ClassX Video Lessons Youtube Channel The Engineering Mindset What's inside a Thermal Expansion Valve TXV – how it works hvac
Hello, everyone! Welcome to an insightful exploration of the thermal expansion valve (TXV) used in HVAC systems. In this article, we’ll delve into the workings of a Danfoss thermal expansion valve, its components, and its role in refrigeration cycles. We’ll also discuss how to optimize its performance for energy efficiency.
Expansion valves are crucial components found between the condenser and the evaporator in a refrigeration cycle. In this discussion, we focus on the T2 Thermal Expansion Valve model. The main body of this valve is crafted from brass, with the refrigerant inlet positioned at the bottom and the outlet on the side. A removable cap conceals a screw that allows for manual superheat adjustments.
Atop the valve is the power head, accompanied by a capillary tube and a sensing bulb, all made from stainless steel. The sensing bulb is strategically placed at the evaporator’s exit to monitor superheat levels.
Expansion valves regulate the refrigerant flow into the evaporator based on the cooling demand. They measure the superheat at the evaporator’s outlet and adjust the refrigerant flow to maintain a consistent superheat level. This process ensures that the refrigerant exits the evaporator as a slightly superheated vapor, preventing liquid refrigerant from damaging the compressor.
The sensing bulb contains a refrigerant that remains separate from the system’s main refrigerant. The superheat causes the refrigerant in the bulb to boil, generating pressure that travels through the capillary tube to the power head, which controls the refrigerant flow.
Inside the expansion valve, a removable cartridge with an orifice works with the valve to control refrigerant flow. Various sizes are available to match different coolant capacities and refrigerants.
Upon cutting open the valve, we observe the main body, which houses all components. The refrigerant enters as a high-pressure, medium-temperature liquid and exits as a low-pressure, low-temperature liquid-vapor mixture.
A small pin connected to a diaphragm in the power head plays a pivotal role in controlling refrigerant flow. The diaphragm, a flexible metal sheet, moves in response to pressure changes, adjusting the pin’s position. A spring beneath the diaphragm allows for superheat adjustments.
The chamber above the diaphragm connects to the capillary tube and sensing bulb. As the cooling load increases, the superheat at the evaporator outlet rises, causing the refrigerant in the sensing bulb to expand and increase pressure. This pressure pushes the diaphragm down, opening the valve and allowing more refrigerant to flow.
As the superheat decreases, the pressure in the sensing bulb and capillary tube drops, allowing the spring to push the diaphragm up, reducing refrigerant flow. This cycle repeats continuously to maintain optimal refrigerant flow.
The valve’s superheat can be adjusted by rotating a threaded plug on the side, which alters the spring’s force on the diaphragm. This adjustment fine-tunes the expansion valve to achieve the desired superheat level.
For those interested in optimizing their thermal expansion valve’s performance, the TXV Superheat Tuner app is available for free download. This app can enhance the energy efficiency of your cooling system in just 15 minutes.
Thank you for joining this exploration of thermal expansion valves. For further learning, feel free to explore additional resources and continue expanding your knowledge in HVAC systems.
Explore an interactive diagram of a thermal expansion valve. Identify each component, such as the power head, capillary tube, and sensing bulb. Click on each part to learn about its function and significance in the refrigeration cycle. This will help you visualize and understand the physical layout and operation of the TXV.
Analyze a case study where a thermal expansion valve was optimized for energy efficiency. Review the initial setup, the adjustments made, and the resulting improvements in system performance. Discuss with peers how these changes could be applied to different HVAC systems to enhance energy efficiency.
Participate in a workshop where you will manually adjust the superheat on a TXV. Use a model or simulation to practice rotating the threaded plug and observe the effects on refrigerant flow. This practical experience will reinforce your understanding of superheat control and its impact on system performance.
Engage in a group discussion to troubleshoot common issues with thermal expansion valves. Share experiences and strategies for diagnosing and resolving problems such as improper superheat levels or refrigerant flow inconsistencies. Collaborate to develop a checklist for maintaining optimal TXV performance.
Download and explore the TXV Superheat Tuner app. Use the app to simulate adjustments to a thermal expansion valve and observe the effects on system efficiency. Discuss with classmates how digital tools can aid in optimizing HVAC systems and improving energy management.
Here’s a sanitized version of the provided YouTube transcript:
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Hey there, everyone! Paul here from TheEngineeringMindset.com. In this video, we’re going to take a look at the thermal expansion valve by Danfoss. We’ll discuss where to find them, their uses, and then we’ll cut one open to examine the internal components and how they work.
If you want to get the most out of any thermal expansion valve, be sure to check out the TXV Superheat Tuner. It’s a free mobile app from Danfoss, who has kindly sponsored this video. You can use it to optimize the energy efficiency of a cooling system in just 15 minutes, which can save you money on energy costs. You can download it for free using the link in the video description below.
So, where do we find the expansion valve? Expansion valves are located between the condenser and the evaporator in a refrigeration cycle. In this model, which is a T2 Thermal Expansion Valve, we have the main body made from brass. The refrigerant inlet is at the bottom of the valve, and the refrigerant outlet is on the side. There’s also a removable cap on the other side, under which is a screw used to manually adjust the superheat. We’ll see how that works later on in this video.
On the top, we have a large head called the power head, along with a coil of very thin tubing known as the capillary tube, and a large bulb at the end called the sensing bulb. These components are made from stainless steel. The coil is extended so that the bulb is positioned at the exit of the evaporator to sense the superheat.
We have previously covered in detail how thermal expansion valves and electronic expansion valves work, as well as the different types of expansion valves used on chillers. Be sure to check those out; links are in the video description below.
What are expansion valves used for? Expansion valves control the flow of refrigerant into the evaporator in response to the cooling load. They measure the superheat at the outlet and adjust the amount of refrigerant flowing into the evaporator to maintain a constant superheat. This ensures that the refrigerant boils off and leaves the evaporator as a slightly superheated vapor, preventing liquid refrigerant from entering the compressor. Liquid refrigerant cannot be compressed, and if it enters the compressor, it can cause severe damage.
The bulb is filled with a refrigerant that is kept completely separate from the refrigerant in the rest of the system. These two refrigerants never mix; they are always separated. The superheat causes the refrigerant inside the bulb to boil, creating pressure that travels along the hollow capillary tube into the power head. The power head controls the flow of refrigerant, which we’ll explore later in this video.
Inside the inlet of the expansion valve, there’s a removable cartridge with an orifice that works with the valve to control the flow of refrigerant. Different sizes are available depending on the coolant capacity and the refrigerant being used.
Now, let’s cut it open and look inside. I’ll secure the valve in a bench vise to keep it steady while I cut it open. Due to the delicate parts inside, I’ll use a hacksaw for this. It takes a bit longer, but it prevents damage to the internals, allowing me to show you these parts.
Now that the first cut is done, I’ll rotate it in the vise to cut the other side open. I’ll use the hacksaw again for this. That’s pretty much cut now. I’ll use a chisel to snap the last bit inside. And there we go! Let’s take a closer look inside.
We have the main body, which holds everything together. The refrigerant inlet comes in from the bottom of the main body through a vertical pipe, and the refrigerant outlet is on a horizontal pipe. The refrigerant enters the valve body as a high-pressure, medium-temperature, saturated liquid. After passing through the valve body, it exits through the outlet as a low-pressure, low-temperature, liquid-vapor mixture.
What causes the change in pressure, temperature, and flow control? We can see a small pin connected to the diaphragm in the power head. The diaphragm is a thin sheet of flexible metal. As the diaphragm moves up and down, it causes the pin to move as well. Underneath the diaphragm is a spring that pushes up against it. We can adjust this to change the superheat, which we’ll look at later.
Above the diaphragm is an empty chamber connected to the capillary tube and the sensing bulb. The chamber, capillary tube, and bulb are all hollow. I’ll cut through the sensing bulb to show you the inside. As you can see, it’s just an empty cylinder usually filled with refrigerant. The refrigerant in the bulb and capillary is completely separate from the main refrigerant in the system. This isolated refrigerant only moves between the bulb, capillary tube, and the top of the diaphragm.
The sensing bulb is positioned at the outlet of the evaporator. As the cooling load increases, the superheat at the evaporator outlet also increases. The thermal energy transfers to the refrigerant inside the sensing bulb, causing it to expand and boil. As the refrigerant expands, it increases the pressure inside the sealed system, which travels along the capillary tube to the chamber above the diaphragm.
As the pressure increases, it pushes down on the diaphragm, which in turn pushes down on the pin. The pin controls how much refrigerant can flow. To facilitate this, we have an orifice assembly inside the valve inlet. This assembly includes a small strainer to protect the valve from blockages and a small orifice blocked by a spring-loaded stopper. The pin in the main valve pushes down on this stopper to open the valve. The further the stopper is pushed down, the more refrigerant can flow.
As the cooling load increases, the superheat at the evaporator outlet increases, causing the refrigerant inside the sensing bulb to boil and increase pressure along the capillary tube. This pressure pushes the diaphragm down, which opens the valve and allows more refrigerant to flow. As more refrigerant flows, the superheat decreases, leading to a decrease in pressure in the sensing bulb and capillary tube. The spring then pushes the diaphragm back up, causing the pin to rise and close the orifice, reducing the refrigerant flow. This process repeats continuously to stabilize the valve and ensure the correct amount of refrigerant flows.
Earlier, we mentioned adjusting the superheat control. The plug on the side is threaded internally, and rotating it moves the slider up or down. This changes the force the spring applies to the diaphragm, allowing you to tune the expansion valve and adjust the superheat.
I’d like to remind you that you can download the TXV Superheat Tuner app for free by clicking the link in the video description below.
That’s it for this video! If you want to continue your learning, click on one of these videos on the screen now, and I’ll catch you in the next lesson. Don’t forget to follow us on Facebook, Twitter, Instagram, and visit theengineeringmindset.com.
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This version maintains the informative content while removing any unnecessary or potentially sensitive language.
Thermal – Relating to heat or temperature. – The thermal conductivity of the material is crucial for designing efficient heat exchangers.
Expansion – The increase in volume or size of a material when subjected to heat or pressure. – Engineers must account for thermal expansion when designing bridges to prevent structural damage.
Valve – A device that regulates, directs, or controls the flow of a fluid by opening, closing, or partially obstructing passageways. – The safety valve is essential in maintaining the pressure within the system to prevent accidents.
Refrigerant – A substance used in a heat cycle to transfer heat from one area to another, commonly used in air conditioning and refrigeration systems. – The choice of refrigerant can significantly impact the energy efficiency of a cooling system.
Superheat – The condition of a vapor when it is heated beyond its boiling point at a given pressure. – Monitoring the superheat is critical in ensuring the optimal performance of the refrigeration cycle.
Evaporator – A component in a refrigeration system where the refrigerant absorbs heat and evaporates, cooling the surrounding area. – The efficiency of the evaporator directly affects the overall cooling capacity of the system.
Pressure – The force exerted per unit area within fluids or gases. – Maintaining the correct pressure in the hydraulic system is vital for its proper operation.
Flow – The movement of a fluid or gas in a particular direction. – Engineers use computational fluid dynamics to simulate the flow of air over aircraft wings.
Diaphragm – A flexible membrane in a mechanical device that responds to pressure changes. – The diaphragm in the pressure sensor deforms under pressure, allowing for precise measurements.
Efficiency – The ratio of useful output to total input in any system, often expressed as a percentage. – Improving the thermal efficiency of engines is a key focus in automotive engineering to reduce fuel consumption.
