Digging deeper to unearth potential for large scale heat pumps in Dumfries.

An aquifer is a body of rock or sediment that holds groundwater deep below the surface. At these depths water can be found at a higher temperature than that which can be found in our rivers or lakes. Natural Power's Geotechnical Team investigated one of these aquifers – The Dumfries Basin Aquifer, which geologists suspected of being a ‘warm’ aquifer. But was it warm enough to be a valuable resource for local decarbonisation?

Natural Power’s investigation utilised a 345mm diameter borehole, reaching a depth of 145 meters. Constrained by the capacity of the available pump they recorded a flow rate of 16.75l/s. There is an anticipation of achieving higher flow rates with suitable equipment. Averaging 10.55°C, this water could be used to generate heat at a much higher COP than a conventional ground source heat pump.

At The Crichton Campus, the objective is to employ larger scale heat pumps to draw heat from this water source to contribute to a district heating network. Typically, such heat pumps would extract between 3°C to 5°C of temperature from their source. However, it's crucial to consider the impact of lower temperatures on the source environment. Based on the specifications, it's estimated to supply between 210kW and 351kW at these respective temperatures per borehole.

In designing heat pump heating systems, it's customary to size the plant to meet a general level of demand, employing thermal storage or other less capital-intensive heating mechanisms to address peak demand. Analysis at the time of drilling showed demand curves for Crichton that suggested relatively smooth usage patterns, with only 5% attributed to peak demand, resulting in a baseline demand of 4,400kW for the initial network and 6,000kW for a full network.

Considering this data, the borehole requirements are as follows:

Further modelling work would be recommended to explore the benefits and challenges of increasing borehole diameter and potentially reducing the original 100m separation between boreholes. Future efforts could also involve modelling interactions within a larger borehole field and utilising detailed energy consumption data to refine heat network models. This comprehensive approach aims to identify optimal technical and cost-effective solutions for the network, while considering input from stakeholders regarding acceptable land usage for a borehole field.

In summary, the combination of analysis on the heat network and hydrogeological investigations suggests that utilising aquifer water as a heat source is entirely feasible. While certainly not warm enough to fill your bath with, it's anticipated to offer advantages over typical ground source temperatures, with reduced variability across the year due to the thermal inertia of significant water bodies.