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Monday - April 11, 2022

Electronic Expansion Valves for Precise HVAC and Refrigeration Control

Air conditioning has been around over 100 years and was initially invented as a means to control humidity within buildings. Over the years, the technology has evolved and gotten smaller so that most modern homes today come equipped with HVAC systems. Within the last few decades, engineers have been working to make HVAC equipment more efficient and eco-friendly. New designs that integrate thermal expansion vales or thermostatic expansion valves (TEV or TXV) have led to a significant improvement in efficiency.

The purpose of this valve is to control the amount of refrigerant that flows to the evaporator within an HVAC system. A TEV contains 3 main components – sensing bulb, diaphragm and adjustment spring. The sensing bulb measures the temperature and pressure, AKA superheat, of the system and can then either apply or release tension on the diaphragm. When tension is applied to the diaphragm, it pushes on the spring which shifts to allow superheated refrigerant to pass through to the evaporator. Once the sensing bulb detects lower superheat, it releases pressure on the diaphragm and the valve closes. This process repeats constantly based on the preset parameters of the valve.

It is critical that an accurate amount of refrigerant is released into the evaporator because after running through the evaporator, the refrigerant enters the condenser. If any liquid refrigerant enters the condenser, it could lead to dangerous consequences.

The Case for Electronically Controlled Expansion Valves

While original TEV technology is still widely used, HVAC system manufacturers are starting to design-in electronic expansion valves (EEV or EXV) that incorporate a stepper motor with a control unit and sensors. This system is much more sophisticated but offers faster response and more precise control over TEVs delivering up to 30% energy savings. The EEV system incorporates both a pressure and temperature sensor to measure the superheat. It sends this information to the control unit which drives the stepper motor accordingly in order to open and close the valve. Standard PM stepping motors are capable of 24 or 48 steps per revolution at 15 or 7.5 degrees each. This incremental movement enables ultra-precise control over the flow of refrigerant.

One downside of EEV is that they require electricity in order to open and close the valve, whereas a TEV does not. If an EEV is installed in an environment that frequently loses electricity, the user should integrate a small, backup battery that can send a signal to close the valve which will prevent any liquid refrigerant entering the compressor.

Stepper motor-driven electronic expansion valves offer very precise control of heating and cooling systems with better efficiency and performance. With a new focus on minimizing environmental impacts – there is strong demand in the industry to improve efficiency within HVAC systems.

Kota Iizuka
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