The Stanley Primary Care Trust building was completed in 2009 to supply an extensive range of Primary Care services all under one roof. The centre provides services such as GP practices, dentistry, x-ray diagnostics and facilities to conduct minor operations.

To provide heating and cooling for the building, OGI Groundwater Specialists have designed and installed a sustainable ground source heat pump system to provide heating and cooling using borehole ground collectors.

To quantify the essential geothermal properties of the ground, OGI carried out a geothermal resource test. This enabled the heating energy potential of the ground to be calculated. This approach also enabled potential drilling difficulties to be identified and design changes made to overcome such difficulties at an early stage.

Using the test results OGI’s mathematical model established the optimum number of boreholes required to provide the necessary energy from the available resource. The borehole layout has been designed to ensure long term sustainability of the resource.

Heat is absorbed from the rock below the building via an array of 22 boreholes drilled to approximately 100 m. The majority of the boreholes were drilled under the footprint of the building prior to construction. Each borehole was installed with two collector flow and return loops to maximise the return from the ground.

The individual borehole pipes are fusion welded to horizontal pipes laid within flow and return trenches.

The horizontal ground loop pipes combine together at one of the two manifold chambers, one located in each of the two interior court yards. The heat transfer fluid from the boreholes combines and passes through the building via header pipes to the Plant Room on the roof of the building, which is where the heat pumps and buffer tanks are located.

 

Unusually, the trenches were excavated and installed after the building superstructure had been constructed. This presented considerable planning and logistical challenges, tying in with numerous other trades, which was possible with careful co-ordination.

The ground source heating system provides water at 45oC which is used to feed the under floor heating system and the electric fan coil ventilation system. The system generates 80 kW of peak heating, provided by two 40kW heat pump units. On occasions of high heating demand, the system is supplemented by integrated gas boilers, which also provide the buildings domestic hot water.

In the summer months, the system provides 80 kW of chilled water. Chilled water is stored in a cold water accumulator. The system can do this passively (whereby cooling water is utilised directly, i.e. heat transfer fluid is circulated around the system but the heat pumps do not operate), or actively whereby cooling water is generated directly from heat pump.

In this mode, a heat exchanger is able to transfer heat generated (as a by-product of cooling) to the ground. The ground then stores this heat so that it can be used in the colder months, which in turn increases the efficiency of the system.