Calculating and Measuring the Air Requirement


The nominal compressed air requirement is determined by the individual air consumers. This is calculated as a sum of air consumption for all tools, machines and processes that will be connected, and estimating their individual utilization factor by experience. Additions for leakage, wear and future changes in the air requirement must also be taken into consideration from the outset. 

How do we calculate the compressed air requirement?

A simple method to estimate the present and future air requirement is to compile the air requirement for connected equipment and the utilization factor. This type of calculation requires a list of machines and their respective air consumption data and expected utilization factors. If data is not available for the air consumption or utilization factor, standard values from lists may be used. 

The utilization factor for tools can be difficult to estimate, therefore calculation values should be compared with measured consumption in similar applications. For example, large air-powered consumers such as grinders and sandblasting machines are used frequently for long periods (3-10 minutes) at continuous operation, despite their low overall utilization factor. 

This cannot truly be characterized as intermittent operation, and it is necessary to estimate how many machines will be used simultaneously in order to estimate total air consumption. 

Compressor capacity is essentially determined by the total nominal compressed air requirement. The compressors' free output flow rate should cover this rate of air consumption. The calculated reserve capacity is primarily determined by the cost of lost production resulting from a potential compressed air failure.

The number of compressors and their mutual size is determined principally by the required degree of flexibility, control system and energy efficiency. In an installation in which only one compressor supplies compressed air (due to cost restrictions), the system can be prepared for quick connection of a portable compressor as part of servicing. An older compressor used as a reserve source, can be used as inexpensive reserve power.

How do we measure the air requirement?

An operating analysis provides key factors about the compressed air requirement and forms the basis for assessing the optimal amount of compressed air to produce. Most industrial companies are constantly evolving, and this means that their compressed air requirements also change.

It is therefore important that the compressed air supply be based on the current prevailing conditions, and an appropriate margin for expansion be built into the installation. An operating analysis entails measuring operating data, which is possibly supplemented with the inspection of an existing compressed air installation over a suitable period of time. This analysis should cover at least one week of operations and the measurement period should be selected with care to allow it to represent a typical case and provide relevant data.

The stored data also provides an opportunity to simulate different measures and changes in compressor operations and to analyze the impact on the installation's overall economy. Factors such as loading times and off-loading times also enter into the total assessment of compressor operations. These provide the basis for assessing the loading factor and the compressed air requirement, spread over a day or a work week.

Accordingly, the loading factor cannot just be read off of the compressor's running hour meter. An operating analysis also gives a basis for potential energy recovery. Frequently, more than 90% of the energy supplied can be recovered. 

Furthermore, the analysis can provide answers relating to dimensioning as well as the operating method for installation. For example, the working pressure can often be reduced at certain times and the control system can be modified in order to improve compressor usage with changes in production. It is also fundamentally important to check for leakage. For the production of small quantities of air during the night and weekends, you must consider whether it is worth installing a smaller compressor to cover this requirement.

Source: Atlas Copco