Carry out air conditioning system testing how to choose anemometer
Air-conditioning system testing The wind speed measurement of the wind system usually requires an anemometer, which can be divided into many types according to the principle, and there are three conventional types: the impeller type, the anemometer, and the Pitot Tube.
In air-conditioning system testing, because the impeller anemometer occupies too much area in the air duct, it affects the distribution of wind speed in the room or in the pipeline, and has low sensitivity to low wind speed, so it is basically unusable. Many people see that the impeller is cheap and it is not appropriate to buy it. The impeller type can usually be used for outdoor testing. For example, the green building standard stipulates that the wind speed in the pedestrian area around the building is lower than 5m/s, which will not affect the comfort of outdoor activities and building ventilation.
Pitot Tube seems to be a method of measuring wind speed invented by a person named Pitot. The principle is to measure wind speed by dynamic pressure difference. The sensitivity of Pitot Tube mainly depends on the sensitivity of the micro-pressure differential meter it uses. Considering that the uncertainty of pressure difference below 1Pa is already very high (if you are interested, you can reverse the wind speed corresponding to 1Pa, which may be 0.xm/s), so the accuracy of its measurement is also limited. Another problem is that the limitation is that the obtained value is the differential pressure value, and the user needs to convert the differential pressure.
If a digital micromanometer with an accuracy higher than 1Pa is used, the price is tens of thousands, which is already close to that of an anemometer. If an alcohol inclined tube micro-manometer is used, the domestically produced price that can guarantee the accuracy is also around a few hundred yuan, but anhydrous alcohol (about 95% purity) must be used. If the air-conditioning system testing business is carried out, it is necessary to calibrate the inclined tube micromanometer of alcohol. In fact, the main purpose is to calibrate the specific gravity of alcohol. However, alcohol is easy to volatilize after long-term use within a calibration period (usually 1 year), and it is difficult to guarantee the calibration results of the inclined tube micromanometer after the volatilization. Because air-conditioning system inspections have to go to the site, this kind of inclined tube differential pressure gauge cannot take many vehicles in consideration of air traffic control and other constraints.
In short, although the pitot tube + inclined tube micro-manometer is a cheap configuration, its operation, use and calibration are very cumbersome to achieve the ideal wind speed measurement accuracy. If Pitot tube + digital micro-manometer is used, the price is almost the same as that of anemometer. The advantage is that the high-precision micro-manometer used here can also measure micro-pressure difference and measure other physical quantities.
Therefore, the most commonly used anemometer for air-conditioning system testing is the thermal anemometer. The thermal bulb is not recommended here because the thermal bulb of many thermal bulb anemometers is not strong enough. For example, TESTO has a disposable anemometer with a market retail price of less than 800 yuan (actually it is an OEM of a factory in Taiwan). The measurement range is narrow, the mechanical strength of the thermal bulb is very low, and the wind speed is slightly higher. If the anemometer is chosen, I will open another article to discuss it.
