Experimental Research On Air Flow Measurement Method By Differential Pressure Type Square Averaging Pitot Tube

The air volumes in different positions of the air conditioning duct system are the important fundamental data for the energy consumption monitoring, operational control and energy metering in air conditioning ventilation system and air quality guarantee. They are also the necessary data of building energy saving. The main reasons for the low accuracy of air flow measurement are the performance of air flow meter, the stability of measurement signals and the layout of the ventilation pipe. Traditional flow meters and measurement methods have been difficult to meet the requirements of high accuracy measurement and low energy loss of air flow. As a new differential pressure flow sensor,averaging pitot tube has the advantages of energy saving, simple installation and high accuracy. It applies to the air flow in-situ measurement of new construction and existing building.It can realize each part of air volume on-line monitoring for air conditioning system as well. Therefore, it is practical and significant for improving indoor air quality and realizing energy saving operation of air conditioning system through experimental research on measurement principle, measurement performance and measurement methods of averaging pitot tube to obtain accurate air flow data.Firstly, in this paper, select a detecting rod of square cross section shape to anlyse velocity measurement based on the available research on the structure of averaging pitot tube and obtain a new expression of flow coefficient. Identify the flow calculating formula of orifice plate for flow standard device through the pitot static tube traverse calibration test based on the existing test-bed.Secondly, refined two structural parameters equivalent diameter of detecting rod cross section and angle between static pressure hole center and detecting rod cross section center based on the flow coefficient theory formula of square averaging pitot tube. Design the main factors affecting flow coefficient of square averaging pitot tube experiment by orthogonal testing method and the main factors’ level contrast experiment in different test target parameters, get the best structural style of averaging pitot tube.Finally, select seven different installation sites to study the influence of different installation position on averaging pitot tube measurement performance by using the best structural style of averaging pitot tube based on the existing test-bed’s ventilation pipe layout conditions.Experimental results show that square averaging pitot tube has the highest measurement accuracy when tested in the standard installation. It provides the experimental reference method and technical realization method in the poor pipe layout measurement environment because of its preferable accuracy at some nonstandard position after revise the flow coefficient by installation site correction.