8.8 Performance Factors
The design of a screw compressor lends itself
to variable speed technology. The table below
lists the minimum and maximum speed limits
for each model compressor. These speed limits
apply to electric motors or any other source
used to drive the compressor.
Motor Speed
Input Shaft
Min.
Max.
05T
60Hz (50Hz)
Speed Speed
Model
#CFM
(RPM)
(RPM)
(RPM)
33
1750 (1450)
05TRQ033
1450
4000
65
3500 (2900)
39
1750 (1450)
05TRQ039
1167
4000
78
3500 (2900)
44
1750 (1450)
05TRQ044
1020
3600
88
3500 (2900)
05TRQ048
48
1750 (1450)
875
3300
05TRQ054
54
1750 (1450)
875
2930
When using an inverter or other variable speed
device, it is important to remember that over-
speeding above the rated condition will result
in an increased brake horsepower requirement.
The brake horsepower will be comparable to
1.05% above the rated brake horsepower
multiplied by the ratio of the design speed to
the rated speed.
The 05T performance data has several items
which should be considered when selecting
the proper compressor and motor size.
1. The 33-54 cfm model’s performance data is
based on 1750 rpm @ 60 Hz
2. The 65-88 cfm model’s performance data is
based on 3500 rpm @ 60 Hz
3. 65°F (18°C) return gas temperature is used
for all conditions and all the superheat is
considered useful
4. The economized data is subcooled to the
saturated interstage temperature plus
10°F (5.6°C)
The evaporator refrigeration effect will be less than
the published compressor capacity if nonuseful
superheat is generated in the return gas lines to the
compressor.
The oil cooling requirement will be very similar to the
oil cooling requirement for the 06T compressor. Use
the calculation from the Carlyle electronic compressor
selection program to determine the oil cooling
requirement.
=
(
1.05
)(
DESIGN SPEED
)
RATED SPEED
DESIGN
BHp
37