Air compressor energy saving step one: correct energy efficiency testing
Now more and more users are paying more and more attention to the energy efficiency of air compressors, which is also one of the important manifestations of our domestic enterprises towards the lean production direction. In this situation, in order to prove their products (air compressors), some suppliers use various means to let users know their energy efficiency. This was originally a good thing. However, if the method adopted is incorrect, it will cause serious deviation from the facts and cause trouble to users and the market. For example, there are currently methods on the market to verify the energy efficiency of the air compressor main body by testing the intake air flow, which is one of the methods that seriously deviates from the facts.
As we all know, gas is a changeable state, and gas is compressible. When a gas is compressed, the pressure and temperature generated by the gas will change accordingly, so measuring the volume of a gas must specify its state (temperature, pressure). For displacement compressors, the flow rate is specified by the free displacement. The internationally used term is "FAD", also known as Free Air Delivery, which translates into Chinese for free exhaust. According to ISO or Chinese national standards, the exhaust flow rate of the air compressor is converted into the air volume flow rate of the entire machine in the intake state. This intake state refers to the ambient pressure, temperature, and relative humidity during intake. It should be pointed out that the exhaust flow under the intake state cannot be equal to the intake flow.
Why does measuring the intake air flow not represent the free exhaust flow of the air compressor (the rated flow of the volumetric air compressor)?
There are several main reasons:
1
Because the compressor runs from suction to exhaust, the ambient air needs to enter the inside of the compressor cabinet, then enter the intake filter, then pass through the intake filter, enter the intake valve, and then enter compression Cavity. For oil-injected screw compressors, they also need to pass through the oil and gas separation barrel, cooler and air-water separator and then be delivered downstream through the compressor outlet. In this process, there are often losses caused by various leaks and losses and pressure changes. Therefore, empirical research finds that there is a large deviation between the intake air flow of the main engine and the free exhaust volume of the entire machine, with a difference of more than 3 ~ 5%;
2
When our air compressor is in normal production, the casing panel of the air compressor is installed, and the air intake filter is inside the compressor. Poorly designed air compressor case temperature may differ from the outside temperature by more than 20 ° C. However, when we use the common intake air flow test on the market, first open the panel of the compressor, then remove the intake air filter and install the measuring instrument to measure. There will be two problems here. One is that the temperature during measurement is completely different from the actual operating temperature, and it is estimated that the difference will be as low as 20 ° C. Another problem is that the filter loss measured before the host is also not considered, which also deviates from the actual operating conditions. The difference of 20 ° C is a difference of more than 7% for a displacement compressor, and the loss of the filter can be imagined. This difference is very large.
3
At present, the common method for air inlet measurement in the market is a thermal mass flowmeter. It measures the flow velocity at a point in its inlet pipe. For incompressible or dense fluids, this problem is not very big. But for air, especially low pressure (ambient air, air inlet), the density of air is very low and the viscosity coefficient of air is very high. The flow velocity in the diameter range of the intake hose pipe made by it changes greatly, and the flow state is unstable. And because of the position of the air inlet, the installation of the instrument usually cannot meet the basic technical requirements of the instrument. It can be seen that the error here is very large. The reliability of the measurement data is low and the error is large.
Therefore, from the above reasons, it can be seen that the method of measuring the flow rate of the screw air compressor inlet does not reflect the true flow rate of the air compressor. It is precisely because of the above-mentioned reasons that this method cannot usually be used as a measurement method of air compressor parameters.
So, what is correct for our users? First, of course, according to the standard test methods, such as the national standard GBT3853 "acceptance compressor acceptance test" or the international standard ISO1217 "Displacement compressors -Acceptance tests" required relevant measurement standards for related measurements. However, these measurements are more suitable to be performed in the laboratory. It is very difficult and costly to perform such tests in the field. Therefore, this is rarely done.
So what is the more applicable and actionable method?
Measuring position
First, the measurement position must be correct, and the measurement position must be behind the compressor. According to the requirements and characteristics of various flowmeters, the flowmeters that are relatively easy to operate in the current market are ultrasonic flowmeters and portable plug-in thermal mass flowmeters, which are relatively easy to install and remove. The flow meter is a precision monitoring instrument, which has relatively high requirements for the measurement environment. For example, it is very sensitive to compressed air containing liquid water. During long-term measurement, the accuracy will decrease and even erroneous values will appear. Therefore, when using a flow meter for flow measurement, it is recommended that the flow meter be installed in a dryer such as a cold drier or a suction drier to ensure that there is no liquid water for the measurement. In addition, installation and Select the flowmeter corresponding to the measurement range to ensure the accuracy and continuity of the measurement accuracy. Of course, no matter what kind of flowmeter is selected, it needs to be regularly calibrated and verified. In the process of use, it must be performed strictly in accordance with the use requirements of the respective flowmeter. Only in strict accordance with relevant engineering and technical requirements can it be possible to obtain relatively accurate data.
Power test
Second, there is the power test. The power test needs to measure the power value at the power line of the whole machine. This data is related to three voltage, current and real-time power factors. Therefore, it is recommended to use a dedicated power meter for online measurement instead of current measurement.
