Compressors - screw or reciprocating?

[Josip]

Hi,

many times on RE forums we had discussion about.... here are, from the first hand some thoughts about....how to save some energy

There is no simple answer to the constantly recurring question of whether it is best to use screw compressors or reciprocating compressors. Both types are viable alternatives in virtually all applications, and both types are normally capable of doing the job.



• capacity required

Larger screw compressors use less energy, whereas reciprocating compressors are most energy-efficient at capacities less than approx. 1200 kW.


• operating conditions

Screw compressors and reciprocating compressors differ greatly in efficiency when not operating at or near their design conditions.
Screw compressors are significantly less energy-efficient under off-design conditions, especially if they have a fixed internal volume ratio. Screw compressors with variable volume ratio are therefore more efficient.


• part-load requirements

If a compressor is to run at part load much of the time, reciprocating compressors are significantly more efficient.


• energy consumption

In smaller plants operating at evaporating temperatures of
-10°C or higher, single stage reciprocating compressors will have lower power consumption than screw compressors. In larger plants, the opposite is the case.
In applications that operate at lower temperatures, a two-stage installation is the best choice. Power consumption for such a two-stage unit is about the same for both compressor types, depending on plant size.


• temperature levels

In air conditioning and other “high-temperature” applications, reciprocating compressors normally use 5–15% less energy than small screw compressors.
Screw compressors working at lower temperatures, and in larger-size installations, use less energy than the corresponding reciprocating compressors.


• refrigerant to be used

The refrigerant usually only directly influences decisions about compressor type when high-pressure refrigerants such as R410A and R744 (CO2) are to be used.
In such cases, reciprocating compressors have significantly lower energy consumption.


• ease of maintenance

Reciprocating compressors have many moving parts compared to screw compressors, which means that more maintenance is needed. However, this maintenance work is relatively simple and can always be done on site.
With screw compressors, on the other hand, replacements and main overhauls usually mean that the entire compressor has to be sent back to the factory.


• financial resources

In smaller plants where one or two reciprocating compressors can handle the requirements, these are normally the cheapest solution.
The opposite is normally the case in larger plants. One or two screw compressors are normally cheaper than six to eight reciprocating compressors.


• available space

Screw compressors are much more compact than reciprocating compressors, especially at larger capacities.
One single screw compressor with double the capacity can normally replace at least two ”recips”.

This is "copy&paste" text, but I believe worth to read, more about you can read here:

http://www.sabroe.com/information/sc...procating.html


Best regards, Josip

[Chunk]

Very good read Josip.

I`ve always liked screws compared to recips but i dont get involved with them as much as i`d like.

[TXiceman]

I do not have any problems with screws, recips or centrifugals as long as they are applied in the proper application.

A lot of people with limited experience will migrate to a compressor which they have some experience.

Take for instance the argument that a recip ins terrible and a screw is better....blanket statement.

I have applied a lot of recips successfully in projects and maintenance hsa not been a problem. The trick is to design the system properly and do not apply the compressors at the extremes of their operating envelopes. Watch the pressure ratios, such superheat and rotational speed.

One very capable compressor in ***** applications is the carrier 5H and 5F series. They are very reliable machines when selected and rated at 1200 RPM instead of the air conditioning rating of 1800 RPM. The 5H**6 series (long stroke) work as well if you keep the piston speed down to something much less than the 1000 plus feet/ minute range.

The big thing is to design the system for the proper fit, application and equipment.

ken

[US Iceman]

A lot of people with limited experience will migrate to a compressor which they have some experience.

Or, it sometimes depends on what the salesman has for sale also. I've seen this go both ways for either recip.'s or screws.

It's not the compressor so much as it is the application (or available space).

Th eCarrier open drive recip.'s are hard to beat for ***** applications. I'm looking at these now for a project. Did you know Carrier used to sell these for ammonia service a long time ago?

[NH3LVR]

Did you know Carrier used to sell these for ammonia service a long time ago?

I still know of a couple that are still running, just a few miles away. They look strange sitting next to a Vilter. Carrier still had parts for them a few years ago. I do not know what the parts situation is at the moment.

[nh3wizard]

We have a few Sullair ammonia compressors, they don't have any real capacity control, but they are great running screws.

Thanks for the info Josip

[TXiceman]

Yepper, I know about the Carrier NH3 recips and have also used them on propane service. I still have some of the old propane data around here.

Also have done several Vilter 440's on propane. If I remember correctly, they went to Israel.

Also done several screws on isobutane.

Ken

ken

[US Iceman]

I always liked the old Sullair screws. It's a shame they got out of the refrigeration business.

The only isobutane project I worked on was for very high temperature heat recovery using thermosyphons. After all of the research and engineering it seemed it was too risky by the owner and the project was shelved. Too bad really... I thought it was pretty slick.

[TXiceman]

Isobutane is tricky to work with due to the way the vapor dome slopes off tot he right. The compression lines do go back intot he dome and you have to have a lot of superheat in the suction to get you clear of the saturated vapor line at discharge conditions. Other wise it is a great refigerant.

Another problem is having long and uninsulated suciton runs in an industrial application. The vapor pressure is so low that it can condense in the suction line at failry warm ambients.

Ken

[US Iceman]

Another problem is having long and uninsulated suction runs in an industrial application. The vapor pressure is so low that it can condense in the suction line at fairly warm ambients.

Yep, it's close to the way R-114 acted also.

What you mentioned above is an interesting fact that most people are not aware of. I've seen this happen in suction lines in ammonia systems when they operate for long periods of low capacity.

During full load the suction pipes are a little colder due to the slightly lower suciton pressures. Then when the compresors unload the suction pressure rises justa bit and the gas starts to condense.

Refrigerants are funny things sometimes.

[Samarjit Sen]

Ken's post of 31.03.08 is perfect I wish there were people with similar thoughts in our country.

[abet_meneses]

hi,josif,
that was a balance statement on both type comp.many thanks for the info.

[TXiceman]

You will get a much more balanced approach from a company that has more than one type of compressor to sell. If all you have to sell is screws....guess what, they are the best compressor for every job ...especially if you want to continue to eat.

I enjoyed working foe many years with a company that could offer screws, recips and centrifugals for a while. It was actually fun to hear some of the "stories" the competitors came up with why you had to use certain type of compressor.

It also helps to have experienced and open minded engineers...but that seems to be something the industrial industry is loosing.

I am currently out of the refrigeration field after 37 years. My choosing due to location and $$$$. I can make a lot more at a large EPC firm.

Ken

[Kh1971]

Thanks for the info

[oilzee]

Hello Josip ,

thanks for sharing those information .

[chilldis]

I have both screws and recips at my facility. the screws have a lot less maintenance issues than the recips and they also load and unload in more precise increments to maintain a constant suction pressure as opposed to recips that load and unload one bank at a time. I personnaly prefer the lower noise levels of the screw compressors

[nh3wizard]

I have both screws and recips at my facility. the screws have a lot less maintenance issues than the recips and they also load and unload in more precise increments to maintain a constant suction pressure as opposed to recips that load and unload one bank at a time. I personnaly prefer the lower noise levels of the screw compressors

What kind of facility do you work in? Cold storage, manufacturing...

[chilldis]

NH3Wizard, I operate a cold storage facility for a major grocery supply chain in the northern US.

[Vinesy]

if its energy savings your after - yorks YCIV variable speed compressors are one of the best options available at present