Episode 281. CO2 Experts: Troubleshooting CO2 Systems using RDM Controllers with Kevin Mullis

Welcome to another CO2 experts. Once again, learning, growing CO2 knowledge. I'd love to see in the chat where you guys are from. If you're listening on the podcast later. Please comment on it. If it's Spotify or Apple, because we're here to grow the industry, grow our knowledge today, once again, returning guests, my good friend, Kevin from Integral, this guy is a control experts.

We, every time we talk, I'm learning something from him and continue adding stuff to my CO2 trainings and my CO2 academies, just from his knowledge, because it is great because all his experience in the field over the years are tips and tricks that you're not just going to go and find in a book. This is stuff that he put his work, hard work in over the years, on call service, working with hundreds of different technicians over the years to build his knowledge up.

And we're bringing it to you today. So if you're listening or watching on the YouTube channel, like, comment, share this because this is how more people find out about these awesome CO2 sessions. Kevin, how you doing brother? How you doing Trevor? Lovely to be back. Thank you for having me back again. I appreciate you.

And we're bringing it to you today. So if you're listening or watching on the YouTube channel, like, comment, share this because this is how more people find out about these awesome CO2 sessions. Kevin, how you doing brother? How you doing Trevor? Lovely to be back. Thank you for having me back again. I appreciate you.

Oh, this is awesome. You know, so I've, I've done you know, a few RDM talks, Chris Prom, see him on there. Hey Chris, what's up brother? And I've been to lots of shows, RDM. I hear so many good things about the RDM, especially down New Zealand, I did one with James Darby down there and he came on the show.

CO2 Mondays back in the day when I did that show and the technicians that I talked to that uses say it's very versatile, you know what I mean? It's very user friendly and open. So if you need to, to share, and this is kind of some of the things we're going to talk about on troubleshooting, because this is important, right?

That you get out in the field. You may have worked in RDM. You may have not worked on the RDM, depending on where you're at in the world. As a technician, you want to kind of understand how to navigate, how to troubleshoot. And we're going to get into some of this today.

I was just looking through the participants that I see, see a couple of familiar names from RDM in there, so I'm sure they will be, they will be policing my answers here today. And it's a, it's a rest up dog. I'm looking at you. We'll be policing their answers, that's right. We'll be policing

And so they've got really good pedigree in especially supermarket controls. And I, as you say, it's a really versatile, really friendly. Easy to use system and just the, even things like the manuals. Yeah. We've talked before about manuals for some of the major control suppliers, and they are not always the easiest to follow.

And when we when we did our Dan Foster Corral, we didn't, when we picked up a particular point that I, I said, I know this works. I just cannot find it in the manual. And one of the things. With RDM, the manual will list you every possible parameter with a description of it in a straightforward way.

And when we when we did our Dan Foster Corral, we didn't, when we picked up a particular point that I, I said, I know this works. I just cannot find it in the manual. And one of the things. With RDM, the manual will list you every possible parameter with a description of it in a straightforward way.

So that you can say, if you do this, this will happen. And that's really useful when you're in the fields, they're all available on their website. You just need to register for their website. You can download all the documentation. And yeah, it's, it makes it a pleasure, much more pleasurable experience.

The tech support team is excellent. They. As you know, they've got a couple of offices. Oh, Charlie's joined to pressure me as well. Like, so that hi Charlie. But yeah, they it's a really, really good setup. So obviously it is a whole control scheme. We're not going to touch too much on things like the data manager today, because we could do a whole full hour session just on that.

What we're going to look at today is using it in the field. So things that people. Can tend to get mixed up with transducers. Yeah. The, the industry has had transducers for years as, as we all know on plant, but with the return of CO2, certainly in the UK markets, transducers, somebody remembered that you could use them for superheat calculations as well.

What we're going to look at today is using it in the field. So things that people. Can tend to get mixed up with transducers. Yeah. The, the industry has had transducers for years as, as we all know on plant, but with the return of CO2, certainly in the UK markets, transducers, somebody remembered that you could use them for superheat calculations as well.

You know, we, for years on the electronic valves in the UK, all we were doing was using a coil in a coil outlet and somebody thought, Oh, perhaps we should be doing this properly. So. It's, there's a wealth of transducers and what have you out there and a lot of issues come across from people connecting them wrongly or not knowing how to share them around the system, etc.

So, ultimately, you don't get your transducer right, or you don't get your probes right, you're not going to be the superheat right, your system is not going to run very well. Or the pack may have a very short and unhappy life if you're sending a lot of liquid its way. So that's a good place to start, I think.

So as you, as everyone hopefully can see on the first shot there, RDM offer a couple of different formats of that controller. The, the one that's shown there is a door mount. It looks a little bit like that, which is, I'm not going to show that too close because it's a really old one. And the RDM boys will be like, why are you showing a really old one?

So as you, as everyone hopefully can see on the first shot there, RDM offer a couple of different formats of that controller. The, the one that's shown there is a door mount. It looks a little bit like that, which is, I'm not going to show that too close because it's a really old one. And the RDM boys will be like, why are you showing a really old one?

But the. That fits in somewhere where a Corella, not Corella, a Dixel or an LAE or something like that would fit a door mount hole. All connections on the back. They also do a panel mount in rail version. Which is really useful when you've got like 30 controllers and you don't want all them hanging off the door because it's going to make the door weigh about a hundred pounds and have about 400 wires hanging off of it.

So there are various options. Just talk a little about what you're going to connect to these controllers. So circle there is the plug for the transducer. As you can see on the main drawing on the left hand side of it. Now, RDM by default likes to use 4 to 20 milliamps for the transducers. Very, very standard thing in the industry.

So there are various options. Just talk a little about what you're going to connect to these controllers. So circle there is the plug for the transducer. As you can see on the main drawing on the left hand side of it. Now, RDM by default likes to use 4 to 20 milliamps for the transducers. Very, very standard thing in the industry. It doesn't, because of that, it doesn't share the transducer directly on that wiring if you've got more than one controller. There are a multitude of ways to share the transducer across the network. And that's how they, they like you to do it. Be that through one of their hubs. Where you can connect a transducer and share it to all the things coming out of the network hub, or it can be broadcast over their network from the rack controller, or it can be connected directly.

We're going to focus today on it being connected directly, simply because a lot of the same principles apply with setting it up wherever it's connected to. So, on this one we can see, I've marked up that plug where it's circled with how the transducer works. With their wiring so you can buy a transducer for any given range you might want like a 20 20 bar range one for Suctions on HFC plant you can buy 65 bar range one for co2 suctions.

You can buy 125 bar range for high pressure stuff. They will connect the same way. So when you buy your RDM transducer, it's got a cable with it It's got red and a green wire and a little thin black wire. Little thin black wire doesn't get used. Red and green get used and I've marked in red and green there how that goes in.

You can buy 125 bar range for high pressure stuff. They will connect the same way. So when you buy your RDM transducer, it's got a cable with it It's got red and a green wire and a little thin black wire. Little thin black wire doesn't get used. Red and green get used and I've marked in red and green there how that goes in. The 12 volt supply and then the 4

input for your pressure reading, which isn't that common a thing to do from a transducer. So people look at the plug and they're like, this is a bit confusing. Cause that says it's an input. So it's important to know that that pin does something different depending on how you've got it configured. So that's, that's the main bit with the, with the transducer.

As I say, you can connect it directly to the controller. There's also, if you use an RDM communication hub. You can wire a transducer into that and then everything that's on the controller side of that hub can receive that pressure reading. You can also, as I said earlier, if you don't want to do that, and you don't want to fit the controller with the transducer, you can broadcast the reading off of the rack controller.

As I say, you can connect it directly to the controller. There's also, if you use an RDM communication hub. You can wire a transducer into that and then everything that's on the controller side of that hub can receive that pressure reading. You can also, as I said earlier, if you don't want to do that, and you don't want to fit the controller with the transducer, you can broadcast the reading off of the rack controller.

All you've got to do is tick a box in the setup to say broadcast, and you can configure the controller to read that off of the network. Obviously there's benefits and pitfalls to both. If you lose network and you're broadcasting the transducer reading, you will lose the, you will lose the transducer reading, but it's Potentially considerably cheaper than installing like 50 transducers.

So it depends on your setup It depends how how much resilience you want. One thing worth bearing in mind with RDM Is that if the transducer goes into fault It will default back to using probe 3 for your inlet temperature, for your evaporating temperature effectively. So you do need to fit probe 3, which is the coil inlet probe, regardless of whether you're using a transducer or not.

So it depends on your setup It depends how how much resilience you want. One thing worth bearing in mind with RDM Is that if the transducer goes into fault It will default back to using probe 3 for your inlet temperature, for your evaporating temperature effectively. So you do need to fit probe 3, which is the coil inlet probe, regardless of whether you're using a transducer or not.

Otherwise, it will flag a fault, and it's not going to work. It is not going to work if it, if the transducer goes away. So just from the probes. Again, as we said on our previous controller training, everyone likes the probes in their own order. So, for RDM, probe 1 is your air on, your return air. Probe 2 is your air off, your discharge air.

Probe 3 is your evaporator inlet, which, in the absence of a transducer, is your evaporating temperature for your superheat calculation. Probe 4 is your suction probe. Probe 5 is your defrost termination probe. Probe 6 is If you want to use a product sensor, so some of the guys on the call, I'm sure we'll have seen you can put like a, what they call a sludge probe, which isn't, isn't a little, you know, a little slimy thing that crawls around the fridge, but is the thing sat in a big block of polystyrene or gel that responds much more like a program back at some of the, UK guys will recognize it being called a plastic chicken back in the M& S, early days of doing this because it was designed to respond at the same speed as a chilled chicken would respond.

Probe 3 is your evaporator inlet, which, in the absence of a transducer, is your evaporating temperature for your superheat calculation. Probe 4 is your suction probe. Probe 5 is your defrost termination probe. Probe 6 is If you want to use a product sensor, so some of the guys on the call, I'm sure we'll have seen you can put like a, what they call a sludge probe, which isn't, isn't a little, you know, a little slimy thing that crawls around the fridge, but is the thing sat in a big block of polystyrene or gel that responds much more like a program back at some of the, UK guys will recognize it being called a plastic chicken back in the M& S, early days of doing this because it was designed to respond at the same speed as a chilled chicken would respond.

So, you can connect that in there, and they call it a log probe now because nobody wants to talk about slugs around the foos. So, but yeah, that's exactly, that's what that, and you can configure the controller to alarm on that probe. With probe types, I think there are 20 different types of probe that RDM supports.

I think it's 10 resistance ranges and you can have them all in centigrade or fahrenheit. So, by default, it will be PT 1000. By, you can select 2K, 10K, 5K, 2K, 25. I'm sure a lot of people on the call will know, PT 1000 is great for many things, and it's a really common use of the probe, but the resistance range is quite tight on it.

I think it's 10 resistance ranges and you can have them all in centigrade or fahrenheit. So, by default, it will be PT 1000. By, you can select 2K, 10K, 5K, 2K, 25. I'm sure a lot of people on the call will know, PT 1000 is great for many things, and it's a really common use of the probe, but the resistance range is quite tight on it.

So if you've got a hundred meters of cable, that cable is going to have a resistance on its own, right? PT 1000 is like 4 ohms per degree, so 8 ohms on that cable, which isn't an awful lot, is going to throw your readings by 2 degrees C. So, if you're doing big installation that's got like a 100 meter long cold room or whatever, you might want to pick a 2K temperature sensor, you might want to pick a 10K temperature sensor, something that's a bit more resilient to that resistance range.

And then I remember when I was doing, when I do control training or doing install training, it's like, well, if you've got to run at 300 feet. Exactly. You got to size that wire. You can't just use a 22 gauge, you know, wire and you're running it a thousand. Yeah.

And then I remember when I was doing, when I do control training or doing install training, it's like, well, if you've got to run at 300 feet. Exactly. You got to size that wire. You can't just use a 22 gauge, you know, wire and you're running it a thousand. Yeah.

And that drives me insane. Not just because if you look at it the wrong way, the wire snaps off, but also because it is only unsuitable because of its resistance for running long distances for probes, and it drives me mad because like I say, you, you got to connect something to it and it just snaps as soon as you look at it, please, anyone doing any install, do not use category five cable for putting probes in you need to use a decent wire gauge.

To do probes as thanks now, by the way, for pointing out when I said evidence earlier evidence is a food convenience retailer in the UK in case that reference was lost on everyone from over the other side of the pond. Thanks for that. Yeah, so you've got to get the right readings into the controller.

To do probes as thanks now, by the way, for pointing out when I said evidence earlier evidence is a food convenience retailer in the UK in case that reference was lost on everyone from over the other side of the pond. Thanks for that. Yeah, so you've got to get the right readings into the controller.

If you want the right CP calculation, if you want the right temperature control. Yeah. And it's you push that resistance up, the reading will go up. And you will end up with a chill room. That's too cold, or you'll end up never meeting set point if it's a freezer. So next next slide that Trevor's put up there is how you set up the transducer.

And the settings are virtually the same, no matter whether you're setting up on it, on the fixture controller, whether you're setting it up on the rack controller or whether you're setting it up on a hub. So you need to tell it some important things. You need to tell it what gas you've got, because.

Obviously, it needs to work out the evaporating temperature for you. You need to tell it what pressure range the transducer covers. You need to tell it whether it starts at zero or not. Glide, you of course don't use for CO2. Hopefully, everyone knows what glide is. That allows you to better approximate the evaporating condition for zeotropic blends.

Obviously, it needs to work out the evaporating temperature for you. You need to tell it what pressure range the transducer covers. You need to tell it whether it starts at zero or not. Glide, you of course don't use for CO2. Hopefully, everyone knows what glide is. That allows you to better approximate the evaporating condition for zeotropic blends.

So, if you don't use the glide, You, depending on how the controller is, you will either end up with a temperature that's at the bubble point for your superheat calculation, which is not going to sit well with you for you, the actual superheat of the outlet. Or if you push to glide too far, you're going to end up with it at the dew point, which can give you starving of the coil.

Now, Trevor and I discussed this. The opinion varies across the industry as to whether you should set that mid point between the bubble and dew point, whether you should set it one end or the Dew, whatever. Wisdom in your company is and what experience is because everyone finds it different. Pressure type gauge or absolute depends on how it interprets the reading.

So as per my notes, their range. Spam in this is the the full range of the transducer. So for an IBM transducer, you might have minus one to 65 bar. So that transducer has a span of 66, but yeah, if, if you if you just set that out, well, it's. It only goes up to 65 bar, you're going to have an incorrect calculation.

So as per my notes, their range. Spam in this is the the full range of the transducer. So for an IBM transducer, you might have minus one to 65 bar. So that transducer has a span of 66, but yeah, if, if you if you just set that out, well, it's. It only goes up to 65 bar, you're going to have an incorrect calculation.

It's from the minimum to the maximum, and then you use the offset to tell it whether it starts below zero or not. Now if you've got a minus one transducer, it starts below zero, so you have to tell it it's a minus one offset, cannot tell you how often I see this saying correctly. If you've transducer, for example, in four to 20 milliamp, very often they start at zero, so you might have a zero to 60 bar transducer. Span 60 offset zero. Yeah. I've seen this,

I've seen this, I was in a CO2 training last week in in one of my groups. And the guy was like, I went to the case and I put my gauge on and it was reading, I think he said 20 PSI off. It's like, what is going on here? The transducer must be failed. Went out, picked up another transducer.

He came back, put it on and cause he's telling me the story about this and it's reading 20 PSI still off again. And then he was like, well, what do I do? I'm like, well, what's the range? I was like, well, the range. Yeah. What's the say? Oh, it's one to 200 PSI. I think it was, I think, no, it was one to a 650 PSI and what was wrong.

It was to 600. I think it was 600. So when he was, went to check it, it was, the controller was reading what it thought it was the range, but actually the range wasn't set up exactly what you're talking about here. And I've seen this many times on when I used to train SH2 controllers, an ALCO controller, Copland controller now, same thing.

Like you'd put in one 40 milliamp range and it's a different one on there. And we see this time and time again on high pressure controls. Cause the Danfoss ones, you know, they're AK 20 50. That's it, yep, AK 20 50. But it looks 20 50, but the range, one could be 0 59, one could be 0 159.

Like you'd put in one 40 milliamp range and it's a different one on there. And we see this time and time again on high pressure controls. Cause the Danfoss ones, you know, they're AK 20 50. That's it, yep, AK 20 50. But it looks 20 50, but the range, one could be 0 59, one could be 0 159. Kevin: Exactly that, yes, and there's no reason you can't use the And they do a zero to minus one to 99 as well.

And so what we what we would see just a slight divergence when we were doing some some Tesco work a few years ago, another major retailer in the UK, if when there was no minus one to 59 is available, you could use a minus one to 99 on the case. But if you had, like we showed previously when we did Danfoss, if you use the programming stick that we had to dump the program into all the cases.

You've got to allow for the fact you've changed the transducer, otherwise you'll get some craziness on the readings. I think what happens sometimes as well is people tweak the span or the range or whatever it's called on the controller you're doing to try and correct errors in the reading. That is not going to be a happy place for you.

If you're 0. 1, 0. 2 out, adjust it with the offset. Don't adjust it with the range because the span, because the span puts, will give you error. right through the operating range. Then you just adjust it with the offset because that is a fixed amount that it moves to reading by. If you, if you adjust the range, it's going to, you're going to be like, why is it out now?

If you're 0. 1, 0. 2 out, adjust it with the offset. Don't adjust it with the range because the span, because the span puts, will give you error. right through the operating range. Then you just adjust it with the offset because that is a fixed amount that it moves to reading by. If you, if you adjust the range, it's going to, you're going to be like, why is it out now?

Why is it out more? Why is it out less? It's going to be all over the shop. And just bear in mind as well not so much with, with the RDM ones, you could get away with the 125 bar transducer on a, on a 60 bar system, but I've seen a few times. People put the 65 bar transducer on a, on an LT HFC system.

And you're operating at like 15 PSI, one bar. Yeah. The transducer will read that, but the amount of current change on a 40, then to move it like 0. 1, 0. 2, 0. 3 of a bar is so small, you're inviting errors into it. And 100 percent

1 or 0. 2. And that's important when you're doing those gases, you know, CO2. If it moves by half a bar, it's like maybe half a degree. It's a lot less of a flout than it is if you move by half a bar on HFC.

Okay. So when you've connected up your transducer and your probes properly, you'll have a screen that looks on your inputs something a little bit like that. So assuming you've connected it directly to your controller, the bit circled in yellow there is where you will read the evaporating condition. So it will tell you your local pressure and what it's worked the temperature out to be.

Yeah, so that then is the number that the controller will use to work out the super heat, which you can see just below the red circle or higher up the image there. So if that transducer goes funny and stops reading for whatever reason, it will default to using the evaporator probe, which is circled in red, and that is the temperature probe you have on your coil internet.

Yeah, so that then is the number that the controller will use to work out the super heat, which you can see just below the red circle or higher up the image there. So if that transducer goes funny and stops reading for whatever reason, it will default to using the evaporator probe, which is circled in red, and that is the temperature probe you have on your coil internet.

But as you can see, there is a, a considerable difference between what they're reading and if you are controlling to six. K superheat, then you've suddenly lost three K pretty much by switching to the probe and inlet probes are not a particularly accurate way of measuring evaporating temperature because they are highly dependent on where you fix the probe, how well you fix the probe and how thick your pipe is.

It's. This is why a lot of people have gone back to do the transducers because if you want things to control tightly expecting it to control on Two sensors that are sensing through a pipe something that's changing. It makes it difficult. It's. This is why a lot of people have gone back to do the transducers because if you want things to control tightly expecting it to control on Two sensors that are sensing through a pipe something that's changing. It makes it difficult.

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I got to look into it. Because you want to insulate that stuff. You want to put it on the right. You don't want to put it on the bottom, like a TX. Well, we talked about this many, many times, you know, there's oil, there infiltration, you've got to put it on the right spot. But that, that there, you don't want they're just so sensitive.

I got to look into it. Because you want to insulate that stuff. You want to put it on the right. You don't want to put it on the bottom, like a TX. Well, we talked about this many, many times, you know, there's oil, there infiltration, you've got to put it on the right spot. But that, that there, you don't want they're just so sensitive. You need a, you need to insulate that stuff, right?

And the valve is going to be all over the shop while that sorts itself out. It makes sure you insulate it. Problem with the inlet probes, especially where we have pretty much always, unless they're really small coils, we have a distributor and we have thin legs going into the coil. Is there's often nowhere good to mount the probe.

People say all the time, people mount the probe on the little bit of pipe after the expansion valve, before you get to the distributor, that is not a good place to mount it because. You're at an intermediate condition in there. You, when you drop through those distributor legs, you get pressure drop. So the, the condition, the gas is evaporating out when it leaves the valve in that little bit of pipe is not the same condition the coil seeing.

People say all the time, people mount the probe on the little bit of pipe after the expansion valve, before you get to the distributor, that is not a good place to mount it because. You're at an intermediate condition in there. You, when you drop through those distributor legs, you get pressure drop. So the, the condition, the gas is evaporating out when it leaves the valve in that little bit of pipe is not the same condition the coil seeing.

And, but people put it there because it's the, it's the biggest bit of flat pipe. to mount the probe on, right? It's really difficult to mount it to like a quarter inch distributor length and a lot of your evaporator manufacturers, they used to give you a little bit of pipe before, after the distributor, before it went into the coil, not a lot of them give you that.

Now they just crimp the end of the pipe down right onto the distributor. It's really difficult to mount the probe. Now. A lot of the manuals will tell you to mount the evaporator inlet probe at the opposite end of the evaporator to where your valve's mounted. Problem with doing that. On

Now that's all fine. That makes perfect sense in terms of you've done whatever expansion you're going to do and you're going to read a proper condition there. Buh. It can hit you with startup. So let's say it's a frozen food case and it's just come off of defrost.

The coil was like 10 degrees. C yeah, 50, 60 Fahrenheit. Yeah. Whatever it works out to be. The problem you'll have then is that the valve goes into startup, starts pulsing a load of liquid in, but you've got a heck of a lot of heat to absorb before that inlet probe. understands what the inlet temperature of the coil is.

You've got, because the coil's hot, you've actually got a ton of superheat. But because that probe hasn't seen any liquid yet, it doesn't know. It thinks it's got no superheat. So depending on how long your controller gives the valve to start up, at some point, if it doesn't see liquid by then it's going to go, no, no superheat, and it's going to stall.

So a lot of the time, controversially, perhaps for some controller manufacturers, It is, in my opinion, better to have it as near to the inlet of the coil as possible. Because it gives you more reliability on startup. The, the flip side of doing it that way is to tell the controller to open the valve more after a defrost startup, or give it longer.

So a lot of the time, controversially, perhaps for some controller manufacturers, It is, in my opinion, better to have it as near to the inlet of the coil as possible. Because it gives you more reliability on startup. The, the flip side of doing it that way is to tell the controller to open the valve more after a defrost startup, or give it longer.

The problem with doing that, you tell it, you know, when you start up, open the valve 100%. If you've got an iced up coil, regardless of what the superheat is, it's going to ignore the superheat while it's in startup. Because it has to, to get the coil going. If you tell it go a hundred percent and you've got an iced up coil, that is a lot of liquid that's going to come back to your rack, whether or not, you know, the whatever that sense is reading. So there are pitfalls to doing it both ways.

Yeah, absolutely. So the correct way to do it, the way we've started doing it. More again now is to use a transducer to give you your suction pressure, to give you your evaporating condition and to use a suction probe, an outlet probe on the coil. So between, with those two numbers, you can work out your true superheat.

What we used to do for cost and because it was a decent enough approximation was Put a probe at the inlet of the coil because just when you get out of the expansion valve and you get into the evaporator, you haven't really absorbed any heat yet. You're almost certainly going to have liquid and vapor there, so you're going to have a saturated condition, which means at that point you should see what the evaporating temperature of the gas is.

It's a decent approximation of doing it, but it's vulnerable for all the reasons I said to you not putting the probe in the right place, or if you do put the probe in the right inverted commas place, whether it actually sees any liquid. If it's not seeing liquid, you're not going to see the evaporating temperature.

But It's still relevant because as I say, RDM uses it, whether you fit a transducer or not, if you've got a transducer there and you've set it up, it will do it the proper way. It will use transducer. If your transducers failed or you've decided not to use one, it will use that in that temperature to calculate the superheat and it's cross coil temperature.

But It's still relevant because as I say, RDM uses it, whether you fit a transducer or not, if you've got a transducer there and you've set it up, it will do it the proper way. It will use transducer. If your transducers failed or you've decided not to use one, it will use that in that temperature to calculate the superheat and it's cross coil temperature.

They call it, you know, the difference between the temperature of the outlet and the temperature of the inlet where you've got saturated condition.

And even when me and Chris Prom did a podcast, talked about, you know, you can use temperature first, superheat second, right? So, cause we want to try to maintain that product. We want to absorb that heat. We want to pull it out. So when I'm talking to technicians in our CO2 program, you want to understand how that's set up.

Cause you don't want one case set up by, okay, it's superheat control. The next one right beside it's temperature control. You know what I mean? And you have them set up in the same range because you want to maintain the product.

If you do it that way and you've got a nice up coil, as we said before, it will, it won't care if the temperature's high because you blocked the discharge air and you are sending a ton of liquid through that coil, that's not gonna care because it's still getting the temperature. So use it with caution.

If you do it that way and you've got a nice up coil, as we said before, it will, it won't care if the temperature's high because you blocked the discharge air and you are sending a ton of liquid through that coil, that's not gonna care because it's still getting the temperature. So use it with caution.

If you use that facility, it's, there are, there is a reason why it comes defaulted to super heat control. I mean, if you've got a, a slightly more exotic system that's designed for low super heat. Then you've got more opportunities to use it, but the system will take that into account and it will have a a means of dealing with overfeed. They're, they're not so common on supermarkets.

So, yeah, no, absolutely. Absolutely. And we could, we could do loads and all that. I mean, RDM has the, the facility to shut the valve. If it detects a superheat problem, you set the temperature at which it sees that superheat issue. And you can tell it, once you see that issue, how much you want me to open the valve.

And you can tell that to be zero. And in fact, there's a good reason, if you're using a transducer especially, to tell it, if you see a problem, go to zero. Because it'll then sit there for a little while to let the coil recover, and then it'll have another go. It'll go back into start, and it will try again.

And You, you've just got to, you've got to balance how you do your start opening, especially if you're using probes and how you do your problem opening with making sure the coil can get away again after a problem, but not so much. It's really tempting to say, go start opening 75 percent because I'll definitely get the coil away then. But it's that iced up coil thing. It gives you. It'll flood the area

And all the, yeah, exactly. And all the controllers are the same, they'll all ignore superheat for a start up period, because they have to, for the probe issue, they've got to ignore the superheat to get the inlet probe cold. And they've got to allow that flexibility, but you've got to use that with some caution.

And if your coils in a, I don't know, a Costco, let's say, and it's. 20 feet in the air and the fans spinning. If you've got a ribbon of ice this high on the front of the coil, you know, probably not going to see it from the ground. And no, and the problem with that is that that because you'll have a multi pass coil with five or six inlets on it, first bit of the coil is going to do no evaporation whatsoever.

And if your coils in a, I don't know, a Costco, let's say, and it's. 20 feet in the air and the fans spinning. If you've got a ribbon of ice this high on the front of the coil, you know, probably not going to see it from the ground. And no, and the problem with that is that that because you'll have a multi pass coil with five or six inlets on it, first bit of the coil is going to do no evaporation whatsoever.

There's no air flowing through that bit. So even though the rest of the coil. is working just fine. That top bit will flood liquid into the suction because there's nothing being evaporated in that section, and you see that a lot. So, I mean, as we say, see on this slide here, you know, bad superheat control due to suction temperature changing.

And you can see the this is just an example, by the way, of what the RDM data manager gives you in terms of graphing as a standard. So, you, once you log your controller onto the system, you don't have to set up data points for logging. It will log everything for you. That's amazing. And, yeah, it's so you've got access to all that data then, and you can drill down, the bar at the bottom lets you get tighter into that graph, or you can set it to a wider.

time period. This is a, what did I do on here? 24 hours. So yeah. So the, as you can see on here, it tells you at the bottom what the traces are and you can see the, the local pressure, which is your effectively evaporating condition is pretty stable on that trace, but the suction temperature. is when you compare it to the superheat, which is a red line, you can see the suction temperatures, what's causing the superheat to fluctuate.

time period. This is a, what did I do on here? 24 hours. So yeah. So the, as you can see on here, it tells you at the bottom what the traces are and you can see the, the local pressure, which is your effectively evaporating condition is pretty stable on that trace, but the suction temperature. is when you compare it to the superheat, which is a red line, you can see the suction temperatures, what's causing the superheat to fluctuate.

You could see, obviously your big spikes are defrost yellow on the bottom is your defrost, but so something is causing that suction temperature to be unhappy. And there's, there's a range of things that can be ice as we just discussed. is quite a common one, little bit of ice, a lot of ice it's, you need to, if you've got weird superheat control like that and everything looks okay in the settings, nobody's gone crazy.

You need to physically check the coil. And I've been told a hundred times, there's no ice on the coil, only for somebody to go up, switch the fan off and finds ice on the coil. So it's a really important one to check. The other one, one of the ones is response time. So RDM gives you for valve control, response on and response off.

And that is a global parameter for how fast the valve reacts to a change in superheat. They've done that, I think, because You know, let's, let's put cards on the table. Not that many people truly understand if you've got P I N D what all those things do is there's a whole group of people who specialize in just tuning PID algorithms.

And that is a global parameter for how fast the valve reacts to a change in superheat. They've done that, I think, because You know, let's, let's put cards on the table. Not that many people truly understand if you've got P I N D what all those things do is there's a whole group of people who specialize in just tuning PID algorithms.

So people tend to fiddle with the numbers and see if it makes a good thing or a bad thing. A lot of the time, RDM simplified that for you. You can have a response on a response off and you can have between zero and 30 for how fast you want that response to be on this particular. type of valve. Now, if you set that to 30 response on, or 30 response off, what's going to happen is, when it sees a change in the superheat, it's going to move the valve very quickly to react to it.

And that seems attractive, because you think, okay, that's going to control my superheat really well, but what it can do is make this system really twitchy, and it can overreact to things it sees. But similarly, if you set it too slowly, It might see a change happening and the valve reacts too slowly and the temperature plummets away because the valve hasn't reacted quickly enough.

And that seems attractive, because you think, okay, that's going to control my superheat really well, but what it can do is make this system really twitchy, and it can overreact to things it sees. But similarly, if you set it too slowly, It might see a change happening and the valve reacts too slowly and the temperature plummets away because the valve hasn't reacted quickly enough.

It's RDM set it by default in the middle. And I think it's really important that if you've got an unstable system like that, that you, you understand why, you know, is it just because of the load changing rapidly? Is it because it just needs to react slower for that type of coil? Does that type of systems, you need to understand why it's doing what it's doing.

Exactly that. It has the customer got a tendency to cover the return air grill with things. Yeah. But yeah, all things that, that can affect the performance of the call. You might need it to react fast for some reason, but don't just go to fast reaction as the first protocol because you will make the system unstable.

I think that's a big thing too that I talk about with technicians is like. Before you change something, why are you changing it? You know what I mean? Like what's the reason? And startups a little bit different. So you're, you're programming, you're controlling, but when you get into that fine tuning, these.

These control manufacturers, they spend millions and millions of dollars on their PNIDs and how to set it up perfectly. Are they perfect for every application? No. That's why they put in these reaction times, but if you go and twiddle it around, because this is what happens, you go in and you change something, and then you change something else and something else, and take a 14 things that change, but you don't know what fixed it. This is where I teach it in my programs, change one thing. Yeah,

If it's, if it's a 30th of the load. You'll see the change on the cabinet, but the effect on the rack is going to be minimum. If, if it's 50 percent of the load, you're going to see, and what you'll, what you end up with. And a lot of this is related to what happens, the interactions within the system. You will drag the rack behind the case or the rack will start leading the case and one will drive the other.

If it's, if it's a 30th of the load. You'll see the change on the cabinet, but the effect on the rack is going to be minimum. If, if it's 50 percent of the load, you're going to see, and what you'll, what you end up with. And a lot of this is related to what happens, the interactions within the system. You will drag the rack behind the case or the rack will start leading the case and one will drive the other.

And yeah, so I mean it just on the other two points I had on there is a super set point to low is the evaporator temperature too high. And, the reason I say superheat set point too low, we talked about it with Danfoss, there's a minimum stable point for every evaporator. If you try and set the superheat below that, the coil is, by design, inherently unstable below that point, and you will never, ever stabilize the outlet.

Evap temp too high is just related to things like floating suction, so if you've got two different racks servicing a meat room, and you're set for zero degrees C, let's say you've got an evap temp of minus five, and a superheat set point of six. You can't achieve that 6k superheat if your return air is zero and your evap temp is five.

Because your suction can never be warmer than the air coming into the coil. Can't do it. Yeah, that's what's determining that temperature. And that will make you unstable because you're trying to hit a superheat set point that's impossible. So, it's one of the things to watch with floating suction. It can very easily upset your system.

Because your suction can never be warmer than the air coming into the coil. Can't do it. Yeah, that's what's determining that temperature. And that will make you unstable because you're trying to hit a superheat set point that's impossible. So, it's one of the things to watch with floating suction. It can very easily upset your system.

Just like you're saying, I like the point of the superheat. You said, set too low. And I've seen this time and time again, doing electronics trainings where. Like the valve's opening and closing and opening and closing. It's the same with a TX valve. If you set it too low, the valve is going to open and close.

So I've always said, as long as you check all the parameters, are they all correct? Is the coils clean? Is the fans running? All the basics done first. And then set the superheat one degree higher. You know what I mean? Warmer. And then one more, and every time you can see, they send me the graphs and you can see it start to stable out because they're trying, it's just too, too much for that coil.

So I've always said, as long as you check all the parameters, are they all correct? Is the coils clean? Is the fans running? All the basics done first. And then set the superheat one degree higher. You know what I mean? Warmer. And then one more, and every time you can see, they send me the graphs and you can see it start to stable out because they're trying, it's just too, too much for that coil. Kevin: Yeah, no, especially in, in the CO2 world where we use thicker pipes. You're, all you're ever seeing with that suction temperature is a time delayed version of reality because it takes time for the changing temperature of the actual gas to conduct through the pipe and to conduct through the probe. So you're only ever seeing what happened a few seconds ago.

And so if you make it too tight, it can't react fast enough to that change because it's seeing it late. It's already got worse or it's already got better before the controller has seen it. So the flip side of the superheat control is, is it due to the suction pressure changing? So on this graph, you can see suction line probe, especially if you look over the night period in the middle layer, pretty stable, the evaporating temperature, pretty all over the place.

That's right. So what's causing that to happen? Are the compressors. Moving too fast? Are the compressors moving too slow? So, that's the yellow line at the bottom there. That's your evaporating temperature. Is, are you loading them on too quickly? People, a bit like adjusting the valve response. RDM also uses response time for compressors.

That's right. So what's causing that to happen? Are the compressors. Moving too fast? Are the compressors moving too slow? So, that's the yellow line at the bottom there. That's your evaporating temperature. Is, are you loading them on too quickly? People, a bit like adjusting the valve response. RDM also uses response time for compressors. It uses it for control valves. You set that way too fast, it sees a change. It's going to ramp up really quickly. And if you go faster than the cabinet valves are ramping up, you'll bring such a pressure down too quickly and it will go, okay, but such a pressure down stage machine off your valves are still catching up.

Then it stages the machine off suction pressure starts rising again. Cause all the cabinet valves just started opening. And you've lost your capacity, you're then waiting for another machine to start. And the flip side happens if you're too slow. The suction, the, the valves are all creeping open, the suction pressure can't respond quickly enough.

When it does come on, it needs too much duty. It'll, and it ends up pulling it down too fast. Is it start limitations? You can only start, especially things like semi hematics, big ones, you, you're only supposed to start them a certain number of times an hour. If you've got that set too tight you can easily, especially when load is low, work through all your available starts or your available compressors, and it then needs more capacity, but it can't start any machines because they're all in start delay.

When it does come on, it needs too much duty. It'll, and it ends up pulling it down too fast. Is it start limitations? You can only start, especially things like semi hematics, big ones, you, you're only supposed to start them a certain number of times an hour. If you've got that set too tight you can easily, especially when load is low, work through all your available starts or your available compressors, and it then needs more capacity, but it can't start any machines because they're all in start delay.

And so the pressure is way too high. And then, all the valves are backing down because they've lost superheat. The compressor then becomes available, starts the compressor. And you don't need it because all the valves are closed and you get into a cycle of chasing, as I said, chasing the, what the one end of the system while the other is doing.

The last one I put on there is on a, is CO2 specific. How's the gas cooler doing? How's the receiver doing? Flash tank, as some, some of us will call it. The other thing that affects suction pressure on a CO2 system is what those two valves are doing because ultimately pressure in the flash tank slash receiver.

Ends up being pushed down into the suction. And if you are up and down and up and down and up and down and up and down on how things are feeding out of the gas cooler and how things are feeding out of the liquid receiver into the suction, you're going to send the suction pressure crazy, regardless of what the cases are doing, because especially when you're operating transcritically, that is a heck of a lot of vapor coming into the suction line.

Ends up being pushed down into the suction. And if you are up and down and up and down and up and down and up and down on how things are feeding out of the gas cooler and how things are feeding out of the liquid receiver into the suction, you're going to send the suction pressure crazy, regardless of what the cases are doing, because especially when you're operating transcritically, that is a heck of a lot of vapor coming into the suction line.

And that can be, I'm sure many people on here who work with CO2 have seen in the summer, if the rack is. heavily transcritical if it's a warm day, you switch all the cases off and the rack will continue running for another half an hour because it's just, it's just circulating the, the heat the compressors are generating through the system and it won't stop, you know, and you've got to often manually intervene to tell it to calm down, but it's a heck of a lot of the load.

And so that can have a big effect on the suction pressure. So, you do with CO2 need to consider maybe the cases are absolutely fine and maybe the compressor stage is absolutely fine, but maybe something further up the system is causing it to be unstable. Yeah. There's a, well, I had a guy in one of my community meetups last week, I think, and he's talking about like.

I don't get any oil. Like I'm losing oil from the rack and it's getting cold here. Like today it's super cold. Like it's minus 20 or minus 15 Celsius. You know what I mean? So we're real, we're real cold and there's only some manufacturers or even some designs that are using split and CO2 because some guys are asking me, is there a split because this is a 16 fan.

I don't get any oil. Like I'm losing oil from the rack and it's getting cold here. Like today it's super cold. Like it's minus 20 or minus 15 Celsius. You know what I mean? So we're real, we're real cold and there's only some manufacturers or even some designs that are using split and CO2 because some guys are asking me, is there a split because this is a 16 fan.

Gas cooler and there is no split. There's no gas bypass on this system and They're running the flashing. I think he told me it's burning it goes down to six 610 or 620 PSI. That's really low. I'm like, what are you running your flash tank at? Or indirect 550. So we're looking at, you know, 40, 40 bar or no. So it's 42 bar, your gas cooler. And then all of a sudden you're running at 38 bar flashing. You got no. Well,

Cause otherwise it's going to be like, I'm standing in the cold. And that does happen. Yeah. And it's, you've got to, some systems cope better with. That lower head pressure. But generally speaking, you need, you've got to keep it above what you expect the flash tank to be at by some degree to make sure it keeps moving.

Cause otherwise it's going to be like, I'm standing in the cold. And that does happen. Yeah. And it's, you've got to, some systems cope better with. That lower head pressure. But generally speaking, you need, you've got to keep it above what you expect the flash tank to be at by some degree to make sure it keeps moving. Well, I'll Trevor: give you an example, Kevin, what would you set your lowest minimum gas cooler pressure at? Like to make, make sure your

mind, I generally don't like to go much lower than about 50 bar. So whatever it probably is, I don't know what that works out to in PSI off the top of my head, but I don't know.

What you say, if you go lower than that, what happens is that it doesn't want to leave, you know, but you can go too high. And what happens if you go too high is that the, the gas cooler side of the controller. is like, well, I need to keep the gas cooler pressure up. So just shut the high pressure valve and you'll end up backing up a ton, especially if you've got a massive gas cooler, backing up a ton of CO2 into the gas cooler.

What you say, if you go lower than that, what happens is that it doesn't want to leave, you know, but you can go too high. And what happens if you go too high is that the, the gas cooler side of the controller. is like, well, I need to keep the gas cooler pressure up. So just shut the high pressure valve and you'll end up backing up a ton, especially if you've got a massive gas cooler, backing up a ton of CO2 into the gas cooler.

And then all of a sudden you have no space whatsoever left. It panics because the head pressure has gone through the roof. Yep, it'll dump a ton into the receiver, which then gets dumped into the suction line and you get a massive suction pressure spike and you know, your rack will be doing nothing for five minutes, it'll be madness for three minutes.

So then you'll go through this cycle all the time. So don't, don't go crazy, crazy high with it. And don't go crazy, crazy low with it. RDM do give you the option on this, but obviously the, the other, the other point about keeping the high pressure valve shut to keep the gas cooler pressure up is you start losing pressure in the receiver because it needs to be fed all the time.

Right? So, RDM and some of the other manufacturers give you the option to override what you've told the gas cooler to do if the receiver pressure's getting too low, which is a really useful thing to do because it lets you keep. Let's say you're doing heat recovery. You want a high head pressure set point, especially in the winter when you actually want the heat, but you also need the receiver to keep working.

Right? So, RDM and some of the other manufacturers give you the option to override what you've told the gas cooler to do if the receiver pressure's getting too low, which is a really useful thing to do because it lets you keep. Let's say you're doing heat recovery. You want a high head pressure set point, especially in the winter when you actually want the heat, but you also need the receiver to keep working.

So you can tell it. Yeah. Okay. I want 70 bar or 80 bar, but if you, as long as you tell your receiver settings, what to do. You know, in the event of a low pressure, it'll keep dumping a bit of gas in to feed it. Right, so,

What's that answer that, that, the minimum gas, it depends. Like, follow up with the manufacturer, because they're designing. Design in the system. And is it split design, is it not? Is it 700 PSI? 'cause your yours, a 50 bar is 7 33 PSI. And then you said 40, which is around 5 85 Yeah, PSI. But you wanna follow the manufacturer, but there may be fine tuning for you if you drop that too low. We need pressure differential. And this is the same with the E EVs. Yeah, go ahead.

So that liquid pressure will be a lot lower. Yeah, it might be, you know, 30 bar, 450 PSI, whatever it'll, it'll be down at the empty suction condition, which does mean you can run the gas cooler lower because you'll always still have the push out of it, but it's a different type of system. So as you say, one size doesn't fit all LT only's do give you a bit more operating range like that. If they float that pressure and sorry, I appreciate we've already run over time.

And I wouldn't make it faster unless it was causing an issue. The temperature drifting up a little bit. It's not a major issue. We worth saying to the, because we've got obviously American and European audience in the U S and Canada and what have you, I think you use a lot more setups with EPRs on the stubs and you try and keep the liquid valve open all the time and regulate the suction pressure.

And I wouldn't make it faster unless it was causing an issue. The temperature drifting up a little bit. It's not a major issue. We worth saying to the, because we've got obviously American and European audience in the U S and Canada and what have you, I think you use a lot more setups with EPRs on the stubs and you try and keep the liquid valve open all the time and regulate the suction pressure.

It's certainly in the UK. And I think in Europe that set up hardly ever exists in retail. And we just cycle the temperature based on using the liquid valve. There are no EPRs because most of the systems are installed in ring mains. So it's a, it's a different challenge because, and to be honest, I think we're missing a trick this side of the pond with it, because actually the EPR based system is likely to be inherently a lot more stable if you get it right.

That is for HFC system in CO2 systems, they're only using the, the CDFLs or electronic heat heater on the suction line just for hot gas defrost. So they're not really, yeah, so they're not really that I know of yet. You know, and I've trained a lot of people and I haven't heard them regulating that because you're running it so cold anyway, and then you can push CO2 down in a lower French electronic valves. But with HFC and TX valves, yeah, we see a lot of that here.

Yeah. So yeah, response on response off there, as you touched on, control type EEV is superheat related, so. Evaporator select on this, REM1, means that it's sourcing the evaporator pressure from a remote source, be that the network or from the local hub it's connected to, rather than local transducer. So, as you can see on this, my problem opening and my minimum opening for the EEV are quite low.

They're not zero, but they're quite low, and the superheat problem is two degrees. That's to make sure that the valve does shut down a bit if the superheat gets too low on it. You can, depending on how stable your coil is, tweak those numbers around, you know, if you with a transducer, most of the time you can very easily go to a problem opening of zero.

They're not zero, but they're quite low, and the superheat problem is two degrees. That's to make sure that the valve does shut down a bit if the superheat gets too low on it. You can, depending on how stable your coil is, tweak those numbers around, you know, if you with a transducer, most of the time you can very easily go to a problem opening of zero.

But all these things are telling you there's a problem with the coil and it's just a question of how much. You need to keep that coil running and doing a little bit if there's a minor problem or whether you're just gonna Rack protection is the key here. So I'm going to shut that valve the moment and see if it looks terrible and you you know your systems better than I do as to what's priority in that regard and what your system can cope with Again, start opening there is the other key one As I said you it's very tempting on systems where it controls on probes to rack that number really high And bomb a load of liquid in when you start with.

With the transducer you don't need to. And actually I checked the latest version of RDM's manual and they actually the thing, yeah, the, they things like the soupy problem and that, they're now recommending you set that number to zero. The transducer doesn't need things like start opening and problem opening to keep a flow in the system.

You, start opening gives you the opportunity to get liquid to your probe if you're running on a probe for inlet temperature. Rather than a transducer, you can set that to 10 percent with a transducer because it will see the true superheat from the get go because it's using the transducer. If you've got an inlet probe as your only source of your evaporating temperature, especially if it's a long way away from the inlet, you need that number to be a little bit higher to get some liquid to it.

You, start opening gives you the opportunity to get liquid to your probe if you're running on a probe for inlet temperature. Rather than a transducer, you can set that to 10 percent with a transducer because it will see the true superheat from the get go because it's using the transducer. If you've got an inlet probe as your only source of your evaporating temperature, especially if it's a long way away from the inlet, you need that number to be a little bit higher to get some liquid to it.

So just wanted to give an example of. What you can get if you get your system running quite nicely and so this is this is actually a factory system With a spiral freezing plant and and the load stable while this product going in that plant The load is pretty stable. So that gives you the opportunity to Get the system running pretty smoothly and not much we can do about the discharge pressure That's related to ambient at the end of the day, which is your blue line there you can see the times when they've had gaps in their production and from the dips in the pressure, that's when they took load off the system.

So just wanted to give an example of. What you can get if you get your system running quite nicely and so this is this is actually a factory system With a spiral freezing plant and and the load stable while this product going in that plant The load is pretty stable. So that gives you the opportunity to Get the system running pretty smoothly and not much we can do about the discharge pressure That's related to ambient at the end of the day, which is your blue line there you can see the times when they've had gaps in their production and from the dips in the pressure, that's when they took load off the system.

But as you can see the, the low, so SO1 generally on RDM is your medium temperature, SO2 is generally your low temperature. So you can see your two suction lines, pretty stable and your receiver slash flash tank pressure, pretty stable. The system runs with a decent amount of load on it all the time because it's production. So

it's beautiful. Like it's running nice and straight, but like you said, it's. It's when the system starts to change its load, they load up, they leave a door open, a fan goes out, whatever. And that's when the dynamics happen. And to get it like this, though, it doesn't happen. You don't just start up a system. This is another thing with case controllers. You don't just put it in and all of a sudden it's going to work. No, no.

And if you stop feeding, or you stop the belt on the spiral, the load will drop through the floor immediately. So, the system demands that you have quite a fast response time, but it's not subject to a lot of tiny fluctuations. The load is stable. If you've got 50 you know, shop floor cases on it, you can't run the system with a fast reaction time because it will overreact.

To every little change in it, you've got to, you've got to let things move around a little bit and let the system stabilize. Visualize that

And like you talked about ice earlier, you've got to try to visualize what's actually happened in those parameters that you set up and just don't change too many too quickly.

So. Yeah, that's, that it, once you know the load type and you know, I just wanted to give the example, sorry, on the next one, Trevor, yeah, the, the parameters we use to get that. So, won't touch on all of them, but pressure target is determined by what conditions you want in the chamber. So in this it's 29 bar because that gives a good, a good temperature in that part of the spiral.

The, the low temperature side is actually 19 bar on this. It's not super, super low. Yeah, that works for this setup. So my target above and target below that is only half a bar either sides. And my response time, you can go up to 60 on the response time for your compressors is 25. So that's reasonably quick, but not crazy, crazy quick.

The, the low temperature side is actually 19 bar on this. It's not super, super low. Yeah, that works for this setup. So my target above and target below that is only half a bar either sides. And my response time, you can go up to 60 on the response time for your compressors is 25. So that's reasonably quick, but not crazy, crazy quick. And so. We've got yeah, just on the second tab, we've got inbound control on. So inbound control on RDM means that when you're within that half a bar above and half a bar below, but not exactly on your set point, it will move the inverter or the variable capacity compressor, whatever you've got to try and achieve it.

But until you drop out of the plus 0. 5 or minus 0. 5, it won't bring another compressor on. So you can. Depending on your system, you know, you can run a wider band where you only let the inverter move, or you can run a narrower band where you only let the inverter move. It just depends how stable you want your system.

We've also got Always Run Last Switched On, which is another really useful feature. Same as Pump Down on Danfoss. So if you get to the last compressor and your suction pressure is below target, it won't switch it off until it hits the low limit. And that, because, especially on CO2, the enemy really is the plant stopping.

When you don't want it to, because once you stop flow, you can't sense what's going on in the gas cooler anymore. You can't, you can't sort of maintain the conditions that you need to get the system running smoothly. You want to keep that running as much as you can. Obviously you do need to stop it eventually when the compressors get out of their envelope.

When you don't want it to, because once you stop flow, you can't sense what's going on in the gas cooler anymore. You can't, you can't sort of maintain the conditions that you need to get the system running smoothly. You want to keep that running as much as you can. Obviously you do need to stop it eventually when the compressors get out of their envelope.

But it pays to give it the maximum opportunity. So we run always run last quite frequently that when it hits the pressure called LP shutdown, we'll stop the compressor anyway. But as you can see, LP shutdown is a ways lower than the target. Soon as it sees some load again, it will start regulating back in the normal way. But. It will just sit there with the VSD at minimum until it hits always running last.

So let's get this big, big rack, all this load. And like I was at, I was at one yesterday where one compressor turns on, it's running for a couple of minutes and then it shut. The whole thing is sadly just over capacity. And they're like, even like, we got to put another drive on, on this one. You know what I mean?

So let's get this big, big rack, all this load. And like I was at, I was at one yesterday where one compressor turns on, it's running for a couple of minutes and then it shut. The whole thing is sadly just over capacity. And they're like, even like, we got to put another drive on, on this one. You know what I mean?

Or change the setting because it's just, and now it's so cold out that gas cooler coils frozen solid, you know what I mean? That pipe is so cold. Like it's hard to move refrigerant when you have. Outdoor, you're like minus 10 minus 20

If you've got a dual temperature pack, do a temperature rack you've got to run the medium temp compressors to keep the low temp compressors running. And if you've got virtually no medium temp duty, but you need to run the LTs, but there are, it's just a little bit of duty. Your MT compressors can be a lot bigger and you can easily get out of the window where they're still running and you need to give them the maximum opportunity to stay running because the moment they stop, the LT discharge pressure, especially if you haven't got much MT load, is going to go way up and then you're going to get unstable.

So, a lot of settings on an RDM controller you can adjust. As you can see, there's, there's like a probably scary number of settings to look at. But as I say, read the manual, the manual for every parameter that's on there, the manual tells you what to do with them. The things I just wanted to point out with it for this gas response on the first column is how fast the gas cooler valve works.

So, a lot of settings on an RDM controller you can adjust. As you can see, there's, there's like a probably scary number of settings to look at. But as I say, read the manual, the manual for every parameter that's on there, the manual tells you what to do with them. The things I just wanted to point out with it for this gas response on the first column is how fast the gas cooler valve works.

I've got that set halfway up the scale, same with the fans. In the middle column, same with the receiver and the last column. And it, it just means that it can react reasonably quickly, but it's not panicking about things. If this was a, if this was a supermarket system with lots of showcases, I'd probably actually set those a little bit lower.

Just so it, when a small change wouldn't affect it. The thing, as I was saying, with this particular plant is I know there will be no small changes. It will be a big change or no change. So, I want it quick because it'll need to be. The setting I just wanted to point out with boosting the receiver pressure.

Last column there, receiver interlock. So receiver interlock watches the minimum pressure for the receiver. And the maximum pressure for the receiver and it will, it will allow the H, the high pressure valve to either shut the receiver gets too high or open if the receiver pressure gets too low. And that's really useful because low, low conditions, easy for the receiver pressure to get too low if you haven't got a gas bypass.

Last column there, receiver interlock. So receiver interlock watches the minimum pressure for the receiver. And the maximum pressure for the receiver and it will, it will allow the H, the high pressure valve to either shut the receiver gets too high or open if the receiver pressure gets too low. And that's really useful because low, low conditions, easy for the receiver pressure to get too low if you haven't got a gas bypass.

You have large ones, or you can have small, but you got to go back and watch the other video that me and Kevin did go check the one out Corel and Dan Foss because he showed all the parameters that he uses, but that's his starting point. And what we want is to not have valves fighting each other. Compressors fighting valves. I see this constantly out there. And this is just gives you a lot more headaches. You're getting more calls for the, for re Well, fine tuning really. It is

Compressors fighting valves. I see this constantly out there. And this is just gives you a lot more headaches. You're getting more calls for the, for re Well, fine tuning really. It is

For one of our sort of partner contractors who, who's got some CO2 racks and because they couldn't get the temperature where they wanted it, the original installer, they've set everything to go too fast. And most of the time what happens if you go too fast is it gets unstable. People I think have a little bit of panic with CO2 because the pressure can rise quite quickly because the numbers are all big.

in terms of pressure that it's going to blow if you don't deal with it immediately. And it's not, you, you've got the opportunity to let things develop. It doesn't, it's not going to be the super stable for temperature, but you can let the suction pressure come up one or two bar. If that's better for the rack control under, you know, in some setups, you, you've got to find what works for your system.

You know, if it's a, if it's a huge cold store evaporator, a short period. To let the rack stabilize on its own without banging compressors in or out is better than having it trying to panic and fight the coolers on the other end of it. Like I say, if it's a supermarket where loads are changing in little chunks.

You know, if it's a, if it's a huge cold store evaporator, a short period. To let the rack stabilize on its own without banging compressors in or out is better than having it trying to panic and fight the coolers on the other end of it. Like I say, if it's a supermarket where loads are changing in little chunks.

Then yeah, you might, you might need it to be a bit more stable on the suction pressure, but you need to, you need to understand your setup and then understand what is driving instability in it. And there's, like I say, the there's a lot of different ways you can control that, but be sure what's causing it before you start fiddling with the ball, as you said earlier.

You got people dropping stuff into drains. But what we want to do is that you don't want to be changing parameters. If you don't know if the coils are clean. You know, if all the fans aren't working, if the airflow is good, like you can't be changing these parameters that we're talking about without doing all the basics first.

You got people dropping stuff into drains. But what we want to do is that you don't want to be changing parameters. If you don't know if the coils are clean. You know, if all the fans aren't working, if the airflow is good, like you can't be changing these parameters that we're talking about without doing all the basics first.

And I see that time and time again, where the pressure transfers, like I said earlier, is reading off because the range is not right. So now you're trying to adjust other things. You're just a rack or just this, where you got to start with the basics. And from there, from the basics, you go into, okay, what is my parameters supposed to be?

If I change this, what should happen? And this doesn't happen overnight. Like this learning, this stuff is RDM. You may have never worked on it. So, and you get your first system with RDM, you got to take the time to read the manuals, watch this video again. You know what I mean? Go through it to get an understanding.

That's it. And, and before you call, before you call any manufacturer, have your questions that you're going to ask and what you expect them to kind of come back with. Because a lot of people don't, they call up and they don't have the questions ready. And cause the first thing is, did you check the transducer?

Is it reading right? The temperature? Did you verify all the components are accurate, but prepare yourself before you make these phone calls. Yeah. When you do that, then you can ask better questions and better follow up questions. Oh, a hundred percent. We've thanks Chris. Yeah, the it's true. We've touched on it in our talks before, haven't we Trevor?

There's nothing worse when you're somebody who. It takes a lot of questions about what's wrong with it. So how something works, then the first thing you say is, okay, well, suction pressure, or what have you set this for? And the person goes, I'll just go and get my gauges. You know, if you're like, no, no, no.

If you've got to, if you've got a phone, you've got to have some information to start with because you're giving me nothing here. You've got it. And I mean, The beauty of, say, things like RDM technical support, if you've got that system online or you've got a computer, a laptop with you, they can connect to your system and they can have a look.

They'll, they'll do a a remote session with you and they can connect to that system and have a look directly at what you're seeing. So do use those opportunities. One of the beauties of having everything IP with, with RDM is that it's very easy to connect it via a laptop or via their, a modem via their front end and that gives them access to what you're seeing and they can help you.

They'll, they'll do a a remote session with you and they can connect to that system and have a look directly at what you're seeing. So do use those opportunities. One of the beauties of having everything IP with, with RDM is that it's very easy to connect it via a laptop or via their, a modem via their front end and that gives them access to what you're seeing and they can help you.

And it's like anything, think about the first time you ever set up a TX valve. It's no different than setting up your first control. You just got to understand it and spend the time. Kevin, man, this, this is amazing. I learned a ton. And once again, those of you listening on the podcast, go to the YouTube video, watch it, check out some of the slides and invest in yourself.

Get out and check that other one that me and Kevin, YouTube video, me and Kevin did on the podcast and, and really learn that stuff. And if you like it, share it, like it, comment on it, because this is how, once again, more people learn about this. Kevin, any final thoughts on troubleshooting RDM controllers?

Get out and check that other one that me and Kevin, YouTube video, me and Kevin did on the podcast and, and really learn that stuff. And if you like it, share it, like it, comment on it, because this is how, once again, more people learn about this. Kevin, any final thoughts on troubleshooting RDM controllers?

Yeah. That is those graphs and the basic information that gives you is your key to understanding it and work back from that. You know, do, and as you said, do one thing at a time. Don't do 10 things at a time.

What, what's it doing? Watch it because you, if you change five, you don't know what fixed it or what made it worse. Got a question here. When we were talking about iced up coils earlier. We're wondering why ice up coils will cause compressor oil issues or compressor starvation. Do you want to just follow up?

Problem when liquid gets back to the rack is it dilutes the oil. And it makes the oil much easier to be carried away through the system. So the oil gets picked up out of the compressor and if you're lucky, it stays in the oil separator if it's warm enough, if the oil separator has gone cold because you're carrying liquid into it, you'll probably find it's going to carry on through and you'll end up with oil out in the system.

It's, it, once it's out in the system, it's difficult to get it back. On some systems, especially because it lags, it sticks in places it doesn't want to be so liquid coming back and with CO2, if the added bit of that is if you're overdriving out of the receiver for some reason, because you haven't got the high side set up right, the, that gas coming off the top of the flash tank is saturated.

It's, it, once it's out in the system, it's difficult to get it back. On some systems, especially because it lags, it sticks in places it doesn't want to be so liquid coming back and with CO2, if the added bit of that is if you're overdriving out of the receiver for some reason, because you haven't got the high side set up right, the, that gas coming off the top of the flash tank is saturated.

It's got liquid and vapor in it. And that on CO2 is probably a bigger issue with wiping out the oil than evaporators. So if you're, if you're thinking you'd lose an oil all the time and you're thinking the cases are all fine, I've checked the solid spirits, they're great. You'll probably, you stand next to the rat.

You hear the receiver valve howling. That's your problem that will lift the oil really quickly. So anything, anything that brings liquid back dilutes the oil and will remove the oil from the sump of the compressor. Oh,

Super pumped up. Thank you, Kevin, so much for doing it. You're welcome. Thanks everybody. And we'll see you all at the next CO2 experts. Super pumped up. Thank you, Kevin, so much for doing it. You're welcome. Thanks everybody. And we'll see you all at the next CO2 experts. Super pumped up. Thank you, Kevin, so much for doing it. You're welcome. Thanks everybody. And we'll see you all at the next CO2 experts.