地热源热泵-孙建军.ppt

Ground Heat Sources for Heat Pumps (classification, characteristics, advantages) Introduction  The underground in the first approx. 100 m is well suited for supply and storage of thermal energy. The climatic temperature change over the seasons is reduced to a steady temperature at 10-20 m depth (fig. 1), and with further depth temperatures are increasing according to the geothermal gradient (average 3 ℃ for each 100 m of depth) The mechanisms sketched in fig. 2 are the only natural means to bring heat into the ground or to release heat from the ground. They have to supply the heat that is extracted by a heating- only ground source heat pump or have to neutralise the thermal impact resulting from an imbalance in a heating and cooling system. In this paper an overview of the methods to access the thermal potential within this depth range is given, and advantages and applicability are discussed. Classification of heat sources/sinks The ground system links the heat pump to the underground and allows for extraction of heat from the ground or injection of heat into the ground. These systems can be classified generally as open or closed systems: Main technical part of open systems are groundwater wells, to extract or inject water from/to water bearing layers in the underground (“aquifers”. In most cases, two wells are required (“doublette” fig. 3), one to extract the groundwater, and one to re-inject it into the same aquifer it was produced from. ●verticalBecause the temperature below the “neutral zone”(ca. 10-20 m) remains constant over the year, and because of the need to install sufficient heat exchange capacity under a confined surface area, vertical ground heat exchangers (borehole heat exchangers, fig. 6) are widely favoured. In a standard borehole heat exchanger, plastic pipes (polyethylene or polypropylene) are installed in boreholes, and the remaining room in the hole is filled (grouted) with a pumpable material. Several types of borehole heat exchangers