Energy Savings with
Variable Speed Drives
Rising energy prices create a need for energy-efficient motor
control solutions.
To help reduce energy waste and spiralling electricity bills,
engineers are turning to variable speed drives as an alternative
to fixed speed controllers and throttling devices such as dampers
in the case of fan systems and valves in the case of pumping.
Things to consider when considering fitting a variable speed
drive to save energy are:
■ Has an energy survey been carried out to identify potential
savings?
■ Is the variable speed drive the correct type for the
application?
Advancements in drive technology, careful selection of the
hardware and power system configuration along with intelligent
motor control strategies produce improved starting and running
performance, speed control so that supply can match demand
and in case of fans and pumps potentially large energy savings.
Traditionally slowing down the rate of flow from a fan or pump has
been achieved by partially closing a damper or valve on either side
of it. However this does not slow down the fan or pump and high
losses and energy wastage occur as a result.
Centrifugal loads such as fans and pumps offer the greatest
potential for energy savings by using drives to control speed.
Energy consumption in a centrifugal fan or pump application
follows the affinity laws, which means that flow is proportional
to speed, pressure is proportional to the square of speed, and
power is proportional to the cube of speed. This means if an
application only needs 80 percent flow, the fan or pump will
run at 80 percent of rated speed and only requires 50 percent
of rated power. In other words, reducing speed by 20 percent
requires only 50 percent of the power.
Energy Savings with
■ Is the variable speed drive listed on the UK governments’
Technology List?
■ Will the equipment be installed and set up by a competent
installer?
■ Will the installer give full support for the newly
installed equipment?
Here at Parker Energy, we have many years experience in energy
saving and can offer a complete package from initial free-ofcharge site survey through to quotation, supply and installation
of the equipment.
As soon as the equipment is installed your fans and/or pumps
will be running super efficiently with a low carbon footprint and
much reduced electricity bills.
Variable Speed Drives
Energy Savings with
Variable Speed Drives - Pumps
3-Phase Hot Or Cold Water Pump
then fitted into the pipe work to reduce the flow to the required
level. The valve can be on the inlet (suction) side or on the outlet
side of the pump and is normally closed by some percentage to
control the flow rate.
Typically installed in many applications operating a continuous
process and used for cooling/heating or supply purposes. When
a pump motor is connected directly to the mains power supply
it can only run at one speed, maximum. Traditionally a valve is
Example (Before)
WAT E R O U T
Pump Motor: 15Kw
Duty: 24 Hrs, 7 Days, 51 Weeks
Control: On / Off
Flow Control: Valve Position: 20% Closed
M A N UA L
MOTOR
S TA R T E R
ON / OFF
VA LV E
Average Cost Of Electricity: 10P/Kwhr
PUMP
Annual cost of operating
= KW x DUTY x COST P.U.
MOTOR
WAT E R I N
= 15 x (24 x 7 x 51) x 0.1
=
£12,852 per year
Example (After)
M A N UA L
MOTOR
S TA R T E R
ON / OFF
VA LV E
1. Install Variable Speed Drive (VSD) between
manual motor starter and motor.
WAT E R O U T
VSD
2. Reduce output frequency until flow from pump is required level of 80%
(same as previous level when valve was installed and partly closed).
PUMP
3. Valve can be removed
(unless required for maintenance).
WAT E R I N
MOTOR
The Laws of
Affinity
1
Flow
Speed
2
Pressure
3
Power
Speed²
Speed³
Cold Water Pump Example
Using Affinity Law 3, Power
Speed³
Reduce motor speed (VSD output frequency Hz) to 80% ie from 50Hz to 40Hz
The same as 80% x 80% x 80% or 0.8 x 0.8 x 0.8 . . . = approx 50%
So the new operating power for the pump will be 15KW x 0.5 = 7.5KW
SO... The new annual cost of operating this cold water pump
= NEW KW x DUTY x COST P.U.
= 7.5 x (24 x 7 x 51) x 0.1 =
a
£6,426 per year
50%energy saving!!
Payback
For simplicity let’s keep the numbers easy . . .
Cost of VSD = say £1000
Cost of Installation = say £500
Total Investment = £1500
Payback time is Investment ÷ Savings made
= £1500 / £6426 = 0.23 Year ie PAYBACK TIME IS LESS THAN 3 MONTHS!
After less than 3 months the VSD will have paid for itself and the energy savings will result in much lower electricity bills.
Simple!
And it works just as well
with fans!
Energy saving Variable Speed Drives for 3-phase motors
■
Single phase input 0.4kW – 2.2KW
■
Three phase input 0.4KW – 375KW
Energy Measurement
Surveys
Solutions...
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01283 542 661
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