Study Of Determination Of Design Flow For Building Interior Drainage

The building drainage design flow calculation method set in China's existing water supply and drainage design specification is based on the one of the former Soviet Union, and it belongs to the method of the square root. The actual situation indicates that the design flow should be caculated by probability methods. The calculation based on probability theory will be more scientific and advanced, and it is closer to the objective reality than empirical method and square root method. Moreover, the water supply and drainage process internal construction is complementary, and the calculation method of water supply design flow in China's existing water supply and drainage specification for residential buildings has been based on probability theory. Under such circumstances, the determination of drainage design flow using original formula of square root is obviously unreasonable. The determination of water distribution pipeline based on probability theory has been promoted universally in the international community. On this paper, we will disscuss how to establish the calculation formula of design flow on the basis of probability theory for building interior drainage in our country.By analyzing the contact with distinction between water supply rules and drainage rules of pipelines inside the building, this paper presents the concept of drainage probability of building interior U₀ and sums up its calculation formula with comprehensive consideration of various factors corresponding to water supply. The characteristic of building interior drainage is not the same with water supply completely. It includes that drainage goes through in short time, its instantaneous flow is large, drainage interval of two-time is long, and the drainage process is inequable. Therefore, we give a correction coefficient of building interior drainage in this paper to distinguish with the formula of water supply.The new approach is built on the basis of Hunter's probability theory. Using probability theory and computation procedure, we can calculate the mean number of simultaneously used fixtures m under different drainage probability U₀ and different total number of fixtures N_p. Then we can get the drainage design flow q_p. To facilitate the use, we draw pictures with the calculated couple number q_p～N_p, and get the fitting formula of each picture. Drainage design flow q_p can be calculated by this formula. Establish a relation table of U₀～q_p～N_p with large number of data. Looking up this table to determinate drainage design flow can greatly reduce the workload.The new method based on probability theory to determinate design flow for building interior drainage matches to the one of water supply, and the result of it is more reasonable and more consistent with actual situation.