Latest / The Refrigeration Mentor Podcast / Episode 317. CO2 Piping Design (Tips to Protect Compressors and Prevent Failures) with Chris Griffiths

Transcript

Episode 317. CO2 Piping Design (Tips to Protect Compressors and Prevent Failures) with Chris Griffiths · The Refrigeration Mentor Podcast

• 0:00
  Welcome to this CO2 Design Fundamentals four part series. So excited that you're all here. We're gonna be diving into some deep CO2 technical piping design. I'm here with my good friend Chris Griffith, and we are always talking about CO2 design, learning, and growing. We wanna share this knowledge.
• 0:01
  No, you're, you're an expert at this and this is what you do day in, day out, helping customers solve some of the toughest problems in piping designs. 'cause they come to you to, to solve that problem.
• 0:02
  So. Primary purpose of pipework is to just, is to generate a cooling effect where we want it. We circulate a refrigerant around the system, a sealed system. We don't want it escaping, but as part of that, the compressor needs to be protected to ensure it can do its job. So we're gonna start off today with what I consider a top free tips for protecting compressors, and they all come back to oil and making sure that oil flows around the system back to the compressors if it does escape from the compressor.
• 0:03
  As we design for, we need to make sure we get a full mass flow of refrigerant through the system, but oil will be entrained within that. For making sure it also returns a part load conditions. 'cause these systems don't operate at a hundred percent capacity for 99% of the year or at all in a year. You may get, , a freak environmental condition once every four years, which we still have to design to, but it won't be operating at those conditions for majority of the time.
• 0:04
  Let's make sure we've got any oil management systems there. Make sure they're operating and make sure they're maintained effectively. So oil management system piping. Is a specialty in itself as well, which is something we do cover in CO2 training course and far more in depth. It's a bit too much to cover in even a four part series as this is but making sure that's actually designed appropriately.
• 0:05
  Such a small application generally, unless it was a very, very specific design with the budget to do so. And we have to work within budgets and constraints, and that's what makes it fun engineering, rather than what do the numbers spit out? What can you do? So with this, if we do get our pipe sizes wrong.
• 0:06
  The system is a failure for liquid lines. You get excessive loc and you end up getting what we call liquid hammer. When it comes up to a valve, there's a lot of energy behind that. Inside that fluid, if you try and shut the velocity down, that's got, that energy's got to go somewhere. It ends up forcing its way into the walls of the pipe work, which can shake the pipes, whereas it in inner walls of pipe, if it's against bends, long radius, elbows, short radius, elbows.
• 0:07
  So try and design these constraints of mind with those two and you won't go far wrong, less common from that we have, if you have too many bends, you get excessive pressure drop. That's gonna reduce the efficiency of our system. Using long radius bends should be preferred rather than short radius bends.
• 0:08
  And this is something important when we talk about in that design program, is when, when you're calculating the price. For do for your customer when we get in there, this is important 'cause that insulation is expensive so you gotta calculate for that as long as, because if you oversize it, just like we said there, there's more refrigerant potentially if you don't have that insulation or the thick enough insulation.
• 0:09
  But what I wanna speak more specifically on is suction pipes and how it impacts that. So we're looking excessive pressure drop and eventually lean to oil issues as well. So we're gonna move swiftly on, and we're just gonna have a look at sort of the actual pipe sizes themselves and what impact it can have.
• 0:10
  Rankine or Fahrenheit. From that, we've also selected our compressors. We've used bits of software here and on. On the right hand side, you can see our medium temperature stage. We've got an evaporated capacity of 14.08 kilowatts, so just above what we need. Absolutely perfect. And you'll see we have a power input of 12.13 with a discharge temperature there of 125 Celsius.
• 0:11
  If we did swap or if we had installed free apes pipe work as a suction, which with CO2, for those who aren't familiar with CO2, we can get away with generally much, much smaller diameter pipe work for the same duties we would have on HFC and even HFO systems as well. It's drastically smaller. It's no longer big pipe little pipe.
• 0:12
  The quality of our oil in our system decreases. It gets, eventually, it'll break down. It won't actually lubricate the compressor as it should do. And we're gonna run into even more issues. And then the nice easy number to recognize when systems aren't performing very well is our COP as in has decreased from 1.43 to 1.28.
• 0:13
  So how do we actually check those pipe sizes are correct? So we had that little bit this table on the top of the last two slides that's done in Danville School selector. That's what I'll be showing on the next several slides. So just to set the basis for this, we're gonna look at an example system, which has a cold room, evaporator, and two display cabinets connected to it.
• 0:14
  It's a Kelian evaporator. We've got 4.2 kilowatts, and then we've got our display cabinets on the bottom right. We've got a 12 foot and a six foot cabinet there. 12 foot is 6.2 kilowatts and our six foot is 3.1. Those all the numbers we need now to be able to start plugging it into our system. So with pipe work, we need to do some sort of schematics to know where the pipes are actually going.
• 0:15
  So what we can do is analyze this section of pipework high license in red.
• 0:16
  So if we are evaporating at minus six Celsius, we'd have a saturated suction temperature. What our compressors would see at minus 7.1 and all our selections for our compressors would be based around that. What if this is incorrect though? What if this is actually installed as three apes? We have a pressure drop there instead of 5.2 kelvin.
• 0:17
  For suction pipe work, a rule of thumb, typically for HFC pipe work would be between eight meters a second and 18. For CO2 can generally go a bit lower, probably about five below you can go lower, but it would be, I'd be hesitant to do so about checking it into some more detail first. We can see here if I can engage with laser point.
• 0:18
  What about the rest of it though? Well, a straight length of pipe immediately after it's 10 meters, 30 feet. We've got a brush drop. Have 2.2 calvan, , maybe five Fahrenheit there alone. That's a huge drop. In reality, if I was concerned that velocity would need to be that high, I would say you'd step all the other pipe sizes up by one size to half inch and leave rises three eight.
• 0:19
  What if the single cabinet is operating? 'cause the other we have a cabinet and the evaporation of satisfied themselves, the temperature may shut off. Well, you've only got probably a quarter of the duty and a quarter of a mass flow through the system, but it still has to go through the same riser. And return all the oil there needs to, to the compressor.
• 0:20
  We've got, for example, , two cabinets and an evaporator. Larger stores, you may have a hundred fixtures on one system. Dual temperature as well. You, and then they decide to move halfway across the store or change it from six cabinets there to four cabinets and move two onto another stu. Rather than having to rerun the entire network again or even simplifying it into sections, you can actually model it exactly as it needs to be.
• 0:21
  Drop it down for it rises up again, or, or pre-manufactured pra ra staffing. So for example, in here, if we look at being too large now, our pressure drops. Drops, yeah. We have no, no pressure drop at all there. Great. Our system's gonna perform very efficiently. However, the level, the velocity here, a 3.84 says to me that is going to not return oil.
• 0:22
  Is that really worth it? Particularly on CO2, I've done, I've designed a lot of CO2 installations, and I don't think I've ever had to use a double riser. It just doesn't happen in retail unless you have a huge number of fixtures only returning up a single point, and at which point I would tend to split those into multiple headers on top of various cases.
• 0:23
  Six meters. Some people think that's probably slightly too much. I see it 30 feet. CO2 is very good at transporting oil though. That's the important thing to consider there. I know for HFO design systems a similar system to this, I would be probably installing a double riser because to, to ensure about velocity can return, can return oil conditions.
• 0:24
  We're not gonna get the CU and what we need and the solution for that. Nice and simply increased pipe size diameter, much cheaper to do this at the design stage and run the numbers rather than install it. Wait for a fault to happen. Go back and repair it then Yeah, you are talking maybe an hour, two hours of your time as a designer to change it and verify it for it is installed versus a day, two days of labor on site, all the materials associated with it.
• 0:25
  Is the oil gain trapped in a riser? Is it again, trapped in the evaporators? So try and go through logically, find out where it would be stuck. Check your velocities for each riser. You can model that in software fairly quickly. If what duty the system needs to be based on manufacturer's data sheets, or even looking at the condensing unit, you can model it fairly quickly.
• 0:26
  And then a very quick summary in decision tree. If you were having false on site led from pipe sizes, which you think, oh, you may need to go and investigate. Has it, has it worked before? If it has, it's probably not pipe sizing related. If it's something recent, it's probably not pipe sizing related. If it hasn't ever worked correctly, could well be pipes.
• 0:27
  'cause my background's not in design. But after working with you and Nabil and with all the students that ca came through the program, we had over. 20 people from eight different countries so far, finished a 12 week design course diving into this and seeing the different options and doing those tasks where they're, they're actually designing it with cool selector two and then going into micro pipe and seeing how much quicker they can do a design saving.
• 0:28
  So. Hopefully that you took a few things away from this because this is just touching the surface. And, and Chris is an expert. He designed hundreds and hundreds of trans-critical CO2 systems and piping is his game. Like this guy knows what he's talking about. So if you're interested in a 12 week design, DM me email me at trevor@refrigerationmentor.com.
• 0:29
  So excited to see some of you there. So remember, reach out if you have questions. DM me on LinkedIn, email me@trevorrefrigerationmentor.com. And Chris, thank you so much for sharing these quick tips because these one or two tips can really change the way you design systems.