Abstract
This study evaluates low-temperature district heating (LTDH) networks with different geothermal heat sources under thermo-economic criteria. In particular, the heat and cold supply of modern neighbourhoods are taken into account in a dynamic simulation model built on the modelling language Modelica. Both horizontal and vertical ground heat exchangers (GHE) were investigated in respect to the load profiles of the consumers, depending on dimension as well as location. The selected base case represents a LTDH network near Stuttgart (Germany). The corresponding results of an annual simulation show that a horizontal GHE is suitable for pure heat supply and can reduce costs by up to 12% compared to a vertical system. This economic advantage remains when the cooling demand is considered. Subsequently, a variation of the system location was carried out. It is shown that horizontal GHEs operate more economically in northern regions, whereas vertical ones are more advantageous in regions with increased cooling demand. For both cases, possible savings of between 3.0% and 4.2% resulted from the simulations. The heating-to-cooling demand ratio was used as a first decision criteria to weigh-up between the two systems. Vertical GHEs were more economical than horizontal systems as soon as the ratio dropped below 1.5.
Highlights
A horizontal ground heat exchangers (GHE) with 200 kW extraction capacity is used as a heat source for the neighbourhood
In the case of a vertical GHE, reducing the system by 15% leads to savings of 3.8%, the average coefficient of performance (COP) drops by 8.5%
Heat pumps and two geothermal heat sources were implemented in the simulation environment and integrated into the overall model
Summary
Within the European Union, the heating and cooling demand of residential buildings accounts for more than 40% of the overall final energy consumption [1,2]. Renewable energy sources are responsible for only 22% of the whole heating sector. This is in clear contrast to the EU’s ambitious climate targets for 2050. A reduction in heat demand between 20% and 30% is predicted due to the energy efficiency of new buildings and the refurbishment of the existing building stock [2]. This goes hand in hand with falling temperature levels in modern heating systems. These developments can be responded to by integrating central low-temperature district heating (LTDH) systems into modern quarters
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