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首页> 外文期刊>Renewable energy >Hydrau1ic and thermogeological design differences between two-loop vertical and inclined coaxial borehole heat exchangers
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Hydrau1ic and thermogeological design differences between two-loop vertical and inclined coaxial borehole heat exchangers

机译：两回路立式和倾斜式同轴钻孔换热器的水力和热地质设计差异

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AbstractOne of the most common geoexchange system in practice today is a vertical two-loop heat exchanger. There is also a growing trend of inclined drilling of multiple 40–50 m boreholes with coaxial heat exchangers, which are efficient when installing in areas where there is a favourable groundwater flow. Special care should be taken in hydraulic design of coaxial system, since laminar flow often occur in annular channel, due to glycol mixture implementation. In this research, vertical and inclined coaxial borehole exchangers were compared in identical geological environment, to express differences in heat extraction and thermal resistances, as well as in flow regimes and pressure drop. Extended Steady-State Thermal Response Step Test was implemented, which incorporate series of power steps to determine borehole extraction rate at steady-state heat transfer conditions. Results show that 2U-heat exchanger has advantages over coaxial heat exchangers, in terms of greater steady state heat extraction rate and more favourable hydraulic. Defined extraction rate at 0/-3 °C borehole temperature, in dominantly clay ground, was 43,5 W/m for coaxial system, compared to 54,5 W/m for vertical 2U-loop. Borehole resistance analysis showed almost double value for coaxial system compared to 2U-loop, due to frequent problems in cementation of inclined boreholes.Highlights•Paper focuses on modelling difference between vertical 2U and inclined coaxial borehole heat exchangers.•Hydraulic modelling was carried out for three typical variants of 2U and coaxial exchangers related to pressure drop, rheology, different glycol solutions and equivalent borehole resistances.•Steady-State Thermal Response Step Test (SS-TRST) novel approach was introduced to analyse BHE capacity and thermal resistance during long term operation for 2U and coaxial heat exchanger.•Case study on two real project was performed performing extended thermal response testing.
机译： 摘要 当今实践中最常见的地基交换系统之一是立式两回路热交换器。使用同轴换热器倾斜钻多个40-50 m孔的趋势也有增长的趋势，当安装在地下水流动良好的区域时，这种方法非常有效。在同轴系统的液压设计中应格外小心，因为由于使用了乙二醇混合物，层流经常发生在环形通道中。在这项研究中，在相同的地质环境中比较了垂直和倾斜的同轴井筒换热器，以表现出热量提取和热阻以及流态和压降的差异。实施了扩展稳态热响应阶跃测试，该测试结合了一系列功率阶跃，以确定稳态传热条件下的钻孔抽采率。结果表明，2U换热器具有更高的稳态吸热率和更佳的水力优势，因此具有优于同轴换热器的优势。在0 / -3°C井眼温度下，在主要为黏土的情况下，同轴系统的提取速率为43.5 W / m，而垂直2U回路的提取速率为54.5 W / m。由于频繁发生倾斜井眼胶结问题，与2U环相比，钻孔阻力分析显示同轴系统几乎具有两倍的价值。 突出显示 •• 本文着重介绍了垂直2U型和倾斜式同轴钻孔热交换器之间的建模差异。 • 对2U的三种典型变体进行了液压建模和同轴换热器，涉及压降，流变性，不同的乙二醇溶液和当量 • 稳态热响应阶跃测试（SS-TRST）引入了一种新方法，用于分析2U和同轴换热器长期运行期间的BHE容量和热阻。 • 对两个真实项目进行了案例研究进行扩展的热响应测试。

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