“Performance analysis of multi-source heat pumps coupled with dual-layer seasonal thermal energy storage: operational data and insights after the first year”
In the face of the need to decarbonise district heating systems, multi-source heat pumps (MSHPs) combined with seasonal heat storage are a viable alternative to conventional, emission-intensive technologies (i.e. coalfired boilers). In this work we present the results of an operational analysis of a full-scale MSHP-based heating system implemented in Lidzbark Warminski, northern Poland, which has been in continuous operation for more than a year, covering more than 90% of the heat demand from renewable energy sources. This heating plant is based on a cascade of heat pumps cooperating with three sources: air-to-water heat exchanger, borehole thermal energy storage (BTES) and pit thermal energy storage (PTES). In this paper we examine the operating conditions and performance for each of these sources, their seasonal availability and the variation of COP with temperature parameters. In addition, an analysis of the charging and discharging strategies of the seasonal storage, with a particular focus on the long-term temperature behaviour of the PTES storage and maximising economic efficiency was performed. Hence, the system is designed to consume electricity from a dedicated local photovoltaic farm, we analyse also the level of electricity selfconsumption. The overview of current MSHP technologies points out their potential for integration with both BTES and PTES. It also identifies the main challenges of implementing this technology, such as the need for adequate space for sources. This factor can be solved by dual-layer configuration when PTES is built above the BTES. In this paper we analyse the data collected from system as an assessment of real energy efficiency compared to design values and results of the numerical simulations. The results confirm that MSHP technology integrated with heat storage is not only technically feasible, but also replicable, providing a solid basis for the development of decarbonised district heating systems.