Episode 318. Designing High Pressure Valves for Summer Heat and Winter Challenges with Chris Griffiths

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This is Part 2 of a CO2 Design Fundamentals series, this one delving into high pressure valves (HPV) with Chris Griffiths, UK Technical Manager for Omega Solutions. HPV’s are crucial for supermarket commercial refrigeration design. This session covers the purpose and function of HPV’s, their role in regulating gas cooler pressure, and the importance of proper sizing to avoid efficiency losses and noise issues. Chris also shares expert advice on control strategies, the use of stepper type valves, and how to use manufacturer software for accurate component selection. 

In this episode, we cover:

-Understanding high pressure valves

-Control strategies for high pressure valves

-Seasonal strategies for CO2 refrigeration systems

-Practical tips for maintenance and troubleshooting

-Valve selection and sizing

Helpful Links & Resources:

(Part 1) Episode 317. CO2 Piping Design (Tips to Protect Compressors and Prevent Failures) with Chris Griffiths

Episode 58. CO2 High Pressure Valves, Flash Gas Bypass and Ejectors controlled by a pRack300T

Episode 144. Troubleshooting CO2 High Pressure Valves Using Trend Graphs with the CAREL Boss System

Episode 30. CAREL's CO2 Electronic Valves and CO2 Controllers with Timo Kaufhold

Learn more about Omega Solutions  

Connect with Omega Solutions on LinkedIn

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Email Chris: [e-mail]    

Episode Transcript

(00:00):
welcome to another CO2 Design Fundamentals.

(00:01):
And this is why we do this. This is why we share this knowledge. This is why Chris is here. He's the expert at high pressure valves designing CO2 systems, and we've been working with so many people around the world. And what we wanna try to do is help you a little bit, if we can teach you one or two things that you can bring value to your customer, to someone in your organization, this is why we do this stuff.
Let's jump in. So, yeah, today, high pressure valves, so also known as a trans critical valve. I'm gonna use the term high pressure valve. That's the term I've always been introduced to it with, and I've always used ever since.
Down in pressure to allow it to start condensing. So we partially expand it into our liquid receiver and we're allowing us to get liquid again where we can send off to our expansion valves. So what happens if we don't size this valve directly? Well, as you can imagine, if it's too small, we're gonna have excessive pressure building up in that gas cooler when we might not want it.
And then the last one there, noise and vibration. If we throttle it too much, same as any other valve, we are sending too much mass flow. We're trying to get too much mass flow through it. That energy is gonna go somewhere, it's gonna go into the body of a valve and shape the point. Work around that. So.
Controller processes. It also talks to the compressors, wrap the rack controller as well. You will or it'll be incorporated into the rack controller generally, and from this it will decide well this am being condition and I'll like ask your outlet temperature. Well, this pressure inside the compressors, I'll want to continue running it this at this frequency and I'll need to throttle the valve back to maximize the COP of our system by boosting that that discharge.
So they all need to work in tandem. So we need to have a really effective control strategy to achieve that. So on the right hand side, we'll see. With this controller, this E-K-E-K-C controller, you'll have the I-C-M-T-S and it'll also have the CCM valve air flash gas bypass valve talking to each other, which will also then relate back to our compressor.
And when you understand that you have a better understanding of the system as a whole, as a designer because you should be able to be able to take those. Support calls and be able to answer that question for a technician and make them help them feel confident that what that valve is doing is actually doing what it's doing with the information they provide you.
So in more technical terms, the high pressure valve regulate regulates the mass flow refrigerant from the gas cooler into the intermediate vessel or flash tank regulating the pressure in the gas cooler. On the right hand side, it's a very helpful diagram from corral's. Literature shows as we lift that discharge pressure.
Our fraction of liquid to our flash gas as reduced from maybe we may be 60% flash gas there, 50 there, 45 there. So we're effectively getting. In proportion must be 30% more liquid than we were getting otherwise to go off to our evaporators and actually carry out our cooling that we need to do on site. So that is why we may want to artificially raise the discharge pressure in an ambient where traditionally you might, you might get away with 75 bar, , our actual temperature, et cetera is a bit lower, but we're not making the best use out of our system now either.
So with HPDs high pressure valves, we tend to use a stepper type valve. There'll be a bipolar valve, which will wind a stem in and a stem out, fill that fine capacity control over the system rather than a pulse width modulator system where you're closing and closing. Don't really want to do that 'cause it's not gonna provide a stable or refrigerant scenario in our vascular.
High pressure valve. So once you've got access to our website, you've signed up on the left hand side, you've got electronic expansion valves inside there, you can input your, your project specific information. So for example, application or a compressor rack, chucked in information, refrigeration, mentor, or solutions as an example, rather than sharing any customer data.
Otherwise, that might be miles out of what you'd be planning for, but it has to be site specific, region specific. The mass flow rate is taken at full flow for your compressors at design condition. So at this point of the scenario, you would've selected your evaporators, you would've selected your pipe work, your compressors, and then your gas cooler.
This scenario here, I think we had 98 to 0.6 bar gauge discharge pressure and about T 0.7 bar pressure loss through our gas cooler, and that is how we've resulted in this gas key outlet pressure here. Our gas key outlet temperature will be our design and mean condition plus. The approach that we want to achieve the lower VA or the tighter VA approach, the larger our gas Q all need to be or the more powerful our fans or pumps will need to be to achieve this.
Once you input information, you can calculate and it will give you this diagram here showing the conditions that we've input. We saw our high pressure valve as it drops down, drops back into a subcritical state, and this is the positional end up inside the VX VR pH H chart.
Yeah, Carell's very helpful. First, it will give you a, a green, amber, or red condition along the working point here. Select something in the green, that's okay. And personally, I always try and select higher up in my range. 'cause that says to me, I'm gonna try control as I drop the requirement down as well.
We've got the mass flow rate that we require, so it's conversely from kilograms per hour to kilograms per second, so roughly 4.7 kilograms per second, or about one and a half pounds. That should be pounds per second, so not pounds per hour. And what we could do is plot that as we go down and see what the capacity would be, how that worked.
That's what we've done here. So in the winter, our mass flow rate has dropped from two and a half thousand kilograms an hour to 707. Yeah, we've, we've effectively quartered it. Condensing temperature, roughly 15 degrees Celsius. We don't tend to go much lower than that. And I think some software won't even likely go over that either.
We need to make sure that valve is opening still enough to allow enough refrigerator through and not, and not jeopardizing the quality of liquid go through. But as you'll see, we got much lower flash gas percentage here, much higher quality liquid.
Again, that should be pounds per second, not pounds per hour, and that's just an easy way to check that the system is working at design conditions of all ranges. And you could also go through and check your compressors at various stages and the valve at various stages. If it's at peak and minimum conditions, you should be okay.
Increase the pressure differential. Increasing receiver pressure reduces our pressure differential again, so we flip that receiver condition up. So we wanna select based on the lowest condensing condition to ensure that valve is sized to accommodate with lowest pressure differential across the valve as well.
Okay, great. That's like, actually you could probably spend a day looking at the stuff on this. No problem. Running through different scenarios, different different selections, how different manufacturers go through and control it as well. It is a great, great in-depth topic to get into, particularly if you've encountered them on site to, I had to rectify some issues if you found them. Yeah.

(00:22):
This is how you get better. This is how you get better and how you get even better is getting into a design course like the advanced CO2 design course, where we walk step by step and get you to design your own system and your own high pressure valves. And who do you use and why do you do use them?
Yeah. Great stuff Trevor. See. Great. So I think, what was the last issue we had on me? High pressure valve.
That is game changing. As a manufacturer, you designed it, you can support it. I love that stuff. Chris, any final thoughts?
And we got a course starting on the 25th. This is, this is it. You're gonna see more depending even where it doesn't matter where you're at in the world. CO2 is continuing to grow. Do you wanna be ahead of the curve or you want a status quo? Check out this program. This is a program that has been game changer for so many people.