VLT
®
6000 HVAC
162
MG.60.B1.02 - VLT is a registered Danfoss trade mark
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Efficiency
To reduce energy consumption it is very important to
optimize the efficiency of a system. The efficiency of
each single element in the system should be as high
as possible.
Efficiency of VLT 6000 HVAC (
η
VLT
)
The load on the frequency converter has little effect
on its efficiency. In general, the efficiency is the same
at the rated motor frequency f
M,N
, regardless of
whether the motor supplies 100% of the rated shaft
torque or only 75%, i.e. in case of part loads.
The efficiency declines a little when the switching
frequency is set to a value of above 4 kHz (parameter
407
Switching frequency
). The rate of efficiency will
also be slightly reduced if the mains voltage is 460 V,
or if the motor cable is longer than 30 m.
Efficiency of the motor (
η
MOTOR
)
The efficiency of a motor connected to the frequency
converter depends on the sine shape of the current.
In general, the efficiency is just as good as with mains
operation. The efficiency of the motor depends on the
type of motor.
In the range of 75-100% of the rated torque, the
efficiency of the motor is practically constant, both
when it is controlled by the frequency converter and
when it runs directly on mains.
In small motors, the influence from the U/f charac-
teristic on efficiency is marginal; however, in motors
from 11 kW and up, the advantages are significant.
In general, the switching frequency does not affect
the efficiency of small motors. Motors from 11 kW and
up have their efficiency improved (1-2%). This is
because the sine shape of the motor current is almost
perfect at high switching frequency.
Efficiency of the system (
η
SYSTEM
)
To calculate the system efficiency, the efficiency of VLT
6000 HVAC (
η
VLT
) is multiplied by the efficiency of the
motor (
η
MOTOR
):
η
SYSTEM
=
η
VLT
x
η
MOTOR
Based on the graph outlined above, it is possible to
calculate the system efficiency at different speeds.
