An extended two-dimensional borehole heat exchanger model for simulation of short and medium timescale thermal response

Abstract

Common approaches to the simulation of Borehole Heat Exchangers (BHEs) assume heat transfer in circulating fluid and grout to be in a quasi-steady state and ignore fluctuations in fluid temperature due to transport of the fluid around the U-tube loop. Such effects have been shown to have an impact on peak temperatures and hence operation of heat pumps systems when short time scales are considered. A model has been developed that combines a two-dimensional numerical model and models of the pipe loop components. A novel heat exchanger analogy is employed to calculate the heat exchanger outlet temperatures such that iterative procedures can be avoided and numerical stability is unconditional. These approaches result in a model that is computationally efficient and captures much of the short timescale dynamic effects represented in fully three-dimensional models. This is demonstrated by comparison with experimental data and by comparing two and three-dimensional model behaviour in the frequency domain. Predicted monthly outlet temperatures and heat transfer rates are furthermore shown to be in close agreement with experimental values and in good agreement with existing borehole heat exchanger models. The model is computationally efficient enough to allow use in routine analysis and design tasks.

Dynamic simulation of steam generation system in solar tower power plant

“…One is three-dimensional numerical model with high spatial resolution, such as the finite volume method [22]. The other is the analytical model with low spatial resolution, such as the LPM [8,23,24]. In order to improve the economic performance and optimize the heat exchanger design, a threedimensional model is applied [25][26][27].…”

FY20 Third Milestone Report for Advanced Techno-Economic Modeling for Geothermal Heat Pump Applications in Residential, Commercial, and Industry Buildings

“…(3.6) Equation 3.5 assumes that the simple mean fluid temperature is an adequate approximation to the true mean fluid temperature. More sophisticated models are available (Rees 2015, Beier et al 2018, but this sophistication is mainly important at short times, below an hour, when transit time effects are predominant. A comparison of experimental measurements presented by Beier et al (2018) to a conventional borehole model using the simple mean fluid temperature approximation gives quite good results over a wide range of flow rates as long as the thermal short-circuiting is accounted for.…”

Modelling HVAC and renewable energy plant and control

“…In the type of quasi-3D nodal models described above, fluid transport up and down the borehole is accounted for explicitly and the physical effects are captured to some degree. Otherwise some representation of the effects can be made by coupling the heat exchanger model with discretized pipe models (Rees, 2015).…”