Best Practice Guide

Food and Beverage Growers and Processors

Introduction

Planning an Energy Program

Funding and Approval

Commissioning

On-the-Farm Energy Use

Lighting

Building Envelope

Central HVAC System

Boilers

Steam

Combined Heat and Power

Compressed Air

Energy Use Basics

Proper Maintenance

Proper Operations

Waste Heat Recovery

Refrigeration

Motors

Demand Response

Distributed Generation

Water Use


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Compressed Air

Energy Use Basics

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Compressed air is one of the most common industrial equipment systems, and is found in about 70 percent of all U.S. manufacturing facilities. The energy needed to operate compressed air systems costs manufacturers approximately $1.5 billion each year.

Compressed air systems vary widely in size, ranging from as little as 5 horsepower (hp) to more than 50,000 hp. These systems also vary in application, most often powering pneumatic tools, but also are applied directly to materials and as an aid to other industrial processes such as combustion and oxidation.

Although compressed air is critical to manufacturing, these systems are some of the most inefficient in terms of energy usage. Roughly 80 to 90 percent of the electricity used to operate compressed air systems is converted to low-temperature waste heat. This lost energy can quickly add up, each year costing individual manufacturers as much as double the purchase and installation cost (first-cost) of the entire system (see text box).

Energy efficiency measures can achieve significant energy savings, as high as 50 percent in some cases. Because of expensive operating costs, improving the energy efficiency of compressed air systems often payback investment in short time. Despite this high return on investment, manufacturers have been slow to address energy efficiency related to compressed air; only about 20 percent have undertaken energy efficiency improvements.

Compressed Air System Basic Components

Compressed Air System Basic Components

Compressors are either positive displacement (reciprocating and rotary) or dynamic (centrifugal or axial).


Supply-Side Subsystems
Compressor - compresses gas, in this case, air
Prime Mover - powers the compressor
Controls - regulates the amount of air produced
Treatment Equipment and Accessories - removes contaminants


Demand-Side Subsystems
Distribution Lines - distributes compressed air to end-use applications
End-Use Equipment -includes pneumatic tools like nail guns, paint sprayers, air drills, sandblasters, assembly staplers, etc.

Calculating Compressed Air Electricity Costs

Calculating Compressed Air Electricity Costs
In its publication, Improving Compressed Air System Performance: A Sourcebook for Industry, the U.S. Department of Energy (DOE) provides a simple formula to calculate annual electricity costs operating a compressed air system at full load.


Data Needed:

  1. Check the compressor motor's nameplate for these ratings:
    1. Brake horsepower (bhp) - this is the power available at full loads
    2. Motor efficiency - this can also be estimated if not listed on the nameplate; DOE suggests 90 percent for new motors, 80 percent for older ones.
  2. Annual hours of operation (hours per year)
  3. Cost of electricity in dollars per kilowatt-hour ($/kWh). For current rates, check out the California Public Utilities Commission website under Energy, Rates and Tariffs.

Formula:
Annual electricity costs = (compressor bhp) x (0.746 kW/hp) x (motor efficiency) x (Annual hours of operation) x (Electricity cost in $/kWh)


Conversion Explanation:
"0.746" in the formula converts horsepower into kilowatts.


Example:
Imagine a 1000 hp system with 90 percent efficiency that operates 2080 hours annually and electricity rates of $0.10/kWh. The calculation would be -
1000 x 0.746 x 0.90 x 2080 x $0.10 = $139,651 per year in energy costs!


Resources

Improving Compressed Air System Performance: A Sourcebook for Industry. Compressed Air Challenge and U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. The Compressed Air Challenge(CAC) is a voluntary coalition of industry, manufacturers, state research and development agencies, energy efficiency organizations, contractors, and utilities. CAC provides a number of resources online, including best practices, tips, and case studies, as well as live trainings held throughout the country. The mission of CAC is to develop and provide resources that educate industry on the opportunities to increase net profits through compressed air system optimization.

Efficiency Improvements in Industrial Compressed Air Systems. Pacific Gas & Electric Company, April 25, 1997.

Air Compressor Energy-Saving Tips. Minnesota Technical Assistance Program, University of Minnesota, 2003.

U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Industrial Technologies Program, Compressed Air Best Practices.

Wise Rules for Industrial Energy Efficiency: A Toolkit for Estimating Energy Savings and Greenhouse Gas Emissions Reductions. U.S. Environmental Protection Agency, ENERGY STAR, September 2003.

The Compressor Guy website, archived files on Profit and Productivity Thieves and Unregulated Use.

Northwest Food Processors Association Efficiency Practices and Emerging Technologies websites offer useful information and tips for the food processing industry.

California Energy Commission websites on Food and Fiber Processing Technologies and Energy in Agriculture.