do we need a hermetic or semi hermetic comp.?

[duraid]

Hi all or society decided to install a small walk-in freezer with volume 6 cubic meters, the supplier asked us if we want to use a hermetic or semi hermetic compressor I know that the initial cost, efficiency, reliability, is higher in case of semi hermetic and the life cost is lower, is there any advice can you do to me to tell me other reason make us use a semi hermetic comp. in other word where or when we use the hermetic and semi hermetic comp.?
Thanks

[afeef]

hi duraid
there is advantage and disadvantage of each one,
the advantages of semi-hermatic compressor is:
1-easely repair of coil burning or mechanical faulty
2-can monitor the oil level by sight glass
3-change of compressor oil is easy

the advantage of hermatic compressor :
relatively lower cost than the semi-hermatic one

now it is up to you to decide the right one
with all the best
regards
afeef:D

[Toolman]

Go for the SEMI HERMETIC one it will last many years . Compared to the crappy " tin can hermetic " , but if you must use a tin can type get a French Branded Hermetique
http://www.tecumseh-europe.fr/index.php
they are a lot tougher and better made than other brands. It also depends on the Condenser that is next to the compressor as to how good it is , if thats too small and runs HOT , nothing will last very long !!!:eek:

[sihombing]

Normally semi hermetic type available from: 1.5 - 40 kW and hermetic type available < 20 kW. Its depend on your requirement.

[sihombing]

[quote=sihombing]Normally semi hermetic type available from: 1.5 - 40 kW and hermetic type available < 20 kW. Roughly estimation, 6 m3-freezer is big enough. So, take the semi hermetic one.:)

[guapo]

Hi Duraid,
Semi-hermetic is repairable, hermetic is disposable.

Guapo

[Toolman]

Get a Bitzer Semi-Hermetic Condensing unit or buy some cheap tin can rubbish and learn why cheap isnt always the answer .

[DeB]

Re: Do we need a hermetic or semi hermetic compressor.
As a general rule hermetics are a cheaper installation than semi hermetics. Semi hermetics tend to be more efficient especially at lower temperatures and are more servicable and reliable than hermetics and therefore are cheaper to run. If you are prepared to pay a little more for the instal, you will recoup this money down the track. A hermetic becomes a boat anchor when it fails whereas a semi can be repaired this makes it a little more "environmentally friendly" once it is installed

[DeB]

As a general rule hermetics are a cheaper installation than semi hermetics. Semi hermetics tend to be more efficient especially at lower temperatures and are more servicable and reliable than hermetics and therefore are cheaper to run. If you are prepared to pay a little more for the instal, you will recoup this money down the track. A hermetic becomes a boat anchor when it fails whereas a semi can be repaired this makes it a little more "environmentally friendly" once it is installed[/quote]

[D.D.KORANNE]

HI,

Go for bock semihermetic condensing units.Get in touch with me if you need my help in selecting the right model. But need condensing , evaporating temp , capacity & refrigerant . With semis you can have multiple parallel operating units etc.


D.D.KORANNE

[Dan]

Hermetic compressors are not so bad, especially in medium temperature applications. Their design was primarily for the highly competitive mass production of air conditioning equipment. But they found their way into medium temperature refrigeration applications with much success.

The compressor manufacturers began to make them more effiecient for the higher compression ratios, for example. And most recently, there are many available for lower temperature applications because of design tweaks to existing hermetic designs.

Surprisingly, the lifetime of a hermetic compressor is not all that much shorter than that of a semi-hermetic compressor. I will try to find my source for that information and post it if I do, but I seem to recall 10 years for a hermetic and 12 years for a semi-hermetic.

Hermetics are much quieter compressors, thus they have an advantage in self-contained display cases and refrigerators. This is because of their inner spring support mechanism, which also removes the chances of leakage from the external torquing of the semihermetic during starts and stops.

Semi hermetics are not often repaired anymore. A valve plate change is about all that is practical and very often too much damage is discovered when the head is pulled, only to find that you spent as much as a hermetic would cost only to have to purchase a new semi-hermetic. (I am talking about 3 hp or less, here.)

The efficiencies of hermetics is still generally below those of semi-hermetics, but I would not so easily dismiss the value of using hermetic compressors when they are applied within their accepted operating envelope.

[ernestlin]

Hermetic compressors are not so bad, especially in medium temperature applications. Their design was primarily for the highly competitive mass production of air conditioning equipment. But they found their way into medium temperature refrigeration applications with much success.

The compressor manufacturers began to make them more effiecient for the higher compression ratios, for example. And most recently, there are many available for lower temperature applications because of design tweaks to existing hermetic designs.

Surprisingly, the lifetime of a hermetic compressor is not all that much shorter than that of a semi-hermetic compressor. I will try to find my source for that information and post it if I do, but I seem to recall 10 years for a hermetic and 12 years for a semi-hermetic.

Hermetics are much quieter compressors, thus they have an advantage in self-contained display cases and refrigerators. This is because of their inner spring support mechanism, which also removes the chances of leakage from the external torquing of the semihermetic during starts and stops.

Semi hermetics are not often repaired anymore. A valve plate change is about all that is practical and very often too much damage is discovered when the head is pulled, only to find that you spent as much as a hermetic would cost only to have to purchase a new semi-hermetic. (I am talking about 3 hp or less, here.)

The efficiencies of hermetics is still generally below those of semi-hermetics, but I would not so easily dismiss the value of using hermetic compressors when they are applied within their accepted operating envelope.

This comment is reasonable.

[Dan]

This comment is reasonable.

Thank you, Ernistlin. I am both flattered and ashamed. I could not find a comparison on the comparitive longevity between hermetics and semihermics as I remembered reading about many years ago.

I did find something of some value which does not bolster my argument, but adds to our thinking. It is from a Copeland compressor Application engineering bulletin from a few years ago. 1981.


The design of the compressor to considerable
extent affects its cycle life expectancy.
Copelaweld air conditioning and heat pump
compressors are spring mounted, with relatively
soft mounts for good noise suppression. Spring
life of 200,000 cycles would normally be adequate
for a 10 year heat pump life. Commercial
applications undoubtedly would see more frequent
cycling, and 300,000 cycles would be a
typical design goal for spring life on commercial
welded compressors.
In Copelametic compressors the mounting is
external to the compressor, and cycle life would
be related to the motor. 500,000 to 1,000,000
cycles might be a typical average life span, with
longer life for smaller lower horsepower motors
and shorter life for larger horsepower equipment.

So, Springs can be a culprit.

[MURAT]

I have just joined the club, but I have seen this title, and very inerested in it.

I am building mid-large cold stores and blast freezers for fish.
I have 3 rooms of 1050mc each and I am planning to offer 6G.30.2 Bitzer single stage for each or 4H15.2 x 2 pcs with R404a. I always use semis for industrial applications and 2-stage or Screws of Bitzer for blast freezing -35 c.

Competition offers LTZ 100 x 3 for the above mentioned cold store. I would never think of using a hermetic for such applications. I have checked, the capacities match.
Do you have any argument for me, why I should go with the semi?:confused:
Is anyone aware of Profroid blast freezers, ı have seen a quote as 2 x 45HP Copeland coupled with single evapprator made by Profroid

I have seen that copeland does not have 45 HP 2stage do they?

Thank you in advance.

[Samarjit Sen]

The use of hermetic and semi hermetic compressors would depend on the application. A semi hermetic compressor is more efficient and can give a better performance. It all depends on what is the application and the temperature range.