The Lanchester Road Hospital, near Durham City, is a long established mental health, learning disability and substance misuse facility.  The most recent phase of development was completed in 2009 for the Tees, Esk and Wear Valleys NHS Trust.  To meet renewable energy targets, together with ensuring a stable and comfortable environment, the heating and cooling was provided by a ground source energy system integrated with gas boilers.  Prior to design, OGI Groundwater Specialists Ltd carried out a ground energy resource test to establish the thermal resource capacity of the ground. 

The ground consisted of superficial drift deposits underlain by Westphalian Coal Measures.

Based on the thermal properties calculated, OGI then designed and installed a ground energy heating and cooling system comprising 15 boreholes drilled to a depth of 100m to meet the specified heating and cooling requirements of the hospital.  This involved drilling through sandstone, mudstone and shale, although no worked coal seams were encountered.  Application of OGI’s in-house mathematical models enabled the design of a borehole layout to optimise the depth and position of the boreholes within the restrictions of underground services, accessibility and future land use.  The boreholes were located primarily within the Central Ambulatory Area and around the south eastern perimeter of the building.  The Central Ambulatory Area is a sheltered and secure courtyard that acts as a heat trap during the Summer. To ensure the sustainability of the system, the heat captured in the ambulatory area during the summer is transferred down in the boreholes to the underlying rock.  In the winter this process is reversed with heat transferred from the rock to the building.

 In order to achieve the required heating and cooling load from the ground energy system to the building, pipes returning to the ground were routed in long loops down the centre of the courtyard, while boreholes and extraction pipes were positioned around the perimeter.  This elegant layout required close supervision from the OGI site engineer to ensure pipes were installed according to design.  This elegant solution results in a substantial heat capture from the ambulatory area in the summer which is stored surrounding the boreholes for later recovery in winter.

Innovative high efficiency turbulence collector pipe was used on this project for the first time in the UK.  Use of this pipe in Sweden has been shown to result in greater heat absorption per unit length of pipe and consequently improves the overall heat transfer characteristics of the system.  OGI acted as a consultant to manufacturer Muovitech in providing theoretical verification of the experimental test results for Turbulence Collector.  The pipe works by having an even flow of fluid across the full bore and also has less pipe friction so reducing the pump electrical energy demand.

The ground energy system supplies underfloor heating, the temperature of which is adjusted for outdoor conditions to maximise efficiency and minimise running costs.  It also provides passive and active cooling through a 100kW heat exchanger. The system recharges heat to the  collector boreholes using two mechanisms. The first is the capture of heat from the surface loops in the ambulatory area in the summer via a heat exchanger.  The second is the return of waste heat generated by the cooling system to the ground through a 40kW heat exchanger.  The system was designed to provide 65kW of cooling at 8?C in active mode and 15?C in passive mode.  The peak heating demand was predicted to be in excess of 450kW, with an annual demand of 908MWh. The target for renewables was for 333MWh, or around 37% of the total. Measurements post completion have shown that the single 60kW NIBE Fighter 1330 Heat Pump comfortably exceeds this target and has been shown to provide over 500 MWh/a which is more than 55% of the total annual demand.  When peak heating of more than 60kW is required, gas boilers top up the accumulator through a low loss header.  The top up signal is controlled by the NIBE degree-minute system.