Performance comparison between optimized design of a centralized and semi-decentralized community size solar district heating system

Abstract

Solar thermal energy is widely recognized as one of the most important renewable energy resources. However, in high latitudes, due to various climatic and mismatch challenges, such solar district heating networks are difficult to implement. The objective of the paper is to optimize and compare two different design layouts and control strategies for solar district heating systems in Finnish conditions. The two different designs proposed are a centralized and a semidecentralized solar district heating system. The centralized system consists of two centralized short-term tanks operating at different temperature levels charged by a solar collector and heat pumps. Borehole thermal energy storage is also charged via these two centralized tanks. In contrast, the semi-decentralized system consists of one centralized low temperature tank charged by a solar collector and a borehole thermal energy storage and decentralized high temperature tank charged by an individual heat pump in each house. In this case, borehole thermal energy storage is charged only by the centralized warm tank. These systems are designed using the dynamic simulation software TRNSYS for Finnish conditions. Later on, multi-objective optimization is carried out with a genetic algorithm using the MOBO (Multiobjective building optimizer) optimization tool, where two objectives, i.e. purchased electricity and life cycle costs, are minimized. Various design variables are considered, which included both component sizes and control parameters as inputs to the optimization. The optimization results show that in terms of life cycle cost and purchased electricity, the decentralized system clearly outperforms the centralized system. With a similar energy performance, the reduction in life cycle cost is up to 35% for the decentralized system. Both systems can achieve close to 90% renewable energy fraction. These systems are also sensitive to the prices. Furthermore, the results show that the solar thermal collector area and seasonal storage volume can be reduced in a decentralized system to reduce the cost compared to a centralized system. The losses in the centralized system are 40 -12% higher compared to the decentralized system. The results also show that in both systems, high performance is achieved when the borehole storage is wider with less depth, as it allows better direct utilization of seasonally stored heat. The system layout and controls varied the performance and life cycle cost; therefore it is essential to consider these when implementing such systems.

Stakeholders’ Interests in Developing an Energy Ecosystem for the Superblock—Case Hiedanranta

“…Because bi-directional district heat is still under development, interviewees received information regarding different options for heat management. Multiple options were suggested, such as combined supply and feed-in substations [43], a low-temperature network with ring topology [44], a distributed solar thermal system with centralized storage [45], and a semi-decentralized system utilizing heat pumps and PV [46]. In addition to energy networks, ICESs include automation systems that utilize data from various sources and enable day-ahead scheduling, smart metering, flexible demand, VPPs, and PCGs [4].…”

EU Emission Targets of 2050: Costs and CO2 Emissions Comparison of Three Different Solar and Heat Pump-Based Community-Level District Heating Systems in Nordic Conditions

“…Research shows that renewable and storage integration with a single building has less benefit compared to a community-sized solution. Storage integration with a community-sized solution can provide a cost effective [39] solution for renewable energy utilization and mismatch issues [40], in contrast to a single building solution [39]. Moreover, in a community-sized solution, the demand profile has lower variations compared to a single building heating system, therefore community-based solutions are needed.…”

Techno-economic analysis of a solar district heating system with seasonal thermal storage in the UK

“…Due to its relatively wider implementation in mainland Europe, solar district heating systems with long-term storage have been the subject of various studies. These include, among others, the investigation on the performance of a centralised and decentralised system [18], the integration into existing district heating system [19], the use of flat-plate and parabolic-trough collectors [20], the optimisation of installation in a high latitude location [21], and the thermo-economic sensitivity analysis of a small solar district heating system in Italy [22]. Nevertheless, most of the studies are based on non-UK locations.…”