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Pipe Sizing and Leak Testing for Compressed Air Systems

Measure Description

Pipe Sizing

The Statewide CASE Team is proposing to require standardized compressed air distribution piping design for the minimization of frictional losses and resulting excessive compressor discharge pressure setpoints.

The pipe sizing measure would standardize the diameters of compressed air distribution piping according to the system pressure and flow at different points in the system. Pipe diameters should be optimized across the air distribution system based on airflow requirements. Improper pipe sizing can decrease energy efficiency since undersized piping can result in excessive frictional losses. In that case, the compressor must discharge at a higher pressure than otherwise necessary to ensure that pressures at end-use locations are maintained. Additionally, inefficient pipe layouts with excessive fittings increases frictional losses by adding effective length the system. Pipe design should also take this into account and minimize fittings, component pressure drops, and sharp bends wherever possible.

To make up for pressure drops in the distribution piping, the compressor must work harder than otherwise necessary. As a general rule, energy consumption increases by about 1% for every 2 psi increase in setpoint. Optimized pipe design can reduce these sources of losses. The Compressed Air Handbook, Compressed Air Challenge, Compressed Air and Gas Institute, and other sources have recommended pipe sizes for various operating conditions that will inform code requirements.

Leak Testing, Remediation, and Metering

The Statewide CASE Team is proposing to require leak detection and metering of compressed air systems as part of the commissioning of new systems and new sections of piping as well as for ongoing operations in a plant.

This measure would establish requirements for leak testing and repair for new piping of compressed air systems. Compressed air leaks unavoidably develop over time and commonly account for 20 to 30 percent of a compressed air system’s load. Leaks develop due to vibration, valve degradation, and general wear and tear of piping and machine components. Properly installed new systems likely have smaller leak load fractions, but leak mitigation and commissioning are still necessary. Leaks not only waste energy but can cause other operational losses, such as decreased functionality and efficiency of air end-uses, reduced system capacity, longer run times and duty cycles, shorter system lifetimes, maintenance burdens, and lower productivity.

According to the Compressed Air Challenge (Piping System Tips for Energy Efficiency, Marshall 2014) proactive leak detection and repair can limit leaks to less than 10 percent of compressor output. Leak detection is typically achieved through two methods: 1) monitoring and testing of system pressure drops and airflow and 2) inspection. In the case of monitoring and testing of pressure drops and airflow, observation of system pressure and airflow by plant operators can provide indications that leaks are present. By comparing pressure drops, cfm, or compressor runtimes to established operating profiles or during downtimes (absence of end-use loads), the presence of leaks can be inferred. However, while this can establish the presence of leaks, it will not provide the location. Inspection of the system piping, fittings, and end-uses is typically necessary to locate leaks. Standard practice is to use a handheld, portable ultrasonic leak detector to pinpoint leak locations. These leaks are then repaired at once or tagged for later correction.

The proposed measures will address leaks in two ways:

  • Pressure testing and leak correction of newly installed hard piping upstream of end-use take-offs. This hard piping is very difficult to repair and replace once a system is operational and leaks present during installation are unlikely to be repaired as part of the typical, ongoing maintenance that most plants conduct.
  • Metering of the system will show changes in load patterns, compressor speed, and compressor energy consumption over time. This monitoring will enable plant operators and owners to flag leaks through baseload load growth unrelated to production changes, thereby streamlining, encouraging, and enhancing the typical O&M practices that are not always observed. Over time, FDD development will improve the effectiveness of this measure.

There may be automatic leak detection products available in the market that can preclude the need for (1) labor-intensive operating profile evaluation or (2) proactive ultrasonic leak inspection. The Statewide CASE team will explore the market options for such automatic leak detection (i.e. fault detection and diagnostics – FDD) and whether they can complement or facilitate the proposed measure.

Language Clean-up

The Statewide CASE Team is proposing simplifying existing language to facilitate ease of compliance with existing 2019 requirements. There have been some discussions and feedback over code cycles that describe difficulties with understanding the coverage and triggers of existing language as well as some questioning of exceptions. The Statewide CASE Team is currently aware of several primary points:

  • Confusion around the term “online” and what it means in practice. The original intent was to have requirements apply to compressors that are typically used (as opposed to redundant or backup compressors).
  • Why centrifugal compressors are excluded from the requirements when trim compressors are advisable for any system with load variation, even if baseload compressors are centrifugal.
  • When code is triggered under different scenarios.

The Statewide CASE Team will review the existing language and recommend changes or clarifications in the compliance manual to address this stakeholder feedback.

Relevant Documents

Measure proposals, supporting documents, and other outside references will be made public as they become available.

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This measure description will be updated as research is developed to support the 2022 code cycle. For questions or suggestions, email Include the measure name in the subject line.

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The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.

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