Cold Storage Design

[permafrost888]

Thanks for your responses Magoo and Ranger1. Speaking of refrigerants, what do you think about CO2/NH3 cascade systems? Pros and cons? My limited knowledge which stems from researching on the web seems to point to CO2 as the refrigerant of the future. Some articles also claim that installation costs/equipment will be cheaper (for one, because of smaller pipe diameters?) than pure NH3 although operating costs are about the same. Is this true? Some people then claim that CO2 is only cost-efficient at really low temps like -40 degrees celsius. Any comments?

[mond13]

just to add a note.... due to the size of the plant and particular in food industry, i suggest neither NH3 nor CO2.
a far cheaper and cost efficient solution is to run a 2 circuit system (primary run R134a or R404a) secondary circuit run with brine..... i successfully run two large plants for Emirates and Qatar Airways now at low costs both equipment wise and energy wise

[Josip]

Hi mond13,

just to add a note.... due to the size of the plant and particular in food industry, i suggest neither NH3 nor CO2.
a far cheaper and cost efficient solution is to run a 2 circuit system (primary run R134a or R404a) secondary circuit run with brine..... i successfully run two large plants for Emirates and Qatar Airways now at low costs both equipment wise and energy wise

I do not agree with above .... bold&underline ...., however I respect your opinion, but numbers and reality are telling us another story ....

This is a theoretical comparison of refrigerants .....

This is a theoretical comparison and as all such, should be used with care. The largest drawback in the study is the use of fixed compressor efficiency, but the real efficiency involves too many para-meters to be of practical use. However, there are some observations:

R134a has a good COP, but the transport properties are bad, thus large pipes and large heat-exchangers.

R410A should be an excellent refrigerant but a number of HP manufacturers have not too good experience of it. The reason is probably not optimized components.

R404A and R507A are similar. Both benefit from condensate subcoolers/vapour superheaters and if use for larger compression ratios, should be equipped with economizers.
A condensate subcoolers/vapour superheater impairs the capacity for especially R717.

R717 is by far the best refrigerant. The draw back is the high discharge temperatures and toxicity.

R407C is a good general purpose refrigerant.

R1270 is still better but has the drawback of being flammable.

Design vapour velocities can be kept astonishingly equal, regardless of temperature and refrigerant.

complete book you can find here:
http://www.scribd.com/doc/47799083/Comparison-of-refrigerants

here is another good link:
http://cienbas.galeon.com/02one_component.htm

one more discussion about refrigerants here at RE forums from 2007:
http://www.refrigeration-engineer.co...hp/t-8880.html

In my opinion, whenever is possible, we should use natural refrigerants especially for industrial purpose .... if its not possible for some real reason then we can use artificial refrigerants ....

Best regards, Josip

[SKviewtech]

Hi, I think you have to made sure tha consulting engineer knows of industrial refrigeration in ammonia system? sorry to say that many consulting companys are more interested to build just cold rooms, building structture and etc..... refrigeration is just a small portion to them. just to quote you one example on Condensing Temperature selection, in your area many like to use 40 deg C condensing temperature for NH3 system, but I will use 36 deg C insteated. Yes, up front your pay a biger condenser, but in long run the lower head pressure help save you compressor motor amp and give you more capacity.. if you want second opinions can contact me my contact details are in my profile. BTW, I am in the same area as you, we are specialists in ammonia system design and consultation in the market for more than 30 over yrs. I started with ' STAL refrigeration AS 'perhaps if you have heard of it before....