UNI-11466 and numerical approach in design of horizontal ground heat exchangers

Ground-coupled heat pumps are a reliable technology for space heating and cooling. When coupled with horizontal ground heat exchangers, the profitability may increase according new advanced shapes may that show high performances. In the present study, the analytical method proposed by the Italian regulation UNI-11466 is applied for sizing a novel type of ground heat exchanger, so-called flat-panel, according the equivalent heat transfer surface for unit of trench of the slinky-coil. Two other configurations of straight pipes have been considered disposed horizontally and vertically inside trenches, all of them working in a four lined geothermal field. The space heating requirement of a building has been evaluated assuming a simplified lumped system and three climate zones, defined by different degree days (2000, 2500, 3000 DD). Then, a 2D finite-element model has been implemented for solving in unsteady state the heat conduction in ground of the former sizing, and the results are compared in terms of average temperature at the wall surface of the exchanger. The two straight pipes configurations achieve the minimum temperature predicted by the regulation, such as for the flat-panel case. Therefore, the slinky-coil equivalent approach can be used for sizing the flat-panel shape by means of UNI-11466