Abstract
Borehole thermal energy storage (BTES) systems are a viable option to meet the increasing cooling demand and to increase the sustainability of low-temperature district heating and cooling (DHC) grids. They are able to store the rejected heat of cooling cycles on a seasonal basis and deliver this heat during the heating season. However, their efficient practical implementation requires a thorough analysis from technical, economic and environmental points of view. In this comparative study, a dynamic exergoeconomic assessment is adopted to evaluate various options for integrating such a storage system into 4th generation DHC grids in heating dominated regions. For this purpose, different layouts are modeled and parameterized. Multi-objective optimization is conducted, varying the most important design variables in order to maximize exergetic efficiency and to minimize levelized cost of energy (LCOE). A comparison of the optimal designs of the different layouts reveals that passive cooling together with maximizing the heating temperature shift, accomplished by a heat pump, lead to optimal designs. Component-wise exergy and cost analysis of the most efficient designs highlights that heat pumps are responsible for the highest share in inefficiency while the installation of BTES has a high impact in the LCOE. BTES and buffer storage tanks have the lowest exergy destruction for all layouts and increasing the BTES volume results in more efficient DHC grids.
Highlights
In European households, heating accounts for 78% of the total final energy use
Exergoeconomic optimization results in system layouts with lower GWP by taking thermodynamic the exergoeconomic optimization results in system layouts with lower GWP by taking thermodynamic inefficiencies into consideration
This can be explained by the passive cooling strategy, which leads to an omission of heat pump (HP) that are usually responsible for significant amounts of exergy destruction and high Operational Cost (OC)
Summary
In European households, heating accounts for 78% of the total final energy use. Cooling of buildings still has a fairly small share in the energy use, but the demand during summer months is continuously rising due to climate change [1]. By 2050, more than 80% of European residents are expected to live in urban areas [3]. This trend increases the benefits of district energy systems, which tend to be more economic for densely populated regions [4]. District heating and cooling (DHC) systems can be environmentally beneficial and pave the way toward the sustainable energy supply, if they are applied appropriately [4,5]
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