Avaliação do potencial de climatização de sistema terra-água-ar auxiliado por energia fotovoltaica

Abstract

Energy is considered the backbone of the modern economy and its consumption intensifies in emerging societies as their quality of life improves. The current global energy scenario indicates that conventional energy resources are depleting, highlighting the importance of exploring and enable renewable resources to meet future energy demand. Buildings’ HVAC is responsible for a large portion of domestic energy consumption, and bioclimatic systems, that use geothermal energy and solar photovoltaic, are suitable and still little explored alternatives to eliminate the need for the use of air conditioners. The temperature of soil at a certain depth is equivalent to the local average yearly temperature. Various initiatives have sought to make use of this resource through Earth-Air-Heat-Exchange system, where the fluid used for heat transfer is air, and only recently emerged studies making use of water as a heat transfer fluid. This paper presents an experimental analysis that evaluates the performance of an earth-water-air system powered by photovoltaic solar energy, for conditioning the air of buildings. The proposed system uses the thermal stability of the soil, through the use of a water tank (WT) at a certain depth, which operates as a source or sink for thermal energy thus reducing the temperature variation inside the buildings. A prototype was built and is essentially made up of an air-conditioned environment (AC) with 0.6 m3 volume, one fan coil, a reservoir (WT) with a volume of 0.38 m3, buried with the bottom at 2 m below the ground surface, and a water pump. It was found that the proposed system has kept AC's temperature constant and in agreement with ASHRAE Standard 55 2004 for naturally conditioned environment, with the temperature around 23.6 ℃. The ambient air temperature varied from 18.8 °C to 29.4 °C and the soil temperature was 21 °C. For a 119 W incoming heat rate on the AC, the heat removal rate in the fan coil was 98.6 W. Based on the experimental data, the system has been validated and the optimal depth and size of the water reservoir were determined for an application in real scale. For the analysed site it was determined that the optimum depth to reach the soil at a constant temperature equivalent to the yearly average of 18 °C is between 6 to 9 m. A photovoltaic power generation system is proposed for the earth-water-air experimental system.