**Abstract:**
Energy conservation and environmental protection are two of the most urgent challenges facing humanity today. The World Summit on Sustainable Development, held in Johannesburg, South Africa, from August 26 to September 4, 2002, brought global attention to these issues. At the conference, the International Energy Agency (IHS) released a report titled *"The Refrigeration Industry's Commitment to Sustainable Development and Mitigation of Atmospheric Changes,"* which highlighted that global warming poses a major threat to the refrigeration sector. A significant portion of global warming—approximately 80%—is attributed to carbon dioxide emissions, many of which are indirect, stemming from the energy required to power refrigeration systems. These systems consume about 15% of the world’s electricity, underscoring the need for more energy-efficient technologies. The report also emphasized the importance of reducing energy consumption by 30–50% per unit over the next two decades. This paper discusses the role of throttling devices in refrigeration systems and focuses on the working principles of electronic expansion valves as a key solution for improving efficiency and reducing energy use.
**Keywords:** thermal expansion valve, electronic expansion valve, principle, control
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**1. Introduction**
Energy conservation and environmental protection are critical issues that require immediate attention. The 2002 World Summit on Sustainable Development in Johannesburg marked a turning point in global discussions on climate change and sustainability. During this event, IHS presented a report emphasizing the impact of refrigeration on global warming, particularly through carbon dioxide emissions. These emissions are largely linked to the energy consumed by refrigeration units. Given that refrigeration, air conditioning, and heat pumps account for approximately 15% of global electricity usage, it is clear that improving their efficiency is essential. The report proposed that the refrigeration industry must aim for a 30–50% reduction in energy consumption per unit within the next 20 years. To achieve this, energy efficiency must be integrated throughout the life cycle of refrigeration equipment. Among the key components in a refrigeration system, the throttling device plays a crucial role. Selecting an appropriate throttling mechanism is vital for reducing overall energy consumption. This paper analyzes the working principles of traditional throttling mechanisms and explores the advantages of electronic expansion valves in modern refrigeration systems.
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**2. Working Principles of Traditional Throttling Mechanisms**
**2.1 Manual Throttle Valve**
A manual throttle valve is one of the earliest types of throttling devices. It resembles a standard shut-off valve but is designed with a needle-shaped or conical spool to allow for fine adjustments. The valve consists of a body, stem, packing, and a handwheel. Operators manually adjust the opening degree to regulate refrigerant flow. However, due to the need for frequent adjustments, it is less suitable for dynamic load conditions. Its typical opening range is between 1/8 to 1/4 turns, and it should not be opened too wide, as this can reduce its effectiveness in throttling.
**2.2 Orifice Plate Throttling Mechanism**
An orifice plate throttling system uses two plates to control refrigerant flow. The first orifice causes a slight flash of gas, while the second adjusts the flow based on pressure fluctuations. This system is designed to automatically regulate refrigerant circulation under standard conditions. However, under variable loads or large pressure drops, the system may fail to maintain optimal performance, leading to issues such as wet compression or reduced cooling capacity. Despite its simplicity, the orifice plate has limitations in adapting to changing operational conditions.
**2.3 Thermal Expansion Valve**
Thermal expansion valves are widely used in central air conditioning systems. They control both refrigerant flow and pressure drop across the evaporator. There are two types: internal and external balance. External balance valves are preferred when there is a significant pressure drop in the evaporator. These valves use a diaphragm that responds to changes in superheat, adjusting the valve opening accordingly. While they perform well under standard conditions, their performance can degrade under variable loads, requiring further improvements for better adaptability.
**2.4 Float Valve + Main Throttle**
This system is commonly used in full liquid evaporators. The float valve maintains a constant liquid level, while the main throttle regulates the flow. Together, they ensure proper refrigerant supply to the evaporator. However, like other mechanical systems, they struggle with rapid load changes and may not provide precise control in dynamic environments.
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**3. Electronic Expansion Valve: Working Principle and Control**
**3.1 Suction Superheat Control**
Electronic expansion valves (EEVs) offer advanced control over refrigerant flow using sensors and microprocessors. In suction superheat control mode, the system monitors evaporator outlet pressure and compressor suction temperature. Based on this data, the controller adjusts the valve position to maintain a desired superheat level. This real-time adjustment ensures efficient operation under varying loads and improves the system’s COP (Coefficient of Performance). EEVs respond quickly, offering a wider adjustment range compared to traditional valves.
**3.2 Liquid Level Control**
In liquid level control mode, the system uses a liquid level sensor to monitor refrigerant levels in the evaporator. The controller adjusts the valve opening to maintain a stable liquid level, preventing both overfilling and underfilling. This method is especially effective in systems with low superheat, where maintaining proper refrigerant levels is crucial. Compared to suction superheat control, liquid level control can enhance evaporation efficiency and improve system performance.
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**4. Conclusion**
To achieve energy savings, throttling mechanisms must be able to match refrigerant supply with evaporator load under different operating conditions. Effective regulation of superheat and liquid level is key to optimizing energy use. Electronic expansion valves outperform traditional throttling devices in terms of response speed, adjustment range, and energy efficiency. Their ability to adapt to changing loads makes them ideal for modern refrigeration systems. With continued advancements, electronic expansion valves are expected to play a significant role in achieving sustainable and energy-efficient cooling solutions.
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