• ### Simple estimation and measurement of indoor and outdoor air pressure difference

DATE：2018-04-11

At present, the new wind system we use mostly follow the design idea of large air volume and micro positive pressure, but many people are puzzled about it. How is the pressure of indoor test in the field? If the new wind system compares the air volume to the swing force of a weapon, then the wind pressure is the sharpness of the weapon. Is the indoor air positive or negative after opening the fresh air system? How big is the pressure difference in the end? How do you measure it? Here is a simple and convenient measuring method for you to refer to.

The wind pressure is when the wind moves forward at a certain speed and meets the obstruction, it will produce pressure on the block, and the wind is the flow of air from a place where the air pressure is large. From the formation of wind, we can see that wind and pressure are inseparable. It is the wind generated by pressure. Since wind pressure causes wind, we have a simple way to measure pressure by using wind.

We can use this formula to estimate the pressure difference inside and outside the chamber by the anemometer. The reason is that the wind speed may vary greatly at different locations, and the mean value is difficult to calculate. Because the external conditions are different, the roughness of the wind propagating medium is different. The wind speed measured at different distances is also not the same.

We consider the room to be measured as a static pressure box. After the new wind system is opened, the pressure in the indoor air is greater than that of the same atmospheric pressure when the new wind system is introduced. The indoor pressure is in positive pressure, and vice versa, the pressure state is negative.

1. Determination of position and determination point

In order to measure the real pressure value of the gas in the room, in addition to the correct use of the pressure measuring instrument, the reasonable selection of the measurement position and the reduction of the air flow disturbance have a great influence on the measurement results. When the test site is difficult to meet the requirement, we can increase the measuring point appropriately to reduce the error. Of course, since it is a simple test, that's a rough number.

We can choose the doors or other available gaps far away from the new wind vent. The wind speed of the holes in the holes (such as the door mirror hole) and the upper and lower crevice of the door is measured by the micro wind meter, the average value and the wind area are measured by multiple points, and the general pressure in the room is calculated, and the indoor air system can be used to achieve the expectation of the indoor air system. Evaluation of the effect.

The choice of measuring points should also consider the convenience and safety of the operation.

Two, test holes and measuring points

Because of the inhomogeneity of velocity distribution, the pressure distribution is also uneven. Therefore, we must measure many points on the same section and calculate the average value of the section.

The usual pitot tube and pressure gauge can be used, but it is difficult to read out the exact differential pressure.

The commonly used direct reading speedometer is a thermo ball thermoelectric anemometer and a blade type anemometer.

The measurement of slit wind speed is usually based on uniform moving method, fixed point method and so on.

For example, the air anemometer can move slowly along the aperture of the gap with the gap area less than 0.3m2, and the anemometer must not leave the measurement plane when it moves, and the result is the average wind speed of the gap. The average value is measured for many times.

The average wind speed at the gap is calculated by arithmetic average.

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