NVQ help - Two stage industrial plant drawing - Technique training

[c2-fm.co.uk]

Hi chaps,
Im new to the world of refirgerant, ive worked in ac and electrical fm field for 15 years so just about now the ropes, and have experience of danfoss & cdk controls.

Ive recently done a course with technique training and got given an nvq portfolio to complete at home...
ive worked my way through it, although im now completly stuck on the last question

"Please generate a drawing of a typical two stage industrial plant including all controls required, provide all pressure readings for the low + high stage compressors"

Has anybody any ideas where i can find any literature on the above subject?

Any help would be greatfully appreciated

thanks

[The Viking]

Loved child has many names...
Try googling "cascade refrigeration systems" or perhaps "ultra low temperature freezers"

Some results in no particular order:

http://www.refrigers.com/content/view/31649/28/

http://www.engr.sjsu.edu/ndejong/Mul...on Systems.pdf

http://www.coldsystemsllc.com/co2-refrigeration.html

http://www.waset.org/journals/ijame/v6/v6-1-5.pdf




.

[aj143]

hi guys, im stuck on the same thing, ive done the drawing but i still can't find out how to find pressure readings for the high and low compressor pressure readings including the reading for the inter-stage (intercooler). im really struggling to find it. any help would be grateful. thanks

[The Viking]

If you are asked to get pressure readings one assumes you got an operational cascade system at hand?


Or is it meant to be theoretical values?

[cool runings]

.

Don't think pressure think temperature.

Two stage refrigeration in my opinion is not the cascade system but a normal compound system.

What temp will the low stage, the intermediate stage, and the final discharge stage be?

Try searching compound refrigeration system.

Basically when you have a low temperature product (say -20deg c) you need to evaporate at about -30deg c.
If the discharge is an air cooled condenser it will be running about 15deg c above ambient temps.
If ambient temp is 20deg c then the condenser will be condensing at about 35deg c.

Then you need a comparitor and work out the saturation pressures for the refrigerant of your choice.

This is where you need the 2 stage or compound compressor system because most industrial compressors
will not pump from such a low suction pressure to the discharge pressure in one go. It will need to pump it
part way up in the first stage and then the rest of the way up in the second stage.

Some compressors have the two stages built into it and some systems need two seperate compressors to
do the same job.

So do a search for compound compressors and systems.

All the best

coolrunnings.

.

[aj143]

hi guys, VIKING - im not sure if its theoretical values or not and i don't have an operational system to hand, im just doing the same ? as c2-fm so not too sure.

COOL RUNNINGS - thanks for the advice and for yours aswell viking, ill try looking googling compound systems. just 1 more quickie, im trying to get into refrigeration/ air con work but ev time i send off cv's etc i get phone calls asking if i have experience or would i be able to do the job myself and obviously i can't as im not experienced so they say, well its not for you then, i live near mansfield, alfreton etc, do you have any advice how i can get into the trade. any advice would be grateful thanks. it getting quite annoying now cause ive spent money on i course on a trade im having trouble getting into, as you can imagine its getting quite annoying. lol. so any advice would help, cheers guys

[sterl]

http://www.scribd.com/doc/48883339/I...dbook-STOECKER

Don't know if you can access it easily, its an entire textbook...>See Chapter 3.

[The Viking]

AJ,
Sorry to say but as you found out, courses on their own doesn't count for much. Whatever trade you are looking at there will always be people with all the right tickets but without a clue what it is all about.
That's why people requiting are asking for experience rather than formal qualifications.

I don't know what your personal situation is like and if you are able to work for (close to) minimum wage but the best advice I can give you is to try and find an employer willing to take you on as an apprentice, or maybe an improver.
Unfortunately even this will be hard to find in the current financial climate.
But if you manage to find an employer and if you are able to put the hours in the rewards will come, not today and not tomorrow but in years to come you will be glad to have gone through with it.


Best of luck,

[aawood1]

iing

c2-fm.co.uk there is good information in the danfoss, GEA, JBT web sites, This drawing was allways used for two stage system training and still used to day. When I did my training with Halls it was in PSI and fahrenheit but that was back in the dark ages. But had a look at some training logs books of one of the new engineers who we used GEA and they still have the same drawing in their training pack.
Redards
Arthur

[krislton]

Hi,

I'm also in need of help on this question please. I have this image016.gif as a guide drawing which I think is applicable but just need help identifying valves marked "a" "b" and "c", I think they are pressure relief valves but don't really understand why they are placed where they are and also what the pressure is on the low side compressor and how they differ at the inter-cooler. Any help would be greatly appreciated

[frank]

hi guys, VIKING - im not sure if its theoretical values or not and i don't have an operational system to hand, im just doing the same ? as c2-fm so not too sure.

COOL RUNNINGS - thanks for the advice and for yours aswell viking, ill try looking googling compound systems. just 1 more quickie, im trying to get into refrigeration/ air con work but ev time i send off cv's etc i get phone calls asking if i have experience or would i be able to do the job myself and obviously i can't as im not experienced so they say, well its not for you then, i live near mansfield, alfreton etc, do you have any advice how i can get into the trade. any advice would be grateful thanks. it getting quite annoying now cause ive spent money on i course on a trade im having trouble getting into, as you can imagine its getting quite annoying. lol. so any advice would help, cheers guys

AJ

Send me your CV...no promises ...

My contact details are in my Profile

[krislton]

Please Help!

[Magoo]

Hi Krislton.
who created the sketch layout, lots of wrongs and missing bitz in sketch.
What is filling the intercooler, check vav between condenser and receiver not necessary. Check vav required between HS compressor and oil separator that is not on sketch, no oil separator or check vav after low stage compressor. No oil coolers indicated either water or thermosyphon Generally with NH3 the low side evap would have hand expansion vavs or electronic vavs, and liquid supply to low temp evap via an ammonia pump drawing off low side accumulator. If you prefer HP liquid supply to low side evaps, add sub cooling circuit through low side accumulator if recip comps as indicated or economizers if using screw comps., there are too many missing bitz to mention. Sorry start again. Vav "C " is a worry, dumping effective liquid into a compressor suction line. Vavs "A " and "B " not necessary, as drawn they are pilot driven pressure regulating vavs.
If I was a tutor and examiner, drg would be fail result. No understanding of two stage system concept

[chilled kiwi]

http://www.frascold.it/software.htm
THis software has the expected pressures, includeing intermediate pressures.

[El Padre]

I can reccommend Principles of Refrigeration by R. Dossat, all the above is coverered, would be the best place to start.

Cheers

[river1710]

hi there how did u get on with this question i have the same one and a bit stuck do u have any advice??

[speny]

I have also just finished this course I have not started the portfolio as yet but I have had a quick look and I think I will stuck on the two stage refrigeration system, also the sizing of air con system, would anyone be willing to help me, I dont want it done for me just shown as I need to learn it for myself, 90% of the coursework is to do with nothing we covered on course, just paid 3500 but luckily I have a job otherwise id be worried, I will appreciate any help at all thankyou