Details and Concept

The performance of ground source system using a closed loop collector, is highly dependent on the design and size of the collector to meet the heating and cooling demand that is to be supplied through a heat pump system.

Incorrectly sized ground source collectors can have impacts on both the environment in which they are installed and can also result in increased running costs and CO2 emissions.

One of the most common problems in the installation of a ground source collector is the reference values of heat delivered per metre of collector installed in the ground.  This reference is used as an estimate for the length of borehole needed to satisfy the heat demand.  Many geothermal systems installed to date in Ireland, have used common rules of thumb or referenced data from other EU standards such as the VDI4640 Guidelines from Germany or published research on UK rock types to arrive at this estimate, these have not always transferred well to Irish geology as they cannot take into account for properties specific to Irish geological formations.  In some cases these have resulted in…

a) undersized collectors – lead to increased pumping costs as the system tries to extract heat from the ground in the heating mode unnecessarily decreasing the ground temperatures and leading to the potential freezing of the collector.  In the cooling mode the reverse happens when the heat pump attempts to ‘dump’ the heat back into the ground raising the surrounding ground temperature.

b) oversized collectors –  these  have potentially much lower environmental impact but the increased size can lead to higher pumping and running costs and lower seasonal performance factors.

This has sometimes resulted in poor performance and perception of the technology in the Irish market and by users. This project sets out to quantify the thermal properties of the Irish ground conditions to facilitate collectors to be sized optimally and to provide a comprehensive reference database of Irish ground conditions to be used by professionals including designers, installers and engineers.