Nh3 Versus R-22

[patilvasudeo]

dear sir,

I WANT TO KNOW THAT WHICH REFRIGERENT IS BETTER NH3 OR R-22, WHY?

[US Iceman]

Ammonia leaks are much easier to locate.:D

[Josip]

Hi, patilvasudeo :)


dear sir,

I WANT TO KNOW THAT WHICH REFRIGERENT IS BETTER NH3 OR R-22, WHY?

Definitely that one which you can smell - natural one;)

Best regards, Josip:)

[Grizzly]

dear sir,

I WANT TO KNOW THAT WHICH REFRIGERANT IS BETTER NH3 OR R-22, WHY?
Irrelevant in the UK. Now as it's illegal to install R22.
In answer to the question Ammonia.
It uses 1/3rd less power for the same output.
Also as it's a natural substance (ref Josip) it's also therefor cheap to produce and environmentally friendly.

The only drawback in this comparison, is the Installation costs.... welded steel joints and code 2000 pipework as opposed to Brazed copper.
Maybe the differential is not so great now given the price of Copper?

Grizzly.

[keepitcool]

Ammonia is definitely the way to go. It is very versatile. High, medium or low temp and that lovely aroma. I guess you could say it has it all.

[patilvasudeo]

Dear sir,

AS PER SAFETY NH3 IS OK, BUT AS PER THERMODYNAMICALLY WHICH ONE IS BETTER ?

[Josip]

Hi, patilvasudeo :)


Dear sir,

AS PER SAFETY NH3 IS OK, BUT AS PER THERMODYNAMICALLY WHICH ONE IS BETTER ?

...... as Grizzly wrote...



In answer to the question Ammonia.
It uses 1/3rd less power for the same output.
Also as it's a natural substance (ref Josip) it's also therefor cheap to produce and environmentally friendly.

Best regards, Josip :)

[mazbut]

is it correct that NH3 needs 1.25 times more power to achieve 1 TR of cooling? Does this mean R22 system requires more power than that ,,,, why?

[US Iceman]

AS PER SAFETY NH3 IS OK, BUT AS PER THERMODYNAMICALLY WHICH ONE IS BETTER ?


Ammonia is typically better. The latent heat of ammonia is about 5X better than R-22, so you have lower mass flow rates.

[icecube51]

if you want to compare, go to the T/P charts,
or look in coolpack by the compare section.

how big or small is the plant youre gone build??;)

, Ice

[GXMPLX]

Not an easy answer, this discussion has been going on for years and it really depends on what aspects you consider more.

In the ASHRAE Handbook 2005 page 19.8 you read in the "Comparative Refrigerant Performance per Kilowatt of Refrigeration" table: Compression ratio NH3=4.94 R22=4.02; Net refrigerating effect NH3=1103.14 R22=162.67; Liquid circulated g/s NH3=0.9 R22=6.13, Coefficient of performance NH3=4.76 R22=4.66. If you look only at this figures Thermodynamically NH3 has advantages, but in the moment you consider HEAT TRANSFER and SAFETY: NH3 is catalogued under Class B2 refrigerant whereas R22 is A1 this means it is not toxic nor imflamable but R22 has an ozone depletion potential of 1.1 while NH3=0. This also makes it a chemically less stable (therefore more enviromentally friendly) than R22. What really kicked off R22 is that it's HEAT TRANSFER coefficients are higher partly because the low flow rates of NH3 play against it if you consider this important. That's why you have lots of flooded evaporators used with NH3, to improve heat transfer rate.
Anyway not an easy question to answer and many people have (strongly) biased opinions as you can see.

[US Iceman]

The safety codes do not consider heat transfer as an important safety criteria (until you get into relief valve sizing discussions).



What really kicked off R22 is that it's HEAT TRANSFER coefficients are higher partly because the low flow rates of NH3 play against it if you consider this important.


Now that's a statement I would like to see explained? NH3 has better coefficients, not R-22.

And the reason for the higher mass flow rates is that it takes more mass circulated to equal the same cooling effect as NH3.



That's why you have lots of flooded evaporators used with NH3, to improve heat transfer rate.


Again, I take issue with this statement also. The reason flooded evaporators were used with ammonia is that you get more heat transfer out of the same surface area than you would if you used DX (or R-22).

What got R-22 kicked off was the global warming potential in my opinion.

[GXMPLX]

This time you are not going to wack me Iceman!
The problem with heat transfer coefficients is that the depend linearly on film coefficients but on the sqare of the refrigerant mass velocity and as mentioned before square(6.13/0.9)=46 times higher (due to different velocity not TOTAL heat transfer coef). Please remember this is based on equal kilowatt of refrigeration! Of course this improves a lot with flooded evaps. But the reason they were not so popular with R22 was oil mixing factor.

[US Iceman]

OK, then here we go...

http://cartoonbank.com/Assets/1/124456_s.gif
source:http://cartoonbank.com/Assets/1/124456_s.gif

:D

It sounds like you are comparing forced convection heat film coefficients versus pool boiling. Pool boiling (or nucleation) have less to do with velocity than what you might compare to laminar versus turbulent flow (or heat transfer).

Even at that, it's not so much what the film coefficient is, as what the impact of the overall U-value makes on the selection of the total heat transfer surface.


Oil miscibility and solubility are indeed big concerns with flooded R-22 evaporators. Can it be overcome? Sure! Can you build a R-22 flooded evaporator? Sure? One benefit of using R-22 though was the ability to use copper versus stainless steel or carbon steel tubes. The tube wall resistance is a killer compared to copper.

And sometimes the fouling factors applied for copper tubes is a lot less than than those traditionally used for carbon steel tubes in ammonia shell & tube exchangers. This is another contributing factor that could slant the view towards R-22 (for cost of the heat exchangers).

I think we can agree on those points without any further discussion. However, I still think we have an issue with defining what effect the film coefficient has on the overall selection, and the mode of heat transfer being compared.

If we are comparing DX R-22 or ammonia at low temperatures then your argument makes some sense because the low mass velocities of ammonia make DX evaporators a real pain to get them to work. But then, I don't think you can make general declaration that R-22 is better in all cases. This is the only I can think of where this applies.

Boy, I am having to remember a topic I have not used in a long time....:rolleyes:

[GXMPLX]

OK, then here we go...

It sounds like you are comparing forced convection heat film coefficients versus pool boiling. Pool boiling (or nucleation) have less to do with velocity than what you might compare to laminar versus turbulent flow (or heat transfer).

That is another problem ammonia mass flow is too low to get turbulent flow AND the surface area you need.




If we are comparing DX R-22 or ammonia at low temperatures then your argument makes some sense because the low mass velocities of ammonia make DX evaporators a real pain to get them to work. But then, I don't think you can make general declaration that R-22 is better in all cases. This is the only I can think of where this applies.

Boy, I am having to remember a topic I have not used in a long time....:rolleyes:

We seem to agree in everything but get to different conclusions. Yes R22 has better heat transfer coefficients in DX, but using it in low temp invalidates another advantage of R22 in that it has lower discharge temperatures than NH3. It also has the ability to mix with oil which made it more apt for automatization, not an issue now a days with NH3.

Your conclusion of me saying R22 is better is wrong I said the choice is difficult, both have different merits and hope this discussion has and end point.

And sorry did I say biassed. Hmmm I will have to think in a stronger word, ... no, better not too strong.

[Shaukat]

for power saver - NH3,
For man power saver - R-22,
- Shaukat