Complete guide to air-cooled screw units: principles, electronic control protection, troubleshooting and maintenance guide

1. Operating principle of air-cooled screw heat pump unit

The air-cooled screw 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 both cooling and heating. It can be combined with a fan coil unit, air conditioning box, and air handler to form a centralized or semi-centralized central air conditioning system. It has the characteristics of flexible layout and diverse control methods.

During refrigeration: the compressor continuously extracts refrigerant vapor from the evaporator. After compression by the compressor, the refrigerant is converted from low-temperature and low-pressure vapor into high-temperature and high-pressure vapor. The high-temperature and high-pressure refrigerant vapor condenses in the condenser, releasing a large amount of heat and being absorbed by the air. The high-pressure liquid refrigerant condensed by the condenser is throttled and decompressed by the thermal expansion valve, and transformed into a low-pressure refrigerant liquid. [Source: Refrigeration Encyclopedia Official Account] The low-pressure refrigerant evaporates in the evaporator and absorbs a large amount of heat from the refrigerant water, thereby 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. After compression by the compressor, the refrigerant changes 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 and releases a large amount of heat which is absorbed by the heat medium water to achieve the purpose of heating. [Source: Refrigeration Encyclopedia Official Account] Low-pressure refrigerant vapor is extracted by the compressor, forming a heating cycle.

Lubrication system: When the compressor is running, the oil in the oil tank is under the exhaust pressure, and the oil continuously flows to the low-pressure area. After the oil flows out of the tank, it passes through the oil cooler and is diverted to the compressor loading valve inlet and the high and low pressure bearing oil inlet. It enters the loading and unloading piston cylinder and the refrigerated oil in the bearings, returns to the low-pressure side of the compressor, and is finally discharged after being compressed by the compressor rotor, and returns to the oil tank through the oil separator.

Electronic control protection of air-cooled screw heat pump unit

Current overload protection
Overcurrent protection is used to prevent motor current overload from damaging the compressor motor during operation. The compressor motor current is continuously monitored and controlled by a limiting function to prevent overcurrents that could damage the compressor motor.

Phase loss protection
Phase loss protection can protect the refrigerator from damage due to phase loss. This control will stop the chiller if any of the three motor phase currents are lost. During shutdown, a fault alarm message will appear on the touch screen.

reverse protection
This feature prevents the compressor from reversing. When an incorrect power phase is detected, a fault alarm message is generated.

Low outlet water temperature protection
Shutdown protection when the outlet water temperature is too low is a safety control method to protect the unit from being damaged by freezing of water in the heat exchanger.

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