How effective is co2 use as a brine in frozen store and freezers?
regards
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How effective is co2 use as a brine in frozen store and freezers?
regards
At -67ºF to 32ºF (-55ºC to 0ºC)
evaporating temperature, volumetric performance of CO2 is 4 to
12 times better than that of ammonia.
[FONT='Ｍ]This translates to smaller CO2 pump and piping
Better heat transfer co-efficient means smaller evaporator and lowair to refrigerant approaches for heavy duty low temperature freezing applicationWe have several installations of our CO2 brine systemIf you need some more info you can always contact your local Mycom (Mayekawa) branch for some details on our CO2 brine systems.Iceman_4000
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Thanks Iceman for the information
1. I want to know is there any difference in power consumption with respect to ammonia?
2. Is there special controls for CO2? who are the manufacturer? How costly these are?
3. Is the system is cost effective?
rajkumar
Quote:
Originally Posted by Rajkumar
1. Your power consumption on the ammonia side should drop. the CO2 carries more BTU/lbs in comparison to other secondary refrigerants.
2. The only special equipment are the pumps and the evap coils maybe some solenoid valves. I have not been involved in a system yet so off the top of my head I could not tell you costs.
3. the system addresses many costs
Alot of places laws on Nh3 are getting tighter
I know here in BC over a certain size nh3 system you need an operator on site 24hrs a day
Currently in eastern Canada they are attempting to amend the code so that all nh3 must be contained with in the machine room
our prepackaged CO2 brine system address both of these large issues and reduces power consumption
I would say that makes it very cost effective
Iceman_4000
I would rather see CO2 used as a primary refrigerant instead of a secondary refrigerant.
Why Iceman?
as a brine you have way less to worry about all you are doing is running pumps you don't required a co2 compressor.
I think it is a great solution. you can drastically lower ammonia charges like on a liquid recirc system. CO2 makes a damn efficient brine as well
That is a debatable. If the liquid overfeed system was designed as most are, then you might have a point. However, it's also possible to design a critical charge liquid overfeed system too.Quote:
Originally Posted by IceMan_4000
If you are running low temperatures, then why not take advantage of the benefits of CO2 for much smaller low temp compressors also?
Might that be because you are selling them?;)Quote:
Originally Posted by IceMan_4000
:rolleyes: Maybe, but I also believe in what I sell.Quote:
Originally Posted by US Iceman
Even with your Critical charged instead of a 4-5 times overfed you will still be pumping the Nh3 out of the machine room. Here code issues are going to stop us from being able to do this.
CO2 out performs the Nh3 on the recirc side.
1. The pipe sized are drastically reduced
2. There are no more oil issues and coil fouling from oil being circulated with the ammonia. all oil is contained with in machine room
3. No CO2 compressor required (Tons of code issues currently here with co2 compressor design) Code states they have to be certified to 5 times the MWP
4. due to better heat transfer co-efficient we can use smaller evaporators and low air to refrigerant approaches for heavy duty low temperature freezing applications
Why not use it as a secondary refrigerant?
If you are using a CO2 liquid overfeed system the ammonia stays in the engine room. It's no different than pumping the CO2 to the evaporators in either case. The only difference is the refrigerant expands by two phase boiling in one system or stays a liquid in the other version.
You might try the HP version of the Sabroe recip. It's a really nice compressor.:)
Or, you could use a modified DX system along with a cascade condenser (on the ammonia system) and eliminate the CO2 compressor altogether.
There's more than one way to get the job done is all I'm saying. The best application is the one the owner can maintain with the least amount of aggravation for the lowest operating cost. That's the best variety.
I think that you have some questionable statements.Quote:
Originally Posted by IceMan_4000
1. Oil issue. Properly designed plant doesn't have the problems with oil return.
2. Better heat transfer coefficient. I doubt that liquid co2 has better coefficient than boiling nh3. Imagine that it is better. However, this coefficient has little influence on total heat transfer coefficient, because major heat transfer resistance from air side not from liquid side. Evaporators won't be smaller.
What about defrosting? What about temperature difference between boiling nh3 and liquid co2?
This is all good debate and discussion, regular technology versus innovative technology.
Iceman 4k. is there a web site that this CO2 brine system is discribed in general terms. I'm liking the idea of reducing ammonia system charge and not puming NH3 all over the place. Tell me more.
magoo
Sergei.
the point you made about oil in NH3 systems. For all intents the best designed system engineer will still install oil rectifying and recovery points on all installations. Show me one that does not and I will bow to you.
My best advise is to keep an open mind on all innovative ideas.
magoo
What am I missing here? :confused:Quote:
Originally Posted by Magoo
What's the difference between pumping CO2 as a secondary refrigerant and pumping CO2 as a primary refrigerant?
Either way you are not pumping NH3 as it simply exists in the engine room and cools the cascade condenser.
You have a temperature step to cool the brine (in a chiller) and this same or smaller temperature step would also exist for the cascade condenser.
In fact, the pumping costs for the secondary refrigerant approach would be greater since it works as sensible heat transfer so you have to pump more CO2 for this method, than what you would for a CO2 liquid overfeed system.
I can certainly see the benefit of using CO2 for low temperature applications however this secondary refrigerant argument needs some explaining.
How? This seems to be based on some logic I don't fully realize yet.Quote:
Originally Posted by IceMan_4000
I'm not trying to trash anyone here, I just want to understand how these points are being developed. There seems to be some conclusions being operated off of that are not obvious to me.
Hi, Magoo.Quote:
Originally Posted by Magoo
Every ammonia refrigeration plant has oil recovery points(oil pots). There is no difference between conventional refrigeration plant and plant with co2. Oil should be recovered and usually from low(intermediate) pressure receivers.
I'm open to any new idea or any new approach. However, this idea should be really new and really useful. Many people try to sell old idea as a new one or try to sell useless equipment.
One example. Refrigeration plant has 2 evaporative condensers equal capacity. First condenser has 20 HP fan, second condenser has 40 HP fan. Fan VFD was installed for first condenser. However, I showed this company that cycling second condenser fan will save more energy than fan VFD of first condenser. So, this VFD is useless.
Sergei
Or, they talk real fast and make their product presentation sound too good to be true or that it is almost like a perpetual motion device and saves more money than was being used in the first place.:rolleyes:Quote:
Originally Posted by Sergei
I don't have any problem with trying something new but whatever is tried should be able to be judged fairly with good data and no solemn silences.
Quote:
Originally Posted by US Iceman
Cascade systems are great for low temp -45F or lower. they require two sets of compressors
the difference between pumping co2 as the secondary refrigerant (Brine) compared to the Primary. The equipment and the optimal temp range 23F to -40F
The CO2 brine system is more like the arena application. The only requirement on the equipment side for the CO2 (Brine) are fluid pumps.
all of our current systems are installed Japan (right around 100 of them) I do not get to see till September when I go to Japan.
Here is a third party looking into CO2 as brine
http://www.senternovem.nl/Robinterna...ng_vessels.asp
US Iceman
What I was trying to say about the liquid overfed systems and ammonia reduction.
Lets take a normal 4-5 times flow rate which is normal old school liquid reccirc.
Lets say with high performance heat exchangers lets say we can reduce that overfeed to 2-2.5 times.
if we use co2 brine we can reduce the amount of ammonia required by 7.5Kg/USRT compared to standard liquid recirc system
**All my numbers are based on system studies done in Japan
I see some obvious misconceptions here.
While cascade systems are generally used at very low temperatures, a cascade CO2 system has a bottom end around -67°F. That's the triple point. So, there is nothing to say you can't use CO2 as a primary refrigerant in the temperature ranges you are describing.
And, depending on how the system is designed and the temperature requirements you don't necessarily have to have a compressor. You can do a primary refrigerant system with pumps only also.
I don't have an issue with the technical aspects of what you are stating on the above. Yours will work as will what I'm suggesting.
What's a high performance heat exchanger? And how will it reduce the overfeed rate?
Overfeed rates are the excess liquid refrigerant (compared to vapor) exiting the evaporator . If you pump less liquid the overfeed rate comes down if the heat load remains the same.
If the refrigerant volume stored in the system is drastically less between the two systems you are describing my guess is the volume reduction is due to the use of plate heat exchangers versus shell and tube exchangers.
This doesn't mean the use of CO2 contributed to a lower refrigerant volume, it just means the volume was reduced by use of alternative heat exchange components.
From what I have been able to understand your system is being compared to a conventional liquid overfeed system using NH3 to a critical charged CO2 brine system. Please correct me if I have stated this wrong as I am taking certain assumptions here based off of what I have seen or read about.
If the NH3 cools the CO2 either for a secondary or primary use, the CO2 is still the refrigerant being circulated out of the engine room. Sure this will reduce the impact of circulating ammonia into a work space with people, however, you can still use CO2 as either a primary or secondary refrigerant.
All I'm saying is there are different ways of doing this and the best way is the safest and most cost-effective, not what someone has to sell.
Could no agree with you more UsIceman
As a refrigeration Mechanic I care about what works not my numbers as a sales guy. I look at it the same was as when I was a mechanic. You can screw them once or service them for ever
So in using a CO2 brine secondary what evap temps can you have on the same loop? Can you have a coil at -20? and another at 20f?
With CO2 loops would you use flow controls like on a glycol loop to control your temps? or use a solenoid?
What pressure do you keep the CO2 at? What is the subcooling coming out of the exchanger and coming back from your evap coils?
How does CO2 pumps stand up? problems with cavitation such as in a glycol loop? or am I wrong in "assuming" its a centrifugal type pump?
Im full of questions :) thats just me. I will wait to ask some more but trust me, I have more :p
dear zeerodegreec,
If you are using co2 as brine your TD should be 4deg to ammonia i.e td to evaporator should be minimum 10-12 deg.
With co2 brine you have to use solenoid for flow control.
Its a centrifugal type or canned pump.
rajkumar
So is it practical to use CO2 Brine for med temp applications? The systems I have heard about in supermarket industry are using CO2 for low temp and Glycol for med temp. I just dont see why you would want two different Brine's in a store if you could just go with one. If your going to use CO2 why not on both systems or if possible one big system for everything. But with just having sol for flow control it would make life tough on the med temp systems.
How are most of these systems piped? It depends on local code I know that much but is it a Sch40 steel pipe affair with having b-pressure welders doing the pipe runs or can you get away with Type K? I have put in CO2 systems for meat plants in the past that use Type K but the systems are not recalculating.
My big question at the end of it all is if CO2 is practical for Med temps or is glycol necessity?