Project on urban metabolism, a concept that perceives the city as a living organism in search of a sustainable energy balance. Madrid City Council’s Department of Urban Planning has already expressed their interest in the tool.
Source: FIUPM
References:
R. San Jose, J. L. Pérez, R.M. Gónzalez. "Sensitivity analysis of two different shadow models implemented into EULAG CFD model: Madrid experiment". Research Journal of Chemistry and Environment 15(2): 319-325, 2011.