TMREES Conference Series 2019 (Beirut)

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TMREES Conference Series

Luogo: Beirut – Libano

Data di inizio: 10 aprile 2019

Data di fine: 12 aprile 2019

Modelling of a Low-Enthalpy DHE Geothermal System for Greenhouses Heating: Thermal and Fluid Dynamic Analysis with FEM Approach

Energy demand has been growing during the last years. Directive 2009/28/CE and Energy Roadmap 2050 have been drafted to identify the main targets in terms of energy consumptions and efficiency, following the new international awareness in matter of pollution reduction. The main targets of theEuropean Directive and International policies are the reduction of gas emissions and general energy efficiency improvement. That’s the reason why petroleum-based fuels are now faced by biofuels, produced by residual biomasses. At the same time, many other renewable energy sources have been studied to optimize conversion processes they are involved in. Renewable resource advantages are mainly its abundancy, its direct use and its easy exploitation in the most cases. Therefore, geothermal energy can be considered as a renewable energy resource. Geothermal plants extract underground thermal energy by using heat exchangers to produce electricity or provide heat to domestic/industrial buildings. In this sense, a sustainability assessment framework for geothermal energy project is required: many efforts to exploit geothermal potential have been made in many countries to reach new energy policies requirements. Low enthalpy geothermal plants should be considered as a suitable solution for industrial and residential buildings heating. Hydrothermal basins are usually characterized by a temperature between 40°C and 80°C, and so this makes them unsuitable for GCHP systems coupling, in this case, it is necessary to choose whether to cover the low external heat demand (e.g. by greenhouses, small houses and buildings) by directly withdrawing the basin water or installing a DHE. The choice depends both on the reservoir charging modes and thermal response stability: extracting underground water could highly affect geomorphology and soil stability. Moreover, even if a basin water refill is provided, feeding fluid temperature should damage the temperature stability of the underground reservoir. To avoid these problems, a DHE system is a suitable solution, since its installation eliminates the problem of geothermal fluid disposal.

The aim of this work is to implement a multi-physical FEM model, to compute the heat transfer and the flow rate in a DHE plant which provides thermal energy to greenhouses. The proposed model has been validated by using experimental data from an experimental DHE pilot-scale plant (located in Viterbo, Italy) as a reference. Geothermal plant simulation should provide relevant information to optimize and check the thermal response of the system. Moreover, the greenhouse heating process should be modified to suit plants’ demand in terms of growing environmental parameters. In those cases, no high temperatures are required, so a low temperature source, such as low enthalpy geothermal systems, should be considered as a suitable solution. The experimental plant’s monitoring and data acquisition have been used as a starting point while implementing the model. Furthermore, acquired temperature trend over time has been used to validate numerical values resulting from the computed scenario. Stationary studies have been solved, in order to analyze operating regime effects on temperature and flow field. Those analysis have computed the temperature trend within the pipe, considering fluid path from inlet to outlet sections; flow velocity has been also investigated to show fluid motion field fluctuations related to stagnation areas.