SCR compressors – energy savings
How Much Does Electric Energy Cost?
It is a well-known fact that compressors for the production of compressed air in craftsmanship and especially in industry are among the machines with the highest electricity consumption. The current situation in the energy market, where we are seeing extreme price increases, should prompt every compressor user to consider whether it pays off right now to invest in improving the efficiency of compressed air production, acquire new and more economical compressors, and thus ensure not only cost savings but also the competitiveness of their company and the elimination of price increases for their products.
Before we look at how SCR compressors can help solve your energy bill concerns, it is essential to know how much 1 kWh of electricity costs and your annual energy consumption volume to derive the potential for achieving savings.
Price Trends for Electric Power
Until 2021, the total price of electricity, including transmission, typically hovered around €0.10/kWh in the industrial sector.
Currently, however, the electricity price is already at the level of €0.20 to €0.28/kWh, and further growth is expected in the near future.
Energy First
It always pays to think about the future, and this applies doubly if you are considering purchasing a new screw compressor. With a compressor that you will operate for 10 to 20 years, you will face various costs such as the purchase of the machine, its installation, regular maintenance, or emergency repairs. However, the main cost is the electricity required for its operation.
Based on our experience, energy costs account for more than 80% of all costs over a 10-year period. This is approximately 14 times more than the typical purchase price of the compressor. Therefore, it is definitely worth finding out how efficient the machine you intend to purchase is before buying.
Especially in times of extreme growth in electricity bills...
electric energy
compressor price
installation
maintenance
Energy-Saving Solutions on SCR Compressors
All SCR compressor ranges have been designed specifically with maximum energy efficiency in mind. You will find many innovative and modern features that help reduce electricity costs and compressed air production costs in industry and energy sectors. Key solutions that help reduce compressor operating costs include:
- infinitely variable speed control
- 2-stage compression
- lossless direct drive
- IE4 permanent magnet motor
- output pressure setting
- economical weekly schedule
- variable speed fan
- low-pressure versions
- oil-free compressors
Variable Speed Control
There are two basic ways to control compressor operation on the market:
- fixed speed compressors (FS)
- variable speed compressors using a frequency inverter (VSD)
For fixed-speed compressors, two pressure values are set – cut-in and cut-out. If the pressure drops below the cut-in value, the compressor switches on the main motor and starts producing compressed air.
Once it reaches the cut-out pressure value, the compressor switches off by first entering an idling state (unloading), where the motor and screw block rotate, but the suction valve is closed and the compressor produces no air. Only after a certain time, usually several tens of seconds to several minutes, does the machine shut down completely.
Two-Stage Compressors
Standard screw compressors use only one screw block for air compression. Compression to the required pressure thus occurs in only one step, a so-called stage. The advantage of single-stage compression is a low price, but from an energy point of view, this method is not economical.
During air compression, a large part of the supplied energy is converted into heat. The result of this phenomenon is reduced efficiency and the production of a significantly smaller amount of air compared to an ideal physical process in an isothermal state, where all supplied energy is used exclusively for gas compression and no heat is generated. For higher compression efficiency, two-stage compressors were developed, using 2 screw blocks connected to each other by a gear system.
IE4 Electric Motor with Permanent Magnets
According to the IEC EN 60034 standard, electric motors used in compressors must have at least IE3 efficiency for power inputs from 0.75 kW as of January 1, 2017; for speed-controlled motors, IE2 efficiency is sufficient.
However, modern compressors use electric motors with higher efficiency, and the most well-known solution is permanent magnet motors, whose efficiency exceeds IE4 requirements. The differences in efficiency and achieved energy savings between IE3 and IE2 standards and PM motors on SCR machines can be found in the following table; compared to IE2 versions, 2 - 5% of energy can usually be saved.
Lossless 1:1 Direct Drive
The transmission between the screw block and the electric motor in screw compressors is implemented in four ways:
- using V-belts
- elastic coupling
- gearbox
- direct connection, the properties of which depend significantly on whether it is used in conjunction with a standard electric motor or a bearingless permanent magnet motor.
Flexible Pressure Setting
Energy is consumed during air compression. The higher the pressure, the more energy the compressor needs to achieve it. Always keep in mind that:
Compressing air by an extra 1 bar means approximately 7% more energy spent!
A well-chosen compressor should therefore have an output pressure slightly above the required level to avoid wasting energy on excessive compression that will subsequently be released. Unfortunately, we often witness situations where a user operates a compressor with a supply pressure of, for example, 10 bar, and then the pressure is reduced to 6 bar at all machine inlet regulators. Judge the economics of such a solution for yourself...
Smart Compressor Shutdown
A major problem in manufacturing plants is the presence of compressed air leaks, which usually reach around 20%, but significantly higher values are also common. Leaks in the piping system are present all the time, even when production is not running, e.g., on weekends, at night, or during shift breaks. It is therefore extremely beneficial to temporarily turn off the compressors during these times so they don't produce air just to cover leaks in the piping.
On modern units used on SCR compressors, it is possible to set a weekly compressor operation schedule and set several time periods for each day from Monday to Sunday when the compressor is on and when it is off.
Model Example
Manufacturing plant with piping leaks at 20% of air consumption and 2-shift operation with a free weekend.
Idle time is 8 h × 5 working days + 48 h on the weekend = 88 hours, which accounts for 52% of the time.
By turning off the compressor outside of shifts, you ensure savings of:
0.52 × 0.2 = 10.4%
By turning off the compressor outside of shifts, you ensure savings of:
0.52 × 0.2 = 10.4%
| Day | Time from | Time to | Status |
| Mon - Fri | 0:00 | 5:59 | off |
| 6:00 | 21:59 | on | |
| 22:00 | 23:59 | off | |
| Sat - Sun | 0:00 | 23:59 | off |
Low-Pressure Applications 1.5-5 bar
In industry, there are many applications that require lower pressure than the standard 7 - 10 bar supplied by screw compressors. Such applications are most common in the glass, plastics, textile industries, or in cement plants, and typically require compressed air pressure between 1.5 and 5 bar.
In these so-called low-pressure applications, it is not sufficient to produce air using blowers, whose upper pressure limit ends at around 1.5 bar. Therefore, standard screw compressors are used, which have an output pressure level of around the mentioned 7 - 10 bar. Although variable speed compressors allow the supply pressure to be reduced down to 4 - 5 bar, they face 2 fundamental problems:
4 - 5 bar pressure range - standard compressors are not optimized for 4 - 5 bar pressure and energy efficiency is very poor in this range.
1.5 - 4 bar pressure range - compressors still have to produce at least 4 bar pressure, which is then reduced to the required pressure in the 1.5 - 4 bar range.
Oil-Free Compressors
Some critical applications in industry require a supply of oil-free compressed air. These mainly include the beverage industry, food processing, hospitals and pharmacy, supplies of industrial breathable air for blasting, or paint shops. Oil-free compressed air is defined by the ISO 8573-1 standard as Class 0, and its production can be ensured either by a standard compressor with an appropriate air treatment system or directly using an oil-free compressor.
The use of oil-free compressors is becoming more suitable even outside of these critical applications, primarily due to zero risk of air quality reduction through oil leakage, but also mainly due to significantly lower investment and technology maintenance costs.
Main Savings of Oil-Free Compressors:
- no need to install filters and activated carbon columns
- no need to install an oil-water separator
- no oil changes
- no oil and separator filter changes in the compressor
- no need for oil cooler cleaning
- no maintenance of thermostatic valve and check valve
- solid particle filter elements have longer maintenance intervals
- no need to change separator fillings
- no need for condensate quality tests
- no wastewater legislation compliance needed
- no pressure revisions of the oil tank in the compressor needed
Variable Speed Fan
Every compressor is equipped with a fan that ensures the removal of hot air present inside the compressor and provides cooling for the oil and air coolers.
The energy consumption of the fan is typically 2 to 5% of the compressor's total power input.
Thanks to regulation, the fan motor draws only the actually required amount of electricity. Compared to traditional solutions where the fan runs at full power without regulation, there is an extreme reduction in electricity consumption in the range of tens of percent, which means several percent of the total energy consumption of the compressor.
SCR AUDIT - Find Out How Much You Can Save!
If you need help achieving energy savings and are unsure about choosing the optimal solution, contact our company.
We have extensive experience in designing compressor stations and optimizing energy costs in existing compressor rooms, based on which we have developed a concept for assessing the current state in the form of an SCR AUDIT.
If you decide to use SCR AUDIT, we will visit your facility and perform as part of the audit:
- comprehensive assessment of the current state of compressors
- assessment of the air treatment system
- measurement of compressed air consumption
- detection and quantification of air leaks
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