【作者】 张文雍；

【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】 太阳能-土壤耦合热泵(Solar-Ground Coupled Heat Pump, SGCHP)系统在用于严寒地区供暖时,由于建筑物的热负荷很大,热泵从土壤中的取热量也很大,系统常年运行地下土壤温度场难以得到恢复,使得热泵的供暖性能系数(Coefficient of Performance, COP)逐年下降。为此本文提出利用系统中原有装置收集非采暖季节的太阳能并通过土壤换热器储存到自然的土壤中,冬季再利用热泵将热量提取出来为建筑物供暖。这种季节性的土壤蓄热,不仅可以恢复和提高土壤温度,而且还能将非采暖季节丰富的太阳能转移到冬季使用,有效的增加了太阳能作为可再生能源热利用的范围,具有很大的节能意义。为了系统准确的了解该蓄热过程的特性,本文首先建立了SGCHP供暖实验系统,监测了太阳能季节性土壤蓄热以及系统冬季供暖的性能,并对地下土壤温度场的变化作了较为系统的分析。与传统的SGCHP系统不同的是,增加了季节性土壤蓄热后,地下垂直U型埋管既是取热装置也是蓄热装置,具有双重功能,因此土壤换热器是蓄热系统中的一个关键部件,是研究该技术的核心和应用的基础。基于此,本文利用FLUENT建立了由多个垂直U型埋管组成的群井土壤换热器的三维非稳态传热模型,并通过FLUENT软件提供的扩展功能——用户自定义函数(User-Difined Function, UDF)编写太阳能集热器等其它设备模型程序动态加载到群井土壤换热器模型中,实现了对太阳能季节性土壤蓄热过程的动态仿真。此外,为研究地下土壤蓄、取热的热平衡问题,将蓄热系统仿真模型扩展到全年供暖系统仿真模型。通过模拟结果与实测数据的比较,验证了本文所建数学模型的可靠性和正确性。通过仿真模拟,从理论上分析了埋管间距、埋管深度、土壤换热器所在位置地表有无建筑以及土壤作为蓄热介质本身参数对土壤蓄热特性的影响,并分析了基于负荷特性下太阳能集热器的倾角、蓄热启动温度对土壤蓄热特性的影响。通过监测蓄热运行参数和土壤温度场的变化,对蓄热指标:蓄热温差、蓄热运行时间、月蓄热量和总蓄热量、蓄热能效比、蓄热功率、单位埋深蓄热量等进行了理论研究。最后,从蓄热后土壤的取热特性以及温变特性出发,主要包括土壤取热量、单位埋深取热量、蒸发器进出口温度、土壤温度场以及热泵、系统供暖和系统全年COP,探讨了整个供暖系统在常年运行条件下土壤的蓄热特性和取热特性的逐年变化以及二者的相互影响。并通过观察土壤温度场的逐年变化分析了土壤的热堆积效应和热平衡状况。研究结果表明,在运行控制条件不变的情况下,土壤温度逐年升高,蓄热效率逐年降低;系统运行的最初3年两者变化较快,随后趋势逐渐变缓;热泵COP逐年升高,但升高的幅度不大,基本维持在较高的水平。因此,在系统运行3年以后可适当减少蓄热量,使土壤热量达到平衡。该部分研究可为该系统的长期运行和推广提供指导。SGCHP系统结合季节性土壤蓄热,克服了太阳能热利用在季节性上不匹配的缺点,扩大了太阳能热利用的深度和广度。通过太阳能季节性土壤蓄热,热泵低温热源的温度得到了提升,从而有效地提高了热泵和供暖系统的COP,节能效果十分显著。在目前环境问题日益严重,国家大力发展低碳产业的大环境下,该系统必将会得到长足的发展和广泛的应用。本文所作的研究工作可以为今后季节性土壤蓄热SGCHP系统的应用提供理论基础和技术支持。更多还原

【Abstract】 Because the heating load of buildings in the severe cold area is very large, when the solar-ground coupled heat pump (SGCHP) system is used for space heating, the heat pump extracts much heat from the soil, which makes the soil temperature field recover difficultly after several years of operations and the heating coefficient of performance (COP) of the heat pump decline annually. This paper presents a new idea of using the existing installations in the system to collect the solar energy in non-heating seasons and the heat is injected into the natural soil through the ground heat exchanger. In winter, the heat is extracted by the heat pump for the space heating of buildings. The seasonal soil heat storage not only can recover and promote the soil temperature, but also can transfer the abundant solar energy in non-heating seasons to winter, which effectively increases the thermal utilization extension of the solar energy as a renewable energy source and has great energy saving significance.To find out the characteristics of the heat storage process systematically and exactly, the experimental heating system of SGCHP was established first. Then, the performances of the solar seasonal soil heat storage and the system heating in winter were monitored. Moreover, the underground soil temperature field variations were analyzed systematically. What is different from the traditional SGCHP system is that the underground vertical U-tube is not only the heat extraction installation, but also the heat storage installation, which has dual function. Based on this, the three-dimensional unsteady-state mathematical model of the multi-well ground heat exchanger which was composed of a number of vertical U-tubes was established in this paper. Furthermore, the extension function of User-Defined Function (UDF), provided by FLUENT software, was used to compile the model programs of solar collector and other equipment. They were dynamically loaded into the model of the multi-well ground heat exchanger and then the dynamic simulation of the solar seasonal soil heat storage process was realized. In addition, to study the heat balance problem of the heat extraction and heat storage of the underground soil, the heat storage system simulation models were extended to the heating system simulation models. The reliability and validity of the mathematical models established in this paper were validated by comparison between the simulation results and the measured data.Through the simulation, the influences on the soil heat storage characteristics caused by the pipe spacing, the pipe depth, the ground heat exchanger position that has buildings or not on the ground surface and the parameters of the soil as the heat storage medium were analyzed theoretically. Also, the influences on the soil heat storage characteristics caused by the solar collectors titled angle and the heat storage start temperature based on the load characteristics were analyzed. Through monitoring the operating parameters and the soil temperature field, the heat storage indexes: heat storage temperature difference, heat storage operating time, monthly and total heat storage capacity, heat storage energy efficient ratio, heat storage power, heat storage capacity of unit depth, etc. were studied theoretically.At last, from the heat extraction and temperature variation characteristics of the soil after the heat storage, which mainly include the heat extraction capacity, the heat extraction capacity of unit depth, inlet and outlet temperature of the evaporator, soil temperature field and the heat pump’s COP, system heating COP and annual system’s COP, the yearly variations of the soil heat storage and heat extraction characteristics under the condition of the entire heating system operating year in year out as well as the interaction between each other were discussed. In addition, through the yearly variations of the soil temperature field, the heat accumulation effect and heat balance status were analyzed. The results show that, when the operation control conditions is not changed, the soil temperature increases year by year, while the heat storage efficiency decreases year by year. During the initial 3 years, the both vary rapidly, and then the variation trend turns smoothly. The COP of the heat pump increases year by year, but the margin is small, which basically maintains at a higher level. Therefore, after 3 years of running, the heat storage capacity can be reduced appropriately, to maked the soil heat balance. The research can provide guidance for the system long-term running and popularization.The combination of SGCHP and solar seasonal soil heat storage overcomes the shortcoming of solar thermal utilization that is not matching with the season and expands the depth and width of solar thermal utilization. Through the solar seasonal soil heat storage, the temperature of the heat pump low-temperature heat source is raised and the COPs of the heat pump and the heating system are effectively increased, which has very significant energy saving effect. Now, under the great environment of increasingly serious environmental problem and the country’s energetic development of the low-carbon industry, the system would certainly get considerable development and wide applications. The researches done in this paper can provide theoretical basis and technical support for the application of SGCHP system with solar seasonal soil heat storage in the future.更多还原