Abstract
BackgroundGround 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.MethodsComputational-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.ConclusionsThe 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).
Highlights
Ground source heat pumps is a building energy conservation technique
The geothermal heat exchangers (GHEs) are the basis for the normal operation of heat pump systems, and the thermal characteristics significantly depend on the rock-soil type and the longitudinal temperature distribution
Based on a CFD numerical simulation method, we analyzed the influence of a GHEs system of ground source heat pump (GSHP)’s on the temperature of rock-soil under the working conditions of heat removal and Studies were carried out on three aspects of performance, such as outlet fluid temperature variation of the double-U buried pipe under continuous operation, intermittent operation and thermal interference arising from different branch pipe spacing
Summary
Ground source heat pumps is a building energy conservation technique. As a building energy conservation technique, ground source heat pumps (GSHP) have attracted considerable attention on the basis of rising energy prices and urgent environmental pressure caused by excessive energy consumption. The geothermal heat exchangers (GHEs) are the basis for the normal operation of heat pump systems, and the thermal characteristics significantly depend on the rock-soil type and the longitudinal temperature distribution. Shang (2011) predicted the rock-soil temperature variation between the operation and recovery period of GSHPs by establishing a 3D model of a single-well, single-U heat exchanger combined with multi-aperture theory. Choi (2011) applied a CFD numerical simulation method to analyzing the influential factors which contains shank spacing, borehole depth, flow velocity and the differential temperature of the inlet/outlet on the heat transfer rate of the GSHP. To facilitate the research, it is assumed that the soil is homogeneous
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