Inverters And Refrigerants; Compressor Cycling - Carlyle 06T 033 Series Application Manual

2.5 Inverters and Refrigerants

The Carlyle screw compressor is compatible
with inverter drives. An inverter drive varies the
speed of a compressor to improve system load
matching.
VARIABLE SPEED LIMITS
For 06TR Low Temp Compressors
Model Nominal
No.
06TRC033
06TRD039
06TRD044
06TRE048
06TRE054
06TRF065
06TRG078
06TRH088
06TRK108
VARIABLE SPEED LIMITS
For 06TA A/C & Med. Temp Compressors
Model
No.
06TAD033
06TAE039
06TAF044
06TAF048
06TAG054
06TAG065
06TAH078
06TAK088
Carlyle recommends screw compressors be
selected to match the system load at 60 Hz.
Overspeeding is a good option during heavy
load conditions. Carlyle does not recommend
the screw compressor operate at maximum
frequency for prolonged periods of time.
Table 1
Min. Max.
HP Hz Hz
15 50 70
20 40 70
20 35 70
25 30 70
25 30 70
30 25 70
35 20 68
40 20 60
50 20 50
Table 2
Nom. Min. Max.
HP Hz Hz
20 50 70
25 40 70
30 35 70
30 30 70
35 30 70
35 25 70
40 20 68
50 20 60
Operation above 60 Hz requires adequate
motor cooling. Inverters have a tendency to
increase the required motor cooling load due to
irregular wave forms. When overspeeding,
there will be an increased power consumption
required to supply the additional capacity. This
will also increase the required motor cooling
load. It is important that the motor cooling
system be capable of handling the increased
cooling required for the motor. Oil return,
economizer return gas, and the motor cooling
valve all assist in cooling the motor. Carlyle
recommends applying the largest motor cool-
ing valve (Carlyle P/N EF28BZ007) with all
screw compressors applied using inverters.
Inverters are an effective tool for efficiently
matching system loads with screw
compressors. Motor size and motor cooling
capabilities must be considered when using
an inverter to increase speeds above 60 Hz.
Following these guidelines will result in
improved system design and performance.
An inverter is capable of changing the
compressor's speed very quickly from full
speed to minimum speed and vice versa.
Compressors should ramp-up to the minimum
speed within 15 seconds at start-up. After
compressor start, Carlyle recommends that the
rate of compressor speed change be limited to
600 RPM/Min for the 06T semi-hermetic. The
rate of compressor speed change for the
05T open drive models is required to be
no greater than 500 RPM/MIN.

2.6 Compressor Cycling

Although compressor cycling is an effective
means of capacity control, frequent starting
and stopping shortens the compressor life.
Carlyle screw compressors should not be
cycled for capacity control more than six
times an hour and should run for at least
5 minutes after each start.
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