| Heilongjiang is located in severe cold area.During the long-term operation,the performance of the ground-source heat pump system decreases and the heat imbalance is easy to occur.The causes and consequences of thermal imbalance are analyzed.Four ways to alleviate the thermal imbalance are summarized,which are using groundwater,optimizing the operation strategy,optimizing the design of buried pipe and adding auxiliary equipment.The comprehensive optimization strategy of the buried pipe soil-source heat pump system is prospected.This paper analyzes the soil temperature change and the heat recovery of the buried pipe soil-source heat pump system after long-term operation.The effect of groundwater on strengthening heat exchange and alleviating heat imbalance is also analyzed.This subject takes a flower cultivation base of Songbei District Academy of Agricultural Sciences,Harbin,Heilongjiang Province as the research object.A comprehensive analysis was carried out on its 600m buried depth soil source heat pump system.Through the thermal response test of the research area,the basic rock-soil thermal property parameters of the underground soil at different buried depths were obtained.The temperature field of subsurface soil and the three-dimensional transient coupled hydrothermal heat transfer model are established.The recovery period after heating was studied.The results showed that after the end of the whole recovery period,the soil temperature value near the buried pipe was still 3.15?different from the initial temperature value at 600m.After the system is simulated periodically and for a long period of time.The results showed that the soil temperature decreased by 0.15?,0.78?,11.16?and 2.15?after the operation of 1a,3a,5a and 10a.The temperature drop at600m underground is the most serious.After running 1a,3a,5a and 10a,the soil temperature decreased by 2.31?,4.8?,5.8?and 8.92?compared with the initial temperature.Under the heating condition,the maximum and minimum values of the average fluid temperature in the buried pipe after running 10a decreased by 0.87?and 0.98?respectively compared with those after running 1a.Under the refrigeration condition,the maximum and minimum values of the average fluid temperature in the buried pipe after 10a operation decreased by 1.35?and1.66?respectively compared with those after 1a operation.It is considered that the outlet temperature and heat transfer power of buried pipe are the performance indexes of heat exchanger.It is considered that the soil temperature near the buried pipe on the last day of the heating operation period and the soil temperature recovery rate after the heating recovery period are the indexes of the soil heat balance near the buried pipe.It is found that seepage is more beneficial to the improvement of heat transfer performance of buried pipe heat exchanger and the balance of soil temperature near the buried pipe than no seepage.With the increase of the seepage velocity in the order of 10,the heat exchange performance of the heat exchanger has been significantly improved.The imbalance of soil temperature near the buried pipe gradually weakens.When the seepage velocity of groundwater is 3×10-8m/s and the condition of no seepage is compared with the performance of the buried tube heat exchanger and the underground soil temperature field,it is found that the influence difference is not large.When the groundwater seepage velocity is below 3×10-8m/s,it can be treated as no seepage.With the increase of heat dispersion,the heat transfer of buried tube heat exchanger is promoted.Under the heating conditions,the temperature drop of the soil near the buried pipe has eased,and the recovery rate of the ground temperature has also increased,which is beneficial to the balance of the soil temperature.However,with the increase of thermal dispersion,the increase in the effect on heat transfer decreased. |
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