Energy Saving Opportunities with Industrial Systems – Compressed Air

When we think of improving energy efficiency and saving energy in the built environment, we most often think of commercial and residential buildings like offices, apartments, schools, supermarkets, or shopping malls. In recent decades, numerous upgrades and updates have been made to the systems and technologies used in commercial and residential buildings such as LED bulbs, heat pumps, solar panels, waterless fixtures, etc. that make these buildings greener. While these improvements are encouraging and important steps towards sustainability, if our efforts were to stop there, we would only be scratching the surface of a mountain of opportunities when it comes to energy savings.

If we combine the energy usage of both the commercial and residential buildings sector, they consume less than one-third of the overall energy demand in the United States. The two other sectors that make up an even larger portion of the energy usage pie are the Industrial and Transportation sectors. According to the U.S. Energy Information Administration¹, the transportation sector consumed 28 quadrillion BTUs (37% of the demand), and the industrial sector consumed 26.1 quadrillion BTUs (35%) annually in 2023 while the residential and commercial building sectors combined consumed 20.6 quadrillion BTUs (28%).

So, what steps can we take within the industrial sector to increase energy efficiency and reduce overall energy usage? One of the key segmentations where we see opportunities to save significant amounts of energy is Compressed Air Systems.

Why Focus on Compressed Air Systems?

Compressed Air is often referred to as “the fourth utility” after electricity, water and natural gas, due to its wide application and importance in manufacturing operations. Compressed Air is used in a wide array of industries, including Automotive, Pharmaceutical, Railroad, Food and Beverage, Agricultural, and Plastics. Because of the complex nature and low efficiency of compressed air systems, it is often the largest consumer of energy in a plant. As much as 80-90% of the energy required to generate compressed air is lost in the forms of heat, leaks, inappropriate uses and mechanical losses. With all of this in mind, it is vital to maintain compressed air systems at their optimum working conditions to achieve the highest efficiency possible and implement all available energy saving measures. We’ve put together seven most effective measures and steps you can take to save energy

1.    Leak Repair

A typical plant can lose approximately 20% of the total compressed air capacity from leaks due to a lack of maintenance or poor system design. Apart from being a source of wasted energy, leaks can also have cascading effects on system pressure, runtime hours and equipment’s life. Some of the common spots in a compressed air system where a leak can happen are couplings, hoses, pressure regulators, condensate traps, shut-off valves and pipe joints.

A simple method to estimate the amount of leakage in a compressor air system with start/stop or load/unload controls is to start the system with all end-use equipment turned off and note the average time taken for the compressor to load and unload. If there are leaks present, it will cause the compressor to cycle between on and off as the pressure drops from air escaping through the leaks.

Total Leakage (%) = [(on-load time X 100) / (on-load time + off-load time)]

 Any system with more than 10% leakage can be improved and achieve significant energy savings.

Leaks are hard to detect since air is invisible to the naked eye and the general noise in a plant environment can mask the hissing sound coming from leaks. The best way to detect leaks is by using an ultrasonic leak detector, which can recognize the high-frequency hissing sounds from the leaks. Most leaks can be repaired with simple fixes such as tightening connections or changing the thread sealants. Some large leak repairs might require replacement of equipment. Once leaks are fixed, a regular leak maintenance program must be implemented to ensure total leaks in the system are minimized.

2.    No Loss Condensate Drains

Condensate is a byproduct in compressed air systems that needs to be removed as it builds up. Failing to do so will affect the compressed air quality, efficiency of the compressors and can even harm the end-use equipment. Traditionally, condensate drains such as manual drains, float drains, or solenoid electric drains are installed in a compressed air system to remove the condensate. These drains are easy to operate and inexpensive, but some types can leak air during their operation, resulting in a pressure drop in the system. As the name suggests, a no loss condensate drain can reliably remove water or moisture from a compressed air system without letting the air escape – thereby saving energy.

3.    Low Pressure-Drop Filters

It is important to strike a balance between pressure drop and filtration efficiency when choosing an air filter. Similar to no-loss condensate drains, a low-pressure-drop filter saves energy by reducing the amount of pressure drop that takes place across a filter. Compressed air systems that require high filtration efficiency often require dense filtration media or smaller mesh sizes, which can increase the pressure drop across the filter. An optimal compressed air system design has adequate filtration that meets the efficiency requirement while achieving minimal pressure drop.

4.    High Efficiency Air Nozzles

High efficiency air nozzles save energy by reducing the amount of air required at end use for different applications and still produce the same thrust as compared to standard air nozzles or open blowing. This is accomplished by leveraging the Coandă effect by which the exiting compressed air draws the surrounding air and produces a uniform, laminar jet flow while simultaneously using a lower volume of air. Additionally, high efficiency air nozzles reduce turbulence and noise in high-pressure systems which can have a positive effect in the manufacturing process.

5.    Discharge Pressure Setpoint Reduction

When the system pressure is set more than the requirement, it leads to energy waste and an increase in operational cost. Reducing the discharge pressure setpoint is a straightforward, no-cost measure that involves minimal operational effort but can result in substantial energy savings. To do this, you will need to identify and verify the pressure requirement at each use point, reduce pressure drops and set the minimum pressure required as the discharge pressure of the compressor. If the pressure requirement information is unavailable, reducing the system discharge pressure in small increments and evaluating the impact is a good practice to determine whether system pressure is set higher than required. Typically, for every 1 PSI reduction in system pressure, approximately 0.5% of power consumption is reduced.

6.    Increased Storage Capacity on Load/Unload Systems 

Adding or increasing storage capacity in a compressed air system will improve buffering of the system’s air demand and can eliminate short cycling. A load/unload compressor will unload when the demand reduces, but they may only do it at certain periods to avoid lubrication oil foaming. A storage or receiver tank will reduce the number of times a compressor transitions from load to unload and thereby save energy. Additional benefits of increasing the storage capacity are improved moisture control and reduced compressor operation during peak demand hours.

As a general guideline, it is recommended to have at least three to five gallons of air storage capacity per air compressor CFM output for most applications.

7.    VSD Compressors

The last measure on this list but also the most effective way to improve energy efficiency is to add variable speed drives (VSD) to fixed-speed air compressors or install integrated VSD compressors.

Typically, a fixed-speed air compressor unloads or chokes the inlet air to reduce the airflow depending on the system’s demand. Simply choking the inlet air or unloading are inefficient techniques since the compressor is still running at full capacity and power consumption remains the same irrespective of the airflow. A VSD on the other hand can automatically modulate the compressor’s speed to match the airflow to production demand, thereby saving significant amounts of energy.

An air compressor with a VSD makes perfect sense when the air demand in a system fluctuates. However, a VSD compressor is not ideal for operations that demand continuous maximum airflow or when used in a harsh environment.

If you are interested in improving your industrial systems and reducing your energy costs, we are ready to meet you where you are and work towards a more energy-efficient future. Contact Energy Sciences today and embark on a path toward a cleaner and more cost-effective future.

Article written by: Karthik Radhakrishnan, Energy Engineer

References:

1. S. energy consumption by source and sector, 2023 (eia.gov)
2. 2024 Illinois Technical Reference Manual – Version 12.0
3. Improving Compressed Air System Performance – A Sourcebook for Industry
4. Minimize Compressed Air Leaks; Industrial Technologies Program (ITP) Compressed Air Tip Sheet #3 (Fact Sheet)
5. Remove Condensate with Minimal Air Loss; Industrial Technologies Program (ITP) Compressed Air Tip Sheet #13 (Fact Sheet)
6. Coandă effect – Wikipedia