Greener Upgrades blog series #16

What are Variable Speed Drive (VSD) driven air compressors?

Introduction

Compressed air is a critical utility for a wide range of industrial sectors, from refineries and petrochemical plants to pharmaceutical sites and power stations. However compressed air can be very energy intensive, so it is important to invest in energy efficient technology.

What is a VSD driven compressor?

VSD is a variable speed drive. In a VSD driven compressor, the VSD adjusts the motor speed directly to match the production of compressed air according to demand. This makes them ideal for projects and processes with variable compressed air needs.

Variable motor speed

Compressors that are not driven by a VSD cannot adjust their motor speed, meaning they must run at their full rate, regardless of the compressed air requirement. Most compressed air applications have a variable air requirement, therefore running at a fixed speed wastes energy. However, by using a compressor with a VSD, the motor speed adapts according to the fluctuations, ensuring it only uses the energy necessary. This can lead to a decrease in utility costs, which makes up a vast proportion of the running costs of a compressor. If using a generator to power the compressor, using a VSD driven compressor reduces fuel use and costs.

Reduced start-up current

As the motor speed in a VSD driven compressor is flexible, the air compressor motor can ramp up incrementally. This means there are no high start-up currents to overcome, in contrast to a fixed speed compressor which needs a considerable increase of energy to start. As an example, our electric 1600 cfm compressor has a 355 kW motor, and therefore requires a 600A grid connection to function effectively. A comparable fixed speed compressor would need an 1000A power connection, to cover the initial start-up. The reduced power on start up not only leads to increased efficiency and reduced consumption, but also helps in situations where available utility is limited.

Versatility

The ability to adjust motor speed according to compressed air demand makes a VSD driven compressor the obvious choice for applications that have variable needs or that require the compressor to stand down and ramp up throughout the duration of the project. On the other hand, fixed speed compressors are suitable for applications with a fixed air demand. In many industries such as petrochemical and manufacturing variable demand is inevitable for processes such as fermentation, pressure testing and instrumentation air. To maximise efficiency in these processes, versatility is key.

Energy efficiency

All the above elements combined ensure that energy efficiency is maximised. Using a VSD driven compressor for a variable air demand application can reduce overall energy consumption. As compressed air is an expensive utility a decrease in energy consumption can significantly reduce expenditure. This is where the VSD driven can be incredibly advantageous. This creates a strong case for replacing ageing, inefficient systems for modern, efficient counterparts.

VSD vs non-VSD compressors

VSD Driven	Non-VSD Driven
Adjusts motor speed according to demand	Runs at a fixed speed
No large start up currents to overcome	Often involves large start up current
Great for applications with variable compressed air demand	Suited only to applications with consistent compressed air demand
Highly efficient, energy consumption minimised	Can be inefficient leading to greater energy consumption

Additional benefits of our electric compressors

100% oil free air: adheres to class 0 air purity requirements, ensuring processes, machinery and products remain free from oil and contaminants.
Aggreko Remote Motoring (ARM): compressors are fitted with ARM this enables proactive diagnostics and monitoring of key performance data. This enables energy consumption to be monitored, we can also ensure the system is correctly sized to maximise energy efficiency.
Low noise: our compressors are incredibly quiet at only 74 decibels (DBA) at 1m
Scalability: our units can be easily synchronised to build larger systems when increased pressure or greater compressed air capacity is required.
Quick commissioning and logistics: easily portable sound attenuated containers for easy transportation and simplified installation.
Reliability: screw compressors require minimal maintenance, ensuring minimal downtime.

In conclusion, Variable Speed Drive (VSD) compressors are a vital asset for providing compressed air in diverse industrial sectors. Speak to one of our experts today about how we could increase the efficiency of your compressed air processes.