A screw blower is a low-pressure air blower that uses a pair of screw rotors operating on the principle of internal compression — unlike Roots blowers, which use external compression. Because the gas is compressed inside the working chamber before being discharged, the screw blower reduces energy losses and consumes less power than a Roots blower at the same pressure range, particularly as operating pressure increases. In the market, the Aerzen Delta Hybrid combines the advantages of both principles in a single unit, targeting high-energy-consumption applications such as aeration of wastewater treatment basins.
- Screw blower = low-pressure air blower, internal compression → higher efficiency than Roots
- Delta Hybrid combines Roots principle (lower pressure) + screw principle (higher pressure) in one unit
- Pressure range designed for low-pressure applications up to ~1,500 mbar (1.5 bar)
- Energy savings of up to approximately 30% compared with standard Roots blowers (varies by model/conditions)
- Suited for wastewater aeration, where blower power consumption accounts for a large share of operating costs
How does a screw blower work?
Internal compression vs. external compression
The fundamental distinction between the two types of low-pressure air blower lies in how the gas is pressurised. A Roots blower (rotary lobe) uses two counter-rotating lobe rotors to push a fixed volume of gas from the inlet to the outlet; pressurisation occurs outside the working chamber when the gas meets the pipe pressure (external compression, isochoric). This approach is simple and durable, but energy losses increase as operating pressure rises.
A screw blower uses a pair of intermeshing screw rotors. As the rotors turn, the volume of the gas cavity decreases progressively along the axial direction — the gas is compressed directly inside the machine (internal compression) before being discharged. Because the gas pressure at the outlet is already close to the pipe pressure, losses from reverse expansion are reduced, resulting in higher overall efficiency. This is why a screw blower typically consumes less power than a Roots blower at the same operating point.
| Criterion | Roots blower (Delta Blower) | Screw blower (Delta Hybrid) |
|---|---|---|
| Compression principle | External compression (isochoric) | Internal compression |
| Energy efficiency | Good, simple, stable | Higher at elevated pressure ranges |
| Construction | 2 lobe rotors, fewer parts, easy maintenance | Screw rotors with optimised profile |
| Intended use | Stable load, lower capital investment | Continuous operation, energy saving priority |
Note: in the low-pressure range (≤1 bar) typical of air blowers, both types are applicable; high-pressure oil-free screw compressors (meeting compressed air cleanliness per ISO 8573-1) are a different equipment category, serving industrial compressed air — not aeration.
Delta Hybrid: a “hybrid” of Roots and screw technologies
One unit, two principles
According to Aerzen documentation, the Delta Hybrid combines two gas-handling processes within a single unit: the Roots principle for lower pressure ranges and the internal-compression screw principle for higher pressure ranges. The machine uses a 3+4 rotor profile specifically designed for low-pressure applications, targeting an operating range up to approximately 1,500 mbar (1.5 bar) — filling the gap between standard air blowers and high-pressure compressors.
Factors contributing to improved efficiency include: an optimised screw profile, optimised process and cooling airflow paths, a motor meeting the IE4 efficiency class per standard, and an auto-tensioning belt drive with efficiency above 98%. The outlet air is completely oil-free.
Energy savings: where do the figures come from?
Machine efficiency + demand-based control
Aerzen publishes energy savings of up to approximately 30% compared with standard Roots blowers in the belt-driven version, and up to approximately 37% in the direct-driven version. These are indicative figures from manufacturer documentation — actual savings depend on model, operating point, and conditions and should not be taken as fixed values for all cases.
In aeration applications, most of the energy is not determined by a single machine but by coordinating the blower station according to the dissolved oxygen (DO) demand of the basin. Energy savings therefore come from two layers: (1) the machine’s own efficiency, and (2) the control system. See the article on energy saving for air blower systems for guidance on rational blower station layout.
| Control layer | Role | Energy-saving impact |
|---|---|---|
| AERtronic | Controls each individual machine | Correct operating point, equipment protection |
| VFD | Adjusts speed to match load | Air supply matched to demand, avoids excess |
| AERsmart | Coordinates multiple machines to DO demand | Optimises the whole station — the primary saving |
In other words, a high-efficiency machine running at the wrong operating point still wastes energy; conversely, a blower station coordinated by AERsmart according to basin DO can achieve significant electricity reductions even without changing the individual machines.
When should you choose a screw blower?
Applications and equipment selection
A screw blower is well-suited when the system operates continuously, the blower power consumption is large, and reducing long-term electricity costs is a priority — most typically aeration of wastewater treatment basins, where blower power commonly accounts for a large share of a plant’s operating costs. Other applications include low-pressure pneumatic conveying, flotation, and drying/ventilation in the food processing, chemical, and cement industries.
Where the load is stable, run hours are short, or capital investment is the primary constraint, the Roots blower (Delta Blower) remains a practical choice thanks to its simple construction, durability, and ease of maintenance. For very high flow rates at stable pressure, the high-speed centrifugal turbo (Aerzen Turbo) is worth considering. A detailed comparison of all three types is available in the article comparing Roots, turbo, and screw blowers.
As a reference operating range: the Delta Hybrid serves flow rates from approximately 100 to 9,000 m³/h and pressures up to ~1.5 bar (indicative figures from manufacturer documentation, varies by model/conditions). Correct sizing requires the actual required flow rate, the system back-pressure of the basin and pipework, and the load range.
AERZEN · GERMANY Aerzen air blower solutions
Aerzen (Germany) offers a range of low-pressure air blowers comprising the Delta Blower (Roots), Delta Hybrid (screw), and Aerzen Turbo (high-speed centrifugal), along with oil-free screw compressors for high-pressure compressed air. TKT Pumps is the authorised distributor, providing technical consultation on equipment selection, AERsmart/AERtronic control systems, and genuine spare parts for aeration and industrial compressed air applications.
Frequently Asked Questions
How does a screw blower differ from a screw compressor?
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A screw blower is a low-pressure machine (≤1 bar, up to ~1.5 bar for the Delta Hybrid) with high flow rates, used for aeration and low-pressure gas conveying. A screw compressor is a high-pressure machine supplying industrial compressed air; the oil-free version from Aerzen meets compressed air cleanliness per ISO 8573-1. The two categories serve different purposes.
Why does a screw blower use less power than a Roots blower?
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Because a screw blower compresses the gas inside the working chamber (internal compression) before discharge, reducing losses compared with a Roots blower, which uses external compression. Aerzen publishes that the Delta Hybrid saves up to approximately 30% in power compared with a standard Roots blower, depending on model and operating conditions.
What is the pressure and flow rate range of the Delta Hybrid?
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According to Aerzen documentation, the Delta Hybrid targets operating pressures up to approximately 1,500 mbar (1.5 bar) and flow rates from approximately 100 to 9,000 m³/h. These are indicative figures; the actual range depends on the specific model and operating point.
What is the difference between AERsmart and AERtronic?
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AERtronic controls each individual machine. AERsmart coordinates multiple blowers within a station according to the dissolved oxygen (DO) demand of the aeration basin, optimising power consumption for the entire system — this is typically the primary source of savings in a wastewater treatment plant.
Should a VFD be used with an air blower?
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Yes, when the load varies over time or throughout the day. A VFD adjusts the machine speed to match air demand, avoiding excess air delivery and wasted power. A VFD can be combined with AERsmart to optimise both individual machines and the station as a whole.
When should you choose Roots, screw, or turbo?
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Roots (Delta Blower) suits stable loads and lower capital investment. Screw (Delta Hybrid) suits continuous operation with a long-term energy saving priority. Turbo (Aerzen Turbo) suits very high flow rates at stable pressure. Always compare required flow rate, system back-pressure, and load range before deciding.
Sources: Aerzen documentation (Delta Hybrid / Screw Blower) and air blower industry knowledge. Compiled by TKT.
