Latest / The Refrigeration Mentor Podcast / Episode 297. CO2 Experts: CO2 System Troubleshooting and Fine Tuning (Part 1) with Chris Brown of Danfoss

Transcript

Episode 297. CO2 Experts: CO2 System Troubleshooting and Fine Tuning (Part 1) with Chris Brown of Danfoss · The Refrigeration Mentor Podcast

• 0:00
  Trevor: Welcome to the Refrigeration Mentor Podcast. So glad you're here. If you haven't had a chance to check out the new Refrigeration Mentor Hub, go check that out. Head to the either description here, or head to refrigeration mentor.com and go check out the hub. This is where it's a community of technicians supporting each other, how to get better, how to grow either in your career, your personal life, and your technical skills.
• 0:01
  Awesome. I enjoyed it all because I learned a ton. He's a wealth of knowledge. He's been doing CO2 forever and he's been definitely showing us lots of tips and tricks. So take some notes, listen closely. Probably have to listen to each one of these a couple of times. Now let's get a conversation going.
• 0:02
  But I didn't see much Danfoss. But now that I'm working with a lot of technicians from around North America, they're seeing more and more Danfoss, CO2 controllers on there. 'cause one of Danfoss, one of the pioneers of CO2 control 20 some years ago back in Denmark, this is where they started working on CO2 systems.
• 0:03
  Honestly, I'm at the gym working out I throw a, a controller talk on, and I'll get a couple tips. 'cause if I'm doing a training and I know I'm gonna be talking about a certain controller, say if it's a 7 82 or if it's a CC five 50, I'll listen to that podcast before I'm gonna do my training, just so I, like, I at least get a brushed up on a few things that you're sharing of that.
• 0:04
  Chris: Yeah. So we wanna get into the, a bit of the controls aspect of these, these jobs and these stores with CO2 trans critical systems. And specifically, I'll, I'll touch a little bit on some of the best practices if we're walking into a startup and, and some of which you can expect or would want to kind of, to take into account before we start charging the rack and as we're charging the wrap with CO2, and then also some of the troubleshooting and, and fine tuning that we're, we would do as well.
• 0:05
  And, and now that there's a little bit more of a comfort level, I think happening in, in the region now we can start to see a little bit of a shift into the next area or, or the evolution into the next step of saying, all right, I've, I've got this system. It's in there, it's running. But what can I really do to fine tune it and make sure it's running the best way it can and, and start to, to look at energy efficiency a little bit in addition to just functionality.
• 0:06
  Any of the HFCs for sure. Better heat transfer. This is the point now where we're gonna see systems become way more efficient in the next five to 10 years because this is what everyone's working, this is what the nvo is working on right now. And this is now where they're gonna learn a ton because now there's more people, fine tuning systems to make them the most efficient as possible.
• 0:07
  And, and, and a lot of this applies to the industry in general re regardless of, of a Dan False or, or anyone else, but, for us, it's, here's an idea of a, a kind of a schematic of what a a CO2 trans critical design would look like with a bit of an overlay of where the, the controls would come into play with the design.
• 0:08
  So. Sending out alarms as things are, are, are happening that we may need to address, or for someone that may need to dial into the system and extract data for history logging, or if they're going in to do something like a fine tuning that that system manager is one layer of the solution that used to be able to, to pull data together maybe give some some low level control and, and also for the remote visibility and, and access standpoint of the system for us, for when we move downstream.
• 0:09
  And we, we have a, a good portfolio. These use a lot of different models. The one that you see pictured here now, the 7 82 A there's also a B model, but this is probably our most prevalent pack controller. It, it's kind of all encompassing where it handles multiple suction groups as well as all the, the high pressure side with the valves and the gas cooler.
• 0:10
  But by and large, when you look at a CO2 trans critical design, 99% of the time it's going to be an electronic expansion valve that's at the evaporator because it's the, the quick response times needed out of the valve. The working pressures we're dealing with that we know how high they are of a CO2 typically requires an electronic valve for that, that portion of the system.
• 0:11
  Yeah, we'll see that happening down the road. It's just figuring out how to make that work. But you already have mechanical, there's already mechanical CO2 valves out there and we've Right on we have subcritical systems out there, CO2, you know what I mean? And you're, you're using solenoid valves for an example.
• 0:12
  Trevor: That which is perfect 'cause we need that system always running. We need those compressors running. We need the store pulling heat out, rejecting that heat. We're removing that heat.
• 0:13
  I was just at a training down in Pittsburgh. A bunch of my friends there friend Ernie was down there, but I learned, and we just talked about this before that, on cool selector two. What's really cool, we'll talk about this tool later. I use it a lot in our design program, but inside it, there you can manipulate that flash tank pressure in the tool you put all your conditions in.
• 0:14
  It was my friend, good friend Chad Bartley from the Vaco lmp. He's like, Trevor. The way I showed it is like if I increase the pressure, watch the, the flash gas line go, do you see when I increase my flash gas, it hits the dew point earlier, which mean there could be potential CO2 liquid if I try to go up way too high and way more gas, which is now we're sending more gas to those compressors.
• 0:15
  And so for. For the rack side and it really, a lot of it trickles down to the cases as well, but we really just wanna make sure initially everything is reading. Okay. And so from a rack standpoint, you have the temp sensors throughout the rack. You have your suction temp sensors, you have the, the temp sensors up at the gas cooler that are very critical to system operation with your your gas cooler drop leg or your gas cooler outlet temperature either an Ambien or a pad temperature, depending on if we're with using a dry gas cooler or a, an a about gas cooler.
• 0:16
  The pressure setting that we're trying to achieve with the high pressure valve. And so it, it becomes very critical that those temp sensors are reading properly up there and, and troubleshoot, or I'm sorry, but not troubleshooting, but just validating that before we start up is a big deal. The one on the gas cooler outlet, for example, that should be insulated.
• 0:17
  'cause all it's doing, that temperature probe is sending a resistance to a controller. So the information it gets needs to be the right information. And exactly like Chris said, if you don't have that strapped properly, insulated properly, it's gonna send the wrong resistance. And it's gonna think it's doing it, it's what it thinks it's working right.
• 0:18
  I'll give you an idea of what this looks like in a few minutes, but there, there's a, a really easy screen to go to on the pack controller called Sensor Calibration. And you get in there and it just shows you every pressure, temperature value that you have in, in the system, all in one screen. And so when that holding charge is on there.
• 0:19
  Chris: we we're, we, so we have some, some different specs depending on whether exactly how much of a vacuum it's going on there.
• 0:20
  And that's going to the sensor calibration section and making sure that if they're off, you don't just keep changing it. Oh, well, it's off by five and then it's off by 10 and it's off by 20. What does that really mean? That needs to be replaced? Yeah. What, what's your, what's it, I don't know, maybe in the manual, what is your what do you guys recommend on the temperature offset before you should replace a temp sensor?
• 0:21
  Trevor: that's a huge tip rate there. If you have a three, four, or 500 a thousand feet, you know, I've seen big runs and big warehouses where they gotta run the wire for a long distance. And if they don't, if there's too much resistance on that wire, then that could be an, oh man, that's, that's golden. Yeah, and the best way to test that would probably be ice water, you know, if you've got a long run like that to see what you're off.
• 0:22
  Think if you're in startup and you're seeing those transducer, one or two, maybe not reading properly. Sometimes it might just be as simple as the wires were reversed somewhere, either in a terminal block, in the, the enclosure that it's being brought back to. If, if the wires are passed through a terminal block before going to our controller, or maybe they're swapped at our controller itself.
• 0:23
  But as a service technician, you could be like, oh, it's been running right the whole time. But it doesn't mean it wasn't loose to the whole time and it was just working and it wasn't tightened in there. And once again, all these rack manufacturers, they do a great job. They have great quality control, but there are some times that they have workers on the line that, you know, it might have been a bad day might have been not paying attention, and they make a mistake.
• 0:24
  Those systems work a lot more seamlessly when you have three or four different manufacturers. And it's, I've seen it so many times, and I talk with technician, they're running into issues and I ask them, and they get this manufacturer, case controller, they got this manufactured high pressure valve, they got this ma manufactured rack controller.
• 0:25
  Whereas if it's a non danfo, and I'd assume it's the same situation with others, that now you have to go in and define all these individual specifications of the valve, like the phase current and how many steps and what the step rate is. And that's as soon as you start talking about extra settings, there's room for air that you might not have had with just saying, I've got this specific valve model and everything happening internally.
• 0:26
  And it sometimes it might take two guys to do this one on the roof and one down controller forcing the, the overriding. But there's that risk too that maybe something in the print somewhere was, was backwards. And we think we're supposed to be driving zero to 10 motors where 10 volts is full speed and zero volts is minimal speed.
• 0:27
  And then it's just more of a traditional TV strategy at that point where if that temperature is, let's say 70 degrees and the gas cooler manufacturer is specified a five degree or a 10 degree temperature differential, then we would just add that that differential to whatever value we're seeing on that temp sensor.
• 0:28
  Chris: Yeah. And, and what we're seeing somewhat with the fans also, and this could be within the same manufacturer, but we have minimum fan speeds. And, and so I. Sometimes that might be, maybe it's 5% signal over a zero to 10 span bolt span that we're, we're looking at. Sometimes it could be 10, 12% that, that's something that you might see.
• 0:29
  'cause you could have split split condensers. You know, we see lots of this, you know, so you could have all the fans ramping up and ramping down. You could have staging of fans kind of like we did h So there's different options out there. So don't just go dump in parameters from a different set unless, you know it's exactly the same setup and design.
• 0:30
  The filter can collect any debris that's in the system. Typically, we would have a high pressure valve that's in parallel with the ejector that will be able to use to still maintain the, the high pressures that, that we would need the ejectors to normally take on. But normally that's what you would see is the system not necessarily being started up with the ejectors, just one from day one, but giving it a few days of runtime first.
• 0:31
  So those are two aspects. If you're getting into a job that has those two things in the design where they probably aren't gonna run on day one. And maybe that means when you do kind of finish up the startup process and all your cases are online and, and loaded and, and operating their expansion valves, that maybe that's the point at the tail end of the startup where these things are being added and you do want to make sure that, that they're operating properly and not overlooked at.
• 0:32
  That's going to, to have an effect on what your super e value is and how your expansion valve is operating. And so we've seen some of that already where guys kind of just start the system up, turn all the case controllers on, and then a week, a month later, they're saying, oh no, the, the super heat I've got back at the rack is really low or really high.
• 0:33
  Chris: And then for us, just going back to the decentralized setup where we've got multiple devices all kind of talking amongst one another this should, again, this is something that's usually part of the process anyway, but we wanna make sure all the devices are talking to each other.
• 0:34
  So here's just a, a quick idea of some of what that, that those checks ahead of time could help with. And so what you're looking at here is you've got two, two colors here on the chart. The red is your. Either your pad temp or your ambient temp. Here, I think it's the pad temp for the store that I pulled this graph from.
• 0:35
  And because of the strategy of when the ambient temperature goes up and down, and we're trying to keep a delta above that value. At the set point we were trying to achieve kept going up and down as well and to be able to try to, to keep up with that. The gas cooler fans were all over the place. And you could see the gas cooler temperature, which is our green line, was just chasing that ambient up and down constantly with it.
• 0:36
  It was single digits in, in either direction. And that kind of would allow us to go to the next step of, of tuning of saying, do we need to speed up or reduce our reaction time on our gas colder fans? But again, the point of the takeaway from this is. Just being able to, to say that our temp sensors are doing what they're supposed to and reading accurately is gonna prevent us from trying to, to point the blame on other parts of the system.
• 0:37
  And so just some key points here. I mean, one is, is tuning is is not a, a a one-time thing. Tuning a lot of times is, is kind of frequent monitoring of, Hey, I'm gonna try to, to change a few settings here. For, for us, in our controllers, a lot of the settings we have are are, are to be able to adjust the PID is what you're focused on of how fast things are reacting.
• 0:38
  I've seen more times than not causing issues like getting the p and i, you know what I mean? Start to change around. Let's speed it up. Let's get more fast reaction time now with CO2 more times than not, and you can correct me. You, you do a lot of this, right? Slowing down is way better than speeding up and you do one set point at a time and you wait a day or two days or, or while.
• 0:39
  And maybe my compressors have 20 cycles an hour and, and all these other things now that are wrong with the system because of what you did just to try to fix one problem. So that, that's always been my biggest takeaway with this every time is. Just the, the more that the more hands off you are really with, with the reaction of the different things, the more you start to see or own a good system a normally functioning system, the more you start to see the balance of these pressures and temperatures do start to flatline a little bit and stabilize if you don't try to do too much to get one part of the system the way you want it.
• 0:40
  But when you have it working in sync. That it is gonna pur and it's gonna work and you're not gonna have run into any issues. You'll have to do your standard issues, plug grains, frozen up coil potentially. But the system will run seamlessly. And it's not, you do the startup and you, what you wanna do is you want to get that unit running good.
• 0:41
  Obviously we want to avoid that, but you want to keep your compressor cycles down and you don't want to be driving the receiver bypass and the high pressure. You don't want these things just constantly swinging every 5, 10, 15 minutes between full open and full close. That that's a, an indicator that you're, you're maybe doing too much and that you, you really need to take a step back and look at going in the opposite direction with, with how you're approaching the, the reaction times.
• 0:42
  Chris: moving that, that kind of transition into the next point, that it, it is something you, you need to be patient with. I mean, we say 24 hours is what I have listed there, but you, you don't want to go in and tune a site. Let's just say as an example, we tune it in the, the middle of the day, two, three o'clock when maybe the, the load's, the largest of the 24 hour window.
• 0:43
  We know things like that got pointed out there with defrost cycles. I mean, if you're tuning it when your largest load is a defrost and you think you've got the, the answer there, then, then obviously that might not be the case. But really let it run through a full day's worth of operation before you make any decisions or, or say that it is set up the way you want it to be.
• 0:44
  CO2 since like 20 15, 20 16. And I used to always, oh, summertime is so hot, you gotta worry about everything going on. And actually summertime is probably the best time the, the, the system run so much load on, they just run seamlessly. It's when you start to get, and I say this all the time, you get the low ambiance, the shoulder season when they're transitioning and that, and you know, you're going from trans-critical to subcritical and then deep subcritical where you're, you know, that high pressure valve's holding back, you know what I mean?
• 0:45
  'cause if you start to DR and depends on the design as well. If you're flash, you're using the flash gas pressure design for your oil reservoir and now you start to drop your reservoir pressure off, or sorry, your flash tank pressure off, which drops your reservoir pressure off, we might not have enough differential to feed the compressors and you get, you're getting a low oil issue, but it might have nothing to do with the oil.
• 0:46
  Usually it's something that's they're adding in. It could be a week or a month, but it's usually out the fact. And so if you've kind of done your fine tuning at the, the tail end of that initial startup week and you've walked away from it, just know that there's a chance that whether it's because of seasonality or because of something like the heat reclaim being added in later on, that it, it's not gonna be a bad idea to maybe periodically go back and look and see is it still tuned the right way or now it's something like he reclaim is is added in and some of that load's being taken off the rack.
• 0:47
  So if you're not working with heat reclaim system, yes you will. You will. And this is something that you want to understand because we know we get the most heat in the middle of the summer where we don't need that a lot of the time. We get less heat in the middle of the winter. What is your strategy?
• 0:48
  Chris: Yeah. Because of me tuning one thing. But from just a protection standpoint, the controllers do a really good job of deprioritizing heat reclaim over just the rack functions to make sure the pressures aren't getting too far out of where we normally wanna see them operate.
• 0:49
  And, and not to say they don't have any influence, they do, but it's the least number of, and so for something like the low temp suction group. Your receiver pressure and then your median temp suction, which is the low temp discharge. Those are the two parts of the low temp suction that that really can have an influence on, on its own operation compared to something like the medium temp compressors where you've got the gas cooler fans, you've got parallel compression, the receiver bypass valve, the load temp discharge.
• 0:50
  And then similar with the gas cooler, it's if we can get the gas cooler temperature knowing that it, it's, it's mainly a function of the fan speeds and then what's happening from the medium temp discharge. But if we can get those two areas tuned, which is an easier. Approach to do than starting with some of the other parts of the system that this can help us stabilize these two parts and then that makes life easier when we do eventually decide to tune the medium temp suction in some of your rack valves.
• 0:51
  I. Then the other part of this is that the gas cooler temperature determines what pressure we're trying to get to. This is the, the equations that we've always done going back to the e KC 3 26 of here's my gas cooler temperature, and if I can achieve this gas cooler pressure by opening, including the high pressure valve, and I can say what the most efficient type or, or most efficient conditions in the system that I can give you.
• 0:52
  And then at that point, now you're just left with the high pressure valve, the receiver bypass valve, and then medium temp. And if you have parallel suction groups, again, less variables there to take into consideration because of what's already been tuned. And it makes it a bit easier now to go into those individual sections and either speed up or slow down their reaction times to get the performance we want with those, those components.
• 0:53
  So anybody that's not familiar, the way the parallel compressors work is that we still have a receiver bypass valve and the parallel compressors are, are more intended for when the load is, is larger. So more in your warmer months and then warmer conditions. But for when that can take over and, and, and run in a stable way, in stable way, meaning that we don't short cycle the compressors for the parallel suction group.
• 0:54
  We're switching over from the receiver valve to parallel compression way too quickly because every time I switch my parallel compressors on, they're pulling down the receiver pressure within 30 seconds and they're cycling off and I'm getting way too many cycles there. So choosing that switch switchover point of when we have enough load in the receiver bypass valve to kind of give us the green light to say that's enough load for the parallels to run for a a good period of time.
• 0:55
  Trevor: Yeah. And there's a lot of variables. Like you could have hot gas defrost and that pumps pumps right into your flash tank. And then if that's acting erratic now making your, a lot of disturbance in there that could be causing an issue with the parallel compressors for here, like if you're we're talking about like a standard supermarket transoral booster application, you're not gonna, like in Canada, you don't really need a parallel compressor.
• 0:56
  Chris, this is amazing for all of you, listen, thank you so much for taking the time to listen. Head to the Refrigeration mentor. Website. We just launched a community for technicians. It's called the Refrigeration Mentor Hub, really to help uplift the industry, to help the more technicians to support you in supermarket refrigeration, CO2 refrigeration.