CO2 Refrigeration Rack Overview

Kevin Compass joins HVAC School to give an overview of a transcritical CO2 refrigeration rack. He goes over its primary components during a commissioning procedure on a new system and talks a bit about charging a CO2 system.
CO2 has a triple point and a critical point within its operating range. The triple point is the lower threshold at which CO2 may exist as a solid, liquid, or vapor, so we have to keep the pressure above the triple point to prevent it from solidifying. (CO2 is often charged in the liquid state under pressure.) The critical point is at around 87 degrees Fahrenheit, and CO2 will become a transcritical fluid (which is neither liquid nor vapor and doesn't obey the rules of saturation). As a result, transcritical CO2 systems have a gas cooler instead of a traditional condenser. In conditions below 87 degrees, a gas cooler will function as a condenser; otherwise, it has to drop the pressure of the fluid to get it to condense.
The system in this video has a 3/8" charging line, which takes new refrigerant in the liquid phase; during charging, you have to watch your vessel pressure to make sure you don't hit the relief point.
The charging tanks have a dip tube to allow for charging in the liquid state. Once the sight glass stops flashing, we can disconnect the tank.
This system has a suction transducer, which measures pressure on the suction line. It also has a coil temperature sensor for defrost termination. On systems where the low-temperature and medium-temperature cases are on the same rack, the low-temperature compressors discharge into the suction line for the medium-temperature cases. The medium-temperature compressors discharge into the discharge line, which travels to the gas cooler. The compressors also have an oil system, which consists of a separator (coalescing, in this case), oil level regulators, and a reservoir (with an oil level sight glass and an oil level alarm). The reservoir is always maintained under pressure and vents off to the flash tank.
The low-temperature side of the system has an accumulator, transducer, and low-temp suction header. There is also a copper medium-temp discharge header. The high side of the system has a pressure gauge and a high-side relief valve, and the flash tank has relief valves, a bypass valve, a pressure gauge, transducers, a flash gas bypass valve, and an oil line bypass. Pressure is often measured and regulated using the bar scale, not PSI.
A heat reclaim valve allows the system to use compressor discharge gas for reheat at the main RTU. More pressure transducers limit the pressure drop to the reclaim condenser.
The gas cooler in this video has four ECMs and fans; it acts as a condenser when the temperature is below 87 degrees. The gas cooler also has a drop leg, which is the line between the condenser/gas cooler and the receiver. There is also a high pressure regulating valve and a flash gas bypass valve. Those valves work together to hold back and then vent off the gas to get the CO2 to condense back down; that keeps the flash tank at a certain pressure. The flash tank drops temperature and pressure at the same time.
The system also makes use of suction drier shells and hot gas injection, which injects hot gas into the medium-temperature suction side to regulate the superheat. If the superheat gets too high, the liquid injection valve helps de-superheat the medium-temp side.
The main electrical panel contains CPC (Emerson) controls, and the digital compressor controller uses pulse-width modulation. It also has a normal compressor contactor and a valve driver for the CO2, which manages communication between the valves. Boards monitor the dry contacts for the switches, sensors, and analog outputs. The main controller displays all of the display temperatures and the sensor data; each case has its own sensor and solenoid valve, which is managed and monitored by the main controller.
The two low-temperature compressors are scrolls, and the two medium-temperature compressors are of the semi-hermetic reciprocating variety. The rack is transcritical and compresses CO2. When the CO2 discharges out of the low-temperature compressors, it gets sent to the medium-temp suction header. That configuration reduces the compression ratio and improves capacity as a result. The compressors are controlled by a Danfoss VFD.
Podcast w/ Emerson on CO2:
www.hvacrschool.com/co2/
Podcasts w/ Hill Phoenix on CO2:
www.hvacrschool.com/critical-...
www.hvacrschool.com/3-flavors...
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/

[@trevorvantiel453]

Thank you, fantastic!

[@davidshellenberger1983]

Absolutely fantastic, great content, love how he explained how the rack works

[@alexl.6592]

Thanks for all your efforts to provide us more and more technical specs...and knowledge.Alexis from Athens Greece!

[@chrism7275]

thanks for the video! tough to imagine alot of us would get to see it this up and close with out the video

[@HVACRDUDE]

THE ABSOLUTE SMARTEST AND INTERESTING GUY IVE EVER HEARD...HOLD MY ATTENTION AND YLUR SMART AZ HELL! APPRECIATE IT

[@john198292]

Thanks guys, excellent overview! Just starting to get into CO2 systems myself.

[@andrewsmith2190]

Very good thanks much the same system we have now being installed all over the uk in supermarkets

[@aukanmeister]

Thank you very much for the effort of putting this together, guys! My head is saturated (!) now;) Have to watch it a few times to get it all in. Very interesting! You use a lot of the same components as us europeans, but the electrical standards are quite different.

[@mastertechnicianmindset2181]

Thanks very much. Very useful and helpful for learning materials that are very hard to find and hardly known or understood.

[@UltraHydrophobiccoat]

Used to have a small Coca Cola cooler for drinks. The Coca Cola company gave it to the restaurant owner. It used Co2 as refrigerant, and leaked. After swapping it with a R134a compressor, it works very good and no leaks any more (Over 2 years now). So high pressure means you have more potential leaks

[@Rollerguitar96]

i disagree. we rarely got any leaks. the most important thing is to use the right components

[@danalan4329]

We have them at our Grocery store I am service tech for. I was amazed how easy these are to work on.

[@dones5224]

Thanks Guys , Great overview indeed

[@bmillwood6666]

Awesome! I miss my rack days. Co2 is the new future

[@dougmilu9652]

Great walk through! Thanks. D.

[@matthewcaldwell6536]

A lot going on there. Don’t deal with co2 but awesome video. He’s a smart mechanic.

[@saghirahmad9634]

thank you sir from France

[@ashbridgeprojects6916]

Hello. Great video, very informative. Could you advise on what the primary design criteria for the drop leg pipe size should be? i.e. to achieve a desired velocity or pressure drop between the gas cooler and vessel. Thank you in advance.

[@realvanman1]

Wow, very interesting. The polar opposite of elegant simplicity. Rube Goldberg? Must be dramatically more efficient, or it wouldn’t be worth it. I would imagine that the upfront cost is high, and the service call costs will be even higher!

[@Flexformfitness]

Awesome video thank you

[@1991elliot]

I find it interesting when someone is trying to describe the trans-critical system; there are a lot of terms thrown about when trying to describe the state of the CO2 above the critical point. As said in the video it is neither gas/vapour or liquid. It is a supercritical fluid. A vapour would refer to a gas that is in equilibrium with a liquid phase, liquid is a subcooled state and gas is a superheated state. Supercritical is some kind of hybrid between liquid and gas and has properties of both. There is a mistake in the video to refer to CO2 above the critical point as 'transcritical' - it is not, it is supercritical. The system is transcritical because it operates on pressures that are both above and below the critical point and hence critical pressure. The system works across the critical pressure, hence 'trans' meaning across. 'Super' refers to above - i.e. supercritical is above the critical pressure.

[@jeremyhall7951]

Like the way mercury is a liquid-solid.

[@donnierobertson3088]

Great job and video

[@davidsr79]

Along the video I see some gauges and pressure transducers connected directly to the pipes. How do you replace those without shutting that line off? I have female pressure transducers 1/4” SAE flare and I cannot find a schrader valve rated for R-744. Of course I could use ball valves but the space is limited. Anyone please? Thanks

[@user-ly2ip1fq4f]

Like your shows hope I'll learn more to become 1of the best in the bizz

[@azhariboerhan3402]

Thank you & appreciated for sharing about CO2 Refrigeration. Need more further information of that systems such as sub critical system, about pipe thickness, power consumption compared to other systems etc...

[@VaclavFucik]

Hi, thanks for great video! I have a question - 7:45 shouldn't there be a relief pipe on the discharge of the pressure relief valve? Or where is the relieved refrigerant directed? Thanks

[@natepeterson7145]

I'm interested in the trailer because of videos like these

[@davenottingham3254]

Don’t know if this is to late but can you do something about Co2 ejectors. We’re just about to start receiving packs with this fitted and it’s hard to get a good basic explanation of how they work

[@alainemerson]

Great video......

[@darksabatta]

Would it be better to have a subcooler to condense the gas into a liquid?

[@deluxairhead]

Super confusing for an old school tech like myself but brilliant all the same, thanks guys for the post, l think l will be watching this a number of times to figure the whole C02 processes, the new techs must be left scratching their heads when it comes to trouble shooting this type of system, I feel like a 1st year apprentice again......

[@MyBallzGotShocked]

What kindve oil is used for Co2 and is it very miscable? I do residential but with all the new weed growers ive become interested in Co2 systems.

[@davildavil5183]

Can we take lower condensing temp... like 32 tp 40 foranheat using the cascade refrigration My questiin is vapor co2 convert into liquid co2 at low condensing temperature

[@wemghon1]

Hi, I am wondering if you could do a study on the vaporizing of CO2 stored in huge CO2 tank for process use. My company uses a lot of CO2 for our process. Liquid CO2 is vaporised using a hot water balh before it could be used. Is there any ways to harvest the chillness from the vaporizing CO2 for used to cool our cooling tower water return?

[@jimmyp5487]

New into c02 racks would love to get this dudes #. Got couple guys from hill phoenix that are pretty sharp but I’d like to work with this guy for a couple months !

[@maheradous9257]

Good job

[@myates4652]

Thanks for the overview. I wonder if they will be able to simplify these systems for residential.

[@jeremyhall7951]

No. They won't get simpler. But they may get cheaper.

[@TheLightningStalker]

With HFCs competing probably not. There would have to be significant reason to use it, such as a dramatic savings in operation cost in those applications.

[@RJMaker]

Whoa.. Mind Bent....

[@darekcieslik6838]

I know of one system in my area and it gives them so much trouble when the temp is in the 90's

[@keithturner4939]

Cool,story 🙄

[@chrisduhaime5689]

Looks you got one expensive maintenance nightmare somebody will be married to that stuff .

[@manoskritikos8021]

Great video, seems though that energy consumption for the same application compared to HFCs is a lot higher! Should we take that under consideration, not to mention the installation costs.

[@billyflanagan9657]

Great question also the fact that it's a big bomb at those pressures

[@MrAnderson3]

This is the transducer for the transducer thats has another transducer for the main transducer

[@codyeaton1818]

The reason its called a transcritical rack is because its a cycle when the system goes above critical point co2 becomes a supercritical fluid and it transitions into the transcritical cycle. If you look at a enthalpy diagram we get a better idea of the cycles. Now when the system is below the critical point thus it runs in a subcritical cycle which is what were used to seeing because all other refrigerants have a much higher critical point.

[@antonemilit2178]

I heard there's currently a C02 shortage. Apperently its a by-product in the petroleum industry.

[@fastlife866]

I think I'll stick to residential, very interesting though, thanks for making this.

[@donnellbaxter8050]

Thanks make more videos

[@Oscarbm1234]

Man, this looks intimidating from a residential point of view.

[@bulkchart3239]

why is co2 used as a refrigerent? wouldn't it be very inefficient?

[@etherealrose2139]

That entire rack looks super fucking expensive. All those specialized valves and gauges and tanks and transfer tanks and rejected etc. Yikes. I get it because CO2 has odd properties but maybe it isn't the best refrigerant. I like the idea but in the deserts... 87 is a nice winter day where you don't really run the AC much. At 115 you'll definitely be using that gas cooler a ton and efficiency sounds like it'd be bad. Wish there was a breakthrough on simplifying this process.

[@erwinvictorio9549]

do we still need p trap in c02?

[@eriknunez8757]

Still need oil return. Oil trap not p trap

[@jimmyp5487]

Hug a tree save the world. Been working with couple Hill Phoenix reps and they say c02 is way easier than 448A rack 🙄 haven’t touched c02 YET but I don’t see how

[@abhilashac8694]

Good

[@TheBdog2009]

So we're banning freon type refrigerants for CO2 to save the planet but CO2 is a greenhouse Gas that can cause a greenhouse effect. Also adding medium temp compressors in the mix and the power to run those. Please someone correct me if im wrong about any of this?

[@alainemerson]

You don’t add CO2 in the atmosphere when leaking, since CO2 you had charged in your system is already fromm mother nature..... only had been dried and clean before bottle it.

[@john198292]

@@alainemerson Hello there! I sat in a class you taught at the Vilter factory, good to see you ;)

[@kaimccalla2936]

R744 co2 has a gwp of 1

[@mohammedwakilansari2587]

hi sir. k 65 Couper pipe using

[@scottjones7279]

What is the noise, compressors?

[@HVACS]

Yes

[@MrJarmore]

Yeah you're hearing the screw modulate speed. They make a shocking noise hahaha

[@Takeithome345]

Need two guys when servicing,one guy to work on these co2 systems and one guy to call 911 when a valve blows off and ripps off the first guys head from the 1500 psi of co2

[@dannydowell6484]

Dave

[@danielallred780]

Wow. IDK ... It d be cool to work on, but probably never going to touch it.

[@superiorcomfortheatingairl3373]

I am not going to complain about the ice cream prices anymore

[@adamwoods3092]

MPA is a good way of reading co2 so 1 MPA is 10 bar and so on 👍🏻

[@VaclavFucik]

19:56 so true

[@arcad1an292]

CO2 is not a good Refrigeration System. IMO. Still, a very interesting video. Good work 👍

[@dietyform8634]

more kevin lol

[@averagebloke4474]

Hey Bryan can I talk to you more privately I'm having a really hard time getting into the HVAC industry. Thanks

[@chrism7275]

what do you need help with specifically ? have you completed school or enrolled?

[@averagebloke4474]

@@chrism7275 yeah man I just wasted 3 years of my life going to school I can't even get a job for thanks.

[@chrism7275]

@@averagebloke4474 what part of the country are you in? i think if you call and apply to all your local shops you should be able to find something. Also alot of the schools out there have job postings through the school you graduated at, give it a look brother. Keep applying sooner or later you will find an opening. In the meantime keep learning and going through your books.

[@averagebloke4474]

@@chrism7275 new Jersey and apparently it's too late mate it's slow season I don't have till the spring.

[@MrJwinne]

Sculpin There’s always work . Plus , refrigeration doesn’t have a season . Try starting off as a maintenance tech . Btw, Heating season up here in the north East is in high demand . That’s the beauty of this industry, there’s plenty of diversity .Good Luck .

[@SvenSigi]

Ur Danfoss Frequency Changer is a little bit tooo nervous, try to get it as stable as possible. if its changing too much all 2 seconds, ur bitzer is going trash very fast.

[@coldfinger459sub0]

👍👍👍 yes I can’t wait, Bring it on, I can’t wait I want one at my house just to have a fun toy to play with. Compared to automotive emission systems and drivability and body module systems that’s just the Childs play toy simple easy. I wish one of the big companies can donate one of those systems here in California to Laney College for our HVAC/R program. I will install it for free just for fun. Our young people coming out of the high school entering college for a career in our industry need a lot of help.

[@arcticzone9223]

What's all the benefits of all these new shenanigans?

[@CT-vm4gf]

GWP - 1. Environmentally friendly.

[@michaelszczys8316]

Probably takes twice the power to run it, but at least it's environmentally friendly.

[@mikhailkurylenak1515]

very very niche market, 99 pct refrigeration guys never touched CO2 system, even most _rack_ ref guys barely worked on these systems, too many potential headaches for my taste

[@kennethsmith2030]

Local 597 here

[@chrism7275]

Go start a business in a state where unions are strong in the commercial and industrial hvacr field and tell me how much you love unions. Unions are only good if you're in one they're a net negative for literally every one else.

[@RinKKinG]

whole lot to go wrong here!!

[@OcRefrig]

Looks Like a Money pit ! Sooooo many parts and pieces to fail. The simpler the better in Refrigeration.

[@commanderosis435]

Thats in anything really. The environmentalists are forcing refrigeration in this direction though. Look at it this way youll never be out of a job.

[@VTdarkangel]

It definitely is, but this is where we are being forced towards. I hate it, but this is coming.

[@vadimkochkin9095]

I am 667th thumbs up, just don't like three sixes

[@keithturner4939]

That just was irritation ... flash tank, it’s a receiver ...yanks 🙄

[@darnellconstant2410]

This is officially Japanese to me 😢

[@michaelszczys8316]

Reminds me of computer tutorial video where some guy from India says " click this, then this, then this, then scroll over here, then click this and this, and that's how you do it."