Analysis On Optimal Selection Of The Two Key Parameters Of The Ground-coupled Heat Pump System Design

The ground source heat pump technology is known for its outstanding economy, environmental protection, energy efficiency and applicability of the advantages is gradually recognized by the majority of the owners. In recent years, the occupancy ratio of ground-coupled heat pump system is increasing year by year and has been developing rapidly.However, accurate and reliable system design and calculation method is one of the main bottlenecks of its development and application.The circulating temperature in the ground-heat exchanger(the highest design temperature in summer and the lowest design temperature in winter) and circulation flow rate are the two key parameters in ground-coupled heat pump system design. If these two parameters are chosen inappropriately, the ground heat exchanger is often designed poorly, the investment of the system is higher, the equipment runs in low load and efficiency and the operating energy consumption is increasing. It can be learned from the existing literature that, because of the different selection methods as well as the larger range of the circulating water temperature and the flow rate, the option cannot be made with the specific project very fast and singly, which would not only increase the difficulty of the design, but also affect the initial system investment and operating economy.For the experience design and calculation methods of the vertical ground heat exchanger which is commonly used in engineering, this paper presents an approach to choosing circulating water temperature and flow rate based on economical efficiency. Illustrate the economical water temperature and velocity selecting method with an actual case, completed the preliminary design of economic program. Therefore, the main contents and achievement are as follows:1) Determination of the existing literature on the ground heat exchanger circulating water temperature and flow rate to summarize and analyze the pros and cons as well as their impact on borehole heat exchanger as well as the performance of the system is running.2) Introduce a selection method of the water temperature and flow rate of the heat exchanger design. The method based on the method of the technical andeconomic evaluation, for different water temperatures and flow rates are calculated circulating its associated initial investment and annual operating costs, the final temperature and velocity to achieve economic comparison is determined by the discounted value of correlation. In the calculation of annual operating costs of the system, established coupling calculation model of the whole system.3) With the above method, introduce a case study of the ground source heat pump system design and analysis about a hotel in Xi’an, economic circulating temperature and velocity circulating optimization selection purposes. After calculation, the actual situation of the project, the economic circular water temperature in summer is 35/30℃ ~ 35/30℃, the economic circular flow rate is 0.34m/s.For specific projects, the above method can not only get an unique design value of the temperature and velocity, but also ensure the economy and reliability of the system, achieve the optimal design.