Like most of the world, we’re finding new ways to stay connected and keep everything moving in the right direction: production lines, distribution channels, and education. We’ve always been active participants in online learning platforms but now it’s even more important to share our knowledge and resources with our customers and compressed air users.
By: Frank Mueller
We are closely monitoring the COVID-19 situation and have implemented guidance from the CDC, as well as state and local agencies to minimize health risks to our employees, our customers and the general public. We have eliminated all non-essential travel, implemented stringent hygiene protocols, and now many of our team members are working from home.
At the same time we remain fully functional and ready to support the many essential operations that depend on compressors, blowers and related equipment. We have a healthy stock of equipment and parts, and maintain frequent contact with our supply chain partners. At this time there is no supply disruption for our products.
Our sales/engineering teams continue to consult on new systems and upgrades. Our national service network is available for maintenance and repair work. If you need help on site, let us know in advance of any special access constraints or personal protection requirements for visiting service personnel.
If you are temporarily closed or for any reason need to delay shipment of pending orders or service visits, please call your local Kaeser branch or distributor to let them know.
We wish your team and their families good health.
President, Kaeser Compressors, Inc.
With over ten thousand air system audits under our belt, we’ve seen it all and learned a few things. One of the most common problems we see is that most systems have far more capacity than needed. On average, users operate at 44% of peak capacity. It’s so common, we’d say it is an epidemic, and even our own customers are not immune despite our efforts to inoculate with education.
How does this happen? In many cases, users select compressors based on what they already have, adjusted with some prognostication about whether they expect to grow, add or eliminate production lines, etc. Generally, very little measurement and analysis goes into it. Plant operators are usually comfortable up-sizing a compressor for the safety factor. They don’t want to hear complaints of equipment with low pressure alarms, nor do they want to re-revisit compressed air system design every few years as they grow. So they purchase as big as their budget allows at the outset. When involved, consulting engineers may add to the problem by making conservative assumptions that all pneumatic equipment will operate fully loaded, all the time. Then they take this bad estimate and add a safety factor. In nearly all cases, there’s fudge factor on top of fudge factor. All believe they are acting in the interest of reliability, without understanding the significant negative impact on energy consumption.
Compressed air efficiency is best measured in terms specific power, which is kW/100cfm, and the Compressed Air and Gas Institute (CAGI) has an excellent program that encourages compressor makers to publish the specific power for each compressor. This is a great point for comparing two compressors side by side, but it cannot be used to predict what the user’s actual system performance will be. As the car sellers say: “your mileage may vary.” So much depends on how the compressors are run. The CAGI datasheets for fixed speed machines assume 100% load, which rarely happens in practice. From our many system studies we know that systems are grossly over sized. Whether a single machine or multi-compressor system, under-utilized compressors do not operate at their datasheet spec.
Let’s look at some actual examples of over-sized systems and the costs that resulted.
The chart above shows how the performance of compressed air systems declines dramatically as demand decreases (shown for the most common types of screw compressors in the field). This is measured in specific power (kW/100cfm), which increases as compressors operate further away from their full output capacity. We’ve added data points showing where a few actual customers operate on this curve to show that this graph is actually showing ideal (e.g. laboratory) conditions. As you can see, some are off-the-charts inefficient, but achieving efficient operation is certainly possible.
This is a greenfield plant (i.e., new construction) where the company specified dual 125 hp compressors, (2) 230 cfm refrigerated dryers, 1000 gallons of storage, an air main charging valve, and a master system controller. They spent $1.10/1000 cubic feet! Their system could be replaced with a pair of 15 hp units.
The current facility operates with a 50 hp screw compressor, a 285 cfm refrigerated dryer, and a 400 gallon receiver tank. Typical operation showed the facility running ~11 hours a day Monday through Thursday, with no operation Friday through Sunday. According to the data on the screw compressor’s controller the average system pressure was approximately 115 psig. The peak demand measured was 65 cfm and the average flow was 22 cfm. This unit is over-sized for the current demand. The calculated system specific power was 65.54 kW/100 cfm. The company would be much better off with a pair of 10 hp compressors. They spend $1.09/1000 cubic feet for their air!
Retail equipment manufacturer
The facility currently operates with (3) water-cooled 200 hp compressors, (3)100 cfm refrigerated dryers, and 3,800 gallons of dry storage. The data was provided from the master system controller. This system is highly variably in demand (891 to 2417 cfm) but was designed with 3 units to supply this full range efficiently. While this is an outstanding example of a well-designed system, they could get even better specific performance if they drop their pressure below the average of 115 that they currently maintain. They spend $0.35/1000 cubic feet including their cost of cooling water.
The cost per unit of compressed air goes up as the % load goes down, which means that your yield on this costly input goes down as well. Don’t be yet another statistic with an over-sized and inefficient compressed air system. Educate yourself on the life cycle cost benefits of multiple smaller units that will provide low costs, high efficiency and reliability. Below are a couple of useful resources:
By: Kaeser Compressors, Inc.
If you are looking for some quick tips to improve your compressed air system, consider starting with our most read blog posts from 2019.
#5 This is Why You Don’t Use PVC: Using PVC in a compressed air system poses significant safety risks. This post covers what you need to know if you are considering using it.
#4 Applying Motor Temperature Ratings: A perennial favorite, this blog post offers useful information to help you apply motor temperatures ratings. Motor temperature ratings are given by the type of insulation used on the wire as well as the utilization rate. These two parameters determine the expected lifetime of the motor windings.
#3 Some Like It Hot…Your Compressor Room Doesn’t: If you are having problems with compressor room overheating, read this post for tips on better temperature regulation.
#2 Choosing Between an Air-cooled or Water-cooled Compressor: This post outlines four questions to answer when deciding between an air-cooled and water-cooled compressor.
#1 The Art of Dryer Sizing: This post has been at the top of the list since it was published in 2015 and is the most viewed post again in 2019. Read this post to understand how temperature and pressure impact water content and to learn how to make sure dryers are properly sized.
Our most popular post published in 2019 was this summer’s How to Keep that Trusty Recip Going! If you have a reciprocating compressor because it’s a good fit for your shop, here are some tips to avoid some common issues as well as some maintenance tips to keep your recip unit going.
Do you have a topic you’d like us to cover in 2020? Let us know in the comments.
By: Kaeser Compressors, Inc.
What were the top posts of 2019? Check back Dec 30 to find out and in the meantime let us know in the comments what your favorite posts were and what you’d like to read more about.