Building A is a 10-story high-rise building with a construction area of 5,000 square meters, a population density of 2 people/square meter, a medium-risk fire rating, and a commercial office building. According to the design specifications, the building needs to be equipped with a 2x100mm fire water supply pipeline system. Now it is necessary to calculate the pump flow and pressure of the fire water supply system and design the layout of the water supply pipeline.
1. Number and distribution of fire hydrants.
2. Fire hydrant flow rate is determined.
3. Fire water pump flow calculation.
4. Fire water pump pressure calculation.
5. Layout of fire water supply pipelines.
Analysis:
1. Number and distribution of fire hydrants. According to the design specifications, when the area of each floor of a commercial office building does not exceed 1,500 square meters and the building height does not exceed 50m, the number of fire hydrants should be no less than 3. According to the title, the building has 10 floors, so 30 fire hydrants need to be installed. According to the distribution specifications of fire hydrants, the effective coverage radius of each fire hydrant should be no less than 20m, and the distance between fire hydrants should be no more than 60m. Therefore, fire hydrants need to be installed on the main risers of each floor of the building, and the distance between each fire hydrant should be no more than 40m.
2. Fire hydrant flow rate is determined. According to the specification requirements, the rated flow rate of the fire hydrant should not be less than 2.5L/s. Since the building is a medium-risk building, the rated flow rate of the fire hydrant should be 2L/s. Considering the loss of the water gun, set the nozzle flow rate to 1.5L/s, then the fire hydrant flow rate is 2.5L/s.
3. Fire water pump flow calculation. The required flow rate of the fire water supply system is Q=2.5×30=75L/s. Considering that there is room for daily fire water needs, 150% of the waterproof pump flow rate is generally eliminated as the design flow rate. Therefore, the design flow rate of the fire water pump is 112.5L/s.
4. Fire water pump pressure calculation. The total lift H of the fire water pump should include the pump inlet pressure, pipeline resistance, fire pool clear water height H1, building floor height, sprinkler head loss lift, etc. Among them, the water inlet pressure, building floor height, and sprinkler head loss head are all specified values, which can be obtained by querying the specification table. Pipe resistance and fire pool clear water height need to be calculated and determined based on actual conditions.
The fire water supply pipeline is generally designed to be 50mm. The design flow rate of each fire hydrant pipeline should be no less than 2.5L/s and the flow rate should be no more than 1.2m/s. After calculation, the pipeline friction coefficient is 0.013, and the pipeline resistance calculation formula is: f=0.013 ×(L/D)×(V^2/2g), where L is the length of the pipeline, D is the inner diameter of the pipeline, V is the flow rate, and g is the acceleration of gravity. The net height of the pipeline can be based on the height of the fire water supply pool in a certain layer of building. Calculated from the farthest nozzle at the top. According to the above formula, the total head of the water supply system can be found to be: 84m.
5. Layout of fire water supply pipelines. The layout of fire water supply pipelines should ensure that the flow and pressure of the water supply system meet fire protection needs and meet the layout standard requirements of water supply pipelines. Based on the number and distribution of fire hydrants, fire hydrant flow, fire pump flow and pressure calculation results, the layout of the fire hydrant main pipeline and fire pump inlet and outlet pipelines can be determined. Among them, the inlet and outlet pipes of the fire water pump should be located outside the fire pump room to facilitate the inspection and maintenance of the water pump. At the same time, a valve or flow regulator should be installed at the connection point of the main pipe of the fire hydrant to adjust the flow rate of the nozzle of each fire hydrant.
