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1. The working principle of the screw hot and cold water unit
Screw hot and cold water unit is a kind of air conditioning equipment that uses a screw compressor as the core component to provide a cold or heat source, which is widely used in the cooling or heating needs of industrial and commercial places. These units can be either chillers, which focus on refrigeration to provide refrigerant water for use in air conditioning or industrial cooling processes, or heat pump units, which are capable of providing hot water for heating during the winter months.
Basic working principle: The screw compressor is the heart of the unit, which sucks in low-pressure gaseous refrigerant through a pair of screw rotors that mesh with each other. As the rotor rotates, the refrigerant is squeezed, causing its pressure and temperature to rise, forming a gaseous refrigerant with high temperature and pressure. Subsequently, the gaseous refrigerant at high temperature and pressure enters the condenser. Here, the refrigerant releases heat to the cooling medium (usually water or air) that passes through the condenser, and the refrigerant is thus condensed into a high-pressure liquid state.
The liquid refrigerant then flows through the expansion valve or thermostatic expansion valve, where the pressure drops sharply, and at the same time, part of the liquid evaporates, and the temperature is lowered accordingly, ready to enter the evaporator. In an evaporator, a low-pressure, low-temperature liquid refrigerant absorbs heat from the cooled medium (such as circulating water or air in a building) and evaporates, turning it into a gaseous state again. In this process, the temperature of the cooled medium drops to achieve the purpose of refrigeration. In the case of heat pump mode, the evaporation process actually draws heat from an outside low-grade heat source, such as air or groundwater, to heat the water.
2. The function of the main components of the screw hot and cold water unit
Screw compressor: It sucks in low-temperature and low-pressure refrigerant gases through two intermeshing screw rotors. As the rotor rotates, the refrigerant gas is compressed, and the temperature and pressure rise accordingly, forming a high-temperature and high-pressure gas.
Condenser: The refrigerant gas with high temperature and high pressure is fed into the condenser. Here, cooling water (usually circulating water supplied by the cooling tower) flows through the outside of the condenser bundle and absorbs the heat of the refrigerant gas, causing the refrigerant gas to condense into a liquid. The heat released during this process is carried away by the cooling water.
Electronic Expansion Valve: The liquid refrigerant then flows through a thermostatic expansion valve or an electronic expansion valve. These valves regulate the flow and pressure of the refrigerant, so that the refrigerant undergoes a process of pressure drop and partial vaporization before entering the evaporator, turning it into wet steam at low temperatures and low pressures.
Evaporator: In an evaporator, a refrigerant liquid at low temperatures and pressures absorbs heat from the medium being cooled (usually circulating chilled water) and evaporates. In this process, the chilled water loses heat and the temperature drops, satisfying the need for refrigeration. The evaporated refrigerant vapor is sucked in again by the compressor to start the next cycle.
Filter Drier: Mainly used in refrigeration systems to remove moisture and impurities from the refrigerant to prevent clogging and corrosion of system components. The filter drier contains a desiccant, such as a molecular sieve or silica gel, that adsorbs moisture, while a filter layer intercepts solid particles.
Oil filter: Installed in the oil circuit of the compressor, it is used to filter out impurities and contaminants in the lubricating oil, ensure the cleanliness of the compressor lubrication system, and prolong the life of the compressor.
Solenoid valve: The solenoid valve is a basic element of automation that controls the opening and closing of the valve by the magnetic force generated by the solenoid coil. In the return line, solenoid valves are used to control the path and timing of the return of the lubricating oil to the compressor, ensuring that the system oil pressure is stable and reducing the shock at start-up.
Shut-off valve: This is a valve that can fully open or close a fluid path, and is often used to isolate a part of a system for repair or commissioning, as well as to regulate fluid flow.
Ball Valve: A ball valve controls the flow of fluid through a ball with a hole that can be opened or closed by a 90-degree rotation. It has the advantages of simple structure, fast switching, good sealing, etc., and is suitable for quickly cutting off or changing the direction of medium flow.
Pilot Pump (Oil Return): In a refrigeration system, the pilot pump uses the low pressure area created when the high-pressure refrigerant flows through its nozzle to pump the oil that collects at the low level back to the compressor, ensuring that the compressor is well lubricated.
Sight glasses (to observe the condition of the refrigerant): Installed in the refrigeration system, it allows the operator to observe the flow state of the refrigerant (e.g., color, whether there are air bubbles, etc.) to determine whether the refrigerant dosage is appropriate and whether the system is free of moisture or other impurities.
Water temperature probe: Also known as a water temperature sensor, it is a key component installed in a cooling or heating system to monitor and measure water temperature. Its main function is to detect the temperature of cooling water or heating circulating water in real time, and feed back these temperature data to the control system to ensure that the system operates efficiently and safely according to the preset conditions. Accurate measurements from water temperature probes are essential to maintain the energy efficiency of the entire system and to protect equipment from damage caused by excessive or low temperatures.
Water flow switch: When the water flow reaches a certain flow rate or flow rate, the mechanical or electronic components in the water flow switch act and send a signal to the control system, indicating that the water flow is normal and the system can start or continue to operate; Conversely, the water switch will also send a signal to trigger an alarm or automatically shut down the relevant equipment to avoid damage to the equipment or system failure due to water shortage.
Water-side exhaust valve: If there is air in the pipeline, if it is not removed in time, it may accumulate at the high point of the system, forming an air blockage, affecting the flow of water and the efficiency of heat exchange. The water-side exhaust valve can exhaust the air from the system through it, ensuring a smooth flow of water and improving the efficiency of the system.
High-pressure protection switch: Installed on the high-pressure pipeline of the chiller, when the system pressure rises abnormally, the high-pressure switch can respond quickly and take protective measures.
Safety valve: It is an automatic valve, whose main function is to automatically open when the system pressure rises abnormally and exceed a predetermined value, and discharge part of the medium (refrigerant), so as to protect the chiller and other related equipment from high pressure damage.
Pressure sensor: In the chiller, it is mainly responsible for monitoring the refrigerant pressure to ensure the safe and efficient operation of the system.
Temperature sensor: It is mainly responsible for monitoring and controlling the temperature of refrigerant and cooling water to ensure the efficient operation and accurate temperature control of the system, and at the same time participate in energy-saving management and fault warning to ensure the safety of equipment.
Circuit breaker: electrical protection device, when the current in the circuit increases abnormally (such as short circuit or overload), it automatically cuts off the circuit to prevent damage to electrical equipment or fire.
Protection devices: condensing pressure protection, current overload protection, low evaporation pressure protection, compressor motor overheat protection, low water flow protection, under/overvoltage protection, under/reverse phase protection, compressor oil temperature protection, low evaporator effluent temperature protection, compressor oil level protection, high and low pressure difference too low protection, evaporator antifreeze limit protection.
3. Maintenance - unit maintenance inspection items
The maintenance of screw hot and cold water units is a comprehensive work to ensure long-term stable operation of the equipment, improve energy efficiency and extend the service life. Here are some of the key maintenance items.
In addition, 1. In the air conditioning technical data package, the operation video of the water machine to change the refrigeration oil, filter, and water treatment has been added.