Research On Simplified Heat Transfer Analysis Method Of Ground Heat Exchangers With Multi-boreholes

The ground source heat pump technology using shallow geothermal energy is more and more widely promoted in our country, among them the most are vertical buried pipe system. The heat transfer of each borehole will be affected by boreholes around when geothermal heat exchangers run for a long time. As a result, it will generate heat interference phenomenon and the heat transfer process is more complicated. The common method to analysis was established based on a heat transfer model between the single buried pipe and soil, under the condition of assumed soil physical property and using superposition principle to analysis the temperature field response when exchangers taking or releasing heat from the underground soil.The article introduces a calculation program based on the finite line heat source superposition principle to calculation the soil temperature of multiple ground heat exchangers. Besides, we can draw soil temperature contours through numerical calculation software MATLAB. On this basis we focus on study the simplified calculation method of soil temperature of buried pipes in different conditions。On the basis of analysis on characteristics of the underground soil temperature distribution after multi-boreholes heat exchangers run a whole life period and the basic principle of heat transfer, a method that using the representative heat transfer matrix of buried pipes replace the primary multi-boreholes is put forward by the distinguishing feature that the soil temperature distribution has the same periodic variation around some partial pipes approximately. Due to the decrease in the analytical number of buried pipes, the amount of calculation is reduced. In addition, the analytical number of buried pipes can reduce further by taking advantage of the symmetrical layout of boreholes.Cases with and without groundwater advections are studied by the simplifying method proposed. In the condition that the geological conditions, pipes geometric parameters, load and the operation conditions are alike, the representative heat transfer matrix of boreholes can be determined by the heat transfer influencing radius of single borehole. In this paper, we take the temperature disturbance at heat transfer influencing radius is selected 0.01 ℃. According to the allowed range of error, the corresponding temperature disturbance can be used as the heat transfer influencing radius in the practical engineering. Then, the number of representative boreholes can be determined.