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Tools for automated circuiting of large vertical borehole fields – a preliminary investigation

West, Timothy N.
Spitler, Jeffrey D.
Recent developments in automated vertical borehole ground heat exchanger design tools can reduce the required engineering time and improve the resulting ground heat exchanger designs by taking full advantage of available property. However, current practice when designing irregularly shaped borefields is to minimize the total drilling rather than the installation cost or life cycle cost of the system. Total drilling can serve as a proxy for total installation cost, but neglecting the cost of horizontal piping and trenching may be misleading in some circumstances. This paper describes the initial development of a tool to estimate the installation cost of a ground heat exchanger corresponding to an arbitrary borefield. To complete this task, the design tool automatically determines the trenching network and pipe network required to connect the boreholes and heat pump of the ground heat exchanger, sizes the pipes in the pipe system to meet given hydraulic constraints, and then estimates the installation cost from the resulting trench and pipe network. The trench and pipe network synthesis consists of a hierarchical k-means clustering algorithm which groups boreholes into individual vaults then circuits. Circuits are separated into groups so that their pipe systems can be routed through a handful of vaults. From this grouping, a trenching network is created with a pathing algorithm, shortest path algorithm, and minimum spanning tree algorithm. Together, these algorithms form a trench network that can stay within irregularly shaped property boundaries, avoid user-defined obstructions, and produce a trench network without a large surplus of extra trenching. The pipe network is created with the trench network, the borehole grouping, and user-given network type (i.e., direct return, reverse return, etc.).