During the operation of the refrigeration plant, the condensing pressure has a great influence on the performance of the system. When the condensing pressure (or condensing temperature) is high, the compression ratio increases, the volumetric efficiency decreases, the cooling capacity decreases, and the power consumption increases. The higher the exhaust gas temperature and the higher the condensing pressure, the greater the degree of adverse effects. The phenomenon of high condensing pressure mainly occurs in summer. At this time, the condensing pressure should be reduced as much as possible to ensure the economy and reliability of the system operation.
However, for refrigeration devices that operate throughout the year, such as air-conditioning room, refrigeration and refrigeration (cold storage) and other equipment, there may be a phenomenon that the condensing pressure is too low during winter operation. When the condensing pressure is too low, the pressure difference before and after the expansion valve is too small, the capacity of the expansion valve is reduced, the liquid supply capacity is insufficient, the evaporator is short of liquid, and the cooling capacity of the system is greatly reduced, thus causing the failure of the refrigeration system. Therefore, the condensing pressure must be controlled within a reasonable range, otherwise it will cause frequent low pressure alarms or low suction pressure alarms in the refrigeration unit.
Different condensers have different condensing pressure adjustment methods. Here are several methods to increase condensing pressure at low temperatures:
1、Exhaust pressure controller：
It can make the condensing fan run intermittently, it is simple and easy to use, and the technology is mature. The controller used is a pressure controller, which can control the intermittent start and stop of the fan; when the pressure is too low, the fan is turned off; when the pressure is too low, the fan is turned off; When it is too high, turn on the fan.
Generally, on small-capacity units, two or more fans are used, one of which is normally open, and the rest of the fans are controlled by a pressure controller. The start or stop of the fans is controlled by the level of condensing pressure.
2、Fan speed control:
The fan speed control method is also a relatively mature method, and the main electrical components used are frequency converters (three-phase) or governors (single-phase). The main working principle is to input the feedback model (1~5V or 4-20mA signal) of the exhaust pressure (condensing temperature) to the inverter (speed governor), and the inverter outputs (0~50Hz) to the fan according to the setting, Realize the variable speed operation of the fan. This is also a common control method, simple and easy to use.
3. Air volume control device:
The main component is a shutter-type air volume control device, and the shutter device can be set either at the air inlet or at the air outlet. The principle is to use a piston-type regulating damper driven by high-pressure refrigerant. This control device can obtain a stable exhaust pressure like the fan speed controller; the most important thing is that the inlet pressure of the expansion valve will not produce higher pressure than the fan intermittent operation method. big fluctuations.
4、Condenser overflow device:
The working principle of the condenser overflow device is to use excess refrigerant to increase the condensing pressure of the system. The condenser overflow device is used in warm or low temperature environments to send a large flow of refrigerant from the accumulator to the condenser, and use the excess refrigerant to increase the condensing pressure of the system, so as to avoid the condensation pressure being too low at low temperatures. Fault.
The advantage of the condenser overflow device is that it can obtain a stable condensing pressure with small fluctuations; the condenser is almost filled with liquid refrigerant, so that the inlet temperature of the expansion valve is lower than the condensing temperature, and supercooling is achieved, thereby increasing the cooling capacity of the refrigeration system.
5. Water flow control valve:
There are two types of water flow control valves: pressure control type and temperature control type:
Pressure-controlled water flow regulating valve: Use the condensation pressure as a signal to proportionally adjust the flow of cooling water. The higher the condensation pressure, the larger the valve opening, the lower the condensation pressure, the smaller the valve opening. When the opening is reduced below the opening pressure of the valve, the valve is automatically closed and the supply of cooling water is cut off. After that the condensing pressure will rise. When it rises above the opening pressure of the valve, the valve automatically opens again.
Temperature control type water flow regulating valve: The working principle is the same as that of the pressure control type, the difference is that it detects the temperature change of the cooling water outlet with a temperature sensor, converts the temperature signal into a pressure signal in the temperature sensor, and adjusts the cooling water. traffic. The temperature control type water volume regulating valve is not as fast as the pressure control type water volume regulating valve, but it works smoothly, and the sensor installation is simple and convenient.
6、Condenser heat exchange area adjustment:
When there are multiple sets of condensers, the open/closed state of the solenoid valves connected in series on the passages of each set of condensers can be used to open or cut off the passages of the condensers to change the heat transfer area of the condensers. This method is used in multi-line connections. To adapt to the large-scale capacity adjustment of the compressor, the condensing pressure can be stabilized within the required range.
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