The advantages of speed control

According to the results of an EU survey each year in the European Union some 80 TWh (80 x 1012 Wh) of power is consumed in compressed air plants. This is equivalent to over 10% of the industrial power requirements of the EU.

Basis: Power costs: 0.06 €/kWh, depreciation costs:: 5 years, interest: 5%

Maintenance costs

Investment costs

Energy costs

2000 Bh/a 4000 Bh/a 7500 Bh/a

0

10

20

30

40

50

60

70

80

90

60-70%

72-77%

83-86%

28-38%

18-23%

10-13%

2-3% 3-3,5% 3,5-4%

2000 Bh/a 4000 Bh/a 7500 Bh/a

0

10

20

30

40

50

60

70

80

90

60-70%

72-77%

83-86%

28-38%

18-23%

10-13%

2-3% 3-3,5% 3,5-4%

Average overall costs of a compressed air station?

The most important reasons for this are:

The costs of energy for:

1. Expensive no-load times of compressors

2. Expensive pressure balance times of compressors

3. Compressed air lost during pressure balance processes

4. Very broad pressure bandwidths of compressors

5. Direct output losses during the production of compressed air (e.g. transmission losses owing to gears, V-belts)

6. Leaks in the compressed air network

Potential savings from using

speed-controlled speed-controlled compressors compressors

Important: A compressed air station should: have as many load operating hours as possible and, if possible, not a single no-load hour!

Why are the energy costs constitute such a high proportion?

Investigations show that the max. delivery quantity is only required during peak times and that on average most compressors only utilise 50 - 70% of their capacity

4,000 operating hours p.a.; average full capacity utilisation 50-70%

20% 40% 60% 80% 100%

Cum

ulat

ive

freq

uenc

y

% capacity utilisation

Capacity utilisation with conventional compressors

exact output adjustment

At 100% air requirement, conventional compressors and speed-controlled compressors work at full load.If the requirement drops, conventional compressors go into load-/no-load control. The drive motor performs switching cycles in which the pre-set coasting-down time has to be taken into account. The VARIABLE series varies its speed, hence reducing the delivery quantity exactly to match the requirements.

Coasting-down time

Compressed air requirement

Time

ConventionalLoad / no-load

regulation Coasting-down time

Speedcontrolby means ofSCD - technology

0 %

50 %

100 %

0 %

50 %

100 %

0 %

50 %

100 %

No-load times

Coasting-down time

No expensive no-load times occur (approx. 25% of full output)

No switching cycles occur, i.e. less mechanical strain on the components

Key data: Compressor drive output: 60 kW

Capacity utilisation 70 full output share

30% no-load time at approx. 25 - 30% full load consumption

Operating hours p.a. 4,000

Required operating pressure: 10 bars

Energy costs: 6 cents /kWh

Example calculation ofthe potential energy savings from using

an VARIABLE

Example calculation:

Average capacity utilisation (70%) 60 kW compressor

70% full load

30% no-load time at approx. 25 - 30% full load consumption

4,000 operating hours p.a.

4,000 operating hours p.a. x 30% no-load share x 25% of 60 kW x power costs (€/kWh)

1,200 operating hours x 15 kW x 6 (cents/kWh)

1,080 € saving p.a.1,080 € saving p.a.

1. Avoidance of no-load times

Uneven networks result in frequent load / no-load changeovers:

The compressor is relieved at each load / no-load changeover.

The average relieve time is approx. 1 minute

45 k

W15

kW

100 %(60 kW)

25 %(15 kW)D

rive

outp

ut [k

W]

Time [min]

approx. 1 min per pressure balance process

No-load consumptionafter pressure balance process

No-load consumption

during pressure balance

process

2. Reduced unloading frequency

Example calculation:

Energy loss due to pressure balance timesEnergy loss due to pressure balance times60 kW compressor / pressure balance time approx. 1 minReceiver volume plant 80 L 15 load / no-load changeovers per hour4.000 operating hours p.a.Energy costs 0.06 € p. kWh

4000 operating hours p.a. x 15 load / no-load changeovers p.h. 60,000 load/no-load changeovers p.a. x 1 min

1,350 € saving p.a. 1,350 € saving p.a. Energy loss due to pressure Energy loss due to pressure

balance timesbalance times

60,000 min pressure balance time = 1,000 h pressure balance x 45 / 2 kW

= 22,500 kWh x 6 cents

45 k

W15

kW

100 %(60 kW)

25 %(15 kW)

Ant

riebs

leis

tung

[kW

]

Zeit [min]

ca. 1 min pro Entlastung

Leerlaufleistungsaufnahmenach Entlastung

Leerlaufleistungsaufnahme

bei Entlastung

45 k

W15

kW

100 %(60 kW)

25 %(15 kW)

Driv

e ou

put [

kW]

Time [min]

approx 1 min pro pressurebalance process

No-load consumptionafter pressure balance process

No-load consumption

during pressure balance

process

2. Reduced unloading frequency

Example calculation:

Compressed air loss caused by Compressed air loss caused by unloading processes:unloading processes:60 kW compressorReceiver volume plant 80 L 15 load – no-load changeovers per hour4,000 operating hours p.a.Pressure balance from 10 bars (OVP) to 1 bar (OVP)

4,000 operating hours p.a. x 15 load / no-load changeovers per hour60,000 changes p.a. x 440 L compressed air loss26,400 m³ compressed air loss p.a. 26,400 m³ compressed air loss p.a.

P1 x V1 = p2 x V2

p1 x V1V2 =p2

11 bars (abs) x 80 LV2 =

2 bars (abs)

V2 = 440 L (loss of compressed air per pressure balance process)

Comment: It costs an average of 2 cents to produce 1 m³ compressed air

26,400 m³ x 2 cents = 528 € 528 € saving p.a.saving p.a.

3. Compressed air losses caused by unloading processes

The VARIABLE compressors run at a constant operating pressure ( p 0.1 bars),

Since high pressure = high energy enormous amounts of energy can be saved here.

1 bar higher pressure ( 6 – 8 % higher energy consumption)1 bar higher pressure ( 6 – 8 % higher energy consumption)

Upper switching point

Lower switching point

Conventional load / no-load regulationConventional load / no-load regulation

Pres

sure

ban

dwid

th (b

ars)

:

Example: Necessary operating pressure 10.0 bars

VARIABLEVARIABLE

Potential saving10.6

10.8

10.4

10.2

10.0

9.8

11.2

11.0

Constant network pressure

Example calculation:

Required operating pressure: 10 barsSwitch-on pressure for standard compressor: 10 barsSwitch-off pressure for standard compressor: 11 bars Pressure band = 1 barOperating hours p.a.: 4,000Compressor consumption 60 kWPower costs: 0.06 €/kWh

Pressure band optimisation: generated operating pressure: 10.1 bars pressure band = 0.1 0.1 barbar1 bar higher pressure 1 bar higher pressure 6 – 8 % higher energy consumption 6 – 8 % higher energy consumption

0.9 bars pressure band reduction 0.9 x 7% of 60 kW x 4,000 h x 6 cent/kWh

907 € saving p.a.907 € saving p.a.

4. Constant network pressure

oberer Schaltpunkt

unterer Schaltpunkt

Herkömmliche LastHerkömmliche Last-- LeerlaufregelungLeerlaufregelung

Dru

ckba

nd (b

ar)

Beispiel: erforderlicher Betriebsdruck 10.0 bar

VARIABLEVARIABLE

Einsparpotential10,6

10,8

10,410,2

10,09,8

11,2

11,0 Upper switching point

Lower switching point

Herkömmliche LastConventional load / no-load regulationConventional load / no-load regulation--

Pres

sure

ban

dwid

th (b

ar)

Example: Necessary operating pressure 10.0 – bars

VARIABLEVARIABLE

Potential saving10,6

10,8

10,410,2

10,09,8

11,2

11,0

10,6

10,8

10,410,2

10,09,8

11,2

11,0

The compressor block drive is effected directly by the drive motor via a

maintenance-free coupling without any transmission loss

Optimal power transmission and constant efficiency throughout the

entire service life

Up to 99.9% efficiency

Less noise emission than with V-belt or gear machines

Great operational reliability

Very easy to maintain and service

Compared to V-belt drives there is no additional maintenance

Savings: direct drive over V-belt drive:V-belt drive ( 96 – 97 %)Direct drive ( 99.9 %)

4,000 operating hours p.a., 60 kW motor

2.4 kW saving x 4,000 operating hours

9.600 kWh x 6 cents / kWh

576 € / 576 € / saving p.a.saving p.a.

5. Direct drive

Compressed air lines always have leaks

The amount of leakage depends, among other things, on the pressure in the pipelines.

If pressure is reduced by 1 bar for example by means of speed control, these leaks are reduced by approx. 10%!10%!

Studies have shown that the average leakage rate of a compressed air station is approx. 20 - 30%20 - 30%.

6. Leak reduction

Example calculation:

Basis:

Required operating pressure: 10 barsSwitch on pressure for standard compressor: 10 barsSwitch-off pressure for standard compressor: 11 bars Operating hours p.a.: 4000Compressor consumption 60 kWVolumetric flow rate approx. 8.5 m³/minLeak rate approx. 25%Power costs: 0.06 €/kWh

Pressure band optimisation:

generated operating pressure: 10.1 bars

0.9 bar pressure band reduction

1 bar pressure reduction = 10% leakage reduction

25% leakage of 8.5 m³/min 2,125 m³/min

2.125 m³/min leakage x 9%

0.19 m³/min leak reduction0.19 m³/min leak reduction

0.19 m³/min x 4,000 h

45,600 m³ / year x 2 cents/m³

912 € / 912 € / saving p.a.saving p.a.

6. Leak reduction

Avoidance / reduction of:1. No-load times: 1,080 €

2. Pressure balance times: 1,350 €

3. Pressure loss during pressure balance: 528 €

4. Pressure optimisation: 907 €

5. Direct drive: 576 €

6. Leak reduction 912 €

Total saving p.a. approx.: Total saving p.a. approx.: 5,353 €5,353 €by using a speed-controlled plant / VARIABLE!

(Compared to: Standards at 70% capacity utilisation, 4,000 operating hours )

Total saving: an overview

Advantage of VARIABLE: Many customers pay according to current peak values

enormous saving of power costs Relief for “weak” networks Enormous relief for the mech. components (“changeover shocks” do not occur) Start-up at 110% rated torque load

GENTLE STARTINGGENTLE STARTINGSTAR - DELTASTAR - DELTA

DIRECT STARTING

VARIABLEVARIABLESTART-UP TIME [s]FU

LL-L

OA

D P

OW

ER C

ON

SUM

PTIO

N B

Y M

OTO

R

Full-loadrated current

0

5

6

7

8

2

3

4

1

- Very energy-conserving start-up behaviour- Very energy-conserving start-up behaviour

Other advantages

Companies with medium voltage transformer station: transformer station must be designed for the high peak currents

By comparison Start-up current for of a 60 kW IEC motor 95 A x 2.7 ( 257 A + changeover peaks (approx. 4-fold) > 380 A> 380 A

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12 14 16 18 20

Time [s]

Pow

er [A

]

Pulse-type starting: 60 kW plant with star-deltastarting

Continuous starting: VARIABLE 60

Inrush load = 2.7 -fold rated current

UChangeover peak, star to delta = 4-fold rated current

Rated current 95 A, standard motor 60 kW

400

Other advantages

- Very energy-conserving start-up behaviour- Very energy-conserving start-up behaviour

Owing to the special type of winding and the top grade sheet packets (high quality dynamo sheet), compared to IEC standard motors the ALUP SCD motor (motor protection class IP 55) is far more efficient over the entire load range

Advantage of VARIABLE: Power cost saving owing to less power loss Less self-heating of the motor or smaller size Flat curve at a high level, especially compared to a < 100 % capacity utilisation

- Efficiency characteristics- Efficiency characteristics

Efficiency characteristics VARIABLE MotorVARIABLE Motor

Efficiency characteristics of a standard asynchronous motor

SCD drive motor

0,90,93 0,945 0,95 0,95 0,95 0,935 0,93 0,92

00,10,20,30,40,50,60,70,80,9

1

1000 1500 2000 2500 3000 3500 4000 4500 5000

Wirk

ungs

grad

Drehzahl 1/min

Drehzahlbereich VARIABLE 100 5 – 13 bar

0,90,93 0,945 0,95 0,95 0,95 0,935 0,93 0,92

00,10,20,30,40,50,60,70,80,9

1

1000 1500 2000 2500 3000 3500 4000 4500 5000

Effic

ienc

y

rpm 1/min

Speed range VARIABLE 90 5 – 13 bar

Typical efficiency characteristics of anasynchronous motor

00,20,40,60,8

1

0 25 50 75 100

Capacity utilisation [%]

Effic

ienc

y

SCD frequency converter

Advantage of SCD technology Power cost saving Relief to network Minor power factor correction

cos phi = constant

cos phi = 0.9 (load)0.5 (no-load)

Idle current: Idle current (smaller than cos phi) must either be paid for or compensated.

No-load cos asynchronous operation

cos phi conventional technologyasynchronous operation

0,0

0,2

0,4

0,6

0,8

1,0

0 10 20 30 40 50 60 70 80 90 100

Capacity utilisation [%]

cos

phi

VARIABLE

General vector diagram Standard Standard motormotor:: SCD technology:

Apparent power

Rea

ctiv

e po

wer

Active power

Below full work load becomes larger cos becomes smaller

cos = constant at any power consumption

General vector diagram Standard Standard motormotor:: SCD technology:

Apparent power

Rea

ctiv

e po

wer

Active power

Below full work load becomes larger cos becomes smaller

cos = constant at any power consumption

General vector diagram Standard Standard motormotor:: SCD technology:

Apparent power

Rea

ctiv

e po

wer

Active power

Below full work load becomes larger cos becomes smaller

cos = constant at any power consumption

Using the „energy savering duo“

VARIABLE + DIRECT

Hours per week

Volu

met

ric fl

ow (m

³/min

)

VARIABLE

0

2

4

6

8

10

12

14

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

DIRECT

VARIABLE

Interaction of several compressors

AIR CONTROL 3 AIR CONTROL 3 Base load controlBase load control

Master

Slave

SlaveSlaveSlave

Slaves

Connection – networking BLCO (up to 9 compressors)• all compressors are managed via a RS 485 bus systemRS 485 bus system

....

1. 2. 4. 8.

Data cable3-wire, 0.5 mm², shielded

Required signals: 1. Motor On / Off2. Load operation / Idling3. Fault message

ModuleDE 200 F

ModuleDE 200 F

ModuleDE 200 F

RS 485interface

Air Control 3MASTER

3.

RS 485interface

RS 485interface

Air Control 3 / BLCO

The advantages of speed control

1. constant pressure

2. exact output adjustment

3. avoidance of idling times

4. reduced unloading frequency

5. extremely energy-saving drive behavior

6. no peak loads

7. very good (high) motor efficiency

8. constant cos

9. direct drive

10. excellent p spezific

11. Air Control 3

12. flexible operating pressure 5 – 13 bar

13. reduction in leakage