Shallow Geothermal Energy systems for micro-scale 5G DHC in the Mediterranean island of Cyprus

Abstract

Shallow Geothermal Energy (SGE) systems find application through the use of Ground Source Heat Pumps (GSHPs) for space heating and cooling. GSHPs provide a higher performance over the alternative conventional Air Source Heat Pump (ASHP) systems, and have seen an increased interest with the continuous energy price increase and the need for lowering the CO2 emissions to meet the European Union “Fit for 55” targets. The high initial capital required for the GSHP systems in the residential sector is the main preventive factor for the GSHP systems. Recent studies revealed that with the nearly Zero Energy Buildings (nZEB) EU derivative in effect, the residential dwellings are built with a higher insulation on the building’s envelop and therefore with a lower heating and cooling demand; hence the potential payback period of such systems is increased.Geothermal energy District Heating (DH) on the other hand could make these systems more viable with the advantage of lower carbon emissions, lower maintenance and a lower cost, but at the moment the infrastructure and availability are mainly present in central and northern Europe, where a higher heating demand is required compared to the southern EU. Having a central unit for distribution however, requires a large plant area, and of course the need for infrastructure and insulated pipes. An alternative to these solutions could be the use of SGE systems at a micro scale level.To this extent, this research aims to computationally investigate the possibility and potential of SGE systems for a micro-scale urban environment. A theoretical case study is developed, with the inclusion of residential blocks categorized as “islands” for the production, use and distribution of SGE as a form of 5th generation (5G) DH and Cooling (DHC) with Mediterranean climate in the island of Cyprus. The case study includes either multiple multi-story residential buildings with nZEB characteristics or multiple detached residential buildings within a residential block, typical for the island of Cyprus. The heating and cooling demands, as well as the peak loads are estimated and the Ground Loop Design (GLD) software is used to size the required vertical Ground Heat Exchangers (GHEs) with different configurations. The effect of the unbalanced ground temperature and the temperature gain/ loss from the heat distribution is examined with the use of COMSOL Multiphysics software. Results indicate a potential advantage of the use of GSHP systems at a residential use micro-scale in terms of costs reduction and promotion of the geothermal energy use.