垂直U型地埋管回水保温换热性能研究
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摘要
节能减排是我国当前的一项重大国策,建筑能耗占到全国总能耗中的40%左右,而空调能耗占到建筑能耗中的40%~60%,因此空调系统节能成为节能减排的重中之重。地源热泵作为一种新型空调形式,由于其高效节能、环境效益显著、运行稳定可靠、适用范围广等优点,正逐渐替代传统空调。
地源热泵系统中最重要的部分是地下换热器的换热性能,而其受到土壤热物性、回填材料、埋管深度、管间距等因素的影响,其中进出水管间的热短路的影响很大,因此本文针对U型垂直地埋管回水保温换热性能进行了研究。
本论文通过搭建实验台和结合实际工程对地埋管的热短路和保温长度进行了实验研究和分析,并采用CFD模拟软件建立了地埋管的换热模型,对不同保温长度的进出口温差和单位管长换热量进行数值模拟,重点分析了不同埋深下保温长度对地埋管换热性能的影响。
本论文通过50米埋深实验台的冬季实验和80米埋深实际工程的夏季实验,针对不同负荷、不同运行工况、不同流量下U型地埋管的换热能力进行了实测,并通过数值模拟分析了80米和50米埋深的垂直地埋管在不同保温长度、不同运行工况、不同流量下换热能力,讨论了这两种埋深下保温长度对换热性能的影响。
论文的研究表明:垂直地埋管回水管保温后的换热能力大于回水管不保温的换热能力,在同一埋深下,无论是连续工况还是间歇工况,保温长度越长,单位管长换热量越大,因此,在经济允许的情况下,应对回水管进行尽可能长的保温。在同一保温长度下,间歇工况要比连续工况的单位管长换热量大,且系统运行的时间越短,单位管长换热量越大,因此,应尽量让地埋管有一定的地温恢复时间。在连续工况时,流量变化对进出口温差的影响很小,但对单位管长换热量的影响较大,而在间歇工况下,流量变化对地埋管的进出口温差和平均单位管长换热量影响都较大。系统在小流量下运行时,地埋管的换热能力随保温长度的增加而增大的幅度很小,当系统在大流量下运行时,地埋管的换热能力随保温长度的增加而增大的幅度很大。当地埋管每米埋深所加负荷小于本文的负荷条件下,土壤温度都能恢复到运行前的水平。
Energy-saving and ejection-decreasing is a major plan in our country nowadays. Energy-consumption in building account for forty percent of total energy in whole country and energy-consumption in air-condition occupies forty to sixty percent of building energy consumption, so it very important to save energy in air-condition. As a new air-conditioning type, the ground source heat pump (GSHP) is taking over traditional air-condition gradually because of its advantages, such as high efficiency, saving energy, less environment damage, stable and reliable, applicable in many place and so on.
The performance of underground heat-exchanger is the most important part in a GSHP system, and its performance is impacted by many factors such as physical parameter of earth, fill material, depth of well, distance between two legs and so on. Heat short circuit between inlet and outlet pipe is an important factor. The performance of U-type and vertical underground exchanger with outlet tube insulated is researched in this thesis.
The effect of heat short circuit and insulated tube length are analyzed and tested through a real project, and the models of underground heat exchanger are established by CFD software. The temperature difference between inlet and outlet tubes and capability of heat exchanging per meter were simulated and its effect on the performance of underground heat pump was analyzed with different insulated length of insulated tube.
The performance of underground heat exchanger was tested with different loads, different operation condition, and different flux through a test with fifty meter depth borehole in winter and a project experiment with eighty meter depth borehole in summer. The performance of heat exchanger with different insulated length, different operation situation and different flux was simulated with eighty and fifty meter depth borehole and its performance were discussed.
Conclusion of this thesis are shown as following: The capacity of heat exchanging with insulated tube in outlet tube is much higher than those without insulation, the capacity of heat exchanging increases along with the length of insulated tube increasing, whatever in intermission and series operation situation. So it is very important to take a insulation measure in the back water pipe as long as possible. The capacity of heat exchanging increases along with the operation time decreasing in a certain insulated pipe, which means capacity of heat exchanging in intermission is higher than that in series, so GSHP should run as less as it can in one day. Flux has a little effect on the temperature difference between inlet and outlet but has large effect on heat exchanging rate per meter in series operation situation, and has a lot effect on both temperature difference between inlet and outlet and heat exchanging rate per meter in intermission operation situation. Earth temperature can be recovered to the level before its running when the load per meter is less than that in this paper.
地源热泵系统中最重要的部分是地下换热器的换热性能,而其受到土壤热物性、回填材料、埋管深度、管间距等因素的影响,其中进出水管间的热短路的影响很大,因此本文针对U型垂直地埋管回水保温换热性能进行了研究。
本论文通过搭建实验台和结合实际工程对地埋管的热短路和保温长度进行了实验研究和分析,并采用CFD模拟软件建立了地埋管的换热模型,对不同保温长度的进出口温差和单位管长换热量进行数值模拟,重点分析了不同埋深下保温长度对地埋管换热性能的影响。
本论文通过50米埋深实验台的冬季实验和80米埋深实际工程的夏季实验,针对不同负荷、不同运行工况、不同流量下U型地埋管的换热能力进行了实测,并通过数值模拟分析了80米和50米埋深的垂直地埋管在不同保温长度、不同运行工况、不同流量下换热能力,讨论了这两种埋深下保温长度对换热性能的影响。
论文的研究表明:垂直地埋管回水管保温后的换热能力大于回水管不保温的换热能力,在同一埋深下,无论是连续工况还是间歇工况,保温长度越长,单位管长换热量越大,因此,在经济允许的情况下,应对回水管进行尽可能长的保温。在同一保温长度下,间歇工况要比连续工况的单位管长换热量大,且系统运行的时间越短,单位管长换热量越大,因此,应尽量让地埋管有一定的地温恢复时间。在连续工况时,流量变化对进出口温差的影响很小,但对单位管长换热量的影响较大,而在间歇工况下,流量变化对地埋管的进出口温差和平均单位管长换热量影响都较大。系统在小流量下运行时,地埋管的换热能力随保温长度的增加而增大的幅度很小,当系统在大流量下运行时,地埋管的换热能力随保温长度的增加而增大的幅度很大。当地埋管每米埋深所加负荷小于本文的负荷条件下,土壤温度都能恢复到运行前的水平。
Energy-saving and ejection-decreasing is a major plan in our country nowadays. Energy-consumption in building account for forty percent of total energy in whole country and energy-consumption in air-condition occupies forty to sixty percent of building energy consumption, so it very important to save energy in air-condition. As a new air-conditioning type, the ground source heat pump (GSHP) is taking over traditional air-condition gradually because of its advantages, such as high efficiency, saving energy, less environment damage, stable and reliable, applicable in many place and so on.
The performance of underground heat-exchanger is the most important part in a GSHP system, and its performance is impacted by many factors such as physical parameter of earth, fill material, depth of well, distance between two legs and so on. Heat short circuit between inlet and outlet pipe is an important factor. The performance of U-type and vertical underground exchanger with outlet tube insulated is researched in this thesis.
The effect of heat short circuit and insulated tube length are analyzed and tested through a real project, and the models of underground heat exchanger are established by CFD software. The temperature difference between inlet and outlet tubes and capability of heat exchanging per meter were simulated and its effect on the performance of underground heat pump was analyzed with different insulated length of insulated tube.
The performance of underground heat exchanger was tested with different loads, different operation condition, and different flux through a test with fifty meter depth borehole in winter and a project experiment with eighty meter depth borehole in summer. The performance of heat exchanger with different insulated length, different operation situation and different flux was simulated with eighty and fifty meter depth borehole and its performance were discussed.
Conclusion of this thesis are shown as following: The capacity of heat exchanging with insulated tube in outlet tube is much higher than those without insulation, the capacity of heat exchanging increases along with the length of insulated tube increasing, whatever in intermission and series operation situation. So it is very important to take a insulation measure in the back water pipe as long as possible. The capacity of heat exchanging increases along with the operation time decreasing in a certain insulated pipe, which means capacity of heat exchanging in intermission is higher than that in series, so GSHP should run as less as it can in one day. Flux has a little effect on the temperature difference between inlet and outlet but has large effect on heat exchanging rate per meter in series operation situation, and has a lot effect on both temperature difference between inlet and outlet and heat exchanging rate per meter in intermission operation situation. Earth temperature can be recovered to the level before its running when the load per meter is less than that in this paper.
引文
[1]中国国务院新闻办公室.中国的能源状况与政策白皮书.人民日报[N]. 2007.12-26.
[2] D.A.Ball. Design method for GSHP [J].ASHARE Trans.DC-83-03:416~440.
[3] A.C.Crandall. House heating with earth heat pump [J]. Electrical World.1946, 126(19): 94-95.
[4] L.R.Ingersoll,O.J.vZoeble, A.C.Ingersoll.heat conduction with engineering[J]. geological and other applications,1954.
[5] Svec O.J.Potential of ground-coupled heat source system.International Journal of Energy Research [J]. 1987(4):571~581.
[6] Bose J E, Parker J D.Ground-coupled heat pump Re-search [J]. ASHRAE Trans, 83 (2):375—390.
[7] Eskison p.Thermal analysis of heat extraction boreholes [D]. Doctoral Thesis, University of Lund, Department of Mathematical Physics, Lund, Sweden, 1987.
[8] Sulatisky M T, Kamp G V D. Ground-source Heat Pumps in the Canadian Prairies [J]. ASHARE Trans, 1991, 17(4):374-385.
[9] Bose J E. Geothermal heat pumps introductory guide [M]. Oklahoma State University. Ground source heat pump publications, 1997.
[10] Mei V C, Baxter V D. Performance of a ground-coupled heat pump heat pump with multiple dissimilar U-tube coils in series [J].ASHARE Transactions, 1986, 92 part 2:22-25.
[11] Dobson M K. Modified analytical method for simulating cyclic operation of vertical U-tube ground-coupled heat pumps [J]. ASHARE Transactions, 1986, 92, part 2:22-25.
[12] Dobson M K .A Non-dimensional analysis of vertical–configuration ground-coupled heat pump start-up [J]. ASME-JSES-KSES International Solar Energy Conference, 1992, part 1, published by ASME, 367-375.
[13] Sanner B.Ground coupled heat pumps with seasonal cold storage[C]. Proceeding of the International Energy Agency Heat Pump Conference, Elsevier Science Pulishers, 1993,301.
[14] Rottmayer S P, Beckman W A, Mitchell J W.1997.Simulation of a single vertical U-tube ground heat exchanger in an Infinite Medium [A]. ASHRAE Transaction: Symposia papers [C]. Vol. 103, Part 2, BN-97-8-1: 651-658.
[15] Stephen P, Kavanaugh, Marita L Allan. 1999. Testing of thermally enhanced cement ground heat exchanger grouts [J].ASHRAE Trans, CH 99 2 2:446 449.
[16] Chiasson, Spitler J.D. A modeling approach to design of a ground-source heat pump bridge deck heating system[C]. Proceeding of the 5th International Symposium on snow removal and ice control technology, Roanoke,VA, 2000.
[17] Harvey M Sachs. 2000. Geology and the ground heat exchanger: what engineers need to know [J]. ASHRAE Trans, MN-00-21:421-433.
[18] James E.Bose, Marvin D.Smith, Jeffrey D.Spitler. Advances in ground source heat pump systms an international overview. 2002.
[19]于立强等.垂直埋管地源热泵系统实验研究[J].全国暖通空调制冷2000年学术年会论文集,2000.
[20]李家伟,廉乐明,于立强等.土壤源热泵的理论与实践研究[J].1995年暖通空调年会论文集,1995:408~410.
[21]高祖锟.用于供暖的土壤-水热泵系统[J].暖通空调,1995(4):9—12.
[22]张昆峰.土壤热源与热泵联结运行冬季工况的实验研究[J].华中理工大学学报,1996,24(1):23~26.
[23]刁乃仁,方肇洪.地埋管地源热泵技术[M].北京:高等教育出版社,2006.10.
[24]刁乃仁等.垂直U型管地热换热器的准三维传热模型[J].热能动力工程,2003,18(4):387~390
[25]曾和义等.地源热泵竖直埋管的有限长线热源模型[J].热能动力工程,2003,18(2):166~169.
[26]曾和义等.竖直埋管地热换热器钻孔内的热阻[J].煤气和热力,2003,23(3):134-138.
[27]曲云霞等.地源热泵系统防冻液的选择[J].节能与环保,2002,8:20-23.
[28]李元旦,魏先勋.水平埋地管换热器夏季瞬态工况的实验与数值模拟[J].湖南大学学报,1999(2).
[29]刘宪英等.浅埋竖直换热器地热源热泵夏季供冷实验研究[J].暖通空调,2000,30(4):1~4.
[30]刘宪英等.地源水-水热泵冬夏暖冷联供实验研究[J].制冷学报,2002(2):10-14.
[31]付祥钊等.两种地质气候条件对岩土换热器的影响[J].暖通空调,2002,32(3):106-109.
[32]丁勇,刘宪英等.地源热泵实验研究综述[M].现代空调(第三缉).北京.中国建筑工业出版社,2001:11~32.
[33]何雪冰,刘宪英.北方地区应用地源热泵应注意的问题[J].地温建筑技术,2004,98(2):85-86.
[34]刘宪英,丁勇.地源热泵地下埋管换热器系统形式及设计计算[J].供热制冷,2004(4):26-32.
[35]张旭.土壤源热泵的实验及相关基础理论研究[M].现代空调(第三缉).北京.中国建筑工业出版社,2001:75~86.
[36]张旭等.土壤及其与黄沙混合物导热系数的实验研究[J].全国暖通空调制冷2000学术年会论文集,2000:478~482.
[37]余延顺.土壤蓄冷与耦合热泵集成系统的蓄冷与释冷特性研究[D].哈尔滨工业大学博士论文,2004:19~46.
[2] D.A.Ball. Design method for GSHP [J].ASHARE Trans.DC-83-03:416~440.
[3] A.C.Crandall. House heating with earth heat pump [J]. Electrical World.1946, 126(19): 94-95.
[4] L.R.Ingersoll,O.J.vZoeble, A.C.Ingersoll.heat conduction with engineering[J]. geological and other applications,1954.
[5] Svec O.J.Potential of ground-coupled heat source system.International Journal of Energy Research [J]. 1987(4):571~581.
[6] Bose J E, Parker J D.Ground-coupled heat pump Re-search [J]. ASHRAE Trans, 83 (2):375—390.
[7] Eskison p.Thermal analysis of heat extraction boreholes [D]. Doctoral Thesis, University of Lund, Department of Mathematical Physics, Lund, Sweden, 1987.
[8] Sulatisky M T, Kamp G V D. Ground-source Heat Pumps in the Canadian Prairies [J]. ASHARE Trans, 1991, 17(4):374-385.
[9] Bose J E. Geothermal heat pumps introductory guide [M]. Oklahoma State University. Ground source heat pump publications, 1997.
[10] Mei V C, Baxter V D. Performance of a ground-coupled heat pump heat pump with multiple dissimilar U-tube coils in series [J].ASHARE Transactions, 1986, 92 part 2:22-25.
[11] Dobson M K. Modified analytical method for simulating cyclic operation of vertical U-tube ground-coupled heat pumps [J]. ASHARE Transactions, 1986, 92, part 2:22-25.
[12] Dobson M K .A Non-dimensional analysis of vertical–configuration ground-coupled heat pump start-up [J]. ASME-JSES-KSES International Solar Energy Conference, 1992, part 1, published by ASME, 367-375.
[13] Sanner B.Ground coupled heat pumps with seasonal cold storage[C]. Proceeding of the International Energy Agency Heat Pump Conference, Elsevier Science Pulishers, 1993,301.
[14] Rottmayer S P, Beckman W A, Mitchell J W.1997.Simulation of a single vertical U-tube ground heat exchanger in an Infinite Medium [A]. ASHRAE Transaction: Symposia papers [C]. Vol. 103, Part 2, BN-97-8-1: 651-658.
[15] Stephen P, Kavanaugh, Marita L Allan. 1999. Testing of thermally enhanced cement ground heat exchanger grouts [J].ASHRAE Trans, CH 99 2 2:446 449.
[16] Chiasson, Spitler J.D. A modeling approach to design of a ground-source heat pump bridge deck heating system[C]. Proceeding of the 5th International Symposium on snow removal and ice control technology, Roanoke,VA, 2000.
[17] Harvey M Sachs. 2000. Geology and the ground heat exchanger: what engineers need to know [J]. ASHRAE Trans, MN-00-21:421-433.
[18] James E.Bose, Marvin D.Smith, Jeffrey D.Spitler. Advances in ground source heat pump systms an international overview. 2002.
[19]于立强等.垂直埋管地源热泵系统实验研究[J].全国暖通空调制冷2000年学术年会论文集,2000.
[20]李家伟,廉乐明,于立强等.土壤源热泵的理论与实践研究[J].1995年暖通空调年会论文集,1995:408~410.
[21]高祖锟.用于供暖的土壤-水热泵系统[J].暖通空调,1995(4):9—12.
[22]张昆峰.土壤热源与热泵联结运行冬季工况的实验研究[J].华中理工大学学报,1996,24(1):23~26.
[23]刁乃仁,方肇洪.地埋管地源热泵技术[M].北京:高等教育出版社,2006.10.
[24]刁乃仁等.垂直U型管地热换热器的准三维传热模型[J].热能动力工程,2003,18(4):387~390
[25]曾和义等.地源热泵竖直埋管的有限长线热源模型[J].热能动力工程,2003,18(2):166~169.
[26]曾和义等.竖直埋管地热换热器钻孔内的热阻[J].煤气和热力,2003,23(3):134-138.
[27]曲云霞等.地源热泵系统防冻液的选择[J].节能与环保,2002,8:20-23.
[28]李元旦,魏先勋.水平埋地管换热器夏季瞬态工况的实验与数值模拟[J].湖南大学学报,1999(2).
[29]刘宪英等.浅埋竖直换热器地热源热泵夏季供冷实验研究[J].暖通空调,2000,30(4):1~4.
[30]刘宪英等.地源水-水热泵冬夏暖冷联供实验研究[J].制冷学报,2002(2):10-14.
[31]付祥钊等.两种地质气候条件对岩土换热器的影响[J].暖通空调,2002,32(3):106-109.
[32]丁勇,刘宪英等.地源热泵实验研究综述[M].现代空调(第三缉).北京.中国建筑工业出版社,2001:11~32.
[33]何雪冰,刘宪英.北方地区应用地源热泵应注意的问题[J].地温建筑技术,2004,98(2):85-86.
[34]刘宪英,丁勇.地源热泵地下埋管换热器系统形式及设计计算[J].供热制冷,2004(4):26-32.
[35]张旭.土壤源热泵的实验及相关基础理论研究[M].现代空调(第三缉).北京.中国建筑工业出版社,2001:75~86.
[36]张旭等.土壤及其与黄沙混合物导热系数的实验研究[J].全国暖通空调制冷2000学术年会论文集,2000:478~482.
[37]余延顺.土壤蓄冷与耦合热泵集成系统的蓄冷与释冷特性研究[D].哈尔滨工业大学博士论文,2004:19~46.