Industrial Utility Efficiency    

Compressor Controls

UniFirst is one of North America’s largest workwear and textile service companies. They outfit nearly two million workers in clean uniforms and protective clothing each workday. Founded in an eight-stall garage in 1936, the Company has grown to 240 customer servicing locations throughout the U.S. and Canada servicing 300,000 business customer locations. The subject of this article is an energy-saving Air Demand Analysis (ADA), conducted by Kaeser Compressors, at UniFirst’s centralized 320,000 square foot hub Distribution Center located in Owensboro, Kentucky.
Treating compressed air as a true utility and outsourcing the entire process is a growing trend in the industry. If a plant does not generate their own power, provide their own water or deliver their own natural gas, then why not treat compressed air requirements in the same manner? This article will use a recent project as a case study to show the benefits one factory received by making the decision to outsource compressed air like a utility.
Years ago, while managing the service department of my compressor distributorship, I received a call from a nearby customer who told me his 200hp compressor wouldn’t make any air. When I arrived at the plant I found the inlet air filter differential indicator showing “Red”, which indicates the filter element was dirty. When I pointed this out the maintenance manager said he had just changed the filter element; however, when I removed the element the compressor immediately started making air. He then admitted that the element was one that they had simply washed out approximately seven times before. Unwittingly, when he tried to save money by cleaning the filter element he was increasing his energy cost several times more than the cost of the element.
The U.S. Department of Energy estimates that air compressors use as much as 10% of all electricity generated in the United States. Further, the DOE calculates that as much as 50% of this energy is wasted. Compressed air leaks alone account for 25-30% of compressed air use.
The objective of a compressed air management system is to improve the Key Performance Indicator (KPI) of “Energy Intensity” as it relates to compressed air. This translates into improving the ratio between the volume of product shipped and the net electricity (kWh) consumed by the compressed air system. How many thousand bottles, per compressed air kWh consumed, were shipped this month?
Production processes get their energy from the air stored at higher pressure in the piping distribution system. The air compressors simply replenish the air that is consumed. It is an important distinction to make. The energy input in compressing the air is supplied to the connecting pipes for delivery to the various demands throughout the facility.
Pneumatic air cylinders play a major role in allowing a modern sawmill to produce at the high-speed production rates required. Stable air pressure is critical to allow the air cylinders to respond in a timely manner and avoid any production delays.
Recently, this major pulp & paper mill made compressed air optimization a mill-wide priority. At the request of the utility company providing energy to the mill, Compression Energy Services performed a comprehensive energy analysis that outlined the following four energy efficiency measures (EEM’s) for the mill to consider.
“First there are the old conventions. The majority of compressor houses still employ fixed speed compressors and a cascaded pressure switch control system. This arrangement will be familiar to many, but it is outdated and inefficient, and needs to be changed. There is a comfort factor with familiar technology, which is exacerbated by constant time pressure due to other day-today responsibilities and a lack of information and good advice on what can be achieved.”  
A Tier 1 automotive plant was spending $364,259 annually on electricity to operate their compressed air system. This figure was expected to increase as electric rates were forecasted to rise from their current average of 7.16 cents per kWh. Our firm, Air Power USA, conducted a full supply and demand-side compressed air system assessment. The set of projects recommended by the assessment, would reduce these energy costs by $218,670 or 60%.
“Compressed air systems with multiple compressors operating to supply demand requirements present unique challenges in compressed air system control schemes.”