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afak
10-04-2007, 06:33 PM
Hi to every one
How does the scroll compressor used in refrigeration field behave in comparison with hermetic and semi hermetic compressors:
1. suction line liquid return and over flooded cases.
2.low gas charge and other over heated cases.
3.In general are there specific advantages and disadvantages in comparison with the other compressors ? I will be glad if the answers depend on practical experience .Thank You

lana
10-04-2007, 07:41 PM
Hi to every one
How does the scroll compressor used in refrigeration field behave in comparison with hermetic and semi hermetic compressors:
1. suction line liquid return and over flooded cases.
2.low gas charge and other over heated cases.
3.In general are there specific advantages and disadvantages in comparison with the other compressors ? I will be glad if the answers depend on practical experience .Thank You

Hi afak,
I think you mean the comparison between scroll and piston compressors.
* Scrolls come as hermetic units.
* Because scrolls have relatively large body then they can stand more liquid refrigerant. This does not mean that flood back is not a problem for them, if large amount of liquid gets into the compressor and reaches the scrolls then there will be the same catastrophic problems as piston compressors.
* Other advantage of scrolls are that they consume less power (for the same capacity).
* Scrolls work very silently than piston compressors.
* In system using scroll compressor, there is no gas pulsation and therefore, less vibration (relatively).
* Some scrolls do not have internal check valves and therefore, there is no possibility of pump down.

These are thing which came to my mind right now. If I remember anything more I will let you know.

Hope this helps,:)
LANA

taz24
11-04-2007, 03:22 AM
1. suction line liquid return and over flooded cases.


.Thank You


Like all comps liquid back to the comp will cause problems because of the issues with the oil.
Scrolls though will take liquid through the scroll asembley. Liquid in its self is not a problem to a scroll because the nature of the workings inside just roll the liquid round.
It vapourises before it does harm.
I have seen a video of ball bearings being put into the scroll and being fired out at high speed with no damage tothe comp.
The scrolls are dsigned to move in the event of liquid.

Try not to let liquid back though. It will flush the oil.

taz.

afak
11-04-2007, 06:16 PM
3.In general are there specific advantages and disadvantages in comparison with the other compressors ? I will be glad if the answers depend on practical experience .Thank You

Thank You taz24,lana I hope you remeber some thing more .I need your notices about the point up.

taz24
12-04-2007, 01:10 AM
3.In general are there specific advantages and disadvantages in comparison with the other compressors ? I will be glad if the answers depend on practical experience .

Thank You



From my practical experience.

Advantages.

1 The comps are small and easy to move around / install.
2 They are reliable and do their job well.
3 They are getting more and more cost effective.

Disadvantages.

1 You can't work on them, when they fail they stay failed.
2 They don,t like running backwards so power input is critical. No swaping phases around.
3 they give off a high pitched whiney noise that after working with them for a few hours starts to hurt my head.

One big last disadvantage.

In my oppinion the will be used as an excuse to replace expensive qualified refrigeration engineers with not so expensive less qualified multi skilled technicians.
My reasons behind that last statment are simple.
Once commisioned and correctly running the use af a qualified refrigeration engineer to diagnose and repair faulty or poorly performing hermetic compressors will not be nessesary. A lesser qualified multiskilled person can just come along and replace the comp singlehanded.

taz.

afak
12-04-2007, 07:39 PM
One big last disadvantage.

In my opinion the will be used as an excuse to replace expensive qualified refrigeration engineers with not so expensive less qualified multi skilled technicians.
My reasons behind that last statement are simple.
Once commissioned and correctly running the use af a qualified refrigeration engineer to diagnose and repair faulty or poorly performing hermetic compressors will not be necessary. A lesser qualified multi skilled person can just come along and replace the comp singlehanded.

taz.

Thank You taz ,highly appreciated your reliable notices.Your opinion is so right . This big disadvantage comes from the commercial principle roles round the idea, in my opinion, of disposable products . This means that you can't change or repair partial things, instead you should change whole things: If a part fails you should dispose the whole other intact parts .That is commercially so great . Do not astonish if one day we should change not Only hermetic compressor, but this time disposable whole systems . Then we jump from the age of Installation and his qualified engineers to the age of Mounting and its every-thing-mounting engineers.

US Iceman
12-04-2007, 08:02 PM
Do not astonish if one day we should change not Only hermetic Compressor (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=60), but this time disposable whole systems . Then we jump from the age of Installation and his qualified engineers to the age of Mounting and its every-thing-mounting engineers.


That is a very good observation afak. Small HVAC systems are almost like this now and refrigeration systems are beginning to also...

If this trend continues the skilled engineer will be in big demand, since everyone will have forgotten how to work on equipment.;)

The MG Pony
14-04-2007, 09:05 AM
I hate modern throw away society :( Only good thing is I get allot of good equipment free, but the sad thing is I know so much good stuff is going to waste that is so easily repaired! I got a 5Ton A/C system free all becuase of a bad contacter! 3 second job to fix rather then figure it out they replaced it!

coolhibby1875
29-05-2007, 08:26 PM
hi i think scroll compressors were designed to be cheaper and easier to install/replace as the compressor manufactures were being nearly forced out off buisness due to remanufacturing off failed semis compressors however it would appear that these remanufacturers are now starting to rebuild scrolls which is not very good

ernestlin
30-05-2007, 06:24 AM
3 they give off a high pitched whiney noise that after working with them for a few hours starts to hurt my head.

taz.
Hi, taz, could you tell me the detail about the scroll's big whiney noise?? I have fixed a few srolls units, and found the noise of those scrolls is more smaller than semi-pistons, so I feel it's weird.

taz24
30-05-2007, 12:10 PM
Hi, taz, could you tell me the detail about the scroll's big whiney noise?? I have fixed a few srolls units, and found the noise of those scrolls is more smaller than semi-pistons, so I feel it's weird.

It's hard to put a definate answer to that question.

From my own personal experience when i've been working in a plant room with scrolls running, the noise seems to penertrate me and hurts my head.
Not bad or debilitateing but just enough for me to notice.
The noise levels are low enough for me not to require the use of ear defenders so this could be the problem.

Cheers taz.

JFK
09-10-2007, 08:09 PM
about the noise on scroll, i believe it's also depend on the evaporating temperature, taz, u remember what evap temp u working on? i know scroll's noise will be quite high when evap temp go lower, for a/c should be fine, please comment

taz24
10-10-2007, 12:06 AM
Hi, taz, could you tell me the detail about the scroll's big whiney noise?? I have fixed a few srolls units, and found the noise of those scrolls is more smaller than semi-pistons, so I feel it's weird.


The noise is somthing that is more felt than heard.
I have worked (for many years ) in plant rooms with three or four packs of upto eight compressors on them each.
The noise level is low enough to be able to talk but after a while in that environment they start to get inside my head its more to do with the noise levels higher than we can hear but are still present.
I have talked to other engineers who work on multi comp systems and they have described similar.
Its hard to explain


Cheers taz.

bersaga
19-10-2007, 08:04 PM
There any many scroll compressors today but the one has the highest population and with high reliability and success is the Copeland ones.

Copeland Scroll compressors have dual compliance i.e radial compliance and axial compliance.

The axial compliance allows the scroll sets to separate axially - allowing for bypass ( capacity control) and high discharge temperature protection ( for some models)

But its the radial compliance ( ability for scrolls to separate radially ) that allows for the liquid refrigerant and other debris to pass through - i.e. making the scroll compressor less susceptible to floodback or flooded start damage. The other factor that helps this is the fact that scroll compression is a continuous process as compared with piston compression. Suction gas ( or liquid) is continually compressed until it is discharged to to centrally located discharge port. And there are no valves to get damaged !

As for the noise, the pulsating noise and the heavy vibaration of the piston does not exist with the scroll BUT the scroll operates on a different sound spectrum - this can be annoying to some people. This is regardless if the scroll is used in HT,MT or LT application.

taz24
20-10-2007, 01:20 AM
about the noise on scroll, i believe it's also depend on the evaporating temperature, taz, u remember what evap temp u working on? i know scroll's noise will be quite high when evap temp go lower, for a/c should be fine, please comment


Hello JFK.

I'm refering to HT / LT packs.
In the same area.

Cheers taz.