Technical-Environmental-Economical Evaluation of the Implementation of a Highly Efficient District Heating System in China

摘要

Over the past 30 years, China has experienced unprecedented urbanization, modernization, and economic development. In the last two decades, China has become one of the largest DH markets in the world, with a total DH production in 2013 amounting to 3,197,032 TJ. This number is still increasing steadily due to the process of rapid urbanization, expansion of the building area, enhancement of building services, and increases in comfort level. The fast pace of urbanization brings out significant challenges to the building heating and water supply in the cities. Therefore, the appropriate technical approaches are urgently needed to improve the efficiency of the DH systems, and create maximum synergy between energy security and air pollution abatement.The main hypothesis of this industrial PhD project was that by comparing Danish and Chinese DH systems it is possible to learn from the Danish experience and transfer state-of-the-art DH technologies to China and thus improve efficiency, economic operation, and environment protection in Chinese DH systems.There were three sub- hypotheses in this research. The first two sub-hypotheses focused on SH systems to improve the efficiency of Chinese DH systems. The third sub-hypothesis focused on integrating DHW supply into DH systems to improve the overall efficiency of Chinese DH systems.A typical issue in Chinese DH systems is that the DH plant has to provide much more heat than the consumers actually need. The main reason for this is the lack of flow control and temperature control at the end-users, which has resulted in significant amounts of energy being wasted. The first and second sub-hypotheses therefore focused on hydraulic control and thermal control, respectively.The first sub- hypothesis was that hydraulic balance can be achieved in multi-storey building heating systems if the appropriate flow and pressure control devices are applied to the terminal heat emitters. The basic configuration of the technical approach is to apply Thermostatic Radiator Valves (TRV) with pre-setting function to radiators, and apply differential pressure controllers to the apartment loops or the risers. The analysis used a mathematic hydraulic model developed by the author to investigate the hydraulic performance of multistory buildings. With hydraulic conditions calculated from the hydraulic balance model, the building’s thermal performance under design condition was simulated using IDA Indoor Climate and Energy 4.6.2. The results show the hydraulically balanced heating system achieves 16% heat savings and 74% pump electricity savings.The second sub-hypothesis was that indoor comfort can be improved by activating the thermostatic sensors of TRV. At present, heating is still billed as a fixed charge based on the floor heating area. This gives heat consumers no incentive to save heat and results in a lack of energy-saving consciousness. Consequently, consumers emit heat into the atmosphere by opening the window when indoor temperatures are higher than the comfort level. A building model was developed based on a real case, and real weather data were used in the simulation in IDA Indoor Climate and Energy 4.6.2. The building model simulation verified that indoor temperature can be controlled around a constant level by setting thermostatic sensors. At the same time, heat consumption and pump power consumption were quantified and shown to be much reduced compared to the situation with no indoor temperature control. The simulation results showed that system-wide use of TRV can reduce heating consumption by 17% and pump electricity consumption by 42% compared to the situation without TRV control. Furthermore, the use of TRV enables a constant room temperature and changes the system from constant flow to variable flow.The third hypothesis was that the efficiency of China’s district heating systems could be improved by changing the current situation with regard to domestic hot water (DHW) applications. The vast majority of DH systems in China only provide SH and do not produce domestic hot water. DHW is mainly produced by individual water heaters powered by fossil fuels, which puts pressure on air pollution and energy supply security. To solve this problem, the hypothesis was developed that DHW production can be integrated into DH systems by using the flat stations concept. A multi-storey building with standard apartments was modelled to investigate the technical feasibility of this approach. On the premise of technical feasibility, an economic evaluation was made using net present value (NPV) to compare the annualized cost of using individual water heaters and flat stations. Environmental impacts were considered in terms of particle and CO2 emissions when various fuels are used to produce DHW. The results show that flat substations solutions are technically feasible if a few technical measures are implemented. The flat station approach is also more economically beneficial than individual water heaters and has less environmental impact.Chinese DH systems are characterized by low efficiency. There is a large margin for system improvement when compared with Danish DH systems. The thesis evaluates Chinese DH systems from the technical, environmental and economical points of view. The major issues in current Chinese DH systems are addressed through the three sub-hypotheses stated above. The thesis demonstrates that the efficiency of Chinese DH systems can be significantly improved if good solutions can be found for their hydraulic and thermal balances and the supply ofDHW.