How to choose the expansion valve of air-cooled chiller How to judge high and low pressure

How to choose the expansion valve of air-cooled chiller How to judge high and low pressure

How to choose and install the expansion valve for industrial chillers, screw chillers, air-cooled chillers, and chillers: The choice of expansion valve and the performance of the air-cooled chiller refrigeration system play an important role, the correct choice The expansion valve will maximize the utilization of the evaporator z* and make the evaporator always match the heat load. It is one of the four major components of the refrigeration system, and an important device for regulating and controlling the flow and pressure of the refrigerant entering the evaporator.

　　 One, the selection of thermal expansion valve

　　In the air-cooled chiller refrigeration system, the selection and installation of the expansion valve are very important. Only the correct selection and installation can ensure the normal operation of the unit. Therefore, when choosing an expansion valve, we can use a thermostatic expansion valve of appropriate specifications according to the evaporator load and the evaporation temperature. The capacity of the generally selected expansion valve is about 20% larger than the heat load of the evaporator. For small chiller refrigeration systems, gas-filled thermal expansion valves are generally used, and medium-sized air-cooled chiller refrigeration systems mostly use adsorption-filled or mixed-filled expansion valves.

　　 2. Installation of expansion valve

　　 1. The expansion valve of the chiller is installed in front of the evaporator, usually in a vertical position. Taking into account the convenience of installation and maintenance, low cooling loss, and should be as close as possible to the entrance of the evaporator.

　　2. The working condition of the expansion valve for the air-cooled chiller is directly related to the installation position of the temperature sensor. Because the expansion valve completely relies on the temperature change of the bulb to adjust the opening size of the expansion valve. The temperature sensor is installed on the pipe at the outlet of the evaporator of the chiller. As the evaporator outlet pipe grows, its superheat gradually increases. Therefore, the position of the expansion valve bulb is directly related to the liquid supply of the expansion valve. Generally speaking, the temperature sensor is installed more than 1.5m away from the compressor suction port. When the liquid supply cannot meet the system requirements, the screw of the expansion valve must be adjusted to adjust the liquid supply.

　　3. When installing the temperature sensing bulb of the expansion valve, it must be in close contact with the suction pipe. The contact surface is required to be clean, with low thermal resistance, and not to be disturbed by factors such as external temperature. The temperature sensing bulb and the return air pipeline are generally tied with metal hoops and fastened with bolts. At the same time, heat insulation and moisture-proof insulation layer should be wrapped around the temperature sensing bulb and the pipeline to reduce external disturbance, so that the thermal expansion valve works stably and adjusts sensitively.

How to judge the high and low pressure of the air-cooled chiller: The high-pressure pressure of the standard chiller is displayed at 12.5～15kg/cm2, which is z*best, and the air-cooled 14～17kg/cm2 is z*best, but not higher than 19.5kg/cm2. When the pressure of the water-cooled type is higher than 19.5kg/cm2 and the pressure of the air-cooled type is higher than 24kg/cm2, the high-pressure switch will automatically trip. Please follow the instructions below: low pressure is 3.1～4.5kg/m2 as z*, but not low If it is at 2kg/cm2 and lower than 2kg/cm2, the low pressure will automatically trip, please follow the explanation (2) below.

　　Explanation (1)

　　 When the condenser of the chiller has poor heat dissipation, the efficiency of the compressor becomes lower and the operating current increases. When the high-pressure pressure of the air-cooled chiller rises to 24kg/cm2 and the high-pressure pressure of the water-cooled chiller rises to 19.5kg/cm2, the compressor is protected by the high-pressure switch and trips, and the compressor automatically stops running, and high pressure will appear at this time Overload alarm and display fault code or fault indication. At this time, it is necessary to check whether the circulating water of the cooling water tower is normal, whether the cooling water temperature is too high, whether the cooling water tower fan and water pump are running, and whether the cooling water valve is fully opened (check for air-cooled chillers) Whether the radiator is dirty or blocked), after confirming that everything is normal, press the reset button (REST) or shut down and restart the chiller to operate normally. If high-pressure overload alarms frequently occur, you need to arrange for the manufacturer to clean the chiller condenser as soon as possible.

　　Explanation (2)

1. When the water temperature of the chiller is above 5℃ and the pressure of the low pressure gauge is lower than 2kg/cm2, it means that the refrigerant is insufficient. Therefore, the leakage of refrigerant must be repaired first, and then the filter drier must be replaced to re-vacuum and supplement Appropriate refrigerant.

2. If part of the leaking refrigerant is found to be immersed in the water, the chiller must be stopped immediately, and the water in the water tank must be removed immediately, and the manufacturer will be notified as soon as possible to send a technician to deal with and repair, so as to prevent the compressor from sucking the refrigerant water into the refrigeration system and causing more serious damage Damage

　　If the thermal expansion valve is not matched with the refrigeration system, the refrigerant flow of the system will be more and less sometimes, so that the cooling capacity of the thermal expansion valve will be greater and sometimes less. When the cooling capacity is too small, the liquid supply of the evaporator will be insufficient, and excessive heat will be generated, which will adversely affect the performance of the unit system. When the refrigeration capacity is too large, it will cause oscillations, intermittently causing excessive liquid supply to the evaporator, causing severe fluctuations in the suction pressure of the compressor, and even liquid refrigerant entering the compressor, causing liquid hammer (wet stroke).