Balanço de energia em telhado verde

Abstract

The knowledge of energy transfers between vegetated surface and the atmosphere is of great importance to characterize the local microclimate and identify interactions between environmental variables and vegetation. In Brazil, the research related to energy balance are restricted to forests and monocultures, leaving aside other vegetable surfaces as is the case of green roofs (TVs). In this sense, this paper presents an analysis of the energy balance on a TV, the extensive type, considering the input and output components of energy in this system. To achieve this objective, a field study was conducted in the experimental TV of the Federal University of Santa Maria (UFSM). The monitoring data were used in an energy balance model. The model considered the radiation balance, or power available, and even three different heat flows: latent, by conduction and convection. These flows were determined by monitoring the following variables: temperature of the plant and soil, air temperature, temperature of the internal environment of the TV, global solar radiation and reflected, and wind speed. These data were obtained from sensors installed on the roof and / or by meteorological station located at UFSM. This monitoring was carried out in two stages: August 2015 to December 2015, from 8h to 17h, with manual equipment; and from January to May 2016, 24 hours a day with automatic sensors. The energy balance of the TV and its components were determined for the time interval (hour), and the analysis was extended to the months of monitoring. The results showed that the available energy used in heat flows came from the short-wave radiation during the day, and long wave at night. This net energy available prioritized the latent heat flux (12%), mainly responsible for evapotranspiration, confirming that this is the predominant form of heat dissipation absorbed in TVs, as cited in other studies. Also, it was observed, on average, about 5% of the radiation is intended to balance heat flow by convection, and thus it was found that 17% of the incident energy available and returns to atmosphere. The energy that is transferred into the building (by conduction heat flux), this amounted on average 4% net radiation. The remaining, 79%, was retained in the cover system, showing the efficiency of the TVs as the energy storage and attenuation of temperature. It was also found that there exists an energy imbalance in this system, which is mainly influenced by the type of surface coverage and the particularities experiment. So, from the above, this study concluded that the methodology applied is satisfactory to reach the desired goal, and the experimental TV as the overall result of the energy balance, which showed positive values for the months analyzed, is gaining and retaining more energy than losing.