An important factor for a comfortable life is clean air. Many enterprises pollute the atmosphere with various substances that affect health. Having made measurements of atmospheric air, scientists draw disappointing conclusions. Therefore, great importance is given to ventilation and air conditioning systems. They help make life better.
General information
Ventilation and air conditioning systems must function well for a long time. To do this, it is necessary to carry out professional tuning, as well as timely maintenance. The list of technical works also includes air measurements.
This procedure occurs in accordance with the developed methods.
Flow rate
The movement of air through the system occurs at a certain speed, which is influenced by various factors. First of all, it depends on the design of the ventilation system (that is, the cross section and length of the ventilation ducts). It is these indicators that affect air flow. To determine the speed of the flow, it is necessary to measure the air, namely its dynamic pressure at several points. The average indicator will show the air velocity in the system.
It should be noted that this indicator for the premises is important for living rooms. Air enters them in a unidirectional flow. Measurements of indoor air are made primarily for residential areas. Unidirectional flow movement occurs here.
Why take measurements of air flow?
The purpose of this event is to determine the amount of flow in the room for a specific time. Measurements of indoor air are made for the flow moving through the system. Its consumption may change after passing through the filter. Regardless of location, the speed will change. Moreover, the cross-section of ducts plays a key role.
To make accurate measurements of air choose a flat area. Its length should be at least 5 sizes of the diameter of the system section. Its beginning is taken from local resistance. The distance to the next resistance must be exactly at least 2 duct diameters. For this, a laboratory is used, in which air measurements are taken at several points. The number of measurements depends on the diameter or length of the rectangular channel.
Types of measuring instruments
To configure the ventilation system, measuring devices are required.
The question arises, which ones? Air measurements are necessary to determine the speed of the flow, as well as the flow rate. Today on the market you can find various devices. They differ in their characteristics, as well as in the accuracy of measurements. First of all, it is necessary to pay attention to the ventilation of the room. There are devices that work in both natural and artificial ventilation.
Before you purchase a measuring device, you need to decide exactly where the measurement will be made. It can occur both in the ventilation grill and directly in the duct. You should also be aware of some of the requirements that apply to a stream. For example, the speed of the flow or its temperature must comply with regulatory indicators.
Air measurements in the apartment are carried out by such devices:
- Hot-wire anemometer. It is used to measure the speed of air movement. A special sensor is heated to a certain temperature and placed under a moving stream. Next, measure the time during which the sensor has cooled. This will be the flow rate.
- Ultrasonic Anemometer. The device is placed in an air stream. Velocity is measured by capturing sound frequencies at different points in the duct.
- Vane anemometer. The flow rate is determined by the moving impeller.
- Pitot tube. When measuring, high-quality digital equipment is used. The tube is placed in a specific area where static and total pressure are measured.
- Balometer It determines the flow rate of air that passes through a specific section of the duct.
Air flow meter
The most common instruments are an anemometer and a hot-wire anemometer.
They are highly accurate and reliable. Many experts use an anemometer. Its design provides for a large impeller. Its diameter can reach up to 100 mm. This is the main advantage of this measuring device. It is she who is able to capture the air flow near the ventilation grill. With a minimum number of measurements, an accurate result is obtained. Therefore, it is to this air meter that you should pay attention.
To simplify the process, as well as to minimize errors, it is worth using additional devices. The simplest of them is a funnel. It has a simple design that allows you to determine the air flow in just one measurement. This feature significantly saves the specialist time. In some cases, it is necessary to take measurements of the air temperature in the room to obtain more accurate measurements.
It so happens that it is necessary to produce them in difficult places. In such cases, a telescopic probe is used. Thanks to its long base, you can get to difficult places and take measurements of the atmospheric air and directly in the duct.
To simplify the procedure, it is necessary to purchase those devices that determine the flow rate due to automation. The final result is displayed on an electronic scoreboard. There is no need to make additional calculations. The instrument will display an average of three measurements. In the absence of these functions, the calculation is performed independently.
Duct flow measurement
Before starting the operation, you must make sure that there are appropriate holes in the duct. They are necessary for the procedure. The diameter of the hole should correspond to the diameter of the measuring device.
As mentioned earlier, it is important to choose a place. If there are no corresponding holes in the duct, they must be made independently. This is done with a drill. So how to choose a place? The hole should be in a straight section of the duct, the length of which is 5 of its diameters. It is placed at a distance of 3 diameters of the pipeline.
Unlike measurements in the ventilation grill, vane anemometers are used in this case, where the working element has a small diameter (approximately 25 mm). During the procedure, thermal anemometers are also used, the design of which provides a pneumometric tube.
Another device is a differential pressure gauge. It is used when the flow velocity is above 2 m / s. Therefore, it is better to use the previous options.
If the duct is located at a high distance, for example under the ceiling, then use a telescopic umbrella.
It can be extended by certain distances, which simplifies the measurement process. If the process will be carried out with the help of a pneumometric tube, then it is necessary to take care of its length in advance.
Tips for Using Measuring Instruments
It happens that a large amount of dust is contained in the air stream. In this case, you should not use a hot-wire anemometer or a pitot tube for measurements. Why so? In the tube, which is inserted into the duct, have small holes that serve to measure the total pressure. In the dusty state of the air, these openings quickly become clogged, and the measurement result will not be accurate.
Hot-wire anemometers are used in those ventilation systems where the air velocity is above 20 m / s. This measuring device contains a temperature sensor, which is a sensitive element. Therefore, with a strong flow rate, it can collapse.
Before starting measurements, you must carefully read the technical documentation of the measuring instruments. It contains indicators of permissible temperatures, flow rates, as well as a description of the environmental conditions in which they can be used.
If these rules are not followed, the measurements will not be accurate, or the device may fail.
In systems in which heated air moves, it is better to use pneumometric tubes for measurements. They are made of stainless steel and therefore are a reliable fixture. Moreover, they should not contain plastic elements, since under the influence of high temperatures they can be destroyed.
When conducting tests related to measuring the flow rate and air flow rate, it is necessary to ensure that the sensitive element of the device is directed towards the flow. If this rule is not observed, the results will not be accurate. The more the sensor deviates from the necessary conditions, the greater the error.
Hatch for measuring air parameters
Another accessory is the hatch. As a rule, its location is foreseen in advance by designers when drawing up a ventilation plan. But sometimes it is installed by employees who are responsible for setting up the system. In practice, the second method is used, since designers do not always correctly position the hatch.
Hatches for air measurements can be installed independently, in the presence of certain skills. To do this, a hole is made in the system using a drill. Therefore, if it is installed in the wrong place, it can be easily moved. Hatches for measuring air parameters should be clearly visible, and also easy to open and close. If removed, the diameter of the hole should allow free penetration of the measuring device.
It happens that the hole is not used to measure speed and air flow. In this case, the hatch is removed, and the hole is sealed with adhesive tape or rubber gasket.
Cost
Instrumentation have a fairly high price. For example, the cost of a hot-wire anemometer ranges from 10,000 to 40,000 rubles. Compared with it, a winged anemometer can be purchased much cheaper, for only 6,000 rubles.
The choice of measuring device depends on the characteristics of the device, as well as the characteristics of the air flow.
In addition, a device with a display and automatic calculation of the necessary data is much more expensive.
The price of additional equipment
As an additional equipment, there is a hatch for measuring air parameters. Its cost ranges from 100 to 300 rubles. It depends on the size of the hole through which the measurement will be carried out.
Reviews
Measuring instruments are purchased only by specialists in ventilation and air conditioning. They are the ones who are setting up the system. Specialists are satisfied with the measuring devices and there have been no particular complaints about them.
The quality of the measurement depends on the person himself. If all the requirements are met, the result will be more accurate. It just makes no sense to buy such a device for measuring air once, since the cost of the equipment is quite high.
Conclusion
If you select the correct measuring device, you can find out the speed of the flow, as well as its flow rate. Thanks to these indicators, experts conclude about the ventilation system. This is especially important for residential premises.
So, we found out how to measure the air flow in the room.