【作者】 杨涛；

【导师】 郑茂余；

【作者基本信息】 哈尔滨工业大学 ， 供热、供燃气、通风与空调工程， 2010， 博士

【摘要】 为了降低夏季空调能耗、利用可再生能源,本文基于自然冷源移季利用的思想,提出一种新型的适用于严寒地区的季节性自然冷源土壤蓄冷系统。该系统以室外自然低温空气作为冷源,大地作为蓄冷储存装置,通过地下垂直U型埋管换热器将冷量储存在土壤之中,到了夏季再将其取出作为建筑空调的冷源使用。它与传统短期蓄冷方式相比,节省了占地面积大、耗资较多的蓄冷装置;由于换热器、蓄冷装置都在地下,系统运行平稳,构造简单;省去了电力制冷装置,运行成本低,无污染。该系统为空气自然冷源利用提出了一个新的应用领域。与传统的土壤源热泵系统不同的是:在季节性自然冷源土壤蓄冷系统中,地下埋管充当蓄冷装置也作为吸热和排热的换热装置,具有双重功能;土壤蓄冷属于人工冻结作用下的土冻结过程,土壤冻结时土壤的物性也随之发生改变,影响地下埋管的传热性能;同时,土壤冻结会导致土壤水分梯度改变,引起土壤水分迁移,改变土壤的蓄冷能力,在热传导和对流换热的共同作用下,使土壤的传热能力增强;此外,土壤作为蓄冷介质,会与地表空气和周围自然土壤发生热交换,导致系统冷量损失。基于此,本文建立了地下垂直U型埋管换热器管群内、外层埋管的水热耦合数学模型以及温差传热冷量损失和预存冷量损失数学模型,提出了一个新的求解非线性相变传热问题的数值方法-“反求时间步长法”,使模型求解大为简化。除此以外,本文补充了室内外换热器传热数学模型,完成了整个系统模型的建立。考虑到第二年系统蓄冷之前,土壤温度不可能恢复至原始状态,采用第二年蓄冷期结束时埋管周围土壤的内能与第一年保持不变的方法来调整第二年蓄冷时间,可保证系统的可持续运行。通过数值模拟,从理论上分析了土壤水迁移作用、埋管间距、蓄冷时间、土壤类型、不同含水量土壤及室外换热器换热面积等因素对系统运行特性的影响,研究了第一年和第二年,以及在不同埋管间距、蓄冷时间及土壤类型条件下系统蓄冷、释冷和停机过程中的冷量损失,为系统的优化设计与参数的合理匹配提供理论支持。选取沈阳和长春两个具有代表性的城市,针对其气候特点进行系统运行方案设计,通过对全年运行过程进行模拟分析得出,该系统在严寒地区应用可以得到较好的运行效果,若在寒冷地区也可以作为空调冷源的重要补充。建立了哈尔滨地区季节性自然冷源土壤蓄冷现场实验系统,并对实验系统进行连续两年的测试。研究了系统的冬季蓄冷量,夏季释冷量,埋管进出口温度和井内土壤温度的变化规律,提出了影响性能系数的主要因素。实验结果表明:该系统在严寒地区应用是完全可行的。通过模拟结果与实测数据的比较,验证了本文中建立的数学模型的可靠性和正确性。针对冻融土壤温度场的数值模拟,分别采用传统计算方法与本文提出的“反求时间步长法”进行相变传热问题的求解,通过对比发现,这种新方法不仅可以较为精确地求解冻融土壤的温度场,而且加快了修正时间步长的速率,使求解过程大为简化。该方法是对传统方法的改进,可为其它多维复杂相变传热问题求解提供参考。该系统为21世纪建筑提供了一种更为清洁、高效的空调蓄冷技术,本文所做的研究将会为该系统的应用提供理论支持和示范作用。更多还原

【Abstract】 To reduce air conditioning energy consumption in summer and use the renewable energy source, a new type of soil cold storage system, which bases on the idea of seasonal natural cold energy transfer and is applicable to cold regions, is presented in this dissertation. Using the outdoor low temperature air as the cold energy and the underground soil as the cold storage device, the system is to store cold energy underground by U-tube heat exchanger and extract cold energy in summer for building air conditioning. Compared with the traditional way of short-time storage, this mode has a lot of benefits. It can avoid using expensive cold storage devices with large area and high cost; due to the heat exchanger and cold storage device underground, it runs stably and structures simply; finally, it has low operation cost and avoids refrigeration equipment and pollution. This system provides a new application field for natural cold air energy.Different from the traditional ground source heat pump system, firstly, the underground tube has a dual function that it not only serves as cold storage devices, but also behaves a role as exchanger for charging and discharging. Secondly, soil cold storage is the soil freezing process under artificial freezing effect, and during soil freezing, the soil physical properties change, which affect the heat transfer performance of underground tube. Meanwhile, soil freezing will lead to water gradient changes and cause soil moisture migration, which alters cold storage capacity of soil, and enhances its heat transfer capacity with the function of both heat conduction and convection. Besides, the soil, as storage medium, exchange heat with the air of soil surface and the surrounding natural soil, resulting in cold loss. Based on the above-mentioned, the mathematical model of the moisture-heat coupling and cold loss caused by temperature difference and pre-existing storage are established for the inner and outer tube in the vertical U-tube bundles; A new method called the backwards calculating time step method is presented to solve heat transfer problems of complex nonlinear phase change, and as a result, the iteration procedure can be simplified; In addition, by supplementing to indoor and outdoor heat exchanger heat transfer model, the model for the whole system is completely finished.Taking into account the sold storage before next year, it is impossible for soil temperature to be restored to its original level. The method, which keeps the internal energy of soil around tube at the end of charging period unchangeably compared with the first year, is used to adjust the cold-storage time during the second year. It can ensure the sustainable operation of the system. Through numerical simulation, this dissertation does a lot of analysis to the factors which influence on the operation performances of the system, such as soil moisture migration, tube distances, cold-storage time, soil type, soil with various water contents and heat exchanger area of indoor and outdoor heat exchanger etc, and research to the system cold loss of the first year and the second year and under different tube distances, cold-storage times and soil types during the three processes of cold storage, shutdown and cold extraction of the system. It supplies theory support and technology accumulation for the optimal design of system and the matching of the parameters. Take the two representative cities Shenyang and Changchun as an example. According to their climate characteristics the operation schemes of system are designed. Through the simulative analysis of operation process over one entire year, simulations show that the system achieved many better operation results if applied in severe cold region and supplied a part of cold energy for air conditioning if the system is applied in cold region.Hereby, the field experiment of soil cold storage system with seasonal natural energy is set up in Harbin while the test work in the continuous two years is implemented. This dissertation researches the charged quantities in winter, the discharged quantities in summer, the changing principle of inlet and outlet liquid temperature of tube and soil temperature in well, and puts forward the main factors of influencing on performance coefficient. The experimental results show that the system is feasible in severe cold region. The reliability and validity of the model established above are validated by comparing the simulation results and experimental data.In view of the numerical simulation of temperature fields of soil freezing and thawing, the phase change heat transfer problems are solved using the traditional methods and backwards calculating time step method presented in this dissertation, respectively. This new method, in contrast to the traditional methods, not only accurately calculates the temperature fields of soil freezing and thawing, but accelerates rate for adjusting the time step. It is an improvement over traditional methods, and can provide reference for solving other complex multi-dimensional problems involving phase change heat transfer.The system will supply a kind of cold storage technology of air conditioning with more efficient and cleaner for the 21st century buildings. At the same time, the researches in this dissertation provide theory support and demonstration effect for the system application.更多还原