| 摘要 |
<p>Heat is extracted from the earth using a borehole extending typically 1000m to 2000m into the earth. Water is conveyed to the bottom of the borehole and is collected from the bottom in isolation from the downflowing water, so that heat gained by the water as it travels downwardly can be recovered. The borehole may be encased to form an outer pipe down which the water passes, externally of a concentric return flow pipe (18). Alternatively, where no encasing is required, because of the quality of the rock strata, the downward and upward water flow may be in one or more tubes. <IMAGE></p> |
