地热换热器传热模型和设计计算的进一步研究
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摘要
目前,国家正在全力建设环境友好型、资源节约型的社会,节能减排成为一项重要的举措,地源热泵这种环保节能的新型空调系统得到了国家的大力扶持。地埋管地源热泵系统在中国的大规模推广应用受到三个因素的制约,即初投资较高、地埋管的占地面积以及系统全年冷热负荷不平衡的问题。本文就针对初投资较高提出了两项措施,一是在适当的条件下采用水平螺旋埋管换热器代替竖直埋管换热器,二是在“地热之星”计算软件的基础上进一步优化地热换热器的设计计算方法。
首先,提出了适合工程设计计算的水平螺旋埋管换热器的传热模型。该模型以无限大介质中的一维非稳态传热为基础,同时考虑水平埋管密度的影响以及长期平均负荷和短期脉冲负荷的不同作用。根据该传热模型编写应用软件,使用者输入参数即可计算所需要的埋管容量。在此基础上讨论了主要的设计参数,如单位面积埋管量和土壤的热物性对水平螺旋埋管换热器的影响。结合一工程实例,计算了在一定的埋管布置形式下埋管的设计容量,并针对所需要的占地面积、埋管长度、系统的初投资情况和竖直埋管换热器进行了比较。
其次,改进“地热之星”计算软件中对多钻孔换热器的设计计算方法,提高设计和模拟计算的准确性。原有的方法采用最不利钻孔的温升作为整个换热器的温升来计算,对于大型的地埋管换热器可能造成较大的偏差。本文提出了采用代表性钻孔代替最不利钻孔来进行设计计算；提出均方差系数的概念,讨论分析了多个钻孔换热器各个钻孔之间的不平衡性；计算了最不利钻孔的温升与换热器平均温升的相对差值,阐明了寻找代表性钻孔的必要性。通过计算多种不同矩阵型布置的地埋管换热器中各个钻孔的温升,找到最有代表性钻孔的位置,并总结出一定的规律,以推广应用于其他更一般的情况。
最后,分析讨论了地下水渗流对地埋管换热器传热的影响。当地下水流向与钻孔矩阵布置不平行时,通过实现钻孔区域温度场叠加,绘制了已知埋管布置形式在一定流向下的等温线族,并将其做成随时间变化的动画。然后,主要讨论了渗流流向、渗流流速、钻孔间距、钻孔的排列形式对换热器平均温升和钻孔不平衡性的影响。同时,讨论了变负荷工况下,有地下水渗流的换热器的温升,以月为时间间隔,计算了钻孔壁和循环液的月平均温度,分析比较了不同的流速对钻孔壁和循环液月平均温度的影响,并和无渗流情况进行了比较。
Nowadays, energy conservation becomes an important measure to achieve the environment-friendly and resource-saving society. The Ground Source Heat Pump (GSHP) systems, as an energy conservation and environment friendly technology, get more and more attention. Large-scale popularization and application of the GSHP systems in China are restricted mainly by three factors, which are their higher initial cost, land area requirement for installation of the Geothermal Heat Exchanger (GHE) as ell as concerns about annual heating and cooling load imbalance in the GHEs. This article proposes two measures to reduce the high initial investment of the GSHP systems. Firstly, the horizontal slinky ground heat exchanger is considered to replace the vertical borehole heat exchanger in appropriate situations. Secondly, some design procedures used in the "Geostar" software for design and simulation of the GHEs are improved so as to enhance its accuracy.
Firstly, this article proposes a heat transfer model suitable for engineering design of the horizontal slinky GHEs. The thermal analyses are based on the one-dimensional transient heat conduction solution in an infinite medium while the effects are considered of the density of pipe disposition and variation in the loads. Key factors which influence the performance of the slinky GHE are discussed such as the thermal properties of the soil and the pipe disposition density. An example of the slinky GHE design is also presented, which is then compared with the vertical borehole GHE.
Secondly, in view of the deficiencies in previous method, this article proposes a new method for thermal analysis of the GHEs with multiple boreholes. That is a representative borehole is selected to replace the least-favorable borehole to determine the temperature rise of the GHE. The concept of standard deviation coefficient is proposed to analyze the thermal imbalance among the boreholes. The radio of highest temperature rise and mean temperature rise is calculated, and the result indicates that it is necessary to find location of the representative borehole. In order to achieve this goal, the temperature rises of every borehole in different configurations of borehole matrixes are calculated, and conclusions on the location of the representative borehole are obtained which may be applied in other configurations.
Finally, the impact of groundwater flow on performance of geothermal heat exchangers in ground source heat pump systems is analyzed based on an analytical solution of the advection around a line source in porous medium. The temperature at any location in a field with multiple boreholes may be obtained by means of the superimposition principle. The temperature response in an 18-borehole GHE with groundwater advection is computed in detail and shown in an animation. Different parameters which influence the temperature and unbalance of the GHE are discussed such as the groundwater flow direction, velocity, the space among boreholes and boreholes configuration. The temperature rise of the GHE is also computed while variation in the load is considered. The impact of groundwater flow is also studied in comparison between results obtained from modes with or without groundwater advection considered.
首先,提出了适合工程设计计算的水平螺旋埋管换热器的传热模型。该模型以无限大介质中的一维非稳态传热为基础,同时考虑水平埋管密度的影响以及长期平均负荷和短期脉冲负荷的不同作用。根据该传热模型编写应用软件,使用者输入参数即可计算所需要的埋管容量。在此基础上讨论了主要的设计参数,如单位面积埋管量和土壤的热物性对水平螺旋埋管换热器的影响。结合一工程实例,计算了在一定的埋管布置形式下埋管的设计容量,并针对所需要的占地面积、埋管长度、系统的初投资情况和竖直埋管换热器进行了比较。
其次,改进“地热之星”计算软件中对多钻孔换热器的设计计算方法,提高设计和模拟计算的准确性。原有的方法采用最不利钻孔的温升作为整个换热器的温升来计算,对于大型的地埋管换热器可能造成较大的偏差。本文提出了采用代表性钻孔代替最不利钻孔来进行设计计算；提出均方差系数的概念,讨论分析了多个钻孔换热器各个钻孔之间的不平衡性；计算了最不利钻孔的温升与换热器平均温升的相对差值,阐明了寻找代表性钻孔的必要性。通过计算多种不同矩阵型布置的地埋管换热器中各个钻孔的温升,找到最有代表性钻孔的位置,并总结出一定的规律,以推广应用于其他更一般的情况。
最后,分析讨论了地下水渗流对地埋管换热器传热的影响。当地下水流向与钻孔矩阵布置不平行时,通过实现钻孔区域温度场叠加,绘制了已知埋管布置形式在一定流向下的等温线族,并将其做成随时间变化的动画。然后,主要讨论了渗流流向、渗流流速、钻孔间距、钻孔的排列形式对换热器平均温升和钻孔不平衡性的影响。同时,讨论了变负荷工况下,有地下水渗流的换热器的温升,以月为时间间隔,计算了钻孔壁和循环液的月平均温度,分析比较了不同的流速对钻孔壁和循环液月平均温度的影响,并和无渗流情况进行了比较。
Nowadays, energy conservation becomes an important measure to achieve the environment-friendly and resource-saving society. The Ground Source Heat Pump (GSHP) systems, as an energy conservation and environment friendly technology, get more and more attention. Large-scale popularization and application of the GSHP systems in China are restricted mainly by three factors, which are their higher initial cost, land area requirement for installation of the Geothermal Heat Exchanger (GHE) as ell as concerns about annual heating and cooling load imbalance in the GHEs. This article proposes two measures to reduce the high initial investment of the GSHP systems. Firstly, the horizontal slinky ground heat exchanger is considered to replace the vertical borehole heat exchanger in appropriate situations. Secondly, some design procedures used in the "Geostar" software for design and simulation of the GHEs are improved so as to enhance its accuracy.
Firstly, this article proposes a heat transfer model suitable for engineering design of the horizontal slinky GHEs. The thermal analyses are based on the one-dimensional transient heat conduction solution in an infinite medium while the effects are considered of the density of pipe disposition and variation in the loads. Key factors which influence the performance of the slinky GHE are discussed such as the thermal properties of the soil and the pipe disposition density. An example of the slinky GHE design is also presented, which is then compared with the vertical borehole GHE.
Secondly, in view of the deficiencies in previous method, this article proposes a new method for thermal analysis of the GHEs with multiple boreholes. That is a representative borehole is selected to replace the least-favorable borehole to determine the temperature rise of the GHE. The concept of standard deviation coefficient is proposed to analyze the thermal imbalance among the boreholes. The radio of highest temperature rise and mean temperature rise is calculated, and the result indicates that it is necessary to find location of the representative borehole. In order to achieve this goal, the temperature rises of every borehole in different configurations of borehole matrixes are calculated, and conclusions on the location of the representative borehole are obtained which may be applied in other configurations.
Finally, the impact of groundwater flow on performance of geothermal heat exchangers in ground source heat pump systems is analyzed based on an analytical solution of the advection around a line source in porous medium. The temperature at any location in a field with multiple boreholes may be obtained by means of the superimposition principle. The temperature response in an 18-borehole GHE with groundwater advection is computed in detail and shown in an animation. Different parameters which influence the temperature and unbalance of the GHE are discussed such as the groundwater flow direction, velocity, the space among boreholes and boreholes configuration. The temperature rise of the GHE is also computed while variation in the load is considered. The impact of groundwater flow is also studied in comparison between results obtained from modes with or without groundwater advection considered.
引文
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[7]Domald Kroeker, J.R.C.C., Chewing.Costs of operating the heat pump in the equitable building[J]. ASHRAE Transactions,1954.60:p.157-176.
[8]Knipe, E.C.R., K.D, Corrosion in low temperature geothermal application[J]. ASHRAE Transactions,1985. 91(2B-1):p.81-91.
[9]Bernier, M.A., Closed-loop ground-coupled heat pump systems[J]. ASHRAE Journal,2006(9):p.13-19.
[10]徐伟译.地源热泵工程技术指南.2001.
[11]GEOTHERMAL ENERGY,2002.NO.4
[12]ASHRAE.2008 ASHRAE Handbook—HVAC Systems and Equipment [M]. Atlanta:American Society of Heating, Refrigerating and Air-Conditioning,2008.
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[17]孙纯武,张素云,刘宪英.水平埋管换热器地热源热泵实验研究及传热模型[J].重庆建筑大学学报.2001：23(6)：p.49-55.
[18]郑祖义.热泵空调系统的设计与创新.华中理工大学出版社.1994
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[20]Chiasson, A.C., S.J. Rees, J.D. Spitler.2000. A Preliminary Assessment Of The Effects Of Ground-Water Flow On Closed-Loop Ground-Source Heat Pump Systems. ASHRAE Transactions.106(1):380-393.
[21]刁乃仁,李琴云,方肇洪.有渗流时地热换热器温度响应的解析解[J].山东建筑工程学院学报.2003:18
[22]Diao N R, Li Q Y and Fang Z H,, Heat Transfer in Ground Heat Exchangers with Groundwater Advection, International Journal of Thermal Sciences,43(12):1203-1211,2004
[23]魏晋.地下水流动对埋地换热器影响的模拟研究[J].专题报告
[24]谭显辉,丁力行.影响地下环路热交换器设计的地下水流动的理论分析[J].制冷空调.2003：(5)14-16
[25]范蕊,马最良.地下水流动对地下管群换热器传热的影响分析[J].太阳能学报.2006：11
[26]范蕊,马最良.热渗耦合作用下的地下埋管换热器传热分析[J].暖通空调.2006：36(2)
[27]李素芬,王金香.热渗耦合作用下U型埋管换热器的数值模拟[J].热科学与技术.2006：5(4)
[28]姚杨,李斌.热渗共同作用下地下换热器的初步试验研究[J].暖通空调.2006：36
[29]林俊,胡映宁.渗流对富水土壤传热特性影响的实验模拟研究[J].暖通空调.2006：37(7)
[30]Cane R L D, Forgas D A. Modeling of GSHP performance[G]//ASHRAE Trans.1991:97(1):909-925
[31]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.2005
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[2]GB50189-2005公共建筑节能设计标准.[S].北京：中国建筑工业出版社.2005.
[3]徐伟.中国地源热泵发展研究报告2008[M].北京：中国建筑工业出版社.2008.
[4]刁乃仁,方肇洪.地源热泵—建筑节能新技术[J].建筑热能通风空调.2004.23(3)：p.18-23.
[5]GB50366-2005.地源热泵工程技术规范[S].北京：中国建筑工业出版社.2005.
[6]Domald Kroeker, J.R.C.C., Heat pump in an office building[J]. ASHRAE Transactions,1948.54:p. 221-238.
[7]Domald Kroeker, J.R.C.C., Chewing.Costs of operating the heat pump in the equitable building[J]. ASHRAE Transactions,1954.60:p.157-176.
[8]Knipe, E.C.R., K.D, Corrosion in low temperature geothermal application[J]. ASHRAE Transactions,1985. 91(2B-1):p.81-91.
[9]Bernier, M.A., Closed-loop ground-coupled heat pump systems[J]. ASHRAE Journal,2006(9):p.13-19.
[10]徐伟译.地源热泵工程技术指南.2001.
[11]GEOTHERMAL ENERGY,2002.NO.4
[12]ASHRAE.2008 ASHRAE Handbook—HVAC Systems and Equipment [M]. Atlanta:American Society of Heating, Refrigerating and Air-Conditioning,2008.
[13]Hayes Jakes. New Twist of Heat Pumps [J]. Popular Science.240(2):69-72,1992.
[14]李家伟等.土壤源热泵的理论与实践研究[A].1995年暖通空调年会资料集[C].1995：408-410.
[15]张昆峰等.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.
[16]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.湖南大学学报.1999：(2)：58-63.
[17]孙纯武,张素云,刘宪英.水平埋管换热器地热源热泵实验研究及传热模型[J].重庆建筑大学学报.2001：23(6)：p.49-55.
[18]郑祖义.热泵空调系统的设计与创新.华中理工大学出版社.1994
[19]Eskilson P. Thermal analysis of heat extraction boreholes[D].Doctoral Thesis,University of Lund,Department of mathematical Physics,Lund,Sweden,1987.
[20]Chiasson, A.C., S.J. Rees, J.D. Spitler.2000. A Preliminary Assessment Of The Effects Of Ground-Water Flow On Closed-Loop Ground-Source Heat Pump Systems. ASHRAE Transactions.106(1):380-393.
[21]刁乃仁,李琴云,方肇洪.有渗流时地热换热器温度响应的解析解[J].山东建筑工程学院学报.2003:18
[22]Diao N R, Li Q Y and Fang Z H,, Heat Transfer in Ground Heat Exchangers with Groundwater Advection, International Journal of Thermal Sciences,43(12):1203-1211,2004
[23]魏晋.地下水流动对埋地换热器影响的模拟研究[J].专题报告
[24]谭显辉,丁力行.影响地下环路热交换器设计的地下水流动的理论分析[J].制冷空调.2003：(5)14-16
[25]范蕊,马最良.地下水流动对地下管群换热器传热的影响分析[J].太阳能学报.2006：11
[26]范蕊,马最良.热渗耦合作用下的地下埋管换热器传热分析[J].暖通空调.2006：36(2)
[27]李素芬,王金香.热渗耦合作用下U型埋管换热器的数值模拟[J].热科学与技术.2006：5(4)
[28]姚杨,李斌.热渗共同作用下地下换热器的初步试验研究[J].暖通空调.2006：36
[29]林俊,胡映宁.渗流对富水土壤传热特性影响的实验模拟研究[J].暖通空调.2006：37(7)
[30]Cane R L D, Forgas D A. Modeling of GSHP performance[G]//ASHRAE Trans.1991:97(1):909-925
[31]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.2005
[32]章熙民,任泽霈,梅飞呜.传热学[M].高等教育出版社.1998：162-179
[33]贺平,孙刚.供热工程[M].中国建筑工业出版社第三版.2005.
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