Latest / The Refrigeration Mentor Podcast / Episode 356. Understanding PID Controllers in Refrigeration Systems

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Episode 356. Understanding PID Controllers in Refrigeration Systems · The Refrigeration Mentor Podcast

• 0:00
  Speaker: Welcome back to the Refrigeration Mentor Podcast. I'm your host, Trevor Matthews. Super pumped up. You're here. I love that. We continue to learn and grow together in refrigeration. I get a lot of people asking me in the community or asking me through emails or social like. I want a better idea on PID and how PID works.
• 0:01
  Quite a few people have taught me about PID and I'm still learning it. So I'll be honest, I'm no expert. I'm gonna teach you what I have learned through different technicians what I teach in my refrigeration training programs and more and more of our advanced programs, because this is. Out there now.
• 0:02
  The way say, a valve works, and I just wanna talk about a little bit of a playbook that I have for like a PID control playbook. Really for refrigeration technician. This is what I'm gonna talk about today and give you an idea, and so hopefully it helps you and once again, it's not going in and just going to adjust the PNI.
• 0:03
  Gonna get into. How each affects an EEV, we're gonna, we're gonna use an EEV for an example, an electronic expansion valve and controller, as a example today, how to adjust it and how to prevent system issues really. And so really what is PID, it's basically, it's a math based control system, so it's really using.
• 0:04
  So if we have a really good running valve, we'll have a system running really good, or the evaporator running really good, which really means that temperature, the heat we remove from product is going to be accurate and doing it at the right time. Things that'll affect us, and we'll talk about it. Is the way the cases are being used, the walk-in boxes, and so this is something you need to understand before you start playing around with tuning and why PID matters for especially electronic controllers and e EVs.
• 0:05
  Probably compressor cycling if it's on a single unit, not really on our rack. Nuisance trips, ? Flood back or starvation. So the valve is just always like opening way too much, flooding the coil, then closing off, starving the coil, and then lots of different potential alarms.
• 0:06
  That Copeland, when they purchased 'em in 2009, Copeland started to move and I was helping contractors all over the country with these different Dix l controllers. So I flew down to New York. It was at the time, I think yeah, down, down to New York and. I sat with him for a day and we went through all these controllers, and one of the things we talked about was the p and ID and one of the way that I, I was teaching people how to learn and read manuals.
• 0:07
  But if you're too aggressive when you're changing this, this can cause a lot of issues. And we, we will talk about that as well. But one of the things that I really notice about it is that you, you, when you change it, you watch it, you don't just change a bunch of them and you start changing a lot of things.
• 0:08
  So if it's higher eye, it tries to fix it faster over that long term. If you lower the eye. That is, it's about more stable, but slower correction. So it's more stable, but lower correction that is. So if you have a lower eye and to adjust the eye to really trim that long-term stability, that's kind of what you're looking at too much.
• 0:09
  So this one here, it is used and I remember for sure it's used in the xm 6, 7, 8, 6, 7 nines. I don't think in like the Danfoss, they use the D very much. And it depends on the controller manufacturers. So one of the things that, like if you increase the D you, you increase the DI believe if the, the suction is noisy, if there's a lot of changing in your suction pressure and if your, I think it is, if your super heat swings a lot or quickly it's swinging really quickly, that's where you may increase the d.
• 0:10
  And this is where you want to follow up with the manufacturer of that controller. But this is really universal for all controllers. It doesn't even matter if it's in the refrigeration industry. PID is is used in many different controls out there, not only for. E EVs. But the biggest thing, the really, the, really the biggest thing is that before you adjust PIID because I told you that these manufacturers have really tuned in the PIs for these refrigeration controllers and electronic valves you gotta go through a critical checklist.
• 0:11
  Damaged wires are not connected wires properly. So if you go and start trying to adjust the p and IDs and any one of these are out. You are just gonna chase your channel. You're not fixing anything. You gotta fix those first. So, 'cause incorrect sensor placement is impossible to tune a PID or, or help with PID tuning.
• 0:12
  I gotta really look into these filters a little bit more, but they're on like a, a certain time constraint. So how long does it take to get to that super heat? Another big one before you start to adjust. The PID is stable suction pressure. So if my suction pressure is bouncing all over the PA place, if it's swinging up and down, you cannot tune API D.
• 0:13
  This is how on a CO2 system, this is how you really gotta take a look at that. Another one you wanna make sure of is. You gotta make sure you have the right charge, right? Refrigerant charge. So if you're working on like a condensing unit with some EVs and controllers. If you don't have the proper charge that you're low on charge, you're gonna have a high, a bit higher super eat.
• 0:14
  Okay, so that's another one. Another big one. So if you're new to electronic valves and controller, is that valve setup that initialization if you don't have the correct steps. If it's not calibrated, if you don't have it wired correctly, if you don't have the right coil on it, the proper driver, all these things can affect the PID if they're not wired in correctly.
• 0:15
  You only want it to open to 80 or 70%, and that will fix the problem without even having to do a PID adjustment or this fine tuning. So this is why it's so, so important to look at all this stuff before you. Think about adjusting PID 'cause a lot of people hear about it. I hear people talking about, oh, should I, I got the valves hunting.
• 0:16
  And also the correct superheat target, like what does that manufacture of that coil? The walk-in box coil, they design these plate heat changers or coils for a specific superheat. That's what they're designing it for. It could be for a low temp, like four to eight Fahrenheit, maybe two to 4K, as well as medium temp could be six to 12 degrees Fahrenheit.
• 0:17
  That's, that's it. So how, how to tune API D. So here's are some steps that I talk about that I've, I've learned and I've read and I've dove into and did some research on. So the, to step one, if you're tuning the, the p, the proportional. This one, tune this one first. Okay. So if the superheat reacts too slowly, raise the P.
• 0:18
  You gotta make sure all those other things are set because most likely it is something else that is taking too long to pull, to pull down. Okay? Now you wanna lower the p If you have super heat swings up and down. If have, like, if the. If it's going up and down quite rapidly. One of the big things that I learned about CO2 especially 'cause there's more controllers, we wanna slow more things down.
• 0:19
  So once the. The p the proportional feels close. You can move on to the I. Okay. So that's the first, the first step. Second step is the tuning That integral. Okay. The next, the next one. So. You want to decrease that eye. And this is more aggressive if you know that super heat stays above target and never reaches set point, so you're always above your set point.
• 0:20
  But once again, PS first, then I, and then only adjust the D. And like I said, some controllers don't have. A d but if you want to increase the d if the super heat changes too fast or the system's really overreacting to load swings. Okay. And these are the things that you gotta watch. You gotta be actually watching the case.
• 0:21
  You can't be somewhere else. And all of a sudden a bunch of customers are opening and closing the doors. The, the product or the, the case. People who fill the case is with product. They're just loading up a warm product. That's something you gotta, you gotta be aware of. You wanna decrease the d if the valve, response is sluggish. So if the valve is not really responding, as, as that system's changing. And once again, this is optional. I highly recommend. There's quite a few videos that I've watched and researched on YouTube. Take a look at them. Once again, I told you I'm not, I'm not an expert at this, but this is kind of what I've seen.
• 0:22
  So I got a good understanding. So if you don't do this all the time. And you don't really understand what should happen when you're adjusting these things. It's going to be, you know, really harder to know if you're fixing it or not. But it, you gotta go back too. If you go and you adjust some stuff, you gotta wait there and watch and then you gotta follow up.
• 0:23
  And all of a sudden it's not that what needed to be changed, it's something else that we talked about. But what good looks like, and maybe good, looks different to you than me, but for me is that you have a stable super, you know, like one K or two degrees Fahrenheit. Plus or minus on that superheat if you're going 10 or 15 degrees or 10 K up and down, or 5K up and down, that is a lot on a superheat.
• 0:24
  What is your suction pressure looking like? So, so important. Does the case temperature hold steady? So when it's running, does it reach set point quickly? Does your system really get to satisfy quicker or is your system just run and run and run and run and run and run? Does the compressor cycle normally or are they just banging on, banging off?
• 0:25
  You know, 'cause really a well tuned system is calm, steady. And maintains a good graph. That's what I say when you're looking at, when you're looking at it, it's a good graph. You look at the opening percentage of the valve, it's smoothly. You look at the suction pressure, it's quite smooth. You look at the super heat that is smooth, you look at the temperature of the case that is smooth.
• 0:26
  Like it's opening up and slamming down. So if you look at the percentage of valve opens up, closes down, opens up, close down, as well as bad tuning would be overshooting. You know that super. He drops all the way down to two degrees. Fahrenheit or one degree one k. That is, that, that can be too low, especially if it's on a medium temp system.
• 0:27
  The product's already closer to temperature. And when you. Add after a defrost, you should be able to come right back down. It should be able, that coil starts, the refrigeration's engaged, that the refrigerant goes down, cools the pipe, cools the fins before the, the, for an example, the, the fans come back on and then all of a sudden that should be able to run and pull out that that any of the heat in that, say glass doors for an example, pull out any heat pretty quickly.
• 0:28
  What else? What else could we do? I guess compressor issues. You know, if you have discharge, high discharge temp, you have compressor, short cycling that you can't really tune when that's happening. Unstable suction pressure, I guess that would consider where it's bouncing all over the place. 'cause that's gonna change your soup.
• 0:29
  Check that the stability of the suction. Is the suction bouncing up and down all over the place. Did you. Do you have the target Super eats set up in the, in the controller itself? And watch the trend. Watch that trend after. If the glass door, the doors are closed, no products being put in, no. People break the air curtain.
• 0:30
  And then if it's getting really close, then you, you can look at tuning that super heat. So when it returns to set point without overshooting, so does it go down? Past 10 degrees F or does it go down past six K? So, while you're watching it, okay. If it does, then maybe you gotta slightly tune the integral and then then look at D.
• 0:31
  'cause if you just keep changing the p and you're not getting closer to what you're looking for and you just keep changing it, changing it, changing it, changing, there's probably something else going on. Y you know, did, is that filter dryer before, before that electronic valve plugged, or is this the screen and the, the EV plugged.
• 0:32
  But this same strategy, honestly will if you do this, and, and you can ask them, you know, I think this strategy will work with spoiling, EVs, Copelands, Dan Danfoss, corres, microthermal, you know, R-D-M-K-E two. It doesn't, it doesn't really matter. All the, all them will have. It's kind of universal. Okay. And, but I highly recommend, this is just my, what I think, you know, and the things that I've learned over the years and the people that shared and the research that, that call up these manufacturers and ask them, you know, not all the, you're not gonna be able to call the support line.
• 0:33
  You can watch it at the same time, as well as does the do a suction, suction test, the fluctuation suction. So if you change that so you close the, close the suction down the suction ball valve on the line a little bit, you know, so you're choking the suction off a bit and then open it back up and see, see what happens there.
• 0:34
  And that there, I think this is some steps. Hopefully this kind of gives you a good idea. If you have questions, shoot, shoot me a email or come into the community. We talk about this in the refrigeration mentor community, ww dot refrigeration mentor.com/hub, and we, we will talk about more of it. ?
• 0:35
  Description, I'll have a link in there for the community to go to, as well as I will put a link to the, the playbook when I when I make it. 'cause I think, I think that'll be pretty good if I make a little playbook for you so you can go and review it, come back to it even after you listen to this podcast.
• 0:36
  I'd love to get them on the podcast to talk about the share this information. Or if you are really good at tuning and you want to correct some of the things some of the knowledge that I have or really help me learn how to pi detune more controllers. I would love that. You know, 'cause honestly, I am still learning.