Commercial air compressors are widely used in facilities across the United States, and can easily become an expensive piece of equipment to operate. Approximately 19% of the total power used in a compressed air system, is converted into clean, compressed air flow. The other 81% is lost as heat. Because of this, compressed air is more expensive than other utilities like electricity, natural gas, and water. Now, couple that with compressed air leaks and your energy efficiency could be on the decline.
COMPRESSED AIR LEAKS ARE DANGEROUS
Compressed air leaks can be financially crippling under the wrong circumstances. The most terrifying aspect of compressed air leaks is just how long they can go undetected. According to the Compressed Air & Gas Institute, a single ¼-inch leak in a compressed air line can cost a facility anywhere from $2,500 to $8,000/yr. The scary part is, you may not even know it
Leaks not only increase energy cost, but they can also upset the functionality of the whole system. Leaks make compressors work harder to produce the same amount of compressed air. This added stress can compromise equipment reliability, increase operating hours and increase overall lifecycle costs.
[Do you want to minimize the number of leaks produced from your air compressor? Download our checklist, Analyzing Your Compressed Air System, to optimize your system and save money.]
Persistent air leaks also decrease the longevity of your air compressors if left unchecked. The first step is to be aware of this threat. The second is to address the issue.
Did you know? When 100 compressed air leaks are found and sized, a tight system should average around 3 CFM each. A typical system should average around 4 CFM each and a high leak system should average around 5 CFM each. The numbers above or below these levels should have a clear explanation! (Source)
HOW TO IDENTIFY COMPRESSED AIR LEAKS
A simple walkthrough with a pair of good ears may detect some major leaks. You also might be able to notice a change in equipment productivity. However, if you can detect issues this way, the problem has already become very costly.
Specialized equipment and a skilled technician should be deployed for reliable compressed air leak identification, especially in loud environments. Ultrasonic leak detection devices are the best tool to recognize compressed air leaks. Their regular use can help maintain consistent and high functionality of a compressed air system. Regular leak audits reduce wasted energy expenses, unnecessary wear on air compressors and help prevent air compressor downtime.
Think you can hear or feel a leak? The bullets below illustrate just how much money you could be losing if you rely on that method. At $0.05 per kWh:
- $100/year leak – can’t be felt or heard
- $400/year leak – can be felt, but not heard
- $700/year leak – can be felt and heard
Since air leaks are almost impossible to see, other methods must be used to locate them. The best way to detect leaks is to use an ultrasonic acoustic detector, which can recognize the high-frequency hissing sounds associated with air leaks.
If you are unsure how much money your compressed air system uses, try using this equation from the Compressed Air & Gas Institute:
Cost ($/year) = motor bhp x .746 x hours of operation (per year) x electric rate ($/kWh) / motor efficiency
QUANTIFYING THE LEAKAGE RATE
Identifying and quantifying the leak load is important when considering the entire effect of leaks on your system. Use a bleed down test to quantify the leakage rate of a whole system. Alternatively you can estimate leakage in systems if there is a pressure gauge downstream of the receiver. This method requires an estimate of total system volume, including any downstream secondary air receivers, air mains and piping (V, in cubic feet). Then start the system and bring to the normal operating pressure (P1) and then turn the compressor off.
Measure the time (T) it takes for the system to drop to a lower pressure (P2). (Which should be a point equal to about one-half of the operating pressure.)
Calculate Leak Rate Using This Formula:
Leakage (CFM free air) = [V x (P1-P2)/(Tx14.7)] x 1.25
- V is in cubic feet
- P1 and P2 are in PSG
- T is in minutes
The 1.25 multiplier corrects leakage to normal system pressure, allowing for reduced leakage with falling system pressure to 50% of the initial reading. Leakage of greater than 10% indicates a more serious problem and leaves significant room for improvement. Carry these tests out once a month as part of a regular leak detection and repair program.
Source: “Fundamentals of Compressed Air Systems” The Compressed Air Challenge
MINIMIZE COMPRESSED AIR LEAKS
Leaks are a significant source of wasted energy. 20-30% of the compressor’s output is often wasted. A typical poorly maintained plant will have a leak rate equal to 20%+ of total compressed air production capacity. On the other hand, proactive leak detection and air compressor repair can reduce leaks to less than 10% of output.
As you know, leaks are worse with higher pressure. By reducing system pressure your system will require less energy and also lower the leakage rates. Plant header pressures should be as low as possible to support the process because it minimizes compressor energy use and leakage.
Compressed air leaks can contribute to problems with system operations, including:
- Fluctuating system pressure can cause air tools and other air-operated equipment to no function correctly, negatively affecting production.
- Excess compressor capacity, resulting in higher than necessary costs.
- Decreased service life and increased maintenance of supply equipment (including the compressor package) due to unnecessary cycling and increased run time.
Leaks most commonly occur at the following locations:
- Pipe Joints
- Quick Disconnects
- FRLs (filter, regulator, lubricator)
- Condensate Traps
- Thread Sealant
- Point-Of-Use Devices
Leakage rates identified in cubic feet per minute (CFM) are also proportional to the square of the orifice diameter. This means that if you double the leak orifice size, you will quadruple the leak flow rate. See the table below:
In addition to being a source of wasted energy, leaks can also contribute to other operating losses. Leaks:
- Cause a drop in system pressure, which can make air tools function less efficiently, adversely affecting production;
- Shorten the life of almost all supply system equipment (including the compressor package itself) by forcing the equipment to cycle more frequently;
- Cause increased running time, which can also lead to additional maintenance requirements and increased unscheduled downtime; and
- Can lead to adding unnecessary compressor capacity.
If you suspect compressed air leaks, we can help. Our compressed air team can perform system audits and repair problem areas. We can assess your system to ensure your air compressors, dryers, storage, regulators, distribution and point of use equipment is right for your application. Keep up with these cost-saving maintenance tips and start saving. Contact us today!