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Energy saving using Mitsubishi Inverters for Fan and Pump Application

Automation Objective

The reasons and benefits of energy saving are numerous and pointless to repeat here. Simply, energy

is to be saved if it is just wasted because of inefficient process, methods of use or use of conventional

control mechanisms. When Induction Motor is run above the required speed, energy is wasted. If

speed is reduced to required operating condition, energy wastage is prevented.

The induction motor is used in industries mainly for following applications:

Centrifugal Fan (Blower)

Pump

Compressor

Plastic Injection Molding Machine

Mechanical Press

Figure 1 Total Cost of Running Motor

The total cost of running motor if considered (Figure 1), the more than 70 % is spend for energy bill

and rest is for investment and maintenance cost. The core objective is to reduce the running cost by

using Mitsubishi Inverters.

Basic Principle

The relationship between Power and speed of induction motor is the base of energy saving. This is

known as Cube Low. This is derived as below:

The 10% reduction in speed reduces 25 % power requirements which results in energy saving.

Centrifugal Fan Application

The centrifugal Fan is used as a blower and conventionally, flow is controlled by throttling device like

http://www.messung.com/images/distri_ener_sav_img_01_big.jpg

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inlet vanes or damper while motor is running at maximum speed. The energy is wasted at flow

regulating devices.

Figure 2 Conventional Method

Figure 2 Air Flow Control using VFD

Using VFD from Mitsubishi, the induction motor speed is regulated as per the input received from flow

sensor. Figure 3 shows the mechanism.

Pump Application

Similar to blower applications, conventionally, pumps are run at constant speed and flow is regulated

by control valve as per the demand. The excess flow is bypassed to the reservoir or tank (Figure 4).

The energy used to generate this excess flow is totally lost. The inverter controlled system removes

the control valve and flow itself is controlled by manipulating speed of pump as per the input of flow

sensor and desired set point (Figure 5). Here, no need to bypass or divert excess flow and hence there

is an energy saving.

Figure 3 Conventional Flow Control Figure 4 Flow Control using Inverter

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Inverter Selection

Centrifugal Fan and Pump are used for variable torque loads and need low starting torque. Hence VFD

with 110% overload capacity is adequate. Further, while selecting the drive, motor Full Load Ampere

(FLA) should be considered rather than motor KW.

Application Area

The major potential areas of energy saving using Mitsubishi drives are:

HVAC systems AHUs, Pumps and Chillers, Cooling Towers (Pharmaceutical and Bio-Tech

Installations, IT Parks, Hospitals, Theaters, Commercial Malls, etc)

Paint Shops in Automotive Industries

All utility management centers across the Industry

Cold storage installations

Boilers (ID,FD Fans)

Advantages of Mitsubishi Inverters

The Mitsubishi VFDs are perfect selection for energy saving applications since it offers following

features:

Electronic protection of motor

High Starting Torque

Soft Starting & Stopping reduces mechanical

stresses

Optimum excitation control

Energy saving mode

PID control

Energy/Cost saving monitoring

Electronic bypass for changeover

Built-in PLC in A700 series

Multiple overload rating according to

application

Diagnostic Capabilities in VFD

Interface With Main SCADA System

Supports all major Field Buses

- Profibus- DP,- DeviceNet,

- CC link,

- LonWorks

Modbus RTU as standard feature

Achievements

Over 4000 installations for energy saving for Fan and Pump applications are completed for Automotive

(Paint Shops of all major automotive manufacturers), Sugar, Pharmaceuticals and others.

Case study: Cooling Tower Pump

This is the case study of energy saving using Mitsubishi Drive for cooling tower pump for leading dairy

product manufacturer.

Inverter Model : FR-A540-11K

Power Rating : 11KW

Parameter Settings : LOAD PATTERN SELECTION Pr 14 = 1 (for Variable Torque Load)

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Following readings are taken for actual operation at full load for calculation of power demand

reduction:

Frequency

(Hz)

I/P POWER

(kW)

O/P CURRENT (A) % Speed

Reduction

%Power

Reduction

50 8.32 18.9 0 0

47.5 7.15 18.3 5 14

45

42.5

6

5.05

16.6

15.7

10

15

27

39

40 4.16 14.4 20 50

37.5 3.42 13.7 25 59

35 2.73 12.5 30 67

32.5 2.19 11.5 35 73

30 1.68 10 40 79

The actual load is operated with 40 HZ frequency and hence there is a 20% reduction in speed

resulting in 50% reduction in power demand.

Calculation of saving and payback period:

Per Hour power saving for 20 hour per day run = (Full Load Actual Load)x20 KWH

= (8.32 4.16)x20 KWH

= 83.2 KWH

Power saving per year for 300 days operation = 83.2 x 300

= 24960 KWH

Using per unit charges for energy bill, per year saving can be calculated.

The investment cost is recovered within 9 moths for this application.