The Life Cycle Cost Evaluation Of Schemes And Analysis Of Key Parameters In District Cooling And Heating System

With the application of district cooling system in China increasingly widespread, it will be of great help to improve all sense of China's unreasonable status of energy use if the district cooling and heating (DHC) system is supplied in northern area where both cooling and heating are demanded. Meanwhile, some new external heat sources could be discovered to replace the traditional heat sources such as boilers. Currently, the most important issue for promoting the application of DHC is the huge initial investment and high operation costs which have great relations with cold and heat sources, cooling and heating parameters.There are many cold and heat sources schemes that can be utilized for DHC. The traditional evaluation system of cold and heat sources schemes is purely analyzed from the economic point of view, but the functional differences between different schemes are neglected. This easily leads to the problems in the stage of the operation and management, such as deficiency of regulation performance, low efficiency in energy utilization, less effective in environment protection, etc. In addition, it is main considered how to save a one-time investment in the traditional design. However, as a huge system, the operation and maintenance costs of DHC are often prodigious proportion of its life cycle cost, particularly as the object which is needed to be focused in the design stage, the cooling and heating parameters greatly influence the initial investment and operation cost of the entire system.The main purpose of this paper is to solve the problems above using life cycle cost analysis method and the value engineering principle. Through the life cycle cost analysis of DHC system, it is found out that the important factors that affect the life cycle cost, then, establish the value engineering appraising model for cold and heat sources schemes of DHC, the optimized design model for choosing the chilled water temperature parameters and insulation thickness based on the the life cycle cost analysis.Firstly, DHC project is to be compartmentalized into investment decision-making stage, planning and design stage, the construction stage, the operation stage and scrapped stage, then the cost control methods are put forward through the life cycle cost factors analyzed of every stage. Secondly, an evaluation model of cooling and heating source scheme for DHC system in cold areas is set up by combining the value engineering theory with life cycle cost analysis method, and the model is demonstrated by the Xinghai Bay DHC project in Dalian. The results show that the value coefficient of the scheme combined heating, cooling and power is higher, and the value coefficient of the scheme using seawater source heat pump is not the highest under the commercial electrovalence but clearly higher than the three other schemes under the civilian electrovalence. Finally, the performances of chilled water temperature parameters and the insulating layer thickness are analyzed, then a optimized design model for choosing these parameters is set up based on the the life cycle cost analysis, and The Dalian City Xinghai Bay project is anyalyzed with this model. The results indicate that the best chilled water temperature parameter is 3/12℃, the best pipeline insulation thickness results are greater than the caculated results according to the traditional design method, and the pipeline insulation thickness results according to ASHRAE standard is reasonable.The relative theory of value engineering and life cycle cost is introduced into DHC system design application in this paper, and on this basis the corresponding optimized design methods for its schemes and parameters are put forward. It has some engineering practice guide to further promote the development of DHC.