1、 Operating principle of air-cooled screw heat pump unit
The air-cooled screw type cold water heat pump unit is a central air conditioning unit that uses air as the cooling medium (summer) and heat source (winter), water as the refrigerant, and adopts a vapor compression refrigeration cycle. The unit has the characteristics of dual use of cooling and heating. It can be combined with fan coil units, air conditioning units, and air handling units to form a centralized or semi centralized central air conditioning system, with flexible layout and diverse control methods.
During refrigeration: The compressor continuously extracts refrigerant vapor from the evaporator, and after compression by the compressor, the refrigerant transforms from low-temperature and low-pressure vapor to high-temperature and high-pressure vapor. The high-temperature and high-pressure refrigerant vapor condenses in the condenser, releasing a large amount of heat that is absorbed by the air. The high-pressure liquid refrigerant condensed by the condenser is throttled and depressurized by the thermal expansion valve, and converted into low-pressure refrigerant liquid. [Source: Refrigeration Encyclopedia official account] Low pressure refrigerant evaporates in the evaporator and absorbs a lot of heat from the refrigerant water, thus reducing the temperature of the refrigerant water and achieving the purpose of refrigeration. Low pressure refrigerant vapor is extracted by the compressor, forming a refrigeration cycle.
During heating, the compressor continuously extracts refrigerant vapor from the evaporator, and after compression by the compressor, the refrigerant transforms from low-temperature and low-pressure vapor to high-temperature and high-pressure vapor. The high-temperature and high-pressure refrigerant vapor condenses in the condenser, releasing a large amount of heat that is absorbed by the heat medium water, thereby achieving the purpose of heating. [Source: Refrigeration Encyclopedia official account] Low pressure refrigerant vapor is extracted by the compressor to form a heating cycle.
Lubrication system: During the operation of the compressor, the oil in the oil tank is under exhaust pressure and continuously flows towards the low-pressure area. After the oil flows out of the tank, it passes through the oil cooler and is diverted to the inlet of the compressor loading valve and the inlet of the high and low bearings. It then enters the refrigeration oil in the loading and unloading piston cylinder and bearings, returns to the low-pressure side of the compressor, and is finally compressed by the compressor rotor before being discharged and returned to the oil tank through the oil separator.
2、 Electric control protection of air-cooled screw heat pump unit
Current overload protection
High current protection is used to prevent motor overload and damage to the compressor motor during operation. The current of the compressor motor is continuously monitored and controlled by a limiting function to prevent damage to the compressor motor caused by overcurrent.
phase loss protection
Phase loss protection can protect the refrigeration unit from damage due to phase loss. If any of the three phase currents of the motor are lost, this control will stop the chiller unit. When the machine is stopped, a fault alarm message will appear on the touch screen.
Reverse protection
This function prevents the compressor from reversing. When an incorrect power phase is detected, a fault alarm message will be generated.
Low outlet temperature protection
Low outlet temperature shutdown protection is a safety control method to protect the unit from damage caused by water freezing in the heat exchanger.
Low temperature shutdown protection for refrigerant
The low-temperature shutdown protection of shell and tube refrigerant is used to prevent water freezing in the heat exchanger. When the low temperature shutdown setting of the heat exchanger refrigerant reaches 4 ℃, an alarm will be triggered to shut down, and a fault alarm message will appear on the touch display. The set value for low-temperature shutdown of standard unit refrigerant is 4 ℃.
High exhaust temperature protection
Exhaust temperature protection is a safety control method used to prevent damage to the unit system caused by excessive condensation temperature, which can be modified through maintenance tools. The set value for shutdown protection when the exhaust temperature is too high is 95 ℃. When the exhaust temperature exceeds 95 ℃, the alarm will shut down after a duration of more than 3 seconds (the delay time can be modified through control software).
Restart delay
This function can provide frequent motor start protection, and the execution of restart delay function depends on the set value.
High voltage protection
High pressure shutdown protection is a safety control method to protect the unit from damage caused by high unit system pressure. The shutdown setting is set by the manufacturer. [Source: Refrigeration Encyclopedia official account] General high pressure shutdown protection standard unit setting value: R22 refrigerant is 25kgf/cm2; When the high pressure of the unit system exceeds the set value and triggers an alarm shutdown, a fault alarm message will appear on the display indicating low pressure protection.
Low voltage shutdown protection
It is a safety control method that protects the unit from damage caused by low system pressure, and the shutdown setting is set by the manufacturer.
Oil level protection
Oil level shutdown protection is a safety control method to protect the compressor from damage caused by oil loss. The shutdown setting is set by the manufacturer and can be modified through maintenance tools. When the oil level in the fuel tank is lower than the oil level switch control point and the duration exceeds the set time, the alarm will stop and a fault alarm message will appear on the touch screen.