Product Manual

Energy consumption
SQ, SQE, CU 331, and SP
20
141
20. Energy consumption
Energy consumption of
submersible pumps
The percentage distribution of service life costs of a
submersible pump for water supply is:
5 % initial costs (pump)
85 % operating costs / energy consumption
10 % maintenance costs.
It is obvious that the highest savings can be achieved
within energy consumption!
The annual energy consumption, E, of a submersible
pump can be calculated as follows:
Example: Calculation of the annual energy
consumption of the submersible pump, type 625S-3.
625S-3 with MMS 8000, 60 Hp, 3 x 460 V, 60 Hz.
Duty point:
By showing the P
2
/Q curve we make it easier for you to
calculate the energy consumption.
P
2
= 35 Hp (power requirement of 625S-3 pump at 88
GPM, from curve P
2
/Q.
Calculation of motor efficiency at duty point
As standard the SP 625S-3 is equipped with a 60 Hp
(45 kW for P1) MS 6000C motor.
At duty point (Q = 528 GPM) the pump requires 59 Hp
(44 kW for P1), thus:
a motor load of 87 % (44 kw / 45 kw) and a power
reserve of 2 %.
From the table on page 86 the motor efficiency can be
read as:
84.6 % at a load of 75 %. (η
75 %
)
85.6 % at a load of 100 %. (η
100 %
)
The interpolated value in this example is
η
motor
= 85.1 %, η
motor
= 0.851.
E = 0.15 USD/kWh x 3200 h x 51.7 kW.
The annual energy costs amount to USD 24816.
The pay-off time, A, (months) is calculated as follows:
Cable sizing
In order to obtain an economical duty of the pump the
voltage drop should be low.
Today large water works already size cables for a
maximum voltage drop of 1 %).
The hydraulic resistance in the discharge pipe should
be as low as possible.
E = c x h x P
1
(USD)
c = specific energy price (USD/kWh)
h = operating hours/year (hours)
P
1
= power input of the submersible pump (Hp).
Flow rate: Q = 528 GPM
Total head: H = 335 ft
Specific energy price: c = USD 0.15/kWh (consisting
of day and night rate)
Operating hours/year: h = 3200.
P
1
=
Q × H × ρ
in kW
367 × η
pump
× η
motor
Q=GPM
H=ft
Density ρ =lb/ft
3
(assumed 1)
367 = conversion factor
η
motor
= (example 84.5 %, in equation 0.845)
η
pump
= (not to be confused with the stage
efficiency curve).
P
1
=
P
2
η
motor
P
1
=
44
= 51.7 kW
0.851
A =
Purchase price of energy - efficiency pump
× 12
Energy savings / year