A Comparative study of district heating and cooling networks of 4th and 5th generation based on shallow geothermal energy: modelling and analysis using OpenModelica

Abstract

Southern-European cities face a simultaneous rise in cooling demand and a policy drive to decarbonise heating and cooling, in line with european climate commitments. In response, fourth-generation (4G) and fifth-generation (5G) district-heating-and-cooling networks have emerged as promising solutions, with 5G representing a more recent development. This thesis compares fourth- (4G) and fifth-generation (5G) district heating and cooling (DHC) networks that use shallow-geothermal energy as a seasonal sink/source and rooftop PV as auxiliary power. Both systems are modelled in OpenModelica (Buildings 10.0.0) under identical set points (65 ◦C for space-heating/domestic hot water, 7 ◦C for space-cooling) on a two-buildings testbed, with three demand scenarios and a one-year horizon. The neutral-temperature single-pipe 5G concept outperforms the four-pipe 4G layout: overall seasonal performance factors (heating + cooling) are 3.33–3.55–2.50 (5G) vs 2.50–2.68–2.00 (4G), yielding about 25% lower electricity use and operational CO2. Levelized Cost of Heat (LCOH) fall in the range 101–142 €/MWh for 5G versus 130–186 €/MWh for 4G. Regarding the thermal balance of the borefield, across demand scenarios, 5G exchanges less heat with the ground (extraction – 10–32%, injection – 17–28%). In the third case studying two demand profile of two single family buildings, an additional 4GDHC scenario with a central biomass-boiler booster and heat storage (obtained from surplus rooftop PV production) reduce electricity use and CO2 by 29% vs 4G (8% vs 5G) at a LCOH of 172.8€/MWh, providing an interesting alternative where a 5GDHC network is infeasible. The environmental assessment focuses on operational emissions (based on grid emission factor); embodied carbon is outside scope.