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Power consumption of speed-regulated water pump in water supply system

27 Jan 2022Email

Compared with the constant speed operation, the constant speed water pump is eye-catching because of its obvious energy saving effect. However, when the speed-regulated water pump is used in the water supply system under different conditions, the energy saving effect is obviously different, and it may even waste energy obviously, and the water supply safety is poor. When the water supply system is equipped with fire-fighting water supply, the use of speed-regulating pumps for water supply without water tanks is an example. "Code for Fire Protection Design of Buildings" (hereinafter referred to as "Building Rules") and "Code for Fire Protection Design of High-rise Civil Buildings" (hereinafter referred to as "High Rules") stipulate that: For buildings with high-pressure (normal high-pressure) fire-fighting water supply systems, if the highest When the water volume and water pressure of fire hydrants and automatic sprinkler fire extinguishing equipment at disadvantageous points are not required, fire water tanks may not be provided. The concept of high-pressure (normal high-pressure) fire-fighting water supply system includes two meanings: that is, during firefighting, the water supply system can supply sufficient pressure and full firefighting water consumption without restarting the special firefighting pump, and ensure that the water supply is not interrupted at any time. Based on this, discuss whether the following water supply systems meet the requirements of fire regulations and the conditions that must meet the requirements of fire regulations.

Fire fighting pump

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The system usually fills the pipe network with a pressure value P1 that meets the requirements of fire protection. In order to prevent the pressure drop caused by the leakage of water in the pipe network, the pressure-stabilizing pump 3 is used. This pump is a small constant-pressure speed-regulating pump that runs all day. The amount of lost water is replenished during operation to ensure that the pressure value P1 of the pipe network remains unchanged. The flow rate of the stabilized pump is generally small, usually 0.5-1.0L/s. During firefighting, due to the large water output of the fire hydrant, when the pressure of the pipe network drops to a specified pressure value P2, the main firefighting pump is started to supply the water consumption and pressure that meet the firefighting requirements. Another form is that the constant pressure pump 3 does not use a constant pressure speed regulating water pump, but uses a small constant speed pump to supplement the pressure, which is called a supplementary pressure pump. At this time, the design pipe network pressure is greater than a certain pressure value P3 of the fire protection pressure value P1. When the pressure of the pipe network drops to P1 due to the leakage of water loss, the supplementary pressure pump starts to supply water to the pipe network, so that the pressure of the pipe network rises to P3. The pressure pump stops working, and the supplementary pressure pump works intermittently. During firefighting, due to the large water output of the fire hydrant, when the pressure of the pipe network drops to a certain pressure value P4 below P1, the main firefighting pump is started to supply water and pressure that meet the firefighting requirements. The flow rate of the supplementary pump is generally about 5L/s. It can be seen from the above that the fire water supply system in Figure 1 needs to start the main fire pump to supply all the water consumption and pressure requirements for fire fighting during fire fighting. It is a temporary high pressure water supply system and does not meet the requirements of fire protection regulations. The system is a tankless water supply system with a speed-regulating pump combined for living and fire fighting. Speed-adjustable water pump! It is a constant-pressure speed-adjustment, which is intended to make the speed-adjustable pump meet the constant pressure of domestic water and adapt to changes in domestic water consumption, so as to achieve the purpose of energy saving. During firefighting, start the firefighting pump to meet the firefighting water consumption and water pressure requirements. It is obviously a temporary high-pressure water supply system that does not meet the requirements of fire protection regulations. The system is a constant pressure fire-fighting water supply system without a water tank for a speed-regulating pump. The working speed-regulating pump 2 (or 3) runs continuously for many years, within the speed-regulating range, it not only guarantees the pressure requirements during firefighting, but also linearly and continuously supplies part or all of the water consumption in the firefighting process. During the firefighting process, there is no link to start the firefighting pump again. The protection personnel only need to connect the hose to the fire hydrant and immediately put out the fire. The system is a high pressure (normal high pressure) fire water supply system.

The high-pressure (normal high-pressure) water supply system must have a reliable power supply to ensure the normal operation of the fire pump, so as to ensure that the water supply is not interrupted. In the respective specifications of the "Building Regulations" and "High Regulations", according to the types of different buildings, the level of fire-fighting power that is consistent with the fire-fighting water supply is stipulated. For example, the "High Regulations" stipulates that fire control rooms, fire pumps, automatic fire extinguishing devices, valves and other fire-fighting power supplies should be powered according to the first-level load requirements specified in the current power design code, that is, powered by two power sources. When the load is not large, the diesel generator set can be used as the backup power supply, and the third power supply or self-provided power supply should be obtained from the power system for special-class buildings. Class II buildings should be powered according to the requirements of the two-circuit line of the secondary load. The two power sources or two circuits should be able to switch automatically, and the self-provided power generation equipment should be equipped with an automatic starting device. The "Building Regulations" also stipulates that the fire pump power supply is required for the first, second and third load power supply according to different types of buildings. This means that the design of high-voltage (normal high-voltage) fire-fighting water supply systems should consider the type of building and its fire-fighting power level. Although the water supply system in Figure 3 is understood to be a high-voltage (normal high-voltage) fire-fighting water supply system, for buildings with a low level of fire-fighting power, a sudden power failure will cause serious consequences of waterless fire extinguishing. Fire-fighting power level is a necessary condition for designing high-voltage (normal high-voltage) fire-fighting water supply systems. The combined life and firefighting variable speed pump tankless water supply system is a waste of energy. The wasted energy is the work done to raise the daily domestic water consumption to the pressure required for the fire hydrant. An example is an 8-story residential building with a population of 10,000 people, the maximum daily water consumption standard is 130L/person·d, the maximum daily water consumption is 1300m3, the pump works for 24 hours, the average hourly water consumption is 54m3, and the required water supply pressure is 36m water column , the pump working efficiency is 73%. When Figure 3 is only used as the domestic water supply system in this residential area, the constant pressure value of the speed-regulating pump is 36m water column, and the daily power consumption of the centrifugal pump is ((0.00272*54*36)-0.73)*24=174KW·h. According to the requirements of the "Construction Regulations", the 8-storey residence should be equipped with fire water supply. The designed fire hydrant diameter is DN50mm, the water gun nozzle diameter is 16mm, the diameter of the DN50mm hemp hose is 20m, and the water gun is filled with water column length of 7m, the calculated fire hydrant outlet pressure is 11.39m water column, Then the residential area uses Figure 3 as the water supply system that combines living and fire protection. The constant pressure value of the speed-regulating water pump should be 36+11.39=47.39m water column. When there is no fire-fighting, the speed-regulating water pump will still raise the total domestic water consumption to 47.39 At the height of m, the daily power consumption is (0.00272×54×47.39)÷0.73×24=229kw/h, and the water supply system consumes more power, (229-174)÷174=0.316, which is 31.6%. The length of the water column is 10m, and the calculated power consumption is 50% more. Considering the low-efficiency operation of the speed-regulated water pump under the low-flow operation, the power consumption is much larger than the above value. The speed-regulating water pump and the tankless fire-fighting water supply system is a device that wastes energy in vain. Figure 3 When it is only used as a fire-fighting water supply system, the speed-regulating water pump runs for many years, and only supplements the volume of the pipe network with little water loss, even to zero flow, which causes the speed-regulating pump to work in a low-efficiency area for a long time. Waste about 40% of energy.

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