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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.
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/a4000 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/a4000 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%
Cu
mu
lati
ve f
req
uen
cy
% 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
kW
15
kW
100 %(60 kW)
25 %(15 kW)D
rive
ou
tpu
t [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 min
Receiver volume plant 80 L
15 load / no-load changeovers per hour
4.000 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)
An
trie
bsl
eist
un
g [
kW]
Zeit [min]
ca. 1 min pro Entlastung
Leerlaufleistungsaufnahmenach Entlastung
Leerlaufleistungsaufnahme
bei Entlastung
45 k
W15
kW
100 %(60 kW)
25 %(15 kW)
Dri
ve o
up
ut
[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 compressor
Receiver volume plant 80 L
15 load – no-load changeovers per hour
4,000 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 hour
60,000 changes p.a. x 440 L compressed air loss
26,400 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
Pre
ss
ure
ba
nd
wid
th (
ba
rs):
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 bars
Switch-on pressure for standard compressor: 10 bars
Switch-off pressure for standard compressor: 11 bars
Pressure band = 1 bar
Operating hours p.a.: 4,000
Compressor consumption 60 kW
Power 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
ckb
an
d (
bar
)
Beispiel: erforderlicher Betriebsdruck 10.0 bar
VARIABLEVARIABLE
Einsparpotential10,6
10,8
10,4
10,2
10,0
9,8
11,2
11,0 Upper switching point
Lower switching point
Herkömmliche LastConventional load / no-load regulationConventional load / no-load regulation--
Pre
ssu
re b
an
dw
idth
(b
ar)
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
10,6
10,8
10,4
10,2
10,0
9,8
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 bars
Switch on pressure for standard compressor: 10 bars
Switch-off pressure for standard compressor: 11 bars
Operating hours p.a.: 4000
Compressor consumption 60 kW
Volumetric flow rate approx. 8.5 m³/min
Leak 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
VARIABLEVARIABLE
START-UP TIME [s]FU
LL
-LO
AD
PO
WE
R C
ON
SU
MP
TIO
N B
Y M
OT
OR
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]
Po
we
r [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
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
1000 1500 2000 2500 3000 3500 4000 4500 5000
Wir
ku
ng
sg
rad
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
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
1000 1500 2000 2500 3000 3500 4000 4500 5000
Eff
icie
nc
y
rpm 1/min
Speed range VARIABLE 90 5 – 13 bar
Typical efficiency characteristics of anasynchronous motor
00,20,4
0,60,8
1
0 25 50 75 100
Capacity utilisation [%]
Eff
icie
nc
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 technology
asynchronous 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 [%]
co
s p
hi
VARIABLE
General vector diagram Standard Standard motormotor:: SCD technology:
Apparent power
Rea
ctiv
e p
ow
er
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 p
ow
er
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 p
ow
er
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
Vo
lum
etri
c fl
ow
(m
³/m
in)
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 / BLCOAir 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
