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Hydrochemistry and energy storage in aquifers - NHV.nu

Hydrochemistry and energy storage in aquifers - NHV.nu

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The most important required boundary conditions of the aquifer selected for thermal <strong>energy</strong><br />

<strong>storage</strong> are depth, transmissivity <strong>and</strong> the hydraulic resistance of the conf<strong>in</strong><strong>in</strong>g layers. The<br />

flow directions are shown for the w<strong>in</strong>ter (w) <strong>and</strong> summer (s) season.<br />

One has to realize that an aquifer (s<strong>and</strong>), <strong>in</strong> between two conf<strong>in</strong><strong>in</strong>g (clay) layers, is a result<br />

of a sedimentological process of deposition. Hence layers of f<strong>in</strong>er <strong>and</strong> coarser material<br />

alternate with consequently a considerable variation <strong>in</strong> permeability <strong>and</strong> porosity <strong>in</strong> the<br />

aquifer. To illustrate this phenomenon, the lithological composition of the aquifer at the<br />

national test facility (for heat <strong>and</strong> cold <strong>storage</strong>) at Delft is shown <strong>in</strong> Figure 3.<br />

PPl<br />

A<br />

5 TEMPERATURE VARIATIONS<br />

The groundwater, act<strong>in</strong>g as the <strong>energy</strong> transport<strong>in</strong>g fluid, is subject to periodical heat<strong>in</strong>g <strong>and</strong><br />

cool<strong>in</strong>g. Figure 4 illustrates the temperature fluctuations of the transferred groundwater <strong>in</strong><br />

time. In the case of aquifer <strong>storage</strong> coupled to a heat-power co-generat<strong>in</strong>g plant the<br />

temperature at the 'hot' side varies between 45 <strong>and</strong> 90°C dur<strong>in</strong>g each yearly cycle.

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