title: Heat transfer analysis of underground U-type heat exchanger of ground source heat pump system.
abstract: BACKGROUND
  Ground source heat pumps is a building energy conservation technique. The underground buried pipe heat exchanging system of a ground source heat pump (GSHP) is the basis for the normal operation of an entire heat pump system.
  
  
  METHODS
  Computational-fluid-dynamics (CFD) numerical simulation software, ANSYS-FLUENT17.0 have been performed the calculations under the working conditions of a continuous and intermittent operation over 7 days on a GSHP with a single-well, single-U and double-U heat exchanger and the impact of single-U and double-U buried heat pipes on the surrounding rock-soil temperature field and the impact of intermittent operation and continuous operation on the outlet water temperature.
  
  
  CONCLUSIONS
  The influence on the rock-soil temperature is approximately 13 % higher for the double-U heat exchanger than that of the single-U heat exchanger. The extracted energy of the intermittent operation is 36.44 kw·h higher than that of the continuous mode, although the running time is lower than that of continuous mode, over the course of 7 days. The thermal interference loss and quantity of heat exchanged for unit well depths at steady-state condition of 2.5 De, 3 De, 4 De, 4.5 De, 5 De, 5.5 De and 6 De of sidetube spacing are detailed in this work. The simulation results of seven working conditions are compared. It is recommended that the side-tube spacing of double-U underground pipes shall be greater than or equal to five times of outer diameter (borehole diameter: 180 mm).
authors.affiliation: School of Civil Engineering and Architecture, Southwest Petroleum University, Chengdu, 610500 China.
authors.forename: Guihong
authors.initials: G
authors.lastname: Pei
authors.affiliation: School of Civil Engineering and Architecture, Southwest Petroleum University, Chengdu, 610500 China.
authors.forename: Liyin
authors.identifier: 0000-0002-9165-0708
authors.initials: L
authors.lastname: Zhang
keywords: Heat transfer rate; Numerical simulation; Thermal interference; U-type ground tube