Abstract

A Case Study documenting the development of a groundwater fed district heat network in Colchester, UK, is presented. The performance of an open loop groundwater heating and cooling system (also known as a Ground Source Heat Pump, GSHP) is a function of the performance of individual boreholes and interactions between the boreholes. When performance does not meet its design capacity or decreases with time, various measures can be undertaken to improve either the performance of individual wells or the performance of the system as a whole.

Output from the first exploration borehole was less than expected, placing the business case for the development in jeopardy. Consequently, refinements to the remainder of the drilling programme were implemented including three to improve the performance of individual wells and two to improve performance of the system in its’ entirety. Results of these refinements are presented and may be used to inform the design of new open loop groundwater heat pump systems and/or rehabilitation of existing systems that have experienced diminished performance.

Yields from three wells drilled using reverse circulation method were more than double those drilled with direct water flush method. A significant improvement in the performance of abstraction wells due to reinjection was observed. Specific capacity in abstraction wells increased by approximately 40% due to reinjection, where the distance between abstraction and reinjection locations was 535m to 717m. Allowing an excess pressure of up to 0.2MPa in the reinjection boreholes meant that reinjection could be achieved with fewer wells.

Outputs from abstraction wells were not increased by extending the depth of boreholes from 135m to 200m or implementing additional acid treatments.

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