渗流对地源热泵土壤温度场及换热量的影响
|
摘要
针对地源热泵长期运行时土壤热失衡导致热泵效率降低的问题,探究地下水渗流(以下简称渗流)以及热泵周期性运行对周围土壤温度场与热泵效率的影响。建立长宽均为40 m,深度为140 m的土壤区域,在土壤区域中打9个120 m深的钻孔,钻孔中心间距为5 m,且按照3×3的方阵排布,在钻孔中埋入深度为120 m的双U型地埋管。基于Feflow数值模拟软件的三维瞬态热渗耦合传热模型,通过土壤热响应实验验证,确定Feflow软件仿真模拟得出的结果准确可靠。在此基础上,分析不存在渗流、存在渗流、改变渗流速度(1×10~(-4)m/s、2. 4×10~(-6)m/s、2. 1×10~(-7)m/s)以及改变渗流层厚度(5 m、10 m、15 m)对地源热泵在供暖工况下120 d连续运行带来的影响,分析地源热泵系统按照1 a中供暖运行120 d,间歇90 d,制冷运行90 d,再间歇60 d的周期性运行模式,运行10 a后对地下土壤温度场以及地埋管单位管长换热量的影响。结果表明:存在渗流且渗流速度大于1×10-7m/s数量级时有利于地埋管周围土壤温度恢复;相对于无渗流条件,渗流层位于38～42 m且渗流速度为2. 4×10~(-6)m/s时,供暖工况下连续运行120 d后的地埋管单位管长换热量提高54%;渗流速度对地埋管单位管长换热量影响明显,渗流速度越大,地埋管单位管长换热量越多;渗流速度不变时,地埋管单位管长换热量随着渗流层厚度的增加而增加,且渗流层厚度每增加5 m,在供暖工况连续运行120 d后,地埋管单位管长换热量增加2 W/m;周期性运行模式下,有渗流与无渗流条件下土壤均没有明显的冷、热量积累,但有渗流条件更利于提高地埋管单位管长换热量。文末附有有渗流与无渗流工况下土壤温度场动态展示的视频,可扫二维码观看。
In view of the problem that the soil heat imbalance causes the heat pump efficiency to decrease during the long-term operation of the ground source heat pump,the effects of groundwater seepage( hereinafter referred to as seepage) and the periodic operation of the heat pump on the surrounding soil temperature field and heat pump efficiency are investigated. A soil area with length and width of 40 m and depth of 140 m is established. Nine holes of 120 m depth with a center spacing of 5 m were drilled in the soil area,and they were arranged according to the 3 ×3 square array,double U-shaped buried pipes with a depth of 120 m were buried in the borehole. Based on the three-dimensional transient thermal-permeability coupled heat transfer model of the Feflow numerical simulation software,it is verified by the soil thermal response experiment that the results obtained by the Feflow software simulation are accurate and reliable.On this basis,the effects of absence of seepage,presence of seepage,change of seepage velocity( 1 × 10~(-4)m/s,2. 4 × 10~(-6) m/s and 2. 1 × 10~(-7) m/s) and change of thickness of the seepage layer( 5 m,10 m and 15 m) on 120 days continuous operation of ground source heat pump under heating conditions are analyzed. According to the periodic operation mode of heating for 120 days, intermittent operation for 90 days,refrigeration operation for 90 days and intermittent operation for 60 days,the influence of ground source heat pump system on the temperature field of underground soil and the heat transfer per unit length of buried pipe is analyzed after 10 years of operation.The results show that the presence of seepage and the seepage velocity of greater than 1 × 10~(-7) m/s are beneficial to recover the soil temperature around the buried pipe. Compared with the non-seepage condition,when the seepage layer is located at 38 to 42 m and the seepage velocity is 2. 4 × 10~(-6) m/s,the heat exchange capacity per unit length of the buried pipes after continuous operation for 120 days under heating conditions is increased by 54%. The seepage velocity has a significant influence on the heat exchange capacity per unit length of the buried pipes,the greater the seepage velocity,the more the heat exchange capacity per unit length of the buried pipes. When the seepage velocity is constant,the heat exchange capacity per unit length of the buried pipes increases with the increase of the thickness of the seepage layer,and for every 5 m increase in the thickness of the seepage layer,after 120 days of continuous operation under the heating condition,the heat exchange capacity per unit length of the buried pipes increases by 2 W/m. Under the periodic operation mode,there is no obvious cold and heat accumulation in the soil under the condition of seepage and non-seepage,but the seepage condition is more conducive to increase the heat exchange capacity per unit length of the buried pipes. At the end of the paper,there is a video showing the dynamic display of soil temperature field under seepage and non-seepage conditions,which can be watched by scanning QR code.
In view of the problem that the soil heat imbalance causes the heat pump efficiency to decrease during the long-term operation of the ground source heat pump,the effects of groundwater seepage( hereinafter referred to as seepage) and the periodic operation of the heat pump on the surrounding soil temperature field and heat pump efficiency are investigated. A soil area with length and width of 40 m and depth of 140 m is established. Nine holes of 120 m depth with a center spacing of 5 m were drilled in the soil area,and they were arranged according to the 3 ×3 square array,double U-shaped buried pipes with a depth of 120 m were buried in the borehole. Based on the three-dimensional transient thermal-permeability coupled heat transfer model of the Feflow numerical simulation software,it is verified by the soil thermal response experiment that the results obtained by the Feflow software simulation are accurate and reliable.On this basis,the effects of absence of seepage,presence of seepage,change of seepage velocity( 1 × 10~(-4)m/s,2. 4 × 10~(-6) m/s and 2. 1 × 10~(-7) m/s) and change of thickness of the seepage layer( 5 m,10 m and 15 m) on 120 days continuous operation of ground source heat pump under heating conditions are analyzed. According to the periodic operation mode of heating for 120 days, intermittent operation for 90 days,refrigeration operation for 90 days and intermittent operation for 60 days,the influence of ground source heat pump system on the temperature field of underground soil and the heat transfer per unit length of buried pipe is analyzed after 10 years of operation.The results show that the presence of seepage and the seepage velocity of greater than 1 × 10~(-7) m/s are beneficial to recover the soil temperature around the buried pipe. Compared with the non-seepage condition,when the seepage layer is located at 38 to 42 m and the seepage velocity is 2. 4 × 10~(-6) m/s,the heat exchange capacity per unit length of the buried pipes after continuous operation for 120 days under heating conditions is increased by 54%. The seepage velocity has a significant influence on the heat exchange capacity per unit length of the buried pipes,the greater the seepage velocity,the more the heat exchange capacity per unit length of the buried pipes. When the seepage velocity is constant,the heat exchange capacity per unit length of the buried pipes increases with the increase of the thickness of the seepage layer,and for every 5 m increase in the thickness of the seepage layer,after 120 days of continuous operation under the heating condition,the heat exchange capacity per unit length of the buried pipes increases by 2 W/m. Under the periodic operation mode,there is no obvious cold and heat accumulation in the soil under the condition of seepage and non-seepage,but the seepage condition is more conducive to increase the heat exchange capacity per unit length of the buried pipes. At the end of the paper,there is a video showing the dynamic display of soil temperature field under seepage and non-seepage conditions,which can be watched by scanning QR code.
引文
[1]马宏权,龙惟定.地埋管地源热泵系统的热平衡[J].暖通空调,2009,39(1):102-106.
[2]王金香,李素芬,尚妍,等.地下含湿岩土热渗耦合模型及换热埋管周围土壤温度场数值模拟[J].太阳能学报,2008(7):837-842.
[3]范蕊,马最良.热渗耦合作用下地下埋管换热器的传热分析[J].暖通空调,2006(2):6-10,82.
[4]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(3):1-5.
[5]杨卫波,施明恒.基于线热源理论的垂直U型埋管换热器传热模型的研究[J].太阳能学报,2007(5):482-488.
[6]范蕊.土壤蓄冷与热泵集成系统地埋管热渗耦合理论与实验研究(博士学位论文)[D].哈尔滨:哈尔滨工业大学,2006:23-30.
[7]张轶星,杜震宇.土壤源热泵竖直埋管换热器钻孔外传热模型综述[J].山西能源与节能,2010(1):62-65,68.
[8]涂爱民,董华,杨卫波,等.基于圆柱源理论模型的U型埋管换热器的模拟研究[J].太阳能学报,2006(3):259-264.
[9]赵军,张志英,刘九龙,等.人工流场影响下地埋管管群换热的模拟研究[J].天津大学学报(自然科学与工程技术版),2016,49(8):835-840.
[10] DIERSCH H-J G. Feflow finite element modeling of flow,mass and heat transport in porous and fractured media[M]. Berlin:DHI-WASY Gmb H,2013:69-80.
[2]王金香,李素芬,尚妍,等.地下含湿岩土热渗耦合模型及换热埋管周围土壤温度场数值模拟[J].太阳能学报,2008(7):837-842.
[3]范蕊,马最良.热渗耦合作用下地下埋管换热器的传热分析[J].暖通空调,2006(2):6-10,82.
[4]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(3):1-5.
[5]杨卫波,施明恒.基于线热源理论的垂直U型埋管换热器传热模型的研究[J].太阳能学报,2007(5):482-488.
[6]范蕊.土壤蓄冷与热泵集成系统地埋管热渗耦合理论与实验研究(博士学位论文)[D].哈尔滨:哈尔滨工业大学,2006:23-30.
[7]张轶星,杜震宇.土壤源热泵竖直埋管换热器钻孔外传热模型综述[J].山西能源与节能,2010(1):62-65,68.
[8]涂爱民,董华,杨卫波,等.基于圆柱源理论模型的U型埋管换热器的模拟研究[J].太阳能学报,2006(3):259-264.
[9]赵军,张志英,刘九龙,等.人工流场影响下地埋管管群换热的模拟研究[J].天津大学学报(自然科学与工程技术版),2016,49(8):835-840.
[10] DIERSCH H-J G. Feflow finite element modeling of flow,mass and heat transport in porous and fractured media[M]. Berlin:DHI-WASY Gmb H,2013:69-80.