What is a VSD (variable speed drive) Air Compressor, and How Can It Save You Energy & Money?

For those new to the air compressor industry, it can be difficult to understand the different types of air compressors, and understand the differences between them.

In this article, we will focus primarily on understanding variable speed drive air compressors and why they are appropriate for modern manufacturers. However, we also draw comparisons to fixed speed drive compressors, too, for comparison and clarity.

What is a VSD Air Compressor?

Previously, only fixed speed air compressors existed. These were  often a rotary screw, single-speed version where the compressor operated at a set RPM. While the fixed speed compressor could perform the task, it used more energy and was costlier to operate.

The market leader in air compressors – Atlas Copco – has for many decades innovated it’s line of air compressors. Perhaps the most significant advancement is their variable speed drive (VSD) models that help manufacturers better control their operating expenses.

The result has been that VSD air compressors offer the latest features while significantly reducing energy costs.

What makes a Variable Speed Drive Air Compressor Different?

A VSD compressor uses an on-demand approach, compared to an always-running one, as is the case with fixed speed air compressor technologies.

Due to greater operational flexibility, managed compressed air demand allows a compressor to use far less power. Indeed, when it isn’t required to be used for a period, a VSD compressor can be stopped completely.

Whilst unloading can be necessary when stopping certain air compressor systems, this isn’t required with high-quality variable-speed systems.

A flexible approach to compressed air generation is possible due to the use of advanced components. These permit an inverter to limit the voltage sent to the VSD compressor. The motor speed is altered to run at the RPM necessary to produce the volume of compressed air at the required (BAR) pressure level. As a result, energy consumption is reduced through less wastage.

A sophisticated onboard controller allows an operator to manage the motor’s RPM, depending upon the air generation specifications. The advanced electronic controls let an operator respond quickly to fluctuating demand in volumes and pressure levels, to satisfy manufacturing requirements.

When a VSD Compressor Makes Sense

Every manufacturer has different requirements. For those that regularly require compressed air, there can be a significant cost to that need.

When demand needs to change day-to-day or even hour-to-hour, this presents a problem for fixed speed air compressor systems. You’re stuck either leaving them operating continually at full speed, or turning them off and then back on again as needed.

By contrast, a VSD compressor makes sense when a business operation has varying needs, for example, with multiple shifts supporting a 24/7 operation. These air compressors can be turned on without the need to idle up first. Each shift can configure the unit specific to their requirements for required volumes and pressure levels.

For example, an Atlas Copco VSD compressor unit is compact, runs below 70 decibels, and includes remote monitoring. OPC UA on production installations allows smart production equipment to communicate, where necessary too.

Air pressure sensitivity is a consideration in some plants too. Inlet valves managing airflow in fixed speed compressors contribute up to 30 PSIG plus or minus the required pressure level. VSD compressors, controlled by electronic systems rather than valves, manage pressure levels down to a 2 PSIG variance.

Heat recovery is strong with improved VSD systems. Also, energy consumption is reduced by up to 60 per cent compared to older models of compressors.

Furthermore, in a situation where an energy supplier levies penalties for high spikes in demand – like those caused by turning on a fixed speed air compressor – VSD compressors avoid this additional expense.

Does a Fixed Speed Drive Compressor Ever Make Sense?

For manufacturers that require a set pressure level and a steady volume of compressed air, with few interruptions, a fixed speed air compressor might be a reasonable compromise.

However, as all business leaders acknowledge, industry requirements can suddenly change dramatically. Being highly adaptable to altered demand levels essentially gives manufacturers a trump card up their sleeve. When only using fixed speed compressors, they’re unable to stay nimble or make rapid adjustments to accommodate different, smaller production requirements.

Internal factors may come into play too. A damp or unclean product environment favours fixed speed over variable speed drive compressors. VSD includes electronics that work best in drier conditions. Modern manufacturing facilities rarely have this concern, though.

Consistent energy flow is also a factor. VSD compressors require a smooth source of energy, rather than dirty energy that’s poorly regulated. Sensitive electronics are vulnerable to inferior power delivery. However, for most major cities and towns, this isn’t a major worry.

Atlas Copco’s GA 30+-90 compressors bring
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Choose Between Fixed Speed and Variable Speed Drive Air Compressors

Typically, busy production environments benefit from having more options, not fewer.

Fixed speed and variable speed drive air compressors aren’t always an either/or scenario. In some circumstances, manufacturers may prefer to keep and maintain existing fixed speed compressors while augmenting their compressed air capabilities by adding one or more VSD compressors too.

The mix ‘n’ match approach might be appropriate where demand remains constant for some production requirements, but a growing need to adapt on the fly is evident too.

While phasing out the fixed speed models over time would still make sense, some facilities may look to completely overhaul their compressors by replacing them all with variable speed technologies.

A professional air audit is worth considering if you’re unsure whether upgrading or choosing a VSD is worthwhile. An audit factors in expected usage patterns in a compressed air environment.

Variable Speed Compressors for Improved Energy Efficiency

VSD compressors are designed for varied use, usually at different BAR pressure levels and volumes. Energy usage is potentially cut by up to 60% compared to other alternatives.

Owners of VSD units benefit when switching from one configuration to another and powering down the compressor when it’s not needed. It avoids wasted energy and excess heat generation from continually running fixed speed systems.

Only in a scenario where a fixed speed system is continually operational at the same pressure level might it outperform a VSD compressor. Otherwise, the flexibility to turn on, encode, and get pressured air on-demand is hugely energy efficient. 

Given the concerns over the rising cost of energy today, businesses can lower their energy bill by switching to more energy-efficient compressed air equipment.

Contact Anglian Compressors today to help you choose your next VSD compressor. 

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