ENERGY & COST SAVINGS ANALYSIS OF USING
VAN DER GRAAF DRUM MOTORS vs. CONVENTIONAL BELT DRIVES
SCOPE
This is a comparative analysis concerning the energy consumption of a conventional conveyor with an electric
motor, a gear reducer and a chain drive, and a conveyor driven by a Van der Graaf drum motor.
HYPOTHESIS
There will be considered that both conveyors, the conventional conveyor and the conveyor driven by Van der
Graaf Drum Motor:
a) have the same rated output power,
b) operate in the same environmental conditions (temperature, pressure, humidity, altitude),
c) supplied power have the same parameters (phase number, line voltage, frequency),
d) loaded at the same constant output power, equal by the rated output power, for the whole period of
the considered operation time.
CALCULATION
a) The conventional conveyor (index C from conventional) operates with a Baldor motor VM3615T, with rated
output power 5 hp, (or 3730 W, rated speed 1750 rpm, rated voltage 3 x 460 V, rated frequency 60 Hz),
a coupling, a right angle gear reducer with a gear ratio 20, and a chain drive with gear ratio 1.5.
The electric motor has the rated efficiency 85.5%, the coupling has the efficiency 99%, the gear reducer is
a right angle helical worm gear reducer with efficiency of 87% [6.5] and the chain drive has the efficiency
75%.
The total efficiency of the Conventional Conveyor is:
NC = 0.855 x 0.99 x 0.87 x 0.75 = 0.552, or 55.2%.
The input power (index 1 for input and 2 for output) of the conventional conveyor is:
P1c = P2c / NC = 3730/0.552 = 6757.25 W = 6.757 kW.
b) The conveyor (index M from drum motor) driven by a Van der Graaf Drum Motor is considered. It has the
same rated output power as the conventional conveyor, 5 hp or 3730 W and contains an electric motor with
rated efficiency 87% and a parallel-shaft gear reducer with efficiency 0.96%. (Diagram A:
Conveyor Driven by a Van der Graaf Drum Motor)
The total efficiency of the conveyor driven by Van der Graaf Drum Motor is:
NM = 0.87 x 0.96 = 0.835, or 83.5%.
The input power (1 for input and 2 for output) of the conveyor driven by Van der Graaf drum motor is:
P1M = P2M / NM = 3730/0.835 = 4467 W = 4.467 kW.
c) An operation time of both conveyors is determined taking into consideration that both conveyors work
8 hours shift, 2 shifts per day, 5 days per week, and 52 weeks per year,
t = 8 hours/shift x 2 shift/day x 5 days/week x 52 weeks/year = 4160 hours/year.
d) The electric energy consumed by the conventional conveyor, in the considered operation time, is
determined by the product of the input active power and the operation time:
EC = P1C x t = 6.757 kW x 4160 hours/year = 28109.12 kWh/yr l 28109 kWh/yr.
e) The electric energy consumed by the conveyor driven by Van der Graaf Drum Motor, in the considered
operation time, is similarly determined:
EM = P1M x t = 4.467 kW x 4160 hours/year = 18583 kWh/yr.
f) An average price of the electric energy in USA is considered:
p = 0.08 USD/kWh.
g) The cost of the electric energy per year of the conventional conveyor will be calculated as the product
between the consumed electric energy in the considered operation time and the specific price of the electric
energy:
CC = EC x p = 28109 kWh/yr x 0.08 USD/kWh = 2248.72 USD/yr l 2249 USD/yr.
h) The cost of the electric energy per year of the conveyor driven by Van der Graaf drum motor will be
similarly calculated:
CM = EM x p = 18583 kWh/yr x 0.08 USD/kWh = 1486.64 USD/yr l 1487 USD/yr.
i) The energy saving per year of the higher efficient conveyor, respectively of the conveyor driven by Van der
Graaf drum motor, is determined as a difference between the consumed energy of the conventional conveyor
and the consumed energy of the conveyor driven by Van der Graaf drum motor, in the considered
operation time of one year period (Graph 1: Energy Consumption Comparison):
ES = EC - EM = 28109 kWh/yr - 18583 kWh/yr = 9562 kWh/yr.
j) The cost saving per year of the higher efficient conveyor, respectively of the conveyor with Van der Graaf
drum motor, is determined as a difference between the cost of the consumed energy of the conventional
conveyor and the cost of the consumed energy of the conveyor driven by Van der Graaf drum motor, in the
considered operation time of one year period (Refer to page 21, Graph 2: Energy Cost Comparison):
CS = CC -CM = 2249 USD/yr - 1487 USD/yr = 762 USD/yr.
ENERGY COST SAVING WITH CONVEYOR DRIVEN BY VAN DER GRAAF DRUM MOTOR IS 762 USD/YEAR
NOTE: If the cost of energy of the conventional conveyor is considered 100%, than the cost of
energy of the conveyor driven by Van der Graaf Drum Motor is 66% and the cost savings with
the Van der Graaf Drum Motor is 34%.
ENERGY SAVINGS ANALYSIS OF A CONVEYOR DRIVEN BY A VAN DER GRAAF
DRUM MOTOR vs. A CONVENTIONAL DRIVE
Diagram A: Conveyor Driven by a Van der Graaf Drum Motor
Diagram B: Conveyor Driven by a Conventional Conveyor Drive
Graph 1: Energy Consumption Comparison
Graph 2: Energy Cost Comparison
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