There's so much information about air compressors out there. Trying to wrap your mind around all the types of rotary screw air compressors can be confusing. Even more so, if you have to decide between them to figure out which on is best for your application. This handy article will walk you through the types of screw compressors and explain their main benefits.
Air quality: oil-free vs oil-injected screw compressors
Atlas Copco has an extensive range of products and can feasibly meet any compressed air requirement out there. So why don’t we start with air quality. The main categories here are Oil-Flooded / Oil-Injected technology and Oil-Free compressor technology. Most air compressors on the market rely on oil in the compression chamber for lubrication, sealing and cooling. Of course, this means that some of the oil will get mixed into the air. Microscopic droplets of oil will carry through the machine and end up in the air network. Eventually, they also make their way into the process or product.
In terms of cost, oil-free compressors are more expensive in the first place. However, their running costs are usually lower in terms of consumables such as replacement filter elements. And of course, there is no risk of product spoilage. Atlas Copco is a pioneer in Oil-Free compressor technology. We were also the first of the major compressor manufacturers to meet the Class 0 ISO 8573.1 standard. This guarantees Oil-Free air in compressed air applications.
The most popular products of these type with Atlas Copco customers are the GA oil-flooded rotary screw compressor and the ZR oilless rotary screw compressor.
Fixed speed vs. variable speed driven screw compressors
We’ve heard about it, but why does Variable Speed Drive (VSD) technology save energy when compared to fixed speed? To put it simply, the clue is in the name! Fixed speed compressors run at one fixed speed. They are very efficient when operating fully on load 100% of the time. These compressors are at their best when the motor is running and compressed air is being produced.
The drawback comes when the unit unloads and stops making air. Although eventually the compressor will stop, it spends some time idling. Essentially, it is turning the motor and using energy whilst not actually producing anything, and therefore wasting energy. Because of these features, fixed speed compressors are typically used as base load compressors. That means they are designated to supply the minimum constant air demand of a factory. The remaining demand is then supplied by what we call a VSD.
A VSD or, to be precise, the variable speed drive unit, turns the motor relative to the amount of air required. If the demand increases then the motor speeds up, if the demand decreases the motor slows down. This way, the motor only uses the energy required to produce the air required – therefore no energy is wasted. In fact, a VSD can reduce energy consumption by up to 35% or even 50%, depending on the VSD technology. It is always worthwhile getting an air usage audit to see if you could benefit by using a VSD compressor.
Check out the more detailed comparison of fixed speed vs. variable speed compressed air technology. At the end of the day, there is a need in the market place for a mix of both technologies. It entirely depends on the air requirement for the given application.
Cooling methods: air cooled vs. water cooled screw compressors
Air compressors typically come in two cooling variants: air-cooled and water-cooled. The water-cooled variant, however, is generally reserved for compressors of a larger size. Think 110kW compressors and above. Site conditions and application will always be the major deciding factors for cooling system choice. What works in one factory does not always work in another.
