A. Low condensing pressure fault
In the refrigeration system, if the condensing unit for cold room is installed outdoors, the exhaust pressure (condensation pressure) of the system will be relatively low in winter (or low-temperature environment), which is more common in the north. For the air conditioner, it is the same for other equipment (cold storage, etc.);
If the condensation pressure is too low, the expansion valve will not get enough pressure drop at both ends, so it is difficult to provide proper refrigerant to the evaporator. On the one hand, the refrigeration capacity of the system can not meet the requirements, and it will also cause frequent low-pressure alarm and other faults of the system;
B. Several methods of increasing condensation pressure at low temperature
Through the above introduction, we know that in winter, the refrigeration system is prone to the failure of low condensation pressure, so what can we do to avoid the low condensation pressure in the low-temperature environment?
1. Using exhaust pressure controller to control the intermittent operation of the fan
2. Control fan speed
3. Control airflow with damper or fan intermittent operation
4. Using the condenser overflow device
C. Method of exhaust pressure controller
The intermittent operation of the fan is simple and easy to use, and the technology is mature. The controller used is the pressure controller, which can control the intermittent start and stop of the fan;
When the pressure is too low, close the fan;
When the pressure is too high, start the fan;
Generally, on small capacity units, two or more fans are used, one of which is normally open, and the other is controlled by the pressure controller. The start or stop of fans is controlled by the level of condensation pressure.
D. The method of fan speed control
The method of fan speed control is also a mature method for many years. The main electrical components used are frequency converter (three-phase) or governor (single-phase).
The main working principle is to input the feedback model (1-5V or 4-20mA signal) of the exhaust pressure (condensation temperature) to the frequency converter (governor), and the frequency converter outputs (0-50Hz) to the fan according to the setting, to realize the variable speed operation of the fan.
E. Method of air volume control device
The main component is the shutter type air volume control device
The principle is to use the piston type regulating damper driven by the high-pressure refrigerant. This kind of control device can live as stable exhaust pressure as the fan speed controller. The most important thing is that the inlet pressure of the expansion valve will not fluctuate greatly as the intermittent operation of the fan.
The shutter device can be set at the air inlet or the air outlet;
F. Method of condenser overflow device
The working principle of the condenser overflow device is to use excessive refrigerant to increase the condensing pressure of the system.
The overflow device of the condenser is used to send large flow refrigerant from the liquid reservoir to the condenser in a warm or low-temperature environment. Excessive refrigerant is used to increase the condensation pressure of the system, to avoid the failure of low condensation pressure at low temperature.
1. The stable condensation pressure is obtained and the fluctuation is small;
2. The condenser is almost filled with liquid refrigerant, which makes the inlet temperature of the expansion valve lower than the condensation temperature, to achieve supercooling, thus improving the refrigeration capacity of the refrigeration system.