low temp screw compressors

[airchung]

What is the best way to check low temp screw compressors if you suspect they are becoming innefficient? I have a blast freezer with 2 x 90HP economised screw compressors on R507 that are no longer able to pull down the load. All other items such as Elec TX valves etc have been checked.

 

[zdas04]

"Low Temp Screw Compressor" is definitely an oxymoron. It looks like you are really talking about a "Flooded Screw in Refrigeration Service".

I'd check suction and discharge pressure and temperature on the screw skid. If those numbers are pretty close to design then the problem is probably in the blast freezers. If the suction/discharge pressure/temperature numbers have a problem then let us know the readings and the expected values and someone here can give you an indication of the problem or where to look to find the data needed for trouble shooting.

David

 

[airchung]

They are dx coils

 

[sterl]

How the machines lubricated and cooled? Are they slide valve machines or does their capacity reduction take another form? Do they have external lubricant cooling or?? Are they hermetics, semi hermetics or open drives? If they are hermetics or semi hermetics, measuring their real performance can involve a lot of instrumentation...If they are open drives, its a lot less instrumentation; and if they are water cooled on both the condensing and the oil cooling: the instrumentation and test get easier....But fundamentally, you make a COP and isentropic efficiency measurement with respect to the Manufacturer's original data which will lead to how badly are they worn?

Screw compressors can tolerate some pretty substantial deviation from the ideal: But to get them highly efficient you want to operate them at 100% load with just enough oil injection to keep them cool and to preclude internal bypassing....Of course, if they are taking liquid refrigerant from time to time, their oil separation, interlobe sealing and so on will suffer a lot.

 

[TXiceman]

How long have the machines been operating?

What type oil is being used and is it suitable for low temp applications?

Have you aded any oil to the compressors?

Ken


Ken
KE5DFR