• Energy Research
• 13. Climate action close

Abstract The use of renewable energy sources to improve the thermal conditions of built environments and hence decreasing the consumption of conventional energy is an important aspect to design a sustainable building. Within this context, it is possible to harness the solar energy that reaches the Earth's surface and is stored by the soil as thermal energy. To do so, the Earth-Air Heat Exchanger (EAHE) device can be employed, consisting of a buried duct through which the external ambient air is insufflated. The flowing air exchanges heat with surround soil, and leaves the device with a milder temperature compared to its input temperature. The main goal of this work was to present a new computational modeling to predict the thermal behavior of EAHE. This new numerical model has the advantage of needing a lower computational effort, allowing the study about the influence of operational and constructive parameters, as well as, the application of geometric optimization methods in EAHE. A case study was developed where influence of the installation depth in the thermal potential of an EAHE was investigated. The results are in agreement with those found in literature; however they were obtained with a reduction in processing time of almost 45%.

Abstract Earth-Air Heat Exchangers (EAHE) work blowing the air through buried ducts to employ the soil as a heat/cold sink. Thus the thermal energy contained in the soil can meet heating/cooling needs of buildings and reduce the conventional consumption of energy. In Brazil, recent research about these devices has been done considering its south region where a subtropical climate prevails. However, there is a lack of studies addressing the thermal performance of EAHE in coastal cities, where one can find the soil very sandy and the water table near the ground surface. In particular, this paper studies numerically the installation of EAHE in three different places located in the coastal south Brazilian city of Rio Grande, where the geotechnical profiles of the soil were obtained in-situ through standard penetration tests (SPT), aiming to promote thermal performance analysis for EAHE. In the simulations presented here, the influence of the water in the soil and a shortage of clayey layers in some sites relatively reduced their performance in more than 60%. Moreover, for these sites, the thermal potential for EAHE is poorly affected by placing the ducts at depths below 2.0 m.

Abstract The Overtopping Device is a type of Ocean Waves Energy Converter (OWEC) which concept is storing water provided by incident waves above sea level to feed a set of low head turbines. Present study aims to perform 2D numerical analyses of near-shore overtopping devices platforms to investigate the influence of curvature of the platforms on water discharge by means of OpenFOAM code, which is an open source software. Current study performs comparisons between Fluent and OpenFOAM solutions as well (first part of results). Therefore, pointing out OpenFOAM as a potential tool for simulation of overtopping devices is also one of the objectives of this study. The software comparison is performed based on a case found in literature considering seven linear overtopping platforms configurations inside a wave tank. The discretization method is the Finite Volume method solving momentum, continuity, and a water volume fraction (Volume of Fluid method) equation used to capture waves air–water interface. Platforms curvatures investigation considers 12.5 m and 25 m length devices, with three different shapes: concave, linear and convex. All of those are 6 m height with 5 m immerse and 1 m above water level. The ramps are submitted to incident regular waves (1 m height, 65.4 m length and 7.5 s period) inside a 10 m depth wave channel. Results showed that OpenFOAM wave model complies with the expected characteristics determined with mathematical classical equations and also it is very coherent with Fluent results. About the ramps shapes, it was observed that ramps curvature may maximize the water mass that overtops into the tank. Moreover, this study agreed with literature that lower ramp height/length ratio leads to water discharge improvement for linear ramps for specified wave and constructions conditions. Other important observation is that curved platforms usage is a very good option to reduce devices sizes without losing energetic potential. This is pointed out because the convex 12.5 m length, which has length/ratio bigger than 25 m length devices, achieved the greatest water discharge among the analyzed geometries.

Abstract The need to develop new technologies that allow the use of sustainable alternative sources of energy is increasingly evident. Thus, this work presents an experimental and numerical study of earth–air heat exchangers, which are used to reduce consumption of conventional energy for heating and cooling of built environments through the use of thermal energy contained in the soil. The experiment was conducted in southern Brazil in the city of Viamao, and its results were used to validate the computational modeling of heat exchangers. In the present work, the variation of air temperature inside the ducts, to an annual cycle, was investigated. The numerical solution of the conservation equations of the problem is performed with a commercial code (FLUENT) which is based on the Finite Volume Method (FVM). Turbulence is tackled with the Reynolds Stress Model (RSM). The transient temperature fields predicted numerically was compared with the experimental ones, the highest difference found was lower than 15%. The results showed the validity and effectiveness of the employed computational model, enabling its use for future researches and projects developments about earth–air heat exchangers.

Abstract Earth-Air Heat Exchangers (EAHE) can reduce the heating/cooling load of a building using buried ducts, where the air is forced to flow and exchange heat with the soil. Due to the Earth’s thermal inertia, the region near the surface of the soil can serve as a heat source or sink. This available thermal energy in the soil surface layer comes from the solar radiation incident on the Earth. Thus, the air leaves the duct(s) at milder temperatures, helping to reduce the use of traditional air conditioning systems. This paper aims to analyze the thermal behavior of an EAHE taking into account realistic data relative to a south coastal city of Brazil, where: (1) the geotechnical profiles of the soil were obtained in-situ through standard penetration tests (SPT), allowing to adopt adequate thermo-physical properties; and (2) the temperature annual variation for the soil surface and the air in the region were obtained from an international forecast center. Still in the methodology, the simulations were performed with a verified and validated finite volume computational model. As the overall results point out, 2 m is the ideal depth to place the ducts locally, which increases the EAHE thermal potentials in the summer and winter seasons. Different of other places, due to the water tables close to the surface in the studied regions, it is not worth to make installations at higher depths there.