Application of solar district heating systems in urban buildings

Background:

In northern China, the annual heating energy consumption is equivalent to more than 181 million tons of standard coal, accounting for about 25% of the total energy consumption of Chinese buildings. China's heating demand is growing fastly while the heating demand in the Hot Summer and Cold Winter areas is also rising. The coal-based fuel structure has caused severe smog pollution in the heating season in northern China. As an abundant renewable energy source, solar energy could play an important role in the heating of buildings. China has the world largest solar thermal market but there are issues and problems remaining, for instance, bad quality and poor durability of the systems on the market, lack of investments on R&D of the technologies, poor economics and high demands for maintenance for small solar heating systems etc. If solar energy should contribute with a substantial share of the energy supply in the future, these issues have to be addressed.
Denmark is well known worldwide as the front-runner for applications of large-scale solar heating plants. The experiences from Denmark will benefit China in its efforts to develop a sustainable heating system of the future with a large share of solar energy. The following technologies could be of high relevance for Chinese solar industry: energy planning utilizing different renewable technologies, design and operation of large solar heating plants, high-efficiency solar collector technologies, seasonal heat storage technologies etc.
Large cities in China are dominated by high-rise buildings, with high urban development density and high population density. It is difficult to apply solar district heating technologies in urban areas due to the high price of land and the high cost of renovation to existing large-scale centralized heating systems. However, for China's vast rural areas, solar energy has a bright future. District heating in rural areas of northern China is not yet widespread. District heating systems create conditions for solar thermal and can significantly reduce operating costs of the entire heating system. And the most important of all, there is enough cheap land for the installation of solar collectors in rural areas. Therefore research will be carried out to exploit the technology for Chinese conditions regarding design principle, design procedure, operation method, and optimization of the system.

Goals:

By this study, the following results can be obtained:
Documented performance analysis of one demo solar district solar heating plant in Beijing, the capital city of China; Recommendations on the design of solar assisted district heating systems for different climates, including type of solar collector, heat storage, pipeline networks, auxiliary heaters, management of the heating plant, etc.
Experiences on the system design and optimization, construction and measurement for solar district heating systems; Identification of barriers; Suggestions for policymakers on the promotion of solar district heating technologies.

The content of the project:

To answer the questions on the feasibility and market potential of the solar district heating in China, the study will:

First, conduct series of literature study to know the development status and the trend on solar district heating in European countries, including seasonal heat storage technologies, phase change material heat storage technologies, large-sized flat plate solar collectors, construction process, system control, and maintenance technologies.
Then, investigate local government officials, planners, and heating companies to know the barriers and demand for clean heating in China, at the same time, to introduce the advanced experience of solar district heating in Denmark and other EU countries.
Based the market survey, practical experience of building large-scale solar district heating plants in Denmark, and the knowledge from the courses in DTU and Tongji University, a demo solar district heating plant will be designed and built.
The project is located at Yanqing District, north of Beijing. The project has designed a solar district heating system with a heating area of 19,000 m2, 180 households, and 450 residents. A solar assisted ground source heat pump system will be used as a heat source for the district heating system.
After the demo project is completed, continuous monitoring and optimization to the system will be conducted by a validated TRNSYS model.

The PhD study is the first systematically research on the feasibility of solar district heating in China. The technological barriers will be identified and possible development road map will be proposed. A TRNSYS model will be developed for the demo solar district heating plant to optimize the system design. Interplay between the heat storage by the borehole heat exchangers and the collector fields will be investigated. The TRNSYS model will be validated by monitoring results of the demonstration system.
The validated TRNSYS models will be used to investigate the influence of climatic conditions, collector field design, heat storage types and demand behavior on thermal performance of the district solar heating system. Optimized designs for the demo solar district heating system will be proposed for cities under different climatic conditions, for example, (1) Copenhagen as a reference with a typical cold climate and poor solar irradiance resources, (2) Beijing with a typical cold climate with good solar irradiance resources (3) Lhasa with a typical severe cold climate with abundant solar irradiance resources.