Mathematical modeling and periodical heat extraction analysis of deep coaxial borehole heat exchanger for space heating

The geothermal energy is considered as one of the most promising renewable techniques for district heating. deep coaxial borehole heat exchanger (BHE) an economic and efficient measure extracting from underground, which attracts numerous attentions recently. However, researches on influences operation modes periodical extraction performances BHE are rare. In this paper, unsteady numerical model dynamic established, based principles conservation mass conservation. proposed verified using operating data literature. Space heating a school building (located at Tianjin, China) taken scenario, different during period simulated analyzed. Comparisons were carried out four modes: continuous mode, “16+8 mode” (run 16 h stop 8 h), “12+12 “8+16 mode”. recovery underground temperature distribution winter holiday was studied. Results show that, except differences between other three total extracted throughout whole year 24 within 90th day unobvious. Under mode”, when reaches stable level, power can be maintained 301.6–528.1 kW in first year, decline rate lower than 15% 20-year period. addition, 1 m center tube depths 500 m, 1000 1500 2000 rates relative to initial vacation 7.35%, 13.78%, 16.57%, 17.74%, respectively.