Research On Key Parameters Calculation Methods Of Domestic Vacuum Drainage Systems Inside Buildings

Vacuum drainage systems inside buildings could complementary and alternative gravity drainage systems, which had advantages in conservation and waste reduction, flexible layout, clean sanitation, etc. This drainage systems could be adapted to achieve the functional requirements of the new buildings, could save water and protect water environment. It was gradually by recognition and affirmation of the designer, and the market demand was increasing. In china, dozens of projects had been applied to outdoor or indoor vacuum system, and get a good social and economic benefits. However, due to the lack of design standards, the relevant parameters, and the calculation methods was not uniform, so that the application of vacuum drainage systems was limited in domestic. Therefore, the research of the key parameters calculation methods of vacuum drainage systems was needed to carry out urgently.In this paper, the systems flow-rate calculation methods had been studied, it compared the calculation principle and formulas of the European standard method, sanitary-ware frequency method, equivalent or percentage method, volume of air calculation method in current design, and analyzed an example. Then, probability theory was combined with to establish the systems flow-rate calculation formula. The consisting of head loss was knowed in the vacuum pipe, and compared the friction loss calculation formulas. Line-fitting a two-phase flow coefficient by assuming experiment, and formed the formula of the experimental method to calculate the friction loss. The air-water ratio, energy consumption, the relations between the size of a vacuum device were discussed, and analyzed the range of the air-water ratio. The calculation methods were applied to the actual project, by comparison and analysis, then, to verified the results and problems of the formulas. The main conclusions are:(1) European standard method, equivalent or percentage method, volume of air calculation method were empirical formulas. The systems flow-rate should be instantaneous sec-flow. European standard method, equivalent or percentage method were sec-flow for systems inside buildings. Sanitary-ware frequency method was the average hourly flow method, suitable for outside systems. Volume of air calculation method was the maximum hourly flow, it could be used in both inside and outside systems. European standard method for a single attribute of the building. Equivalent or percentage method could calculate the total sewage flow only, and not for the total volume of air. Volume of air calculation method considered the operating system principle, but won’t distinguish the difference between inside and outside systems in the flow transition and time, and the results differed from the actual.(2) Summarized the sanitary-ware flow and probability table, then, in view of domestic water features to combined Hunter probability method and the central limit theorem for derived the systems flow-rate calculation methods which could calculate the air-flow and water-flow. The convergence analysis on calculation methods showed that the results trend was close to high flow-rate, and it could be applied in outside system. The methods was universal, which was consistent with previous analysis calculations.(3) Knowed the causes and research methods on the losses of static, dynamic and friction. And compared amended Hazen-Williams formula, A-H algorithm, Dukler two-stage algorithm, L-M curve methods and Duan Jinming formula that based on the five different models formula, and referenced the simulation experimental data to analyze the accuracy and availability of the various methods.(4) The calculation results of the amended Hazen-Williams formula was most realistic operating conditions require, but because it didn’t consider the impact of different air-water ratio on gas-liquid two-phase friction. So the introduction of a two-phase flow experiment coefficient Φ’, which remedied defects of Hazen-Williams formula, then the line-fitting coefficient Φ’ obtained from assuming experiment. Then, formed a vacuum pipe friction loss calculation formula for two-phase flow experiment.(5) When the systems capacity and pressure in certain conditions, the sewage pump energy consumption was relatively stable, the main energy consumption came from the vacuum pump. A large range of system was equal equipment of large capacity. Vacuum energy is proportional to the size of equipment. The volume of air and the number of computing vacuum pumps were directly proportional to the air-water ratio. The air-water ratio is proportional to the energy consumption. Equipment scale impacted on energy consumption, and energy consumption could in turn determine the size of equipment. To reduced the consumption of the entire facility energy, it was necessary to control the vacuum pump’s energy consumption. A reasonable range of air-water ratio was determine that was from 5:1 to 32:1.