Factors to Consider When Purchasing a New Industrial Air Compressor

September 6, 2024

Selecting a new industrial air compressor involves a thorough understanding of several key factors to ensure the unit you choose meets the specific needs of your operation. This guide delves into the critical aspects to consider, providing you with the information needed to make an informed decision.

1. Air Compressor Type

Air compressors are generally categorized into two main types: dynamic and positive displacement.

Dynamic Compressors:

Centrifugal Compressors: These are designed for applications requiring large “base load” volumes of compressed air at a stable pressure. They are highly efficient and suitable for continuous duty cycles. They’re oil-free by design and generally have lubricant only for the gear cases and bearings.

Axial Compressors: Used in scenarios demanding high flow rates at lower pressures. They are less common in industrial applications compared to centrifugal compressors.

Positive Displacement Compressors:

Rotary Screw Compressors: These are ideal for applications requiring continuous duty cycles at medium pressure. They are known for their efficiency and long service life.

Scroll Compressors: Oil Free by design and extremely quiet. Scrolls are best suited for smaller flow requirements that may vary throughout the day. Units are built with multiple air end systems that start up each as needed. Minimal maintenance is required.

Reciprocating Compressors: Best suited for smaller air systems with intermittent use. They typically operate with a duty cycle of 70% loaded and 30% unloaded or off. Ideal for high-pressure applications, these compressors capable of reaching up to 5,000 PSI or more.

2. Compressor Control:

Choosing between a fixed speed or variable speed drive (VSD) compressor depends on your operational patterns and energy efficiency needs.

Fixed Speed Compressors: The drive motor runs at full speed during operation. These units operate on/off, load/no load, and may have control variations to provide a smooth operation if system demand does vary.
Variable Speed Drives (VSD): Adjust the motor speed based on demand, offering significant energy savings and consistent pressure. They are ideal for applications with fluctuating air demands. This technology is generally only applied to rotary screw compressors.

3. Cooling System:

A robust cooling system is essential to maintain optimal operating temperatures and extend the life of the compressor.

Air-Cooled Systems: Utilize fans to cool the compressor and are generally sufficient for most industrial applications.
Liquid-Cooled Systems:
- Closed-Loop Dry Cooling Systems: These operate similarly to car radiators, using a coolant to remove heat from the compressor.
- Open-Loop Evaporative Cooling Systems: These systems use fresh water and moving air to cool the compressor, suitable for large-scale operations.

4. Pressure, Capacity, and Flow Rate

Understanding the required pressure, capacity, and flow rate is crucial when selecting an air compressor.

Pressure: Measured in pounds per square inch (PSI) or Bar. All applications will have a design specific pressure requirement. It is essential to match the compressor’s PSI to these needs.

Capacity and Flow Rate (CFM): Cubic feet per minute (CFM) measures the volume of air the compressor, storage, and distribution system can deliver. Calculate the total demand in CFM that the system will consume simultaneously and add a safety buffer to ensure the compressor and system storage can handle peak demands.

5. Tank Size

Storage plays an integral role in any air system. Tanks help balance the supply of air from the compressor with the demand of the system. Typically, 3 to 5 gallons per CFM is recommended, with up to 10 gallons per CFM depending on pressure differential. Without a pressure differential, no effective energy is stored, and the tank functions similarly to the distribution piping. Properly sizing the storage tank plays a crucial role in optimizing energy efficiency.

6. Air Quality Requirements

Your decision on the type of compressor, dryer, and filtration will depend on the quality requirements of general air used in the facility or a specific application. Refer to the ISO 8573.1 compressed air quality standard to identify what your facility requires.

Oil-Free Compressors: These are crucial for industries where air purity is essential, such as food and beverage, pharmaceuticals, and electronics. They ensure no oil contamination in the compressed air stream, complying with stringent air quality standards. Compressor types to consider are centrifugal, axial, scroll, reciprocating, and oil-free screw.

Oil-lubricated Compressors: Suitable for general-purpose applications where some oil presence is acceptable. These compressors tend to be more cost-effective and provide reliable performance for a variety of industrial uses. Compressor types to consider: Oil flooded screw and reciprocating.

Air Dryers: Desiccant air dryers provide low pressure dew points: -40°F down to -100°F, while refrigerated dryers provide 35°F to 40°F.

Filtration: Filtration downstream of the compressor is generally required to remove contaminants such as particulates, condensation, and lubricants. It is important to only filter the air down to the required level to reduce the pressure drop and minimize energy consumption.

By carefully evaluating these factors, you can select an industrial air compressor that meets your facility’s needs, enhances operational efficiency, and offers long-term reliability. For more detailed information and assistance in choosing the right compressor, contact us today.