Latest / The Refrigeration Mentor Podcast / Episode 344. Basics of CO2 Controls - Service Calls & Troubleshooting Rack Controllers with Kevin Mullis (Part 4 of 4)

Transcript

Episode 344. Basics of CO2 Controls - Service Calls & Troubleshooting Rack Controllers with Kevin Mullis (Part 4 of 4) · The Refrigeration Mentor Podcast

• 0:00
  Trevor: Welcome everyone. Welcome to this part four session. I'm super pumped up, stoked. 'cause this always comes down to the biggest and most the, the most interesting stuff. And that is, you know, service calls and troubleshooting on rack controllers, controls on refrigeration systems, CO2 systems. And I see a ton of our good friends here hanging out with us for this four part series.
• 0:01
  Kevin: Hi Trevor. Thanks for having me back again.
• 0:02
  Kevin: Yeah. So it's good to have some chance to talk about some things and give some strategies to how you approach problems like that before you get thrown into them. I think.
• 0:03
  Kevin: Absolutely. And you do, you do get used to how the thing sounds normally. And what, when you walk into it and it's doing something weird, you're like, no, no, no, no, no, no. But it's really important as well, because some, some guys will walk into a plant room or in, you know, walk on the roof or whatever and they'll, they'll see some things' not right, but they'll be like, the cases are all down.
• 0:04
  I noticed this. I tried to fix it. It, it's six o'clock. I got a, I got a sporting game. I got a date with my spouse. Whatever it is. I don't know. I tried to fix it but I just wanted to give you a heads up and this is what I did. You know, that goes so far in our industry, and that's called teamwork. You know, maybe you didn't fix it.
• 0:05
  Trevor: remember doing that when I was on the tools for sure. Like we would, we would just help each other out, you know, even, even, yeah. Because this is the, it is a community. We're trying to help each other out and, and the more you can help each other out, the easier our roles get and the more we learn faster.
• 0:06
  We'll dive onto the parameters and we need to know there could be 50, 60, 70 data points. We wanna know what, what's the key points that we're gonna look at on these controllers so we can get a quick overview of what that system's doing. Yeah. So I'll just share my screen.
• 0:07
  Kevin: yeah. We'll pick it up as we go. Yeah. So, just pulled out some critical inputs and outputs that you might wanna look at on a rack. We started with RDM here. Just picked it across the same pages. When you first go onto the data manager, which is the, the front end for that RDM system and you go onto the device, you've got some options, you've got inputs and outputs, tabs as they call them on there where you can select the data you wanna see.
• 0:08
  We, we are gonna know that 'cause we're gonna know how that rack runs normally and we know what to expect from a CO2 rack. You know, if we've got 800 PSI in the flash tank, we're probably not. Right, for example. Yeah, we want a quick overview of that. I know it all in bar that I can look at that and go, that's all good.
• 0:09
  Numbers aren't important on this. This is just an example. I've also a corral shot. So when you go onto a corral front end it, and you look at the device you wanna see, that's a rack. You get a really handy summary on the very first page at the top there of exactly what the rack's doing. This rack's the other way around.
• 0:10
  So that's what you get. Instead of pressure on a Carell. You can see the pressure when you go further into the page, you can see, and it obviously tells you on the very front page your pressures as well. But yeah, again, if we look down the inputs and outputs, we've got things like receiver pressure in there.
• 0:11
  So what I've done is, and many thanks to all of the manufacturers whose pictures I've pinched for this schematic. I've drawn up a very quick system. I've intentionally not done it attached to anyone's controller because it's the numbers that are important. I've also done it obviously in PSI and bar, so hopefully everyone can recognize where we are.
• 0:12
  We've got maybe some high pressure alarms going off, maybe not. Depends how we're set up. Ambience not too bad. 68 Fahrenheit 20 C. We're not in extreme conditions. So we've had a quick look at that. And the first thing I'm seeing when I see this is my discharge pressure is real high for 20 degrees Ambien.
• 0:13
  I'm thinking the valve between the gas der and the receiver's wide open, but yet my receiver's real low pressure. So my problem is somewhere between those two things, right? There's no way if that valve is a hundred percent open, my flash tank pressure would be really low. And it just to confirm that if I then look at what the receiver valve's doing, it's not even open because the pressure's so low in the receiver.
• 0:14
  It means the driver thinks it's a hundred percent open. Use your use your fridge knowledge. If you stick your ear near that valve and it doesn't sound like it's rocketing through that valve, it's probably not working properly. And if you're lucky enough that it happens to say zero on the top instead of a hundred when the controller thinks it's open, you might think, okay.
• 0:15
  Things like a corral valve, you can drive with a manual magnet. You can drive an I-C-M-T-S with a manual magnet. Just way to tell if the valve's actually getting any drive. It could be that the only way you're gonna be able to try it is to let the rack stop and reset it, and you will hear the valve try to drive when it reboots.
• 0:16
  They won't put your ball valve in and you'll have to dump the contents of the gas cooler to do it. But you know your problem's in that area. If you've got this kind of setup on the system and that valve is saying a hundred percent open, you've got nothing getting out the gas cooler. But you know that.
• 0:17
  Trevor: I think the, one of the big things that you, you stated there that we didn't show, like, but if you go into like a PT chart for CO2 and you go to 95 bar or 1378, they have a theoretical temperature would be Yes, there's no pressure, temperature relationship, but there's a theoretical temperature that they, we would expect and now, now people say, oh, well it's not right.
• 0:18
  Kevin: And you lose complete track of what the gas cooler is doing because you've got no flow. In that line. Yeah. All you will see is ambient temperature because that that CO2 will settle to ambient temperature.
• 0:19
  You're gonna find the rack is flat out. Every compressor's gonna be running. Empty suction's gonna be high because it's getting a heck of a lot of flash gas. And what we get with a heck of a lot of flash gas is we get low soup heat because flash gas is saturated. We might have a heat exchanger in there to take some of the, some of the suspended liquid outta that gas, but it's gonna leave that receiver as a little mixture of vapor and liquid.
• 0:20
  In this case, the gas cooler's not doing enough work. So simple things, have we got fans running? Are the fans running fast enough? Have we got a VFD trip? If we've got a VFD on the unit, have we got a real dirty gas cooler going on? Yeah, it does happen. You know, you get into autumn, you've got trees around your site.
• 0:21
  And the nightmare scenario, as we were sort of alluding to at the start is you walk in that rack room and it's silent. You see? Right? Everything's off on oil. Okay? So you are gonna do all the good stuff and get ev, get all those machines started again. And you are gonna watch in the space of like one minute flat, the rack will be going flat out again and you'll be like, whoa, what's going on here?
• 0:22
  The other thing I would say to watch with this is the outlet pressure outlet temperature probe, sorry, reading correctly, that probe being slightly off can get you into a flash gas runaway. It won't usually throw the head pressure as high as, as in this circumstance. This is much more like your fans aren't running, but you get that probe two or three degrees out.
• 0:23
  The controller's gonna go, gas cooler's doing too much. I'm holding the liquid too long in the gas cooler, it's getting too cold. It's gonna open the high pressure valve, it's gonna load up the receiver, it's gonna load that valve up, which is gonna push a whole world of pain around the system. Yeah. So it's less common to have that prob come loose.
• 0:24
  They'll wanna fit gas cooler probes for you. And frankly, some of them do a damn good job. But I wanted to know when I was doing it exactly where the probe was, because that way, if I was seeing a problem with it, I'd be like, no, I know it's not that because I put it on and you know, you've got control of it then.
• 0:25
  And it's like you put it on the gas cooler, you want it on the common off, the gas cooler. If you've got a gas cooler that's got two halves, don't just stick it on one half of the header, put it on the common. You need to know what's coming back to that valve. Not one little bit of it. It's the same when you do evaporate suction probes.
• 0:26
  So, you know, I talk to people all, all around the world, and I mean, like everyone has their own opinion and course looking, I don't have an answer for you because I know the people that are listening to this that I talked to already, they're like, no, Trevor, it is at the one side of that where the pre cool fan is, and that's the side that's always running or it's a split.
• 0:27
  That's, that's the valve you're trying to drive with that probe. Right? The gas core outlet probe is controlling that valve. So all it really cares about is what's going on at that valve. And if you don't tell it what's coming into it, it's not gonna react the way you expect. Opinions may vary. That's my take on it.
• 0:28
  Ambient probes are one of the most overlooked things because some people see it and it's just dangling on a bit of wire outside the rack. Housing if it's on the roof and they're like, well, that's outside, isn't it? But if the gas cooler is 20 feet away, it could be right in the sun. The ambient probe could be going, oh, it's 50 Fahrenheit.
• 0:29
  'cause this is another thing I do a lot of CO2 design courses and, and in the design you'll see where people are like, oh, the ambient here is only in Canada's the max 35 Celsius, you know, 95, but on that roof, on those hot days. And you don't know what's on there. Do they got rocks? Do they, is it black? It could be 5, 10, 15 degrees hotter where that gas cooler is.
• 0:30
  Any, any probe that's there is doing a job. So they don't put 'em on for the fun of it 'cause they cost money. So, you know, make sure, make sure they're doing the job. You're you need 'em to do the, the next one I've put in here is a slightly more unusual one though. You'd be surprised how often you see it.
• 0:31
  And we are seeing low suction, super heat, the rack keeps going up in load, going down in load and we're like, what's going on with this? Why will that not stabilize? And what we are then gonna do is we're have a look at what the receiver's physically doing and we're gonna see there's liquid in the top site loss of that receiver.
• 0:32
  So we're gonna get low super heat. The other problem is when we're opening that high pressure valve, we're getting a big in rush of gas and vape and liquid. And we haven't got an awful lot of space if we're full to there with liquid, we've got very little space to absorb that pressure change. We've got a much higher pressure up here than what we have in the receiver.
• 0:33
  And the simple answer on this is you are gonna have to vent some CO2 off. That is gonna be the fix straight away for this problem. And I'll tell you how we end up in this problem quite a lot. It's not from startup, it's not because something weird's gone on downstairs. What'll have happened is nine times outta 10 is somebody's come out.
• 0:34
  And we might look a little bit low on the receiver at sometimes. Somebody will come along, throw a couple of bottles of gas in, the problem will naturally solve itself, whatever it was, and they'll go, great. Did a great job. Yeah. Or you'll say another favorite is the temperate filter or whatever separator you've got fails.
• 0:35
  And it's perfectly acceptable in that situation to dump a lot of that CO2. The, my personal feeling is this is part of the reason sometimes that CO2 systems get a bad wrap for leaks because when that goes in the report to your service company, they will say, well, I put eight bottles of CO2 in that system this year.
• 0:36
  And people get real keen on putting gas in. So beware of high liquid levels. High liquid levels are bad on co2. Oh
• 0:37
  Kevin: and the difference with CO2 systems is that compared to a, an HFC system is that receiver is usually below ambient temperature. So when, when you've got an HFC system, you've got your receiver sap, wherever it's at, and what you feed into it out of the condenser, when it hits that receiver, it'll be liquid, but there's vapor in that receiver.
• 0:38
  So when you pull that liquid out, unless you've got a subcool on your liquid line, there's always the possibility of seeing bubbles. And the number of conversations I have had with consulting engineers and the like, who want me to put sight glasses in by the expansion valves, and I'm like, I can, but why?
• 0:39
  It hasn't got enough gas in it. One thing I will say on liquid receivers while I think about it, is you cite glasses on. Liquid receivers on CO2 are big, heavy, thick things, and they're not always the easiest to tell what's going on. I generally have seen two types of sight glass. You get one that's got like a circle in the middle with etched, with an etched surface, and when it's empty, it looks white.
• 0:40
  But if anyone has seen on my LinkedIn a few months ago, I posted a picture of a psych glass that was full with the P floating right in the middle. Sometimes with CO2 CO2 is an awkward fluid sometimes, and things like those little peas in the sight glasses sometimes absorb a little bit of CO2 under certain circumstances, or they'll get gas trapped in them and that ball will sometimes sink, even though the glass is.
• 0:41
  Right? So, so they, I prefer, and people have contacted me off the back of that post and gone, I spoke to 20 people about this and they all prefer the p and I'm like, give me the X class any day. Everyone has something they prefer on this. If you're really lucky, you might have a real old school flag column next to the receiver that we all used to get on the racks with the 500 flags at the side that with a magnet that floats behind them and flips over real old school.
• 0:42
  Watch the receiver as it fills up to that point. Yeah. Even, even if you have to pump it down after you put a bit of gas in and physically see the liquid come up into it, at least you will know because the one thing it doesn't fall you on is when the line comes up through the glass. You can definitely see that, but don't always trust it.
• 0:43
  Exactly. I have put 400 pounds of CO2 in and it's still showing low liquid. Don't always believe the sensor. Sometimes because the receivers are below below ambient, they're very often wet. Problem. We don't really get on HFC receivers and condensation gets pound of glass, either rust, the sensor or it disturbs the reading.
• 0:44
  When you overfill the receiver on A-H-H-F-C system, all that would happen is you'd back the liquid up into the condenser and eventually when you're run outta space in the condenser, you go off on head pressure. What will happen on a CO2 system is, as we said, if you pump it down, that receiver can't hold the capacity of the system.
• 0:45
  And that's not so much of a problem on CO2 because ultimately if we need to work on that system, we just pump the whole thing down, we can blow it off. We don't have to try and recover. 300 pounds of CO2 out of it. We can blow it off, but have a bit of a look round and give yourself a bit of chance to think about it.
• 0:46
  So be that gas cooler not performing, or overfilling the receiver and it's real easy for me to sit here now going, yeah, just open it up again. But when that's happening to you and you've got five or six. Big empty compressors banging because they're full of liquid. It gets quite scary quite quickly. So don't think we've said it 400 times.
• 0:47
  Because you could have four receivers on one system or three receivers. I mean, I mean, big receivers that are all connected in, in series, you could have just one single tiny receiver in a condensing unit. So, so it all depends. What's your recommendation when you talk to your technicians? 'cause most of the time, one, one ball valve, one glass with everything running.
• 0:48
  So you run that thing at 50%, you've not got a lot of pump down capacity left. You know, and it doesn't matter, you know, if you've got to a degree, it doesn't matter if you, if you've got three receivers, if you've filled that system, it's all three receivers are full to that level. You've still took away half your pump down capacity.
• 0:49
  And it's time and everything else. If you run it nearer to the level sensor, somewhere between there, just above that bottom site glass, when you get a leak, you're gonna know a lot sooner that you've got a leak. It. Putting that margin in it just means it takes you a heck of a lot longer. And then you just get, you just get a complaint from your boss when they go, how much do I need to put the level back to where it should be?
• 0:50
  Well, what do you do? Well then you maybe you open it back up, like Kevin said, maybe you shut down the, the system. Maybe you turn it off and vent them off outta the, the receiver. Exactly. Exactly.
• 0:51
  You can shut the rack off, then do your service task. You're not going to over pressure anything, but you've gained the whole system of volume. So just to see if there's an easy make your way, your life easier. When I did distribution centers on CO2, I had it built into the control panel, the control panel in the plant room so that I could flick a switch that would shut all the controllers off in one switch so that.
• 0:52
  Possibly winter scenario, so it's winter minus three. I've said C 26 Fahrenheit outside. My store's not doing anything. It's nighttime. All the blinds are down. Everyone's gone home and the rack's on and off. Now let's say for example, we wanna do heat recovery in this store. So somebody's told the rack controller, I need you to push the head pressure up to a thousand PSI.
• 0:53
  They're now seeing like 40 PSI across them. The flow's very small, and so this machine's ticking over, the lts still running because we've still got a decent pressure difference and that's making the MT run occasionally, but we've still got tons of capacity in here. And this pressure's getting lower.
• 0:54
  Kevin: And they're gonna put gas in it. But we need, this is where some of our controllers have safeties. RDM has safeties. Carell has safeties. I believe Danfoss also has safeties, and I'm sure other manufacturers do as well.
• 0:55
  This is gonna happen pretty quick because that's gonna stop generating any empty duty 'cause you haven't got it. You will lose pressure in the receiver pretty quick 'cause it is much rather gonna be in the gas cooler because. And you'll watch it. You'll see the graph for a couple of hours and the racks just come to a dead stop.
• 0:56
  Trevor: Yeah. And one of the big things about this is, and I say this in all the CO2 courses that I do, is that summertime, your system's gonna run, that's gonna run. In the wintertime where's a lot of the issues are happening. And this is one good example. I've seen lots of them now systems where you'll have actually hot gas injection into the flash gas flash tank for winter or low ambient to keep the flow running, as well as solenoids into the liquid side to keep the liquid the low temp, sorry, the low temp compressors running.
• 0:57
  We can't hold it against suction. A lot of the time where we have parallel compressors, especially we, we've gotta boost it even above receiver pressure to get oil into our parallels. And if you've got a parallel compressor to hold of the ball game, the first thing that's gonna lose pressure in this scenario is your parallels will stop working.
• 0:58
  So again, something to watch for. If you've got heat recovery. Heat recovery is popular on CO2. It's a real good feature, we know that. But we need to make sure everything's working and everything's working in sequence.
• 0:59
  Further sync, and then that's where it leads to the, the rat crash. And it is totally true. Fine tuning is something that is so, so important where you can start to learn and see, see this stuff happening, just like you talked about in this slide here. That heat recovery now is taking all the heat we're we got, because I see big coils, like I was at one site here five or six months ago.
• 1:00
  That's a heck a big range. You're asking that thing to work over and it's one of the reasons, again, why you don't want your minimum target. We talked about minimum target the other day for HPVs, you don't want your minimum target too low because you always want the pressure higher in the gas cooler so that it wants to go to the receiver.
• 1:01
  We, we could sp spend five hours talking about different scenarios, but what we want you to do is really kind of think about the, some of the things that we talked about. Hopefully you wrote that down. How can you go and start looking at these numbers now? From what we just talked about, and Kevin, you crushed the, the, the units man.
• 1:02
  And this, this is so, so important. So if you enjoyed this, like this, I'm gonna put this into the refrigeration mentor community, these videos and this this series, because you want to learn, you want to grow, and you're gonna have to go back and re-watch some of this stuff. This is, this is the stuff that you as a technician will see out there.