How does air compression work? An overview
Industrial air compression is an energy-intensive process. Up to 80% of the cost of operating a compressor is its electricity expenses. Therefore, it's important to consider efficiency and total cost of ownership when researching various models. With this, you might be wondering "how does air compression work?" and why does it require so much energy?
In this guide, we'll go over how compressed air is made and various ways to reduce and offset operational expenses. If you find you require more information at any time, feel free to reach out to our team. We're happy to provide information about our compressor models.
Compressed air basics
Simply put, compressed air is everyday air that's pressurized in relation to atmospheric conditions. Essentially, air molecules are pushed against each other, creating force when the air escapes. This force or pressure is measured in pounds per square inch (psi) or bar.
Air compressors are capable of producing different psi or bar levels. It's important to pay attention to this in relation to the demands of your applications. In addition, you’ll want to note the correct flow, expressed in cubic feet per minute (cfm), liters per second (l/s) or cubic meters per hour (m3/h).
Investing in equipment that's either too big or too small can result in production inefficiencies. An air compressor with a higher pressure and flow rating than your application(s) results in wasted electricity. On the flipside, a machine that's too small will become overworked and break down quickly. It's important to make sure your machine is a perfect match.
How does air compression work?
Compressing air is rather simple and usually involves an intake, element (air end), motor, and storage tank. This is facilitated in different ways. The most common methods are with piston and rotary screw compressors, which will be covered more below. Before getting into how those function, it's worth pointing out air treatment.
Air treatment
Since compressed air is made up of ambient air, particles and other impurities enter before or during the compression process. To ensure high-quality operations, it's important to remove these before the air is used on the end product. This is where equipment like filters comes in.
There are other air treatment products, including dryers and aftercoolers. The products you need will depend on your application's recommended ISO 8573-1 Class for air quality. They all come with different capabilities, and shouldn't be used interchangeably.
Drying
Drying is worth focusing on as it can protect both your application(s) and equipment. During the compression process, heat is generated. This rapid change in temperature results in water vapor. If untreated, this humidity can lead to rust, corrosion, and microorganisms in your equipment. A dryer will cool down compressed air to remove moisture.
There are various methods for how this is achieved, including refrigerant and desiccant dryers. Generally speaking, refrigerant dryers are suitable for 95% of applications. However, if you work in a sensitive industry like food and beverage or medical, you'll want a desiccant dryer. These are capable of a lower pressure dew point.
You can learn more about dryers in our related article.
How does air compression work: types of compressors
While there are many types of air compressors available, including centrifugal, scroll, piston, and rotary screw, you'll likely only come across the latter. This is because they are the most commonly found in industrial settings. Since this article focuses on the energy involved in producing compressed air, we'll compare these machines from an efficiency perspective.
Energy benefits: piston vs. rotary screw
The composition of the piston compressor hasn't changed that much through the years. This is because these machines contain a simple piston air end, typically operated by a crankshaft and motor. As a result, they are relatively easy to maintain, but aren't as technologically advanced as rotary screw machines.
Rotary screw compressors use two opposing rotors to compress air. They are powered by different motors, which allows for more flexibility than piston compressors. In addition, rotary screw machines come in both fixed speed and variable speed drive (VSD) models. By comparison, piston compressors only come in fixed speed. With VSD, you can save up to 45% on energy costs. Read more about this below.
What is variable speed drive (VSD)?
As mentioned, compressors will either come in fixed speed or VSD. Fixed speed means the machine operates at the same speed. By comparison, VSD matches its motor speed depending on application and air demand, producing a range of air flow levels. This means if you need less air, the motor slows down - resulting in increased efficiency. There’s also near frictionless interior permanent magnet (iPM) motors available for VSD, which result in the greatest energy savings.
Energy recovery and uses
As a final point, it's worth mentioning energy recovery. This process re-uses the waste heat generated from an air compressor, in the form of air or water. For example, it can be used to offset a facility's heating costs or in a water boiler. This can reduce the energy needed for such utilities.
As always, please get in contact if you'd like more information about any topics covered. Our team is available to answer any questions you may have.