Abstract
The aim of this dissertation was to investigate the potential for building ground energy systems (BGESs) in the UK by analysing key country specific attributes. More recently these systems have been presented in the UK as having the ability to reduce carbon emissions in comparison to conventional heating and cooling plant. Due to the essential transition to a low carbon economy, this was the main driver and motivation to conduct the research in this field. An initial distinction was made between closed and open loop systems. The former system type utilises a network of pipes installed in the ground to abstract and reject heat via a circulating fluid. Using existing well technology, open loop systems abstract and discharge groundwater whereby the heat transfer between the ground and building effectively occurs within the building via a heat exchanger. Both technology approaches are relevant in the UK where the temperate climate provides a thermodynamic advantage for heat rejection and abstraction from a building, i.e. to aid cooling and heating respectively. A reversible heat pump unit is commonly used in non-domestic installations to allow the prevailing temperature from the ground side system to be reduced or increased accordingly. The research project was split into three main themes. Firstly, a technology specific spatial review of the geology, hydrogeology and climatic effects throughout the UK was conducted using a GIS software package. Secondly, a design phase analysis concentrated on the impact of climate change by applying different weather files to thermal models, different carbon factor projections for electricity, part load sizing, energy prices and the marginal cost of carbon abatement over the lifetime of the system. Finally, an operational phase analysis concentrated on the actual performance of four existing systems monitored over a 12 month period. Four different case study buildings were used for the design phase analysis, and a different set of four building for the operational phase analysis. Using referenced values for the thermal properties of the geology, the resulting heat exchanger length for vertical closed loop systems is primarily led by the respective heating and cooling loads. For the same building type this varied significantly in the three different UK climate types. Following this the thermal conductivity and starting borehole temperature was also shown to make significant differences. For horizontal closed loop systems the heat exchanger length is again led by the building location. The lead ground related parameter is the saturation of the ground as this is likely to vary considerably from location to location. A high thermal conductivity is not necessarily beneficial as this can increase the alignment with the prevailing air temperature and reduce the thermodynamic advantage. There is limited potential for open loop systems due to availability of productive aquifers. The yield analysis showed very large ranges in yield and hence the peak heating and cooling capacity from a single well. This was true when analysing particular aquifer zones and also when comparing sub regions of different aquifer types. The percentage change in peak heating and cooling capacity and annual demand due to climate change was very significant for all the four buildings analysed. The use of dynamic carbon dioxide projections in comparison to static factors currently stated in government publications also highlighted significant variations in projected carbon dioxide savings for a BGES over a 20 year period. The bivalent energy and economic assessment underlined the difference in marginal utilisation and cost effectiveness by varying the size of the BGES relative to the peak load. As the utilisation reduced the cost effectiveness also reduced. These results were translated through to huge variances in the marginal cost of carbon abatement. The operational monitoring results showed that existing BGESs are not performing according to efficiencies quoted by manufacturers. This sometimes led to marginal or negative carbon reduction and operational cost savings versus conventional plant. The poor performance was linked to the commissioned flow rates through the heat pump, buffer tank sizing, the heating distribution installation, maintenance and servicing frequency, insufficient owner knowledge and part load efficiency of heat pump plant. (Abstract shortened by ProQuest.).