| Abstract |
Utilising deep geothermal energy for decarbonizing district heating networks (DHN) has a tremendous worldwide potential. In typical direct-use projects, the geothermal capacity is limited by the return temperature of the DHN, since this determines the minimal achievable reinjection temperature. At the same time, most existing geothermal DHNs experience heat demand during cold winter periods that exceeds the conventional geothermal capacity. Thus, normally, peak load boilers running with oil or gas are used to cover this peak load heat demand. Large-scale heat pumps have a high potential for decarbonising this peak load because they enable a significantly higher heat supply from the geothermal project by decreasing the reinjection temperature. However, existing geothermal DHNs indicate that such large-scale heat pump systems will have low capacity factors, which might prevent an economic business case. Simultaneously, most of the year, the geothermal capacity exceeds the actual DHN demand. Therefore, so-called reversible heat pumps, which can operate in two modes using the same equipment, may offer an attractive solution. This work presents a thermo-economic assessment of two novel reversible heat pump systems, currently studied also experimentally by the authors: A reversible compression heat pump, which can also operate as an Organic Rankine Cycle for power generation and an absorption heat pump, which can also operate as an absorption chiller. By providing either power or cold during the summer months, the capacity factor of the heat pump increases significantly. The study presents detailed thermo-economic results for reversible concepts, their potential application cases, and economic threshold conditions. |