How to judge the presence of air in the air conditioner

How to judge the presence of air in the air conditioner

I. Overview

　　In the refrigeration system, the non-condensable gases are mainly nitrogen, oxygen, hydrogen and water vapor in the air; because these working fluids do not condense with the refrigerant, they generally gather in the condenser or the liquid reservoir.

As the non-condensable gas occupies part of the condensing space, it will cause the condensing pressure (discharge pressure) to rise, make the compressor's high-pressure meter pointer jitter, reduce the cooling effect and increase the compressor's power consumption; therefore, we must Most refrigeration workers judge whether there is air in the refrigeration system based on the jitter of the pointer of the high pressure meter.

But for the Freon system, it is unscientific to judge the presence of non-condensable gas based on the jitter of the high pressure gauge, because there are many reasons for the jitter of the high pressure gauge, such as:

　　 1. Deformation of exhaust valve plate (piston compressor)

　　2. The system flashes, causing the throttle valve to oscillate, and the condensing pressure may oscillate;

　　3, expansion valve failure

　　 So the high-pressure meter shakes, it cannot be assumed that there is non-condensable gas in the system.

　　 2. Judgment principle

According to Dalton’s law of partial pressure of gases, the absolute pressure in a closed container is equal to the sum of the partial pressures of the gases present. Therefore, we believe that the pressure in the condenser and accumulator is equal to the condensation pressure of the refrigerant plus the non-condensable gas. The sum of pressure. Therefore, if there is a non-condensable gas in the system, the pressure must be high. We can also determine whether there is a non-condensable gas in the system by measuring the temperature and pressure.

　　 Below we divide the air-cooled and water-cooled condensers to introduce how to determine the presence of non-condensable gas in the system.

　　 Three, air-cooled

Connect a thermometer at the outlet of the air-cooled condenser. After stopping the compressor, close the exhaust valve and the liquid supply valve; wait quietly, when the degree of this thermometer is the same as that of another thermometer that measures air temperature (or Very close), please record the pressure in the condenser at this time and compare it with the saturation temperature corresponding to the ambient temperature. If the former is higher than the latter, it can basically be determined that there is non-condensable gas in the system.

　　 Four, water-cooled

　　 Connect a thermometer at the outlet of the water-cooled condenser. After stopping the compressor, close the exhaust valve and the liquid supply valve. At this time, the cooling water is open and running as usual.

Connect a thermometer to the inlet and outlet of the cooling water, measure the water temperature, and wait quietly; when the temperature of the inlet and outlet water is equal, please record the pressure in the condenser and the outlet temperature of the water-cooled condenser at this time, if the condenser pressure is high Based on the saturation pressure corresponding to the outlet temperature, we can determine that there is non-condensable gas in the system. The greater the difference between the two, the more non-condensable gas.

　　 5. Actual case

　　 I have seen so many above, but you still don’t understand, let’s take a look at the following practical example:

E.g: 　　 The measured condensing pressure of the R22 system is 13.2kg/cm2 (gauge pressure), and the ambient temperature at that time is 35 degrees.

　　 Check the "R22 Refrigerant Temperature and Pressure Comparison Table", the corresponding pressure at 35 degrees is 12.81kg/cm2 (gauge pressure), which is lower than the measured condensing pressure, indicating that there is non-condensable gas in the system. The pressure content of the non-condensable gas is:

　　 13.2-12.81=0.39kg/cm2 (gauge pressure).

　　 This method of identification and detection is very simple, practical and practical.

　　 6. There is a non-condensable gas separator in the system

　　For large-scale ammonia refrigeration systems, there is generally a non-condensable gas separator;

The non-condensable gas is easily separated from the refrigerant when the system is standing at low temperatures. Its specific gravity is smaller than that of the refrigerant. After separation, it gathers at the high place (above) of the system. Therefore, it should be selected during the lowest temperature period. The system has the longest downtime and discharges at the highest point of the system.

　　 can also be discharged directly from the top of a container in the system by opening the valve directly, or by discharging the containers one by one.