6 Common Air System Mistakes
It has been our privilege to meet and interview hundreds of individuals that are involved with compressed air systems. The experience has given us an insight into the problem areas that are common to most air systems. This report covers 6 mistakes found in almost every air system audit.
1. Believing compressed air is cheap
Air compressors powered by electrical motors will use a surprisingly large amount of energy each and every year of operation. The annual power cost to operate a compressor can equal the initial cost of the unit.
The initial purchase price of a 100 horsepower air compressor will range between $30,000 and $50,000, depending on the type and options. The same 100 horsepower compressor operating 6000 hours a year (a power rate of $.07 per KW and a motor efficiency of .90) will have an annual power cost of $34,800.
You can determine the approximate annual electric power cost of your compressors with this formula. The first step is to multiply the horsepower of the compressor times .746 times the hours of operation times your power rate (HP x .746 x hours x power rate). Then, divide that number by the motor efficiency.
Everyone in the plant should be made aware of the total power cost for operating the compressors. This is especially important for anyone that works with air operated equipment.
2. Air leaks
The most common opportunity to recover energy cost is to control leaks, because most plants have leaks wasting 20% to 30% of the air that produced by their compressors.
Effective leak control in an air system can pay huge dividends. A quarter inch leak in a 100 psi system will pass about 100 CFM of compressed air. This is approximately $12,000 in annual wasted power cost based on 24 hours a day compressor operation with a power rate of $0.07 per kW.
The process of detecting and monitoring leaks should focus on more than the basic header and piping system. The fact is that you will find a majority of your leaks at valves, drains, fittings, connections, tools and at the point of use.
It is important to remember the interdependent relationship between air system components. Controlling air leaks will not translate into reduced energy cost unless the compressor controls and air delivery system are in proper working condition.
3. Compressor controls
There are many types of control systems in operation for reciprocating, rotary screw and centrifugal compressors. It is common to find a variety of these in use in the same plant.
Over the years, an Industrial Plant may add compressors to handle growth or replace older units with newer compressors. The air system must be able to accommodate the different types and brands of control systems that are installed as a result of these changes.
There are specific rules (not rules of thumb) that govern the performance of a compressed air system. You, or someone you trust, must know the rules to prevent problems and to get the most from your air system.
Compressor control systems are a common cause of wasted energy. However, it takes more than an understanding of controls to correct the problem and recover the energy savings.
There is an interdependent relationship between the various components of a compressed air system. A good example of this is the impact that the air delivery piping and the air storage system can have on compressor controls.
Excessive pressure loss between the compressor discharge and the system can preclude capacity control efficiency by eliminating the required effective storage. The effective storage requirement varies by the type of compressors and controls.
Compressor controls make it possible for you to translate lower air usage into lower energy cost. However, the typical plant is operating multiple compressors at part load which is inefficient and expensive.
Are your controls under performing? If so, we would suggest that you get some advice from an expert, before you spend money on a new control system. Send an email to email@example.com with a few details about your situation. Be sure to include your phone number and the best time to reach you, and we will put you in touch with someone who can help.
4. Poor condensation management
Condensation is the moisture that drops out of an air flow as it cools. The condensation in a compressed air system is a constant threat to cause expensive problems. The following are a few examples:
- Moisture washes lubrication from air tools and production equipment causing downtime and maintenance.
- An inconsistent supply of dry air causes production quality problems.
- Excessive rust and scale often forms in the air distribution system.
- Water can back up into the compressor and wreck the machinery.
- Air dryers can become overloaded.
- In line filters can be destroyed.
The problems get worse if you operate lubed reciprocating or oil flooded rotary screw compressors, which is just about everyone. Compressor oil makes its way into the distribution system with the compressed air. The mixture of oil, water, dirt and heat tends to build up a sludge that will ultimately jam or clog production equipment, air tools and drains.
The situation is further complicated by climate and seasonal weather changes. This is because the amount of condensation generated will change according to changes in the temperature and the relative humidity of the inlet air.
Consider that a 200 horse power compressor operating in a climate of 60 degrees F with 40% relative humidity will generate approximately 50 gallons of condensate a day. However, that same compressor operating in a climate of 90 degrees F with 70% relative humidity will generate approximately 260 gallons of condensate a day.
The typical compressed air system is designed to remove condensation at strategic locations. This means there are drains at the aftercooler separator, receiver tank, air dryer, in line filters and at drain points in the piping.
The type of drain you select, for these locations, will affect the reliability of the draining process. However, the marketplace will often unnecessarily confuse customers looking to match a drain to an application.
If you want some help, send an email to firstname.lastname@example.org with a brief description of the drain location and problem. We will reply with a recommendation and contact details for someone you can trust, who understands how to match a condensation drain to an application.
5. Pressure loss in piping system
It is important to minimize pressure drop throughout the compressed air system. This prevents you from producing pressure that never reaches the demand point which is a direct waste of energy.
Every pound of increase or decrease in pressure requires a one half of one percent increase or decrease in power. Therefore, a 10 psig decrease can save you 5% in power costs.
This amounts to $1,740 in annual savings for the 100 horsepower compressor in the earlier example. This adds up because most Industrial plants have more than one 100 horsepower compressor.
The pressure of an air system is often raised to overcome pressure drop. The cause is usually found to be shortcomings in the piping system and pressure loss at the filters and dryers. Each of these problem areas will cost you money on an annual basis.
The following are some common problem areas:
a) Delivering air to the point of use in pipe that is too small. An example; using 30 feet or more of 3/8 inch rubber hose rather than 1 inch pipe with a short hose at the tool.
b) Using tee pipe connections rather than 30 or 45 degree angle entry connections when introducing air into a flowing stream of air.
c) Saving money by using undersized filters and dryers that have a higher pressure drop.
6. Producing higher pressure air than is needed
The key is to determine the specific pressure required for all the air requirements in your plant. Plants that have studied this issue often found that they were producing high pressure air for the entire plant just to satisfy an isolated high pressure requirement.
The solution is to install a small high pressure compressor with its own receiver tank and dryer in or near the area that needs the high pressure air. Then lower the pressure being produced by the primary compressors and immediately save energy cost. The annual energy savings will typically cover the cost of the new equipment within 2 years.