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In this PCP episode, I cover a brewery plagued with evap freeze-up issues. When service techs are running around with their hair on fire trying to process as many calls as possible each day, we don’t take the time, unfortunately, to take a closer look at root causes to repeat or intermittent process chiller shutdowns that inevitably leads to unhappy customers.
To check out the diagnostic steps I took to figure out the root cause of this customer’s evap freeze-ups and improve your process chiller skills, use the link below to check out this episode making your way towards technical excellence.
Links referenced in this episode:
1. Like to prior Process Chiller Pro episode covering how to perform a chiller system pump runout test. Click this link to jump to this episode page: https://bit.ly/30JEvwT
2. Link to recent conversation I had with Gary McCreadie host of the HVAC Knowitall Podcast. Click this link to jump to the episode: https://bit.ly/2ZvIi05
Important note: The topic I will cover in this episode of the Process Chiller Pro podcast falls under the “Technical excellence” or foundational component of my skilled trade’s success pyramid.
If you want to get more information on my skilled trades career success pyramid, pop into the Process Chiller Academy site, resource page, link below.
TO ACCESS THE PCA RESOURCE PAGE AND GET MORE INFORMATION ON THE SKILLED TRADES CAREER SUCCESS PYRAMID
Martin King 0:08
Hey guys, Martin King here your process chiller pro in this episode of the podcast I’m going to be covering process chiller evaporator ice ups. I want to send a quick shout-out to Gary McCready with HVAC, no at all. I was on his podcast a week or two ago. And he brought up some interesting things about glycol. And we talked about a lot of different things, you should check out that podcast, it was very interesting. And I got to say that Gary is extraordinarily inspirational for me, because He’s truly a curious technician. And he has gone to the limit of sharing his knowledge with the market. So Gary, it was awesome. And I hope you and your audience, if you check this out that get a lot of benefit from what I’m talking about today. We’re going to take a look at a medium-size brewery. And the backstory on this particular situation is they have a chiller that was in for a couple of years, and it was getting chronic ice ups on the evaporator. Now the customer really didn’t know that what was going on. All they know is that chiller was going offline. And as you may know, in a brewery application, if which is considered mission-critical, by the way, if that chiller goes offline, their production is dramatically impacted. If not, they’re stopped in some cases. So this is a real problem. Now, we had had other technicians go out to this site in the past and they’ve checked it out. And you know, they determined that yes, there was a restriction in the evaporator that caused a problem with icing up. And the the bad thing about icing up on an evaporator in a process. Chiller is it’s very insidious, it happens. And then by the time the technician gets back out there that ice is gone, right. So the refrigeration system is shut off usually on low pressure, low flow, something like that. And the started up and everything’s hunky dory only to have another intermittent problem a couple of weeks a couple days later. So it was real, real issue. And I want to point out, there’s some similarities in the evaporators, meaning that between a process chiller and air conditioning, they work the same way pretty much you have a metering device that’s pumping refrigerant in there, you have the boil off effect, the only real difference is the medium, right. So in a process chiller, you have water or water glycol mix on an air conditioner, you have just air right. The main difference though, is that in an air side application, you do have freeze ups that happens all the time, right. The thing about that is is that that ice has a place to go. So the ice is going to build up on the outside of the tubing outside of the piping. So you’ll see the ice on the coil and but it has room to grow. So it’s most cases there’s a few exceptions, you’re not breaking stuff. The thing is on an on a process chiller is the opposite the the ice is building up inside an enclosed space. So if you don’t address that, let’s say you don’t have a hot gas bypass or the low pressure switch low pressure trip is not set correctly, that ice will continue to grow and grow and eventually it could rupture your evaporator and when that happens, you have no separation between your process fluid and the refrigeration system, which essentially means all that glycol and water is coming on into your refrigeration system. And in a lot of cases, it’s catastrophic enough that that entire chiller needs to be replaced. You can get away with it by cleaning it up. But by the time you look at the labor rates nowadays, a ruptured evaporator is a major deal and it could be a real problem. So we’re going to delve in this episode in the steps that you need to take when you know you’re having intermittent shutdowns usually low pressure, low flow and you’re starting to see signs that it may be an ice up problem inside the evaporator. Now in this case with this brewery, what I did was I got a history I’d been out there before, but I got a history from the office to find out well,
you know, what was the history on this thing? How often is it failing? What are some of the technicians notes? So when I was on the way out to the call, I had a briefing by the dispatcher to find out what the heck, you know what the history is on it and immediately I thought all right, we need to look at this as possibly a an ice problem. And the first thing I did when I got on site, I had to have a conversation with the customer because I already knew it was gonna take a while to figure it out. And they did I was blessed to get the authorization to To proceed because they knew this problem had to be fixed, they just could not continue to deal with the symptoms of the problem and all the downtime that goes along with it. So when I got there, I said my prayers and now I’m going to take you through the process on how you diagnose a evaporator ICEP issue. Before I begin, I want to make sure you’re aware that I produce this content in both video as well as audio only formats. So what I’m going to do as I proceed through this episode, I’m gonna do my very best to try to explain what I’m putting up on the screen. If you can, if you want to check the video version out, and you happen to be listening to this podcast while you’re driving around. Make sure you bookmark it or and you come back to this landing page that you’re probably on right now. And you can check out the video portion to really drill down on what I’m covering in this particular episode. Also, this content is actually for experienced technicians. If you are a beginner, and you’re checking this out, or maybe you’re an end user learning about what I’m talking about here, if you get yourself into a situation where you’re not comfortable or you don’t feel safe doing some of the things that I’m talking about, make sure you stop and you get help with what you’re working on. From somebody who understands more about it, I do not want you to get hurt out there. So without further ado, let’s get started on this episode covering the issue of freezing up evaporators.
Well, the first thing that I want to do here is do a quick review of both sides of a process duty chiller, we’re going to look at first at the refrigeration. Just do a quick review of how the refrigeration system operates in a process chiller. As I said before, you’re going to notice it’s very similar to a basic refrigeration system you’d see in air conditioning, that type of thing. And then we’re going to flip over, we’re gonna look at the fluid side of a process chiller just to get reconfigured, get our mind around exactly what’s going on here, which will help it make a lot more sense when it comes to doing the diagnostic steps that I’m going to go over. And again, I’m going to do my very best to verbalize what you’re looking at here. But like I said, bookmark this landing page and come back and look at this in video format to get all of the value out of it I’m trying to express here. So first of all, let me get my glasses on here because I can’t see without him these days. On the screen here you’ll see the refrigeration system for this particular chiller that we’re working on at this medium sized brewery. So I always start my review. Looking at the compressor off the left side of the compressor here you’re gonna see our discharge line which will be high pressure gas, and that high pressure gas feeds into our air cooled in this case, condenser that refrigerants can come off as a high pressure liquid. Then you have your normal characters here you have your filter dryer, your moisture indicating site class solenoid valve, which is something that’s pretty common on a process chiller that prevents migration of refrigerant in the off cycle and we have our expansion valve which this is a thermal expansion valve T XV comes out of the TX v. So we’ve had a we’ve created a pressure drop right that liquid refrigerant at a lower pressure now it’s going to make its way up to this braised plate refrigerant to fluid heat exchanger, you’ll have four pipes, so we’re going to get into the different types of heat exchangers here in a minute, but we got four pipes on the CD exchanger. So you have your refrigerant going in as a low pressure liquid, it’s boiling off boiling, boiling, and is exchanging heat with our fluid. So second law of thermodynamics, the suction of that gas is colder than the fluid so your means your temperature is colder, so it’s going to transfer heat energy from the fluid to the refrigerant system. So very similar to an air sight it comes through here we come down our suction line now we’re dealing with a low pressure gas into an accumulator. an accumulator is very common on a process great chiller, through the accumulator back to the compressor. Now a couple of side notes here, this particular refrigeration system is equipped with hot gas bypass so you have a tea that is diverting hot gas off of your compressor to a hot gas bypass solenoid and then you have a hot gas bypass valve or regulator. And we’re going to cover that in another episode. So there’s a I’m going to be doing an episode of the process chiller pro podcast that covers how to properly calibrate these in a refrigeration system. That is the basics of what we’re looking at here. I’m going to flip over now to looking at the flute inside one of the thing too, before I flip this over to the next drawing here, on the right hand side of this heat exchanger is going to be your fluid side flow. So you have refrigerant going in on the left bottom, that’s going up to the top left, this is a co current flow. So that means that the fluid is coming in the top on the right side and coming out the bottom on the right side. So the refrigerant in the water or glycol mix is going in opposite directions. And you do that because of your surface area, right, you want to create more of an exposure to the refrigerant as you can. So that’s why we have Coker. So what we’re going to do when I flip over to this next drawing here, we’re going to see this completely on the on the water side. This is the water side of the system. And I’m going to cover this real quickly here in the middle of this drawing is going to be a tank. Now on this particular brewery, this is an open tank, it’s showing kind of as a closed tank, but this particular brewery had an open tank, so this would have a spin top off of it, you could reach your hand down there and actually touch the glycol this was an open tank. And that is a little hint as to what we’re going to find later on.
We call that foreshadowing This is a typical plumbing configuration is that it has two loops or dual loop are also referred to as a research loop. And I’ll explain that now you have a chiller research pump that’s drawing off of this tank. And it’s going to be drawing to the inlet of your research pump. And it’s coming out of the research pump going out to your evaporator, which we just looked at, and it’s coming back from the evaporator into the open tank. That is the research. And the benefit of that is the refrigeration system in the chiller doesn’t really care what’s going on and on out the process. The refrigeration system is simply trying to maintain that tank temperature at whatever temperature is designed to maintain that right. So that’s what that’s all about. So then we also have a second pump, which is a system pump. And that draws off the same open tank discharges, it’s out output, you’re going out to the process. So in this case, this medium sized brewery will have jacketed tanks, heat exchangers, all kinds of stuff. Basically, it’s the process so he energy is picked up from whatever the customer’s cooling, and it comes back to the tank so that that’s why this is a dual loop refrigeration or process chiller application. The nice thing about this type of an application is that the fluid is constantly mixing in this tank because these two pumps and this particular configuration is nice because if the customer has a large chunk of heat energy come in from the process, it’s going to load into this tank. And the volume in this tank kind of acts like a thermal capacitor, the if you have a big chunk of heat come in that hot fluid is going to be mixing with the cold already in that tank, the refrigeration systems gonna kick on to deal with it. So in these types of systems, assuming it’s sized correctly, you’re gonna see very little degradation on the to process temperature, because you have all that mixing going on. This is an ideal type of a setup a research loop for this type of an application. So that is a quick review of how these, the refrigeration setup and the fluid side setup are on this little brewery chiller. The next thing we’re going to look into is the three most common types of heat exchangers or evaporators that you’re going to see on a process chiller. So what we’re showing here on the screen is a brazed plate heat exchanger. Most of the process duty chillers, below about 50 tons will have these not you know there’s always exceptions to every rule, brace plates are reliable. They are generally less expensive than the other types. Well then then shell and tube which would be its alternative, typically they’re very compact, so they they don’t take up a lot of room. The downsides to the brace plate concept is they’re very difficult to clean. You cannot take them apart. Typically, you can buy bolt together brace plates, they’re not real common in smaller tonnage, process chillers. But the only way to actually get these things clean if you get them plugged up. And we’re going to talk about that a little while as far as maintenance recommendations. These things, the only thing you can do is really back flush them and it’s about a 5050 if you back flush these to get the fluid cleaned or the debris out of these things. What we’re looking at here is just a stack of plates. This particular one is stainless steel on the left hand side. So you have four ports. You get two on the top, two on the bottom on the left hand side, you have The refrigerant going in at the bottom left tube. And it’s going in, it’s boiling off, boiling off boiling off and it’s actually coming out the upper left as your low pressure gas. So that is when that’s that, that’s your saturated suction. So it’s absorbed energy from your fluid. And on the upper right in upper left, you
have the upper right meaning the fluid going in your glycol mix is going in, it’s rejecting its heat, and it’s coming out on the bottom right, so upper right going in, bottom right going out, that’s supposedly going to be coming out a little bit colder than it went in. So that is how the brace plate operates. The next type of evaporator which is usually going to be for larger tonnage process chillers is what we call a shell and tube. Same kind of concept. You have four pipes, you’ve got two refrigerant, you’ve got to fluid and it’s pretty simple how it works, you have the refrigerant usually flowing through the tubes on the inside of the tubes, and then you have your fluid flowing across the outside. However, I have seen it the other way around. It just depends on how it’s designed. So the benefit of this particular type of a heat exchanger is that it is typically it’s cleanable you can pop the in bells off of these. Now this particular drawing that I’m showing on the screen, sorry about the guy’s audio only. But this particular drawing does not show these bolts, but typically there’s bolts holding the ends of these things on and you can pop those ends off and rot out the tubes, which is helpful, you know, it’s it’s common to have these in larger tonnage units. These these are typically more expensive than brace plate, which we looked at last they take up a lot more room. So if you’ve got a very small cabinet chiller, you need a small footprint, typically not going to see a shell and tube on those applications. The third one we’re going to look at here, this is what we call an immersion heat exchanger or evaporator. Now, these started showing up actually, they’ve always been around, but I’ve seen them, usually when the economy’s not doing so great. Or you have an emerging market or you have some ancillary type applications that require a process chiller dry cleaners come to mind. These people buying these chillers typically don’t have a lot of money. And they’re you know, they’re going to try to find the least expensive that they can. But as you can tell from my tone here, I’m not a big fan of immersion heat exchangers they do have their place. But I don’t think they’re the ideal situation for process chiller. So in this case, what we’ve got is two pipes going in, I’m trying to explain it here for you audio only people. But we got two pipes actually coming out of this the square box basically, down inside the square box, we have coiled up in this case, stainless which is better than just copper, but you’ll have coils that are that are emerged in this square tank basically is what this is. Now this tank vessel could be pressure rated. Typically they’re not, they’re just going to have a tarp on them, I don’t know which this particular one we’re looking at is and you’re just basically going to have a couple of pipes, one pipe from your pump pulling fluid out and one pipe coming in. So that’s how this works. The downside to these is they can be very susceptible to freezing. Because it’s possible if you don’t have enough flow rate going across this thing, you can get stagnation in certain nooks and crannies of this particular heat exchanger and they can be very conducive to freezing up. So I personally do not like this however, I do understand that they have a price point that makes them popular. So this is what we call an immersion style heat exchanger. So what I’ve got back up on the screen here is the same picture I was showing early earlier of a brace plate heat exchanger because this particular brewery had a brace plate heat exchanger. So that’s what I’m using as my example. I’m going to give you before I get into this, I’m going to give you a spoiler alert. This particular problem which I’ll share in detail in a minute that came on this particular site had to do with the fluid side of the system. It did not have to do with the refrigeration system. That’s just something I wanted to share with you guys. That’s the ultimate end we’re going to look at and in about 80% maybe higher than that. If you have a process chiller that’s this freezing up on Yeah, it’s typically not going to be the refrigeration system. So you have to do the fluid side first and make sure that you got everything on the fluid side operating correctly before you even start getting into issues with the refrigeration system and as I proceed on here it’s going to get more evident what I’m talking about that is just the spoiler alert of this episode
This episode is brought to you buy GND chillers if you find yourself in need of a process chiller, check out GND at GE D chillers.com. Or better yet give Andy or Paul a call over there 800-555-0973 Any and Paul are my go to guys over at GND whenever I get approached by resellers and users even though we are looking for a quality chiller to be designed and built for them, so check them out. If you do call them make sure use promo code chiller pro so they know how you find out about them. GND chiller, I love their tagline it goes big enough to produce and small enough to care and that’s definitely the truth out there for sure. So again, called G and D chillers asked for Andy or Paul 800-555-0973 or check them out online at G D chillers.com.
When it comes to looking at the refrigeration system, we’re going to take a look at that in other episodes because the refrigeration system is is a lot of information. We want to keep this episode going as quickly as possible. If you have any questions about the refrigeration system, and typical problems that maybe have to do with icing up because of a refrigeration system. Just send me a message on LinkedIn. Share your experience with me. And we can certainly include that when we get into more detailed episodes on the refrigeration system as it pertains to ice ops and freeze ups. Let’s talk about what actually happens when a freeze up starts in evaporator in most cases, the freeze up begins at the exiting point of the evaporator. And that makes sense, right? Let’s say for example, and again, I’m showing this exploded view of this brace plate evaporator on screen here, you’ll see that the warmer fluid is coming in on the upper right, it’s coming in at whatever temperature it’s coming in at. And as it as it’s proceeding across these plates, it makes its way down because the channeling how it’s all done, it makes its way down to the bottom right where it comes out and exits and goes back. In this case it goes back to our tank. In most cases, it’s going to start freezing up at the what we call the tail end of the evaporator. So I’m going to give you kind of a hypothetical explanation here of how this works. So let’s say this, this customer’s setpoint they need to maintain 40 degrees in their tank, let’s say right at about the the shutdown of the refrigeration system. Let’s just say for example, this fluid is going to be around 40 degrees coming in from the tank. So as it’s winding its way through this evaporator it’s getting colder and colder and colder. And let’s just say for hypothetical that it’s very close to 32, maybe below 32 at the tail end of this evaporator. So if you’re not running any glycol, what’s going to happen is you’re going to start to see water molecules that are going to start to freeze and build up on these these bottom plates. And when that occurs, it creates a chain reaction if you will. Now without getting too far in the weeds, the refrigeration system is going to try and react to thermal expansion valves going to try and react because your superheat is going to begin to change but it usually what’ll end up happening is your suction pressure. As you start building up, ice is going to start to come down. And in most cases, you’re gonna shut down this refrigeration system and lock it out typically on low suction pressure. If not, it’s going to be off shutting down on low flow. And that’s an extraordinarily bad case. Because that usually means that the low pressure suction has not been set correctly, which we’re going to cover when we get into setting the hot gas bypass that whole process in another episode. So that is how the process of an ISEP begins. Before we begin getting into the diagnostic steps, I want to have a discussion real quickly about glycol. There’s a rule of thumb here that will keep you out of trouble in the field. There’s two reasons why you’re going to want to run glycol and process chiller The first one is for your process. Let’s say you have none of your chiller your chillers not exposed your piping or your process. None of its exposed to the outdoor ambient. So all you have to worry about is what’s going on with the process. So in this case, what I recommend is that anytime you have a fluid temperature approach temperature going to your process that’s colder than 44 degrees, I recommend that you invest in glycol. For example, if we have a 40 degree process, in other words, your process requires 40 degree approach, I want to see your confirmed freeze point around 20 degrees. So you want a 20 degree margin. And if you have a question as to why how I come up with that, send me a message and I’d be happy to explain it. Or maybe we do another video diving deeply into that particular subject. So the second reason why you want to run glycol that can be in addition to your process is your ambient temperature. So if any part of your process chiller application connects, or is exposed to ambient, whether it be the piping, I don’t care if it’s insulated or not, whether it be the process itself, or the chiller especially, you need to make sure that you have a confirmed freeze point that is 20 degrees colder than the coldest it’s going to get outdoors. So you may have to go on to the National Weather Service, you may have to do some sleuthing to determine what that number is, if you’re a contractor you probably already know. But let’s say the coldest day that you can anticipate is going to be minus 10 Fahrenheit. That means that you want to make sure that you have a bottom minus 30 or 50%, propylene glycol freeze point. So those are the two instances. And if you use those rules of thumb, you’re going to be in great shape. Alright, now on higher concentrations of glycol, and we can get into this other episodes, let me know if you want to cover this, you may have to also when you order your chiller, you need to make sure that adjustments are made in the number of plates on your evaporator. If you’ve got to go any percentage of glycol percentage that is higher than about 20%. If you go higher than that, most likely you need to have a heat exchanger or an evaporator that’s designed to run those higher concentrations, or your refrigeration system is going to complain usually in the in the area of low suction. That’s just sort of a side note you need to keep in mind. So that is your rule of thumb on glycol. And I hope you make note of that because it’ll save you a lot of heartache. If we’re going to get into now steps that you want to take as you’re looking into this freeze up problem on our little sample brewery here. Alright, so the first thing you want to do is you want to have a little device that is called a optical refractometer. And I put one of these up on the screen, check it out, you can Google it, you can get these in a variety of different venues. I saw them on mcmaster carr, you just need to make sure that it’s designed for heat transfer fluid, not automotive. This particular one I’m showing here, I’m going to try to describe it. It’s just a little eyepiece, and it’s got a a blue lens on it that’s got a little plastic cover. And all you’re going to do is you’re going to take a little sample of the fluid from your process, they usually come with a little squeeze ball, eyedropper gizmo, and you want to lift the plastic cover, you want to flood the glass with your sample, glycol water mix, and you’re going to put the the flapper back down gently over the top of your your glass that you just flooded with your glycol, give it a little bit of a tap and get all the air out of it. And then you simply hold it up to light and you’ll see what it tells you so the only thing you really need to know is what glycol you have in there is it ethylene, which is a petroleum based glycol, or is it propylene, which is usually a food grade product. Most of the breweries out there, in this case, that’s what we’re working on, are going to be using a food grade HVAC grade heat transfer fluid or glycol. For this example, we are dealing with propylene glycol, the sample that they show here, you’ll see there’s a separation, light color to dark in your when you hold your lens, your eyepiece, you face your the sample that you just took towards light. And it’s going to reflect I have no idea how these things really work. It bends the light. It’s magic to me, but you’ll have a clear line that’s going to show up in the reading Oh, in this example, the right hand scale is propylene glycol. So you’re going to have it says here that we have 19% propylene glycol, and our freeze point is at 20 degrees Fahrenheit. So in the example I said in this particular example, you have a 40 degree approach temperature I said 20 degrees is a good confirm freeze points. So this is a 20 degree freeze point. You’re good to go. So that’s a good confirmation. And it lines up with the example pretty darn well. That is a refractometer that’s real briefly How to use it. If you’re doing service on any process chiller that has anything to do with glycol here near or far, you need to make sure you have a refractometer that is in your toolbox because you have to have this to be able to do the job. The next thing you’re going to take a look at is going to be your strainers and filters. I’m going to revisit our plumbing drawing, that’s what I’m putting up here on the screen that shows the fluid side of our inside of the chiller on this particular chiller. And most have these, especially if you have a research system, you’re going to have a strainer, I have a y strainer here that I’m showing and that is upstream of the evaporator. What its job in life is to protect debris from going into your brace plate heat exchanger, any process chiller, any single process chiller, you get away with it a little bit more if you happen to have a shell and tube heat exchanger, but you always should have some type of a filter or strainer on the inlet of your evaporator. If you do not, that’s one of the first things you need to advise your customer on. Especially if you’re dealing with an ISEP problem, that is going to be a important thing to have, it’s a must have in my opinion, the first thing you’re going to do in this case is you’re going to check this particular strainer here and make sure that this thing is clean. And this particular manufacturer provided ball valves, so you have to isolate it from the system or you’re going to get a bath, and you want to pull the cap off of that, that y strainer, get the basket out of there and clean whatever smoking might be hanging around in there. So that’s really important. While you’re at it, what you want to do is go around the entire system, external to the chiller as well. And you want to do the customer huge favor. And check all those strainers and filters as well. This gets missed a lot, you want to make sure that everything is good. As far as straining, you do not want any restrictions to flow across your key components, the next step we’re going to do is going to be a run out test. Now in this case, since this is a tool loop, we I mean, we obviously care about what’s happening on the system pump, because remember, we talked about this earlier, there’s two pumps in this chiller, there’s a research pump is taking fluid out of the tank, through the evaporator back to the tank and there’s a system pump pulling off that same tank, going out to the process coming back to the tank. The one we really care about is the restart pump because it’s doing its thing, it’s it’s pulling off and it’s servicing this evaporator. What you want to do is you want to you’ve already checked your strainer, there’s a video that we put out a while back on process chiller Pro that goes over the details on how to perform a run out test on a pump. And what the runoff test does for you, just to let you know is it tells you if that pump is running within its manufacturer’s specifications, you need to have a gauge mounted on the discharge of the pump, you obviously need to have isolation valves. And you also need to have the pump curve on the pump. And I’ll provide on this on this episode, I’ll provide a link in the show notes on that other episode that covers a run out test for the pump. So you want to make sure that you do that. Okay, so that’s that the last thing on the fluid side is another rule of thumb. So we talked about a rule of thumb a minute ago with glycol, we’re gonna have another rule of thumb that has to do with the evaporator flow rate. Now you can’t they don’t put flow meters on evaporators they just typically don’t do that there are a few exceptions to that. But for the most part, you’re not going to have a rota meter on your evaporator to actually give you a live reading on your flow rate. So that gets back to your run out test in your pump curve. I will probably be putting out another episode that shows you how to determine what your flow rate is to your evaporator using the pump curve. However, I’ve got other stuff to produce on so you can figure out what your flow rate is using your pressure gauges and your pump curve. So if you want me to express lane that content let me know and I’ll put put out another video on it. The rule of thumb I want you to burn into your brain cells is going to be your design flow rate across your evaporator. Now when the evaporator was selected for this particular chiller, it was selected with a certain GPM a rule of thumb that served me very well is most designers when I designed I always designed for two and a half gallons per minute per ton of cooling. I round that up to three. So if you have a five ton chiller, 60,000 VTH then you’re going to have a design evaporator. flow rate of around 15 gallons a minute. So if you use that as your target, in most cases, you’re gonna be pretty darn close, it’s going to be pretty close to the way it was designed, it’s always better, it’s okay to have more flow rate than not enough. If you go below that flow rate, you’re going to have suction, you’re gonna have refrigeration complaints, use three GPM per ton or more, and you’ll be good to go on that front. So that wraps up if you’ve done all these things, you’ve dealt with your glycol, you’ve looked at your flow rate, you’ve made sure that your freeze point is correct. And you’ve done your run out tests, you verify that your pumps running, okay, you’ve done all those things on the fluid side, then, and only then do you go over to the refrigeration side. Now in a few minutes here, I’m going to I’m just going to jump on the refrigeration side real quick. And then I’m going to actually tell you what I found. And hopefully with all I’ve showed you, it’s going to make a little bit of sense to you. But Jumping over to the refrigeration side. Now, before you get even touch this refrigeration system, I want to give you a couple qualifications. So let’s get real as far as this brewery we’re talking about, if you’re doing a service call, you’re getting a call in that the chillers not running most likely, unless you just happen to be right next door getting a cup of coffee, most likely, it’s going to be a while before you get over there. And you never know what condition that chiller is going to be in. When you show up. I’ve seen situations where the refrigeration system shut down, the customer just left it running, which means the pump, the pumps or pumps, kept running pumps generate friction, so pumps will continue to heat that fluid up. With your refrigeration system locked out, it could be for several hours before you get there, you could find that fluid quite hot, I’ve seen it over 200 degrees, especially if they let it go for quite a while. So that’s one extreme. The other extreme is that you do have glycol in it, and the chiller is exposed to ambient, you’re in a cold climate. So that fluid temperature could be sub zero, you could have fluid that’s totally smashed up, can’t run it. So there’ll be extremes that you need to address. And to do an effective diagnostics. On the fluid side, the refrigeration side especially, you need to have your fluid temperature somewhere within a reasonable range, a reasonable range is going to be usually above freezing. And you want to have it cooler than about 70 degrees or so. Because it’ll just make your troubleshooting diagnostic less difficult what you do when you get the customer on the phone or have dispatch tell them get the story on what’s happening. And the best thing to do would be to shut that chiller down and let it sit. And many times you might have to wait a day or so to get out there to look at it. Now if it’s super cold outside, it’s another level of challenge to deal with, you may in that case want to leave the pump running however, you don’t want to leave the pump running too long to where it overheats your fluid. So each situation is going to be a little bit different our troubleshooting situation here, we’re going to try and get the chiller running again. So one of the most important tests that you can do on any refrigeration system, it doesn’t matter if it’s a chiller, or if it’s an air conditioner, you want to be able to know how to perform a test to give you superheat which gives you the performance of your evaporator and sub cooling, which gives you the performance of your condenser. So those two tests. Now if you don’t know how to do superheat and sub cooling, I do have a basic refrigeration troubleshooting course that’s available for purchase. It’s a paid course. However, I think it’s well worth the investment. You can learn how to how to do these tests, you’ll also learn a lot more stuff like thermodynamics, the second law primarily and it’s it’s a great place to start if you don’t understand what that is. So I’m going to assume for right now you do know how to do superheat and sub cooling readings. What you’re going to do is get the system running you want to get it running stable before you take superheat readings you need to make sure if your chiller is equipped with a hot gas bypass it needs to be bypassed. In other words, disconnected off getting superheat readings with a deployed hot gas bypass is a waste of time so you want to make sure that you have that disconnected before you actually start your readings. Rule of thumb we covered a few of those in this in this episode. You want to make sure that your superheat and sub cooling on a process duty chiller is going to be anywhere between eight and 12 degrees Fahrenheit they’ll be pretty balanced on either side. So if you I’ve run your chiller for maybe three, four minutes, you’ve taken your readings hot gas bypass disconnected, and you’re getting balance with your superheat and sub cooling. It’s running between eight and 12 degrees,
you’re good to go, you’re, you’re most likely you have no issues on the refrigeration side. Get to the grand finale, what exactly did I find on this particular system? As I touched on earlier, I did not take a dive like I did on the fluid side into the refrigeration side. If you guys want to do that, definitely let me know I will probably be getting to that sooner or later in other episodes of the process, chiller pro podcast but I’m going to focus on the cause of the problem. And the cause of the problem as I mentioned earlier in my spoiler alert has to do with the fluid side of the system. So here’s what I found. The first thing that I found is that the strainer that I taught I touched on in earlier in this episode was full of debris, it had a lot of debris in it, which was restricting the flow going through our evaporator. Now one test that I was able to do on the fluid side that is germane to the conversation is a TD split test across the evaporator. Typically those split tests mean the fluid and fluid out temperature on a stable running a refrigeration system. Can it be anywhere between two degrees and five degrees is pretty typical. One other giveaway that I got that I had an issue before I cleaned the strainer was I had a very high split. So I had roughly nine degrees split between fluid into fluid out what that was telling me was that fluid that was going into the evaporator was hanging out in there a lot longer than it should. And that was pretty that’s pretty typical for flow restriction. So that pointed me directly towards the strainer, I cleaned the strainer out was the first thing that I did. Now while I was at it, I went ahead and did a run out test which the pump failed. However, I want to tell you that this does happen. The pump failed because I had the wrong pump curves. And so do yourself a favor. This is a pro tip. When you’re looking at a pump curve and you’re using that pump curve to calculate a run out test on a pump, you need to spend a couple extra minutes and verify that that manufacturer that’s what happened. In my case, the manufacturer actually sent me the right pump curve and turns out the first trip around they didn’t fortunately, I knew that I figured it out pretty quickly. I had them send me the right pump curve. So I was able to affordance performance test that pump and lo and behold, it did perform at spec are pretty darn close to it. So I knew that my pump was essentially healthy. The other thing that I noticed is that this particular customer had a 40 degree approach, which I’ve been using for my example. So he wanted his fluid to leave his chiller going to his process at about 40 degrees Fahrenheit.
What I found when I ran my freeze point test will actually was I had a if I remember correctly, I said I want to have a 20 degree difference. So I was looking for a freeze point, there was gonna be somewhere around 20 degrees, four degrees approach, I wanted at least a 20 degree split spread on the freeze point versus the setpoint. What I noticed was my freeze point was actually 30 degrees, three zero. There you go. That’s I didn’t have enough CLI call. So that also made a lot of sense. I had a plugged up strainer, and I had a refrigeration system that was pulling down getting close to setpoint. And that fluid temperature getting to the tail end of the evaporator. It had a perfect setup to start freezing up. That was what that was now the owner says to me, well, we just you guys just put glycol in this thing. I said okay. Now what a lot of people don’t know about breweries is they tend to be when it comes to glycol they tend to be very leaky. What I mean by that is they will be constantly disconnecting tanks reconnecting tank same thing with heat exchangers. Spit spit spit you have a little bit fall here a little bit fall there it goes down the drain, it’s food grade, no big deal. But ultimately what’ll end up happening is the glycol tank will get a little bit low. A lot of the chillers that we would sell had sight glasses on them. We did do a little bit of training to tell them if the the level gets below this your low. Well inevitably what happens is the owner will have his maintenance guy or whatever walked by there and say hey, my level of fluid in this tank is a little bit low. The particular glycol that we formulated we had our own had no color to it. So it was just clear so you can tell the difference between the glycol and the water they did was a walk over to that that tank, they hook a garden hose up to it. But boom, Bada bing, they filled it up and guess what they just did. They diluted their glycol. So when you dilute your glycol, what happens to the freeze point, it goes up. So that ultimately ended up being what it is. So I had to do some additional training, we recharged them with glycol, we put a big old note on the chiller do not add just water to this tank because it was an open tank, they could do it really easily. And that ultimately solved the problem. So there, they were back up and running. They were not super happy about how much money they had to spend because I was there a few hours but they got a resolution and it was a permanent fix. And we had a customer for a very long time. After that I want to talk real quickly about maintenance on a process chiller actually covered a lot of it right, we covered the freeze points, we covered, you know the need to check that stuff. Other than that other than the stuff that I covered, you know, the strainers and the filters and things like that, you’re going to find that the maintenance on a process chiller is going to be very similar to maintenance on an air conditioning unit. You still have a condenser, you have an evaporator although it’s doing water, right, you have a compressor, you have a metering device, you have a bunch of controls, you have a bunch of pipe. So it’s going to be very, very similar to what you would do on a regular air conditioner. We do offer consulting services. So if you happen to be an end user out there, and you’re having your in house guys do it. We also provide customized maintenance inspection lists for process chillers based on the type of application. So if we can help you with that, let us know it, we do also have a course that’s available on the resource page of the process Tiller academy.com site that covers more in depth on a process chiller maintenance, it does the electrical covers all that stuff. So check that out. So that wraps up this episode. And I hope you got good value out of this. We covered how to deal with a freeze up on a brewery. And I just want to say a couple things to you. If you get a chance, you’re hopefully still on the landing page. For this episode, check out the landing page. Sometimes we put promos in there from our valued, awesome sponsors. And make sure that you keep the conversation going and connect up with me on LinkedIn. If you see my posts that are promoting one of our episodes and on one of the social feeds. Just a quick reminder, again, I know you get asked this a zillion times to the point you’re sick of it but it is very, very helpful if you hit the thumbs up and let everybody know that you like what I’m doing. And that helps get the word out to more people. So that’s super important. Thanks again for checking in with us and let’s let’s keep in touch and we’ll be back next week for a new episode of the process. Chiller pro Have a great day.