Screw or Reciprocating chiller. 1

[naifmbo]

Hi Every Engineer,
We are working in a replacements of 7 reciprocating air-cooled chiller with new chillers with the same cooling capacity,but we are concerning about screw chiller technology as some big company's represintative told us that this technology needs high experience, is that right?
Is there any web site talks about this kind of chillers in details?

any resonse will be appreciated,

 

[stevenw]

Screw chillers typically require a factory tech to work on the screw compressor. The other parts of the chiller are the same. With 7 chillers you could send your tech to the factory school and save some money.

 

[fredb]

Hello

go to

http://www.trane.com/worldwide/commercial/rlcprc003e4pdf.asp

 

Hey you need refrigeration tech for both screw or Recip. Sounds like the guy you spoke to wants to sell you recip chillers. Well don't buy them!!

Benefits of screw chillers over recips.

1. Fully modulating capacity controls via slide valve. i.e. load match exactly with your building load and avoid overcooling you get with stepped control. But check maufacturer first.

2. Compressor servicing virtually nil with screw. With recips you need to do top end overhaul every 15000 hrs operation (costly). Again check screw manufacturer as some need bearing inspections regularly.

3. Reliabilty - screw compressors typically have three moving parts, recips have 40 plus. My experience is that on a four compressor recip chiller you get a failure every year. Its unusual to get a screw fail.

Which manufacturers for screws:

Trane, Carrier and Mcquay. I've seen bad reports about Macquay reliabilty and remember reading a post in this forum some time ago on them. On balance nothing between Trane and Carrier, although Trane have been in screw market longer. The Carrier compressor is high speed (upto 14000rpm) gear driven and generally the chiller is smaller footprint. Trane is conventional two rotor (2800rpm)and focus on reliabilty.

I'd get the Trane and Carrier reps in and get them to give presentation.

 

[Natepj]

Regarding the different brands, I've noticed a lot of failures with the McQuay 'A' Vintage screw chillers, but on the current 'C' vintage I have yet to hear of one. Apparantly there is a new "condenser enhancement" feature which has taken care of the slugging problems. I've never personally worked on any one of the brands, but I hear Carrier is the simplest to work on should that be needed. I haven't heard much about the Train screws except that Trane has good brand name recognition and reliability, but I think most of that is based on their recip units. I am unsure if York even has any screw chillers on the market since I haven't heard of them first-hand. They probably do. Any way you go about it the screws do tend to be less of a maintenance problem and more efficient in relation to load requirements.

 

[lilliput1]

Require attenuator package with the screw chillers if noise will be a problem.

 

[VSSriram]

At the expense of sounding repititive.....

Advantage of screw over recip

1. Lesser moving parts.
2. Better part load power consumption (in most cases).
3. More reliable.
4. Generally, resistance to liquid slugging is better in screw compressors.
4. Not much to choose between Trane and Carrier, though Trane ventured into screw technology earlier. High speed of Carrier machines makes the machine smaller. I don't think that's an issue. York also has good units, not sure of McQuay though. Footprint of Carrier is generally smaller as compared to others.

 

[ClydeMule]

BTW, York has screw chillers. One of my little (12.5 ton) chillers is setting next to 2 160 ton dual compressor screw chillers.

Other than that, dunno jack about screws.

Between the F18's landing at MCAS Miramar overhead and those two chillers a cell phone is useless!

Clyde

 

[jimmyjam]

Hello Naifmbo,
The best thing to do,no matter what,is scrap the the recip.air cooled program.Rotary Screw cillers are so much more economical in operation and maintenance!I'm with a large chiller manufacturer as a mechanic,and I will simply state that recips are fragile compared to these rotaries.However,like anything else,the technology is getting fierce.But to meet the wide application criteria that so many buildings require now,you are not going to do it with a recip,so they changed the rules on us both.Rotary screw chillers have magnificent capacity control with a computer on board to protect them.Hang in there when the recips are changed out,like I did,you'll get used to them as
well.The best thing always is,pay a flat rate on a service contract,and let that be their problem.TRUST ME ON THIS!
Be aware of one thing,you can really damage these machines if you goof up on procedures.Let me know if I can help in any way...

 

[SolutionsProvider]

I do not know how your mechanical space is or if these are located in the same area, but if they are you may want to consider moving to a Centrifugal Chiller or Two, the kw/ton on a rotary are .75 on a centrifugal ASRAE 90.1 standard are .60. Lot's of energy savings can be achieved.

Agree, that rotary's are loud but, the dba is just a tad over a recip. Also failure rates are about 1%.