The Use of Trees as a Strategy to Daylight Control and Thermo-luminic Comfort in the Built Environment

The current artificial light sources represent a very recent technological advancement in human history, having major implications on their relation with work and the use of built environment. Hereof, several studies have shown a relation between the increasing of human's visual problems with a strong spectral anisotropy presented in most of such light sources. On the other hand, the daylight spectrum represents a pattern to which the human eye physiology is adapted, and its presence in built environment is highly desirable. Even so, its availability is usually associated with the presence of sunshade devices, as the high intensity and the presence of IR / UV spectrum could bring health risks and thermovisual discomfort. The point is that such shading devices frequently end up hindering the very availability of the natural light in buildings, bringing back the need for use of artificial light sources. In addition, these devices often can not cope with the high thermal load present in solar radiation, absorbing too much heat and overheating the shaded area. Based on this perception, this paper discusses the use of trees as a solar protection device that does not impair the light penetration into buildings while giving a shaded area with a well balanced mean radiant temperature. Usually the environmental role of vegetation has been addressed from the thermal comfort standpoint, as its physiological processes are highly important in the local thermal balance. However, more than a physical barrier the foliage of trees acts as an optical filter that generates a luminous ambiance of high visual quality. In this paper these facts are discussed by both light intensity and distribution under the canopy, as the level of thermal alleviation provided. Usually people enjoy arboreal shading more than the artificial covering shading. Nevertheless, they can not explain objectively why, since the processes involved are not obvious to the naked eye. This paper addresses precisely this limitation by using special images to uncover the thermo-luminics qualities that the tree shade hide from human vision. For this purpose two photographic techniques were used: 1 - Pixels analysis luminance in HDR photos; 2 - Thermal images. The HDR images are created by joining a number of 7 to 9 consecutive photographs of the scene in question, performing an EV (exposure value) variation. Thus one obtains an image with brightness and contrast close to those observed by normal vision. After that the HDR images are processed in a software of pixels luminance analysis (in this case the WebHDR) creating a mask of false colors with graduations according the luminance levels. The camera used in this stage was a Fujifilm - Finepix S1800 with a tripod. For the thermal images was used a thermographic camera model Testo Thermal Imager 875-2. This camera has a thermal sensitivity (NETD) of 0.08°C, with manual focus from - 20 to + 280°C for hot and cold spots recognition. With the use of thees two techniques it was possible to show, from the pedestrian's point of view, the distribution of luminance and surface temperatures in arboreal shaded areas. The experiment was conducted with two species of trees: Sibipiruna - Caesalpinia peltophoroides and Flamboyant - Delonix regia. This selection was based on the following criteria: perennial foliage, native species, canopy with broad projection area, high leaf area index, good representativity of the study area. The experiment was conducted in Baráo Geraldo, a suburb of Campinas - Brazil. In this area, subtropical climate with high temperatures during the summer makes the presence of trees a major factor. The analysis of shading provided by the selected species was conducted (a) mid-morning (09:30h); (b) noon and (c) mid-afternoon (15:30h). The analysis of results obtained with the masks of false colors demonstrates tha places under direct influence of arboreal shading present better temperature and luminance than places shaded artificially. The images also indicate a direct correlation between areas of luminous alleviation and these of thermal alleviation, coinciding with areas with arboreal shading. In this sense the paper exposes the importance of isolated tree elements to the comfort of pedestrians, through shading. Although specialized literature downplays the effects of punctual arborization in the urban climate, the test results indicate a more significant role when pedestrians and buildings directly under its shade are considered. Thus the paper brings up some considerations on the application of these trees' properties in the shaping of an architectural space visually and thermally more comfortable, through passive conditioning.