Construction of transfer functions for standing column wells operating with bleed
Standing column wells (SCW) offer a cost-effective and space-efficient alternative to conventional closed-loop ground heat exchangers, making them particularly suited for urban environments and retrofit applications. By recirculating groundwater within a deep uncased borehole and discharging a controlled fraction during peak loads, a process known as “bleed”, SCWs take advantage of advective heat transfer to enhance the system’s performance. However, the design of SCW systems remains challenging due to the absence of simulation tools capable of simultaneously accounting for both hydraulic and thermal interactions between SCWs operating with bleed. This study presents a modelling framework for constructing transfer functions for fields of SCWs connected in parallel. The method combines numerically simulated thermal responses of an individual borehole and pairwise thermal interactions between SCWs with the successive flux algorithm, enforcing uniform inlet temperature boundary conditions. When bleed is active, all SCWs in the ground heat exchanger are explicitly modelled to accurately reproduce the groundwater velocity field and its influence on advective heat transfer. The method is verified against a large-scale 3D finite element model representing six SCWs located in a stratified and fractured aquifer and operating under different flow rate scenarios. Results show strong agreement with the reference simulations when the groundwater velocity field of the complete ground heat exchanger is represented. In contrast, modelling only two SCWs at a time yields accurate results solely in the absence of bleed.