Thermo-Economic Analysis of Near-Surface Geothermal Energy Considering Heat and Cold Supply within a Low-Temperature District Heating Network

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.

Environmental Impact Comparison of Geothermal Alternatives for Conventional Boiler Replacement

“…The uses of this energy can be segregated into three main clusters according to their destination and in four sections according to their temperature. In this way, the taxonomy based on their use is as follows: First group: housing, leisure, and health [11][12][13][14][15]; Second group: Agriculture and food [16,17]; Third group: industry [18,19]. The temperature sections used are: a very low temperature, less than 30 °C; a low temperature between 30° and 90°; a medium temperature between 90° and 150°; and a high temperature, higher than 150°.…”