Every industrial, commercial, and domestic refrigeration system uses a refrigerant expansion device. This device takes the refrigerant at high pressure from the condenser outlet and creates a cold low-pressure zone in the evaporator. In domestic systems, it is sufficient to use a very small-capacity capillary tube. However, in industrial and commercial applications, electronic or thermostatic expansion valves are required to create the cold zone in each evaporator.
The first expansion valves were thermostatic valves, also known as TXVs in English. These are basically mechanical devices automatically controlled by a temperature bulb and a pressure tap. With these elements, TXVs regulate the flow and pressure of the refrigerant entering the evaporators based on the system’s load.
Subsequently, electronic expansion valves, also known as EEVs in English, entered the market. These expansion devices are a technological evolution of the previously mentioned TXVs, taking advantage of the significant advances in electronics. EEVs do not use temperature bulbs or direct refrigerant pressure taps; instead, they rely on electrical signals from temperature and pressure sensors.
Components of electronic expansion valves
Electronic expansion valves consist of a body, solenoid, controller, pressure sensor, and temperature sensor. All of these parts are essential for their operation. Let’s discuss each of these parts in more detail.
Body of electronic expansion valves
The body of electronic expansion valves is typically made of brass or stainless steel and closely resembles the bodies of TXVs. This part is soldered right at the evaporator inlet. Inside the body, you will find the calibrated orifice, refrigerant filter, valve seat, stem, and plunger. All of these elements come into direct contact with the refrigerant, regulating its flow and pressure.
Solenoid of electronic expansion valves
The solenoid is the electrical component that controls the stem and plunger inside the valve body. The solenoid moves the stem and plunger using the force of a magnetic field. Typically, the solenoid is located at the top of the EEV body but does not come into direct contact with the interior of the body.
The solenoid is made up of coils of enameled copper wire that generate a magnetic field when carrying an electric current. Therefore, the solenoid must be connected to an external power source using cables to generate this magnetic field.
Controller of EEVs
This controller is a programmable electronic device specially designed to produce an electrical voltage output with a specific amplitude and frequency. Its output voltage is primarily used to activate the solenoid of the EEV. However, it also has other electrical outputs to control or deactivate the industrial refrigeration system’s compressor, alarms, lights, etc.
The electrical signals from the temperature and pressure sensors are connected to the controller’s inputs. The controller’s software then processes these input signals to generate the previously mentioned controller outputs.
The controller has a display to show the system’s temperature and pressure. Additionally, the display shows the parameters programmed in the controller and facilitates changing them through an adjacent keyboard. Typically, the controller is installed outside the cold room in an accessible and convenient location.
Pressure and temperature transducers
Pressure and temperature transducers are devices that convert these physical variables into electrical outputs, which are then transmitted via cables to the controller. Therefore, these devices come into direct contact with each evaporator in the industrial or commercial refrigeration system.
The temperature of each evaporator is measured using transducers such as NTC, PTC, PT-1000, etc., depending on the technical specifications required by the controller. On the other hand, pressure is measured using a ratiometric sensor that transforms it into a proportional voltage signal.
What advantages do electronic valves offer to an industrial refrigeration system?
The advantages of electronic expansion valves compared to older TXVs are extensive. First and foremost, they provide much faster, stable, and precise temperature and pressure control, ensuring optimal preservation of beverages, meats, fruits, and more. They also reduce compressor start and stop cycles.
Precise control of temperature and pressure in each evaporator maintains refrigerant superheat at more optimal values. This leads to an approximate 12% energy savings, which automatically offsets the expenses associated with implementing this type of control.
Furthermore, electronic expansion valves greatly facilitate the calibration and monitoring of these valves compared to the older TXVs. In this regard, technicians do not need to enter the cold room where the evaporator is located; they can do it remotely using the controller.
Types of electronic expansion valves
There are basically two types of electronic expansion valves: pulse width modulation electronic valves and step motor electronic valves. Each has a different design for the body, solenoid, and electronic controller, resulting in different operation methods to regulate refrigerant flow in the evaporators.
Pulse Width Modulation Electronic Valves
The bodies of these pulse width modulation electronic valves are similar to typical on-off solenoid valves. The regulation of refrigerant flow is achieved by sending electrical pulses to the valve solenoid from the controller. These pulses have variable durations (duty cycle) based on the desired flow rate. Normally, these electrical pulses can have durations between 1, 2, 3, 4, 5, and 6 seconds, repeating periodically every 6 seconds.
Step Motor Electronic Valves
Step motor electronic valves are more precise than pulse width modulation valves. Additionally, they do not have the disadvantage of producing water hammer in the refrigerant lines, which is typical of pulse width modulation valves.
The bodies of these valves contain a rotor with permanent magnets inside. Therefore, the initial movement is rotational. However, the stem is threaded into the valve body, transforming the rotation into a linear movement inward or outward. This final stem movement ultimately regulates the refrigerant flow.
Furthermore, the solenoid of these valves is also different from that of pulse width modulation valves. This solenoid has two internal windings that are excited at different times to create a rotating magnetic field in one direction or the other.
Finally, the controller also operates differently, producing an electrical signal distributed over 5 wires, which are connected to the solenoid.
Are you interested in installing electronic expansion valves in your refrigeration system?
The successful implementation of electronic expansion valves depends on a comprehensive technical procedure that begins with an evaluation of the system’s evaporators. Therefore, it is important to seek specialized advice on evaporators. In this regard, at Intersam, we are a company specializing in the design and manufacture of industrial evaporators. Contact us and seek our advice before installing electronic valves to ensure a trouble-free implementation.