Compressed Air

Summary

Compressed air is a crucial, yet costly, resource widely used in manufacturing for powering tools, actuators, and various processes. Although convenient, compressed air typically has efficiency rates of only around 10–15%, making it significantly more expensive than direct electrical power.

Compressed air systems consist of two main areas:

  • Supply Side: Includes compressors, dryers, filters, and storage tanks.
  • Demand Side: Includes distribution piping, secondary storage, leaks, and end-use applications.

Improving compressed air efficiency is vital for reducing energy costs, minimizing environmental impact, and achieving sustainability targets.

Check out this video detailing the main parts of a compressed air system

Supply-Side Energy Saving Measures

1. Cold Air Intake

Using colder, denser air for compressor intake reduces the energy required for compression. Cooler air lowers energy consumption and improves the efficiency and lifespan of your compressor.

Best Practice:
Draw compressor intake air from a cooler location (e.g., outside air or air-conditioned spaces) rather than from the hot compressor room.

2. Turn Off Compressors When Not in Use

Running compressors unloaded wastes significant energy. Older rotary screw compressors can use up to 85% of their full load power even when idle.

Best Practice:
Use controls or scheduling to ensure compressors are turned off during low demand periods. Consider smaller compressors for low-load conditions.

3. Reduce Setpoint Pressure

Compressors often operate at higher pressures than needed. Every unnecessary 2 psi increase in pressure can increase energy use by approximately 1%.

Best Practice:
Regularly measure pressure requirements and lower compressor pressure setpoints to the minimum needed by your facility’s processes.

4. Optimize Storage and Distribution

Adequate storage (receiver tanks) and proper piping reduce pressure drops and stabilize system performance. This minimizes the need for extra compressor runtime.

Best Practice:
Design piping with minimal bends and appropriate diameter. Strategically place air receivers near heavy-use areas.

Demand-Side Energy Saving Measures

1. Avoid Using Compressed Air for Personal Cooling

Using compressed air for personal cooling is highly inefficient and wasteful.

Best Practice:
Educate employees about compressed air costs and provide alternative cooling solutions, such as fans.

2. Use Engineered Air Nozzles

Open-ended tubes or basic air guns consume excessive air. Engineered air nozzles significantly reduce air consumption and noise levels.

Best Practice:
Replace open-ended hoses and simple nozzles with engineered alternatives designed to maximize efficiency and airflow.

Diagram Suggestion:

  • Side-by-side demonstration of airflow and consumption rates of engineered nozzles versus open-ended tubes.

3. Detect and Fix Leaks

Leaks typically account for 20–30% of a plant’s total compressed air usage, resulting in considerable waste.

Best Practice:
Conduct routine leak inspections using ultrasonic detection or simple auditory inspections, and promptly repair identified leaks.

4. Optimize End-Use Applications

Compressed air is often used where more efficient alternatives exist, such as electric motors or blowers.

Best Practice:
Identify non-essential compressed air uses and replace them with more efficient alternatives.

Examples include:

  • Electric blowers instead of compressed air for continuous cleaning.
  • Mechanical agitators instead of compressed air for liquid mixing.

CAGI Datasheets

We use CAGI datasheets for a lot of the recommendations because they have a lot of good info about power draw and efficiency. They can usually be found by searching the compressor’s model name. Take a look at this sample datasheet and follow along, identifying where all of the important metrics are located on it.

Sample CAGI Datasheet

Compressor Basics

Compressor Type (e.g., Screw Compressor)

  • Describes the method the compressor uses to compress air.
  • Screw Compressors compress air using two rotating screws that trap air and push it through smaller spaces to increase pressure. Ideal for industrial applications requiring continuous airflow.

Cooling Method (Air-cooled vs. Water-cooled)

  • Air-cooled compressors use ambient air to dissipate heat, suitable for environments with sufficient ventilation.
  • Water-cooled compressors rely on circulating water for cooling, beneficial in facilities with available water infrastructure or limited airflow.

Number of Stages (Single vs. Multi-stage)

  • Indicates how many times air is compressed within the compressor.
  • Single-stage compressors compress air in one step, common in simpler systems or moderate pressure applications.
  • Multi-stage compressors compress air multiple times, improving efficiency, especially at high pressures.

Key Performance Metrics

Full Load Operating Pressure

  • The pressure at which the compressor typically operates under full-load conditions, measured in psig (pounds per square inch gauge).
  • Determines if the compressor aligns with facility requirements and downstream equipment specifications.

Capacity (Flow Rate - acfm)

  • Actual Cubic Feet per Minute (acfm) measures the actual airflow delivered by the compressor under specified conditions.
  • Directly influences how effectively the compressor meets the facility’s air demand.

Input Power (kW)

  • The electrical energy consumed by the compressor at a given operational state.
  • Critical for calculating operating costs and identifying energy-saving opportunities.

Specific Power (kW/100 acfm)

  • Indicates compressor efficiency by showing how much power it takes to produce a standard quantity (100 acfm) of compressed air.
  • Lower values represent better efficiency, making it an essential metric for comparing compressors or assessing upgrades.

Motor and Fan Specifications

Drive Motor Nominal Rating (hp or kW)

  • Indicates the rated power of the compressor’s main motor.
  • Provides insight into energy demands and the scale of electrical infrastructure required for operation.

Motor Nominal Efficiency (%)

  • Measures how effectively the electric motor converts electrical energy into mechanical energy.
  • Higher motor efficiency reduces energy waste and operational costs.

Fan Motor Nominal Rating and Efficiency

  • Specifies the power and efficiency of the cooling fan motor, relevant for air-cooled compressors.
  • Efficient cooling fans lower total energy consumption and reduce the overall thermal load in the compressor environment.

Advanced Efficiency Indicators

Total Package Input Power at Zero Flow (No Load Power)

  • The compressor’s energy consumption when running without delivering air (idle state).
  • Lower no-load power indicates reduced energy wastage during low-demand periods.

Isentropic Efficiency (%)

  • Compares the compressor’s performance to an ideal (isentropic) compression process.
  • Higher percentages indicate a compressor closely approaching ideal operation, suggesting superior design and operational efficiency.

Here’s a video going a bit more in-depth about air compressor efficiency and why we use isentropic efficiency over other metrics.

More Information

Check out these two videos by Mike Muller going over compressed air systems in more detail:

Here’s a publication from the Department of Energy detailing several practices to improve compressed system performance:

Improving Compressed Air System Performance

Activity

Scenario Overview

You are conducting an energy assessment at a manufacturing facility. The facility operates daily from 6:00 am to 4:00 pm, Monday to Friday. However, from 2:00 pm to 4:00 pm, only the warehouse is active, which does not require compressed air.

Observations from Site Visit:

  • One large air compressor continuously operates at 120 psi.
  • The maximum pressure required by equipment is only 90 psi.
  • The compressor requires 208V
  • Compressor intake air is drawn from the hot compressor room (~90°F).
  • Audible leaks were identified throughout distribution piping and at an old, unused packaging machine still connected to the system.
  • At 6 workstations, employees regularly use compressed air guns rated at 14 cfm @ 100 psi to clean workstations. Observations showed each worker used compressed air for 2 minutes per 30 minutes.
  • Previous calculations have established that each CCF (100 cubic feet) of compressed air consumes 0.24 kWh.

You have been provided two weeks of compressor CT (current transducer) data.

Task: Analyze the scenario and calculate the annual energy savings (in kWh) achievable by:

1. Turning off compressors during non-production warehouse-only hours (2:00 pm–4:00 pm).
2. Eliminating the inappropriate use of compressed air for workstation cleaning.

Download Data

Step-by-step Guidance:
  • Production Schedule:
    • Operating hours: 6:00 am–4:00 pm (10 hours/day).
    • Facility operates 5 days per week, 50 weeks per year.
  • Workstation Cleaning Usage:
    • Number of workstations: 6
    • Usage per workstation: 2 mins every 30 mins
    • Total daily cleaning time per workstation: 4 mins/hr × 8 production hours (6 am–2 pm) = 32 mins/day/workstation
    • Air nozzle rating: 14 cfm at 100 psi
  • Energy Usage:
    • Conversion rate: 1 CCF (100 cubic feet) of compressed air = 0.24 kWh

Analysis Questions:

  1. Calculate the annual energy savings (in kWh) from turning compressors off during non-production warehouse-only hours.

  2. Calculate the annual energy savings (in kWh) from eliminating compressed air workstation cleaning.

  3. Discuss which measure provides greater savings and whether implementing both measures is beneficial or not.

If you get stuck, check out this page for a bit more guidance:

Compressed Air Activity Help

Quiz

1. What's the yearly kWh savings for shutting down the compressor? Round to the nearest kWh.

2. What's the yearly savings for discontinuing the use of compressed air for cleaning? Round to the nearest kWh.

3. Which recommendation is likelier to have a higher implementation cost?

Shut Down Compressor
Stop Using Compressed Air for Cleaning

4. If the compressor setpoint were lowered from 120 psi to 90 psi, how would this affect each of your recommendations?

Decrease savings for both
Increase savings for both
No effect on savings
Decrease savings for shutting down, increase savings for stopping cleaning

5. What's the most common type of compressor seen on assessments?

Rotary Screw
Reciprocating
Centrifugal
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