Simulation-based seasonal underground sensible heat storage integrated in a district heating network

Abstract

This study assesses the role of (seasonal) thermal energy storage in the next generation renewables based central heating systems for the built environment in the Netherlands. Specifically, the neighbourhood "Karwijhof" in the city Nagele which is transitioning to a collective renewable district heating network incorporating 24 users. The study focus on the technology for storing thermal energy and two different heat collection technologies. The storage of heat is done using an underground seasonal thermal energy storage (USTES), in this case an underground sensible heat storage tank using water as storage medium. The system relies on a small scale district heating network (DHN) for the distribution of heat. For this research two heat collection technologies are considered both incorporating the USTES as main system component. The first system relies on heat collection by solar thermal collectors, the second on an air-water heat pump. Both systems are modelled in Matlab-Simulink making use of KNMI weather data. Different system sizes are evaluated. The investigated components include: volume of the USTES, surface area of the solar thermal collectors, and air-water heat pump capacity. Key performance indicators include the levelised cost of heat (LCOH) and the seasonal COP of the system which gives an indication on the autonomy of the system. To increase the autonomy of the systems a photo-voltaic (PV) array is considered for both systems to offset the electricity use. However, the systems are allowed to exchange electricity with the grid translating into the goal of "zero on the meter" autonomy. The results show that both systems can ensure heat throughout the year for the users considered during this study. However, systems cannot compete with traditional natural gas heating systems based on the LCOH. This is partly due to the high cost of the district heating network. The systems including a PV array show a LCOH that can compete with the traditional natural gas HR-boiler but are constraint by the rooftop area available during this study leading to a non-competitive LCOH. When considering the environmental benefits, the systems are already competitive to the traditional natural gas heating systems.