All right, this video is about a transcritical which means beyond the critical point, co2, Grocery refrigeration system. So a rack system is what this is often called. This video is made by Kevin compass. Kevin is one of the smartest rack, refrigeration technicians.

I've ever had the privilege of interacting with and he gets a chance to work on a lot of co2 systems, and so he was doing a commissioning on a new system and decided to just give us a quick rundown of that commissioning and the charging. You know adding in co2 to the system as well as some features of the system. Now he jumps right into some advanced concepts, so this video will be valuable to those of you who maybe already have some experience with co2, and you just want a little further knowledge of it and also those of you who are completely new to it. This will give you some familiarity, but let's start by taking a look at this diagram from Emerson of a transcritical booster co2 system.

So a few things you need to know about co2 is first off. It has something called the triple point, which is the lower threshold on co2, where it no longer exists in the liquid form. So we have to keep co2 pressures above the triple point, which is why you often hear him talking about charging with liquid and making sure it doesn't change to a solid so, for example, co2 at atmospheric pressure. We call that dry ice.

It goes directly from dry ice and sublimates directly to a vapor, so we have to have it under high enough pressure in order to keep it from hitting that triple point at the bottom and then, whenever co2 gets above about 87 degrees, Fahrenheit, that's where it hits. The trans critical point: whenever we were using co2 as a refrigerant, it gets very odd by our standards when you get above 87 degrees because it doesn't change into a liquid the way we're used to in condensing it becomes what's called a trans critical fluid, which is Really neither a liquid or a vapor, it's kind of its own thing and it no longer obeys those sort of rules of condensing and boiling or saturation that we're used to. So when we're working in that trans critical zone, you'll hear Kevin talk about a gas cooler and a gas cooler is essentially what we would normally call a condenser and, in fact, does become a condenser when it's under 87 degrees outside. So it functions as a condenser.

But then, when it gets above 87, it's no longer condensing it's now functioning as a gas cooler, and then we have to drop the pressure in order to to condense. So there's some interesting things about co2. If you want a more advanced description of this, I've done a couple podcasts edit one with Andre potting out from Emerson a while back and then also one with rusty Walker from Hill Fenix, and you can take classes from those organizations for a little bit. More in-depth.

Look at that, but just know that we have to treat co2 a little differently one because it's very high pressure. So when we're on the very high pressure side, we have to use special tubing either stainless steel or copper. That's specifically designed for those really high pressures. It actually has some steel in it, and then we have to kind of think of unique ways of designing the system in order to stay above that triple point on the lower level and to try to maximize what we can do before we hit transcritical, and so In this particular case, he's going to talk through the different controls and everything that goes into this transcritical booster system.

So this is our charging line up here. Charging when you charge up, I like to see balls floating, I mean we're having the co2 in right now. Are these siphon tube bottles that have a dip tube in them to allow liquid to come out like a refrigerant tank, would and we're just watching waiting for the sight glass to stop flashing? There's no really other way to do it. Besides having a pressure gauge on they're, not really worried about the hose blowing out of the sight glass, I mean it's going into a vessel, it's four times as large.

The tank only running 500 pounds we're charging right. Now you see it's going pretty fast about a minute to two minutes of tank, usually it's already kind of started to die down a little bit, there's only about 50 pounds on one of these tanks, pretty much empty, disconnect it now to the next one. This is one of the cases that's using the co2, so we have a suction transducer pressure. We have a suction transducer, then we're using two suction line now quickly.

If you look at this diagram, you're gon na snow dis down at the bottom right side of the diagram you have, the scroll, compressors and the scroll compressors are the compressors for the low temperature part of the system. So your freezers in this grocery application, but rather than having their own condensers like you, would often have instead, these compressors instead of discharging into a condenser they discharge into the suction of the medium temp compressors. And so you see, you have the scroll compressors on low temp and you have semi-hermetic sand the medium temp, which is exactly what Kevin is describing here and then those medium temp condensers. Those are what discharge into the gas cooler or / condenser.

Depending on the conditions. Then they go into that high pressure valve the flash tank bypass tank and then your expansion valves back so depending on your conditions, whether or not you are above or below 87 degrees. That's going to make a big difference in how those valves function and whether or not that heat rejector up on the roof that we would normally call a condenser is indeed a condenser, where it's condensing from vapor to liquid or if it's just cooling the gas and Then the condensing is happening after you have that pressure drop. It is a coalescing oil separator, the use of filter, that's inside of it to miss the oil out.

The oil drops down. Then there's this little sensor down here, but it's sensor, senses oil level in the oil reservoir. It's going to open. Similarly down right here is pretty.

This present were think we can prevent heat off to our flash. Take this reservoir take is always main feed at 500 pounds. It's a hundred pounds over the Lotus, the medium screws in its. So that way you can push oil into the compressor controls the old poem sea controllers.

So we have plenty of oil pressure to go in here. The pretty good system is pretty trouble. We didn't transfer pretty easy, so this is the back side of the rack where you can get some more service stuff, here's our low temp system accumulator. So we have one freezer for the entire stores chain-store.

We got our gauges for our low temp. We have our transducer for pressure relief, our service tab for the low temp side. This. This is our medium to discharge header.

It's all copper over here. It's the stainless Kritika transfers goes into the you're 130, far copper and over here we have our heater claim belt, so we're using discharge gas compressors we're setting this to keep the air. We got two transducers on here. We got a one right here.

We got one right here. What we're doing is we're close. This rack, pretty much has a gauge the trade. This was our old friend.

He use a gauge. We have a hydraulic gauge on this side. This is our eyesight paper. So right now pounds our equalization for the heater claim.

We got our main made: highside relief for 120 bar relief 17:40. The main fish are at least 1740. Then up here we got our flash take reliefs, so we got a 650 and 800 so 600. 800.

One word you're gon na hear Kevin use here is drop, leg and drop leg and refrigeration is the line in between the condensers and the receiver, so in between the condensers and the receiver is the drop leg so generally the line that comes down from the condensers? That's what they call the drop leg generally tend to call that an air conditioning the liquid line, but in grocery refrigeration the line that leaves the receiver is what they would call the liquid line most often and the line between the condensers and the receivers. What they would traditionally call the drop leg, you'll notice here, that you have four hundred psi suction, and so that's what you're gon na see on co2? You have much higher head pressure and you have much higher suction pressure than what we're normally used to. But again it all comes down to what is the saturation temperature of that refrigerant? Another thing you see a lot with co2 is you'll, see the pressure measured in bar and bar is sort of European pressure. Standard.

That's used quite often, and a bar is one atmosphere or very close to one atmosphere, it's 14.5 psi or approximately 14.5 psi. And so, as you know, our atmospheric pressure is, you know, 14.7 PSI a at sea level and that's where they get that 14.5 from so one bar equals one atmosphere of pressure, so two bar would be double that so on and so forth. The way I like to think of a flash tank is sort of like how, in a metering device a typical metering device, we have high pressure liquid and then we drop the pressure and then it starts to evaporate. In this case, we have transcritical gas a transcritical.

It's not, I can't really say vapor, because it's not vapor, but you have this transcritical gas and in order to get it to condense, we have to drop the pressure, and so we do that in that flash tank we drop the pressure and now it actually can Condense and become a liquid before we feed it into those metering devices, regardless of whether or not that piece on the roof that rejects heat is a gas cooler or ik and answer either way. It's job is to reject heat to that atmospheric air just has to do it a little bit differently depending on those outdoor ambient conditions and of course it doesn't more efficiently when the temperatures are below eighty seven, then, when they're above eighty seven we're gon na hit Our receiver we're doing these two valves, they're accomplishing two things: they're working together, holding gas in the gas into the tank, starts to it's about a thirty degree, evaporator every condensing temperature. The tank starts to drop pressure and temperature at the same time, and we end up with a liquid again, so this valve is constantly shutting and opening shutting and hoping they're working in unison together to keep this and a certain pressure. This Dallas castle would be the discharge fresh-ground plate pressure and to take pressure to make sure those it hasn't high has we're opening this cooling up here, so the superheat gets too low from this lasting five pass for the Supre coming back, it's gon na start, injecting Hot gas into the into the suction group to maintain the superheat and then down here we have our liquid injection valve.

It's doing the same thing if you freak gets too high from the cistern in there it's gon na to the D superheat the mediums have side to keep the compression or heating. So it's on here we're using CPC for our controls. We have our digital controller. That's so it's constantly monitoring and changing this valve the valve driver from here mr.

filter. It's constantly opening and closing that balance to maintain everything in here. These four words are the dry contacts for all the level switches. All our sensors analog outputs finger compressors.

This is our completed trailer. This is the front end for using, so you can see your low temps case temperatures cooler sensors. So we got our we're using like dryer in here. Okay, a pulse no, this day Elvis is pulsing ass, Illinois on and off on and off on and off to maintain super heat that is calculated from a controller from the suction pressure Burton temperature, a temperature sensor.

It's pulsing the superheat that way it's pulsing available, allowing liquid to come in and feed the coil, so that that's how it's doing it. It's super heat, control and defrost. So when it shuts off it stops and you got to medium temperatures, so this Rack is free. Is critical, so it's actually compressing co2.

We have to see of one goofy compressor, tracer they're, using discharge such a matter. So what we're actually doing? This is a Tuesday frame. We're taking the dis shirt discharging into the media section will reduce the compression ratio, or else we going to for anthias. This is a that would be a huge compression ratio and a huge efficiency loss.

So we, instead going into the medium Frasier's to our medium to professor's. We have one standard compressor number one is a variable. Speed drive compressor BFD over here and the other side, so we have a day in philosophy, FG up here, controlling air compressor, based on the signal, our oil spill to here with the buckets down, I big thanks to Kevin for taking the time to do this. It's always time-consuming to take pause and pull out your phone and take some videos, and I appreciate it anytime.

Someone does that for the benefit of helping train the trades. I think the old-school thinking of you know hiding information so that new people don't learn. Those days are over it's all about sharing, so that way we can get more people in the trade. So that way, we all don't have to work such crazy hours.

So I thank you Kevin for doing that. I really appreciate it. So hopefully you learned something and watching this. If you want to learn more about this, you can go to companies such as Hill, Phoenix, Keizer, Warren Emerson, all great resources for co2 training, and, like I mentioned before, we have a couple great podcasts in the HVAC School Archives, one with Andre Patton out from Emerson And one with rusty Walker from Hill Phoenix, those podcasts help describe this in further detail, but hey thanks for watching we'll catch you on the next one.