Kings Mill Reservoir at Mill Waters

Going green is a concept the general public has embraced in the last few decades, whether through actions such as recycling, going plastic-free, or taking fewer flights abroad. Energy efficiency is often top of the agenda, with insulation, draught-proofing, and upgrading boilers being some of the ways to help the environment. As Ashfield residents aim to keep up with their green credentials and reduce their carbon footprint, it’s perhaps heartening to know that the district is the site of the largest geothermal lake loop installed in Europe.

Geothermal system
Thousands of people use King's Mill Hospital in Sutton in Ashfield every week, but what they perhaps don’t know is that a geothermal system installed at the hospital provides 90 per cent of the cooling for the building by using heat exchangers at the bottom of Kings Mill Reservoir. This award-winning installation, created in 2008, reduced Sherwood Forest Hospitals NHS Trust’s annual waste costs by around £200,000, and saves 9,600 MWh of gas and electricity a year. A 1,400 ton lake-source heat pump cooling and heating system that can produce 5.4MW of cooling and 5MW of heating was installed by submerging a network of heat exchangers in the nearby reservoir. The heat exchangers are connected to 42 heat pumps in the hospital that help regulate the temperature.


The innovative scheme was led by engineering and construction company Skanska working with Coventry-based firm Geothermal International. The heat exchangers are connected to Kings Mill Hospital through pipes installed up to 2 metres below the reservoir that generate air conditioning and heating. 

Picture caption: Kings Mill Reservoir


Military hospital
King's Mill Hospital opened in 1942 as a military hospital for American patients and German prisoners of war. Later in 1945 part of the site was used for students from Mansfield Secondary Technical School, who used the Nissen huts left by the US Army. The hospital officially opened on 17 September 1951 by the Minister for Health, Hilary Marquand, with the Dukeries Maternity Centre opening in 1975. 

Natural habitat
The reservoir is known for its wildlife with fish including carp, pike, perch, bream, eels, and roach, as well as birdlife like whooper swans, water rail, snipe, and phalarope. Skanska consulted wildlife groups, including Friends of Kings Mill Reservoir, about the project's impact on the area. 

Picture caption: Bird at Kings Mill Reservoir

The heat exchangers were installed in the winter months to reduce disturbance, and a floating reed bed was added to hide the exchangers, as well as encourage new wildlife habitats.