Abstract
The transient temperature response is of great importance for evaluating the thermal capacity of ground heat exchangers (GHE). Based on the composition line source theory and superposition principle, we have developed a novel analytical model in Laplace space for calculating the temperature transient response. In comparison to the existing models, this proposed model can account for the fluid thermal storage effect and heat rate difference between the two legs of the single U-tube. With the aid of this proposed model, we conduct a thorough sensitivity analysis to investigate the effects of different influencing factors on the thermal transient response. The calculated results show that fluid thermal storage and the rate difference can significantly influence the thermal response during the early studied period. Therefore, the effect of fluid thermal storage should not be neglected when the early-time thermal response is investigated. The thermal interference between the two legs will reduce the heat capacity of GHEs. A large distance between these two legs can be favorable for practical use.
Highlights
Heat transfer models have been used for thermal performance analysis for the ground heat exchangers (GHE), such as in-situ test, borehole length calculation, ground heat pump management [1,2,3]
GHEs is to decompose the thermal process into a steady part and an unsteady part [1,2]
The heat mainly influences the space inside the borehole and the effect of fluid thermal storage can cause a lag in temperature change
Summary
Heat transfer models have been used for thermal performance analysis for the ground heat exchangers (GHE), such as in-situ test, borehole length calculation, ground heat pump management [1,2,3]. In the traditional model Equation (1), the heat transfer inside the borehole is assumed to be steady which can be oversimplified, these methods cannot is assumed to be steady which can be oversimplified, these methods cannot provide sufficiently accurate results for characterizing the thermal behavior at the early period This will lead to the fact that when one conducts the thermal response test analysis using the line source theory, the simulated results cannot agree well with the measured data of the early period. Based on the equivalent diameter approach, Lamarche and Beauchamp [17] developed an analytical solution for short-time temperature analysis of geothermal vertical boreholes Their model [15,16,17] considered fluid thermal storage capacity and the thermal properties of the grout. We attempted to develop a 2-D composite line source model considering the thermal storage effect of fluid and the heat rate difference between the two legs
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