Ultra Low Refrigants CO2 or Amonia?

[jcook1982]

Is it possible to design an ultra low system with Co2 or amonia? If not what kind of systems can be designed with these Natural Refrigerants?
:cool:

[nh3wizard]

What kind of temperatures are you looking for and whats the application? Cold storage, blast freezing...

[jcook1982]

we look for -80, and -150. even -30. cold storage mostly.

[nh3wizard]

we look for -80, and -150. even -30. cold storage mostly.

Why would you need those types of temps for a cold storage? I know for the top brand ice-creams -20 is required, but for everything else storage wise -5 to 0 degrees is good, and for those temps you want I dont know if co2 can get there, you will have to check the pressure / temp chart.

[US Iceman]

CO2 will get you down to about -65°F (or so). Ammonia can work reasonably well down to -50°F (or so) depending on how much money you want to spend on compressors due to the large volumes of gas that need to be pumped.

If you are looking for temperatures below this, you will need to look at hydrocarbons or other less environmentally friendly refrigerants.

[jcook1982]

Well i'm in the bio medical field. So we do alot of tissues sample storage, bone marrow storage and the such.

[jcook1982]

CO2 will get you down to about -65°F (or so). Ammonia can work reasonably well down to -50°F (or so) depending on how much money you want to spend on compressors due to the large volumes of gas that need to be pumped.

If you are looking for temperatures below this, you will need to look at hydrocarbons or other less environmentally friendly refrigerants.



Iceman,
Does CO2 require large compressors? How bad would it be to use CO2 in the first stage of a 2 stage Cascade system? Would it be somewhat effecient?

[US Iceman]

CO2 has a high vapor density, so the compressors will be relatively small compared to ammonia.

As far as efficiency goes, I have not looked at this. I doubt you could use CO2 in a two step cascade system unless you only have to go down to -60°F or so. If you have to run colder than that you will need a different refrigerant.

If you use CO2 as the middle step of a three step process, then you still need a good refrigerant on the highest temperature.

If you use CO2 as the high temperature step the pressures will be horrendous. That would be like using a cascade refrigerant on the high side of the system.

[jcook1982]

CO2 has a high vapor density, so the compressors will be relatively small compared to ammonia.

As far as efficiency goes, I have not looked at this. I doubt you could use CO2 in a two step cascade system unless you only have to go down to -60°F or so. If you have to run colder than that you will need a different refrigerant.

If you use CO2 as the middle step of a three step process, then you still need a good refrigerant on the highest temperature.

If you use CO2 as the high temperature step the pressures will be horrendous. That would be like using a cascade refrigerant on the high side of the system.


so you could not use CO2 in the 1st stage ( high Stage ). It has High operating pressures. It wouldn't be good to pull down from say room temp to -40 C. i think it would be best to use the 1st stage as the condenser for the second stage. So you get the heat exchanger condenser dwon to -35 with the CO2 1st stage and then use some other refrigerant in the second stage. Suva 95 is what i've worked with in the past.

[US Iceman]

It depends on the refrigerant used, the cost of the components, and the complexity of the system. You can make anything work, but is it worth the trouble?

[jcook1982]

I work in ultra low. Of course its worth the trouble. I love being a Bio Med Tech. I don't have to worry about the seasons. I have work all year around and I am very thankful for it.

So its all worth the trouble. I'm looking for a way to make it greener. They sayt they are green but lets make the products able to go back to nature with out harming nature.

[Plank!]

This should give you enough info on what can be done with CO2.
http://www.star-ref.co.uk/star/images/stories/pdf/Case%20Study%20No%2005%20-%20Nestle%20UK,%20Hayes%20new%20logo.pdf

Hope it helps

[yucatin]

What's the approximate size of the space you are trying to refrigerate?