Latest / The Refrigeration Mentor Podcast / Episode 341. Basics of CO2 Controls - Programming RDM with Kevin Mullis (Part 2 of 4)

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Episode 341. Basics of CO2 Controls - Programming RDM with Kevin Mullis (Part 2 of 4) · The Refrigeration Mentor Podcast

• 0:00
  Trevor: Welcome to this second part of this CO2 control training with my good friend Kevin Mills. This is awesome. If you miss the last session on the basic controls, you gonna, you're gonna have to watch it, like honestly getting into the. Inputs and outputs, digital versus analog, and even talked about a little bit of strategy.
• 0:01
  This is what it's all about. Today we're gonna be diving into programming controllers, programming and staging compressors. Why do you do it this way? And we're gonna be talking about R dm, but it doesn't matter if you're gonna be on Microthermal, Danfoss E two, E three it doesn't matter the controller to me because the process is the same.
• 0:02
  Kevin: again. So sorry, having to talk to me two days in a row. I love it, man. I'm always learning. Yeah, no, thanks. Thanks for having me back. Yeah. As you said, Trevor, we'll sort of reference a little bit from yesterday, but this bit hopefully today, will we use RDM as a, as a basis for what we need to talk about, but.
• 0:03
  You know, they send it to me and it's like a phase loss or something like that, but what does that actually mean? So you can go right to the phase monitor and see if it's tripped or not. You could fix the phase monitor and I'm, oh, the phases are still good, but you still have a phase alarm. So what is that phase alarm?
• 0:04
  Kevin: will any pack, any rack controller, pack controller, depending on where you're from in the world that you wanna set up, main thing you've got on that rack is compressors, right?
• 0:05
  So we should see some common things across here. So the black part of the screen I've got here is just captured straight off of an RDM rack controller, and it's from the compressor parameters. So the things that we're looking at on there, how many compressors have I got? Are they fixed or variable? How big are they?
• 0:06
  So it knows right off the bat how many compressors it's got to play with. The next thing I'm gonna tell it is how big they are. And you see it's in kilowatts there. It's, that is just a convenient way of doing it that makes it more important for the controller. Controller doesn't actually care how many kilowatts or BTUs or whatever, whatever unit we're gonna talk about.
• 0:07
  Sometimes you'll have a VFD machine that's much smaller. You know, we used to operate a thing called a trim compressor, where we'd want the main fixed speed stages to take up all the slack and the VFD machine. Just to trim it a little bit, what we sometimes do now is we want the VFD machine to be bigger because it gives it a much wider operating range.
• 0:08
  Kevin: I, correct me if I'm wrong, Trevor, I don't think the ultimate number matters as long as the relative number's, right? Because all it's doing is working out, do I need a lot of power? Do I need a little bit of power? It only needs to know. Relative to each other really.
• 0:09
  Kevin: on RDM, the ultimate numbers don't matter and I don't think they matter on the manufacturers I'm familiar with. It is, it is just relative to each other.
• 0:10
  You'll then start your second stage and your VFD will drop to minimum. So you'll be effectively like one and a half machines at that point. And then you'll go up and you'll end up just, you know, two, two and a bit machines. If you overspeed it, then you start the next one and you'll be at two and a half.
• 0:11
  So that's why it needs to know. So on that screen we tell it how many compressors we've got, what their relative sizes are, are they VFDs? If we were doing fans, let's say we'd gone old school and we haven't got VFD fans, we might stage three. On RDM is usually a condenser or gas cooler stage. When we went S so three, we'd have maybe stage one to stage six and we could say it was a fan.
• 0:12
  What analog output is it sending it to? So there's another page in within the RVM called mapping, and this exists in different forms in different controllers. With Corel, there is an IO menu and you do the same thing. Same thing, but with different parameters there. And I know I'm old school on multiplex Paks and what have you, but on Paks, you set what relay was, what output didn't you?
• 0:13
  We can see how that ties into a wrap controller in here. So the ones I've circled at the bottom where it says relay position one, relay position two, relay position three. That's saying, right, relay position one. That's stage one. Where is it? And we, we can tell it that it's on the main board and it's output number one, so it knows where that is.
• 0:14
  Number five, what we can do on many controllers, RDM included is we can have slave boards as well. Boards that have got no brain, just relays analog inputs and outputs. When you've got a bigger rack that's got a normal IDM control has 12 relays. If you need more than that or you need more analogs or more status inputs, we can put boards on using canvas, and on here we can see that status, position nine, whatever we've got configured as digital input number nine is actually on board number one, on input four, and that's just gonna be where it's convenient to put it for hardware reasons you can map it to anywhere.
• 0:15
  Certain controllers are wired with the relays on the top. So when you come to your electrical panel, if you put an RDM controller on relay one's at the top, if your old controller had relay one at the bottom, you are not gonna extend 12, 14, 16 wires to make it reach the top. What you can do is just, if you only need to use six of the relays, just tell the controller that stage output one is on a six.
• 0:16
  And there'll be a million times when you are retrofitting something, and if you can move the outputs where the wires reach your life will be much easier. So, as I've said on here, this applies to all io. So everything that's connected to that control, all inputs and outputs need to be mapped. If you haven't mapped something on an RDM, it will cease to function.
• 0:17
  It will ask you how many compressors you've got. It will ask you how many compressor fault inputs you've got. You tell it, and it will automatically set a lot of this up for you in a logical way. So if you've got six compressors, it'll use the first six relays. You can always go in that list and change it later, but it will make your life a lot easier.
• 0:18
  Kevin: Yeah, yeah, yeah, yeah, yeah. And the thing is, everyone, everyone knows they need a recovery machine.
• 0:19
  They, they go on the screens and stuff, ? If it has like an interface or an Hm, I, they go on a, but you'll see they'll be on their, their Surface Pro or a tablet or a computer do doing their, their setup. So if the manufacturer, field startup people are using this in the controls, this is what we should be doing too, because now you can save all your documents there as well.
• 0:20
  So when you, if you, one of these controllers dies down pro carel, RDM, whatever, if it dies and you've got a program it from scratch. It is a pain, not because it's difficult thing to do, but because they're doing a lot and there's a heck of a lot of points to program whatever manufacturer it is. If you can save the config to your laptop, and let's say that stays in a USB stick on the site, or you every, you know, your company has a record of it on their server, that becomes a five minute job.
• 0:21
  'cause that was not a fun thing if the battery went. So do get a laptop. The the, the flip side of that, I think, which we'd all acknowledge is that having to be a little bit computer literate, little bit IP literate, little bit USB standard literate is now kind of required in the fridge game. You know, we already have to be masters of a lot of things.
• 0:22
  Now it's a game changer compared to 15 years ago. But I could go right onto the microthermal and I could see the alarms from my house at, you know, whatever time it was before I left for the store. So it'd give me an idea of where am I going? Oh, the, it's the walk-in box. And it's been open since 7:00 PM And I know this is a whole nother story, but that's when they started talking, they started stalking.
• 0:23
  Yep. And so we've set basic inputs and outputs up now. We've got everything where it needs to be on the hardware. So we need to start deciding what we're gonna put into the controller to make it run. So this first page is your basic RDM compressor settings. And again, you have got many different versions of these settings, but they're all doing the same thing.
• 0:24
  It might bring on a compressor, it might take off a compressor, et cetera. So what we need to know is what's our target gonna be? How big's the dead bandwidth? It's gonna do nothing. And how fast do we want it to to start doing things when the pressure changes? And how do we decide that? The first thing we need to consider is what we said a minute ago.
• 0:25
  So when you, when you talk about this, 'cause a lot of technicians don't really, we don't deal with that, you know, pressure, understanding pressure drops like that. Mm-hmm. But we do it in temperature. Yes. And so what does that really mean? The restriction in the pipe? Yes. Instead of doing it, it's, we, we think about that saturated.
• 0:26
  Kevin: yeah, exactly. And if it's a big supermarket, that could be a very long piece of pipe. And so even though you would love it to be, the pressure at the compressor is always gonna be a little bit lower than the pressure at the cabinet.
• 0:27
  Kevin: we, we don't see EI mean, gas defrost is only just coming back to Europe, really? In the UK for CO2. You guys guys are way ahead of us on that.
• 0:28
  Yeah. So, so important we're talking about today.
• 0:29
  So that means it'll be a little bit colder than what the, those evaporators that are 200 feet away or 60 meters away. But,
• 0:30
  Kevin: it's a, a dual temp, as I say, you'll make the, if you'll make the load stage effectively bigger, but you'll make the, if you alter the, the upper stage, but you'll make the upper stage smaller and it will not be happy about it.
• 0:31
  And that worked out to like, almost minus what is it? Minus six, minus five Celsius. Yeah. 22, 23 Fahrenheit sst. So your rack suction. So this is your header pressure at that rack. Exactly. Or packed. Exactly.
• 0:32
  And target below is 0.5 bar, which is about seven and a half PSI or 7.25 PSI. So that means that we can go seven PSI or 0.5 bar above it and below it, and the variable speed drive will be just, that will be taking all the load so that one, there'll be ramping up and ramping down before it makes a decision for the other compressors.
• 0:33
  Does it let it come up slowly? And there's arguments for both. Again, it's knowing what's connected to the end of it. A bit like setting the deadband it. If you've got what you want with CO2 racks overall list stability, you don't want the compressors up and down because that makes the valves go up and down, makes the valves go up and down, makes the whole thing hunt, chase after itself.
• 0:34
  If you bring that back slowly, slowly, it'll, it'll take a long term to have any effects on it. If you've got, and the, the likelihood is that it won't rise hugely, it will settle because you're not bringing on a huge load chunk. You're bring on a small load chunk. If you've got just five big evaporators on the end of the fixture, the chances are if that pressure's rising, you've bought on one fifth of your total load.
• 0:35
  Okay. And it's not, it's not got a, a quantity as such. It feeds into its calculation, but 60 is fast. Zero. You know, one is slow. Okay. And it's a little bit like if anyone ever has to do PID on a controller, tune in, you know, how you put values in for p and i? Yep. To make things happen faster or slower. It's really like a unitless quantity for this.
• 0:36
  You'll have to do the, the PSI conversions for me, Trevor, but if we are operating at like minus 40 on on CO2, which we could be in some scenarios, we could be down at nine bar. So we're at that point we're five bar freeze point.
• 0:37
  Trevor: though, I wanna ask you this though. You've been doing CO2 for 20 years. Have you ever seen it run low enough in a supermarket, say, or an industrial application where you cause dry ice because of the compressors running through too low? No, I, I've
• 0:38
  So it's the evaporators, right?
• 0:39
  Kevin: It, I think we've said on here in the past when, when I used to do the CO2 training years ago, we, we had a little mini liquid receiver that we used to fill up and we could either bleed liquid off the bottom to form dry ice through a really narrow tube, or we could just open the tap on the top and let the vapor off and depressurize to the point where it froze the vessel was about a foot high foot and a half high.
• 0:40
  I think the biggest place you could get dry ice, if you don't know how to add gas to a system and you don't get the pressure up in the lines, you and you have a liquid bottle. So like that's probably the most place, like as a service technician, but in a system running, it's very unlikely. Could it happen?
• 0:41
  Trevor: no, the only thing about that too, though, this is what I'm trying to teach in my CO2 programs too, is like if you do it fast, there might be more oil coming out the system. ? So this is, this is like I'm getting more in an environmental stuff and like that stuff is not good. So just remember, can you do, there's no laws against it right now.
• 0:42
  Kevin: So yeah, we're onto HP and lp. As we said, we keep the compressor in range and we don't want those alarms going off all the time because it's not gonna be useful. We want the alarms going off when there's something serious going on. So RDM on low pressure on the left hand side of the screen there gives you an LP alarm and an LP shut down.
• 0:43
  It's never gonna get there in normal operation. It's only gonna get there for pump down. I don't want the alarm going off for no reason. There's no benefit for that. There's no benefit to the boy who cried wolf for alarms because the alarm goes off all the time. People ignore it. So at the other end I've got discharge trip and discharge stop.
• 0:44
  Yeah. And 10% ish below that. Again, for the discharge stop because it's gonna take time to stop. Right. You switch four compressors off, the pistons are still moving, the cranks still turning when they switch off, so it is gonna overshoot that by a little bit. Give yourself some room.
• 0:45
  Kevin: So Yeah. So majority of systems in Europe, UK are 120 bar on the high sides. 30 is becoming more common. We're struggling still for materials for 130 bar.
• 0:46
  Trevor: Okay. And so we're talking about in, in PSI, so that would be like 1740 would be the relief, which is one 20 bar. Yeah. The mechanical stop to CS or to Danfoss 1 0 8 bar, which is a hundred 1,566 PSI. And then this discharge stop that's in the controller.
• 0:47
  And at that point, what will happen is we haven't got enough headroom to start another compressor because you are always gonna get a discharge pressure spike when you start a compressor. If you are running, you know, 1,450 PSI and your trip's at 1,560 or something like that, you're too close to that limit and you will hit it when you start the compressor.
• 0:48
  You are producing a heck of a lot of flash gas when the temperatures are up there. That's right. And the majority of what your rack is doing at that point is processing flash gas. So we move into things like having parallel compression at that point where we have compressors that are dedicated to pumping flash gas.
• 0:49
  If the super heat gets too high, it will just activate a relay out of this, and you'll put it in the mapping. You'll find the output that's relative to the super heat control, be that high or low, and you will map it to where that function is. But you've got targets and you've got alarms. Alarms is where it's gonna tell you it's all gone wrong and your super heat's too low or too high.
• 0:50
  You need the PNID, you need the IO schedule. 'cause you gotta, like Kevin said, you gotta map this. Yeah. So like that's on board 1.1 that there is looking at that. So when that said that was absolutely three Celsius, ? Or mm-hmm. That need, we really need to understand, okay, well history Celsius, that board point needs to open or close that other, that other point.
• 0:51
  There is no point in having slow reaction on the compressors and fast reactions on the valves because you will make it unstable. You need to have everything working relative to each other, and RDM does the same thing with response on and response off for the valves. Again, these are set middling. You know, you can go up to 60, these are set for 30, they're dead halfway response on and response off with the high pressure valve, what it's gonna give you is what's the maximum It's allowed to set its target to what's the minimum it's allowed to set its target to, and that is because your ambient temperature changes, right?
• 0:52
  Trevor: And then you'll see on, on these, in this controller. Now here in Canada we got split. So you might have split, you might have the gas cooler bypass. We see that here. Yeah. So these are things that you, we don't, we're not talking about them right now, but when you're in these controllers, understand what, once again, what's on the system you're working on when you're going into program.
• 0:53
  Don't set that too low because you set that too low. You will ship more gas to the flash tank in high ambiance, which is gonna put more load on your system. You can afford that system to come up. As we were saying before, we'll talk more about it in part four. Yeah. But there's a balance. Don't set it too low.
• 0:54
  You've got a band where the valve is gonna do nothing. This is seven PSI above seven PSI below half a bar and it's middling on the speed. 30 on the speed. We've got a really useful thing called receiver interlock. Carell does something very similar whereby if the pressure in the receiver falls below the minimum number that it's allowed on this, it's 35 bar, which is gonna be what?
• 0:55
  Similarly, if you get above the max pressure 48 bar on this, it's gonna be what, like seven a bit. Seven and a bit. Yeah. It will force the HP valve to close so we don't over pressure the receiver. Really useful features because in cold ambience it is definitely possible to equalize out the system. It'll all wanna stay in the gas cooler because it's nice and cold and we know all the go where it's.
• 0:56
  So like you say, we often balance the oil reservoir pressure on a CO2 system against the, the city, the flash tank. So if you drop your flash tank pressure too close to suction there and CO2 oil is thick stuff, it don't wanna move by itself, you've gotta push it. Right last page, 'cause we are, as say we're running out of time, is the fans gas cooler, fans similar setup.
• 0:57
  Trevor: Yeah, so 50 Fahrenheit is 77 Fahrenheit, so that's, yeah. And that's a lot lower than the HFCs, ? Yeah. Hs, you know, was always for me, some people said it 50, but for me it was 55 Fahrenheit, 60 Fahrenheit, ?
• 0:58
  Yes. And I want, I want us to dive into this a little bit. I know we're getting close to time. Yeah. I wanna spend a little bit of time here because I have a lot of conversations with people where you got fans, you got water, you got sometimes split valves and you got the high pressure valve. And if you don't set that up, you might, it might work in the summertime 'cause it's, I think the, with the heat, it's easier to run the system running, then you can make the run easy instead in the summer with the set point you put in there.
• 0:59
  You've got the HP valve and you've got the fans. And I was talking to somebody about this just the other day. A lot of controllers don't coordinate them very well. And they're both trying to do the same thing in different ways. They're both trying to control the pressure and the gas cooler. The, your fan minimum target, let's say, has gotta make sense with your HP valve minimum target.
• 1:00
  The, the fans are gonna be going flat out, but the HP valve isn't gonna wanna open because the pressure's not high enough. So you'll end up backing all your CO2 in the gas cooler. Your, your set points have gotta make sense together. Yeah. So like on this, my minimum HP valve set point is 45 bar, which is fairly similar to what 10 degrees Celsius is on CO2.
• 1:01
  What people tend to do as well is we want efficiency. So people will put massive gas coolers on systems, which is great when it's under full load, not so brilliant when it's under low load, because your tendency, again, is your gas cooler will be hugely oversized. And you'll end up, you'll be like, where's all my liquid at?
• 1:02
  And then that's gonna affect how it's controlled if it's looking for sub cooling. It's gonna go, I've got enough sub cooling I need to stay shut to let the CO2 stay longer in the gas cooler. Because how we get more sub cooling is we make the CO2 spend longer, which means the valve stays shut, which means the pressure comes up and you end up with a big surge.
• 1:03
  You some, some places you're gonna see. Minus 20 Celsius some parts of the year and plus 30 Celsius other parts of the year that's gonna get, you've gotta set your range to account for that, but respecting the fact that if you set the minimums lower than what your receiver wants to be, your CO2 ain't gonna the receiver, it's gonna stay in the gas cooler.
• 1:04
  And that's really what ke Kevin's saying When you're setting this up. We can tell you numbers and give you exact numbers, but it's gonna be different here in Canada than it is in the UK where Kevin is, and then different where it is down in Florida, where some people are calling it or New Zealand, ?
• 1:05
  Mm-hmm. But I counted 15 days, I think it was no, 28 days above 30 Celsius. ? Yeah. But there was no average above that. So how many of those hours you gotta do a specific hour and every year it continues to change. But when you set up these controllers, you set them up with those differentials and you're gonna have these highs and you're gonna have these lows.
• 1:06
  And, and the other part of course, as we touched on earlier on is if the HP valve is shut, the receiver pressure, the flash tank pressure is falling. If you, you, you can have a safety to boost it up, but now it's falling. And the problem when that falls is your expansion valves on your fixtures don't work as well because they've got less pressure across them, which means they generate less duty, which means the rack slows down and you get to the point where you've basically unwittingly pump the rack down and at some point then somebody has gotta force it to run again because it, it ain't gonna want to go.
• 1:07
  You know, 20 years ago we didn't breach 32. Hardly ever. Now we breach every year, so we give ourselves more headroom. Last thing I just wanna mention there, Trevor, on this page is set back and that is purely for noise. You know, we, we've got sites where noise is sensitive, sensitive, especially at night.
• 1:08
  Kevin: The the other thing you can do, 'cause it also has day reduction, is if your gas cooler is designed with the duty only to be the fans, 80%, you can put a day reduction in there. So it will then hold the fans during the day as well, unless.
• 1:09
  Trevor: Yeah, I love that. You know, I love that. And, and I really believe that, you know, putting more work in, we, we just talked about some programming, some great programming there because that, that there, and this is a starting point, if you never did it before, but you work on the controllers and once again, it doesn't matter, the controller, what we talked about, the process behind it is the same.
• 1:10
  And then when you get into the staging and the dead bands. It's something that you, you start learning now for tomorrow when you get to it. 'cause if you're not learning it today, when you get to it, you're gonna have to start learning it then. It's better to learn it now than tomorrow. Next week we're gonna be diving into programmable crowd, just similar to this, but we're gonna be diving into some different features.
• 1:11
  Way to go all around the world, some chats out here. I really appreciate this, Kevin. Honestly, thank you so much for all this, my pleasure and knowledge that you shared. And if you're listening on the podcast like it shared, send us some comments on LinkedIn. Message us on LinkedIn. We're here to help and to support the industry, support you if you're a technician in the field.