Experimental Research On On-line Measurement Method Of Fan Air Volume Based On Static Pressure And Apparent Power

Because most of the measurement instruments used now are affected by the field environment conditions,their own performance and pipeline layout,the accuracy of the system air volume measurement by instruments is low.The on-line measurement of air volume of air conditioning and ventilation system is very important for the real-time monitoring of energy consumption,operation control strategy and thermal comfort of the system.In order to meet the requirements of online monitoring of fan air volume in engineering air conditioning and ventilation system,a doubleinlet back-curved blade centrifugal fan is selected as the research object in this paper.Two online measurement methods are explored,one is to measure the static pressure of the fan and the other is to measure the apparent power of the fan motor,so as to obtain the fan air volume indirectly.After obtaining the fan characteristic curve,the static pressure curve or apparent power curve of the fan can be determined by knowing the fan speed or frequency.By measuring the static pressure or apparent power of the fan,the fan air volume can be obtained according to the corresponding relationship of the curve within the allowable operating air volume range of the fan.Firstly,the fan characteristic curve test was carried out,and the static pressure curve and apparent power curve were calibrated at an interval of1 Hz.The air volume,static pressure and apparent power of the fan are calculated by measuring the static pressure difference between front and rear of the fan,the current and voltage of the motor,and the pressure difference between front and rear of the nozzle box and the nozzle.Then the air volume-static pressure curve and air volume-apparent power curve in the fan characteristic curve are fitted and drawn,and the polynomial of the curve is obtained.Given the characteristic curve polynomial at 1Hz interval,all frequencies in the range of 50-20 Hz were tested to explore the deviation of static pressure or air volume measured at apparent power.If the frequency is in the middle,the characteristic curve polynomial at the frequency is obtained by interpolating the adjacent integer frequency.The static pressure or apparent power measured at each frequency was put into the characteristic curve polynomial to calculate the air volume,and the deviation was compared with the standard air volume measured by the nozzle box.The experimental results show that the fan air volume can be obtained indirectly by measuring the fan static pressure or apparent power when the characteristic curve data at integer frequency is known within the range of the calibrated air volume,and the overall deviation is less than 3%compared with the air volume measured with the standard nozzle.Then the principle of this method is combined with automatic control to realize online real-time monitoring of fan air volume,and compared with the standard application of hot-wire anemometer to simulate the field measured air volume,which has higher accuracy and faster efficiency.Then explore the feasibility of this method in engineering application:when the characteristic curve data obtained is not enough,the impact of interval interpolation on the measurement accuracy.Influence of belt wear on accuracy of two measurement methods.In comparison,the advantages of using static pressure or apparent power to indirectly monitor the air volume of the system are high precision,economic and reliable,fast response speed,stronger anti-interference ability,and lower requirements for on-site pipeline layout.