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Nonresidential Pipe Sizing and Leak Testing for Compressed Air Systems

Measure Description

Pipe Sizing of Compressed Air Distribution Systems 

The pipe sizing measure requires selection of pipe diameters in line with recommended best practices to mitigate frictional pressure losses in the distribution network. This requirement would apply to any new construction piping installation or added piping over 50 adjoining feet in lengthThis measure would reduce unnecessarily high compressor discharge pressuresCompressor discharge pressures are often elevated to overcome excessive distribution piping pressure drops, which can be avoided through proper pipe sizing specificationsCompliance would be achieved through a plans design review and potentially a visual inspection after installation to confirm that diameters are equal to plan specifications. 

Monitoring for Leak and Efficiency Maintenance 

The monitoring measure requires the installation of meters which would facilitate continuous monitoring of load and efficiency of any new compressed air system with capacities greater than or equal to 100 horsepower (hp). Additions or replacements of compressors to existing systems would also trigger this requirement if the 100 hp threshold is met. The measure would require that system pressure and airflow be monitored as well as power of each individual compressorThe monitoring system shall include load trending (in cfm) and specific efficiency (in kW/100 cfm), at a minimum. This would ensure that load growth due to leaks is identified, providing direct economic feedback when leakage rates are excessive and necessitate detection and repair. When combined with isolation valves, one could potentially use this monitoring system to identify which portions of the compressed air system is leaking. Even if existing code requirements are satisfied, specific efficiency monitoring could help flag issues – those caused by control system parameters or otherwise – that can cause a system to operate inefficiently. Compliance certification would be achieved by an acceptance test conducted by the installing technician of installed meters and monitoring output. 

Leak Testing of Compressed Air Piping 

The leak testing requirement applies to new construction of compressed air system and to additions and alterations of over 50 adjoining feet in length. Any adjoining lengths greater than 50 feet would be tested for leaks according to a pressure test and any shorter lengths can be tested using a leak-detection fluid. Both of these methods are already codified for natural gas systems in the California Plumbing Code. This would ensure that leaks are not present at installation, codifying best practices and mitigating leaks in inaccessible header and distribution piping before plants or new end uses are operational. Compliance would be confirmed by the submission of an installation certificate by the installing contractor and perhaps confirmed by pressure gauge observation by the building inspector, similar to how gas piping installations are verified. 

Clean-up of Existing Language 

Several clean-up measures that do not impact stringency are recommended. Removal of the term “online” from the existing language is necessary to streamline compliance, reduce confusion, and facilitate downstream programs. The use of “online” to designate which compressors are back-up is not an industry standard term, nor is it evident in any given plant whether a compressor should be considered “online. This change would help mitigate confusion generated by the existing language as reported by stakeholders. 

The current language includes an exception of all existing measures for any system that has a centrifugal compressor, even if it there are compressors of other types as well. Although the 2013 CASE Report found that the existing measures were cost-effective for systems with centrifugal compressors, they were given an exception during rulemaking due to uncertainty of feasibility with trim controls on centrifugal compressors. Centrifugal compressors are often run as baseload and can have limited turndown, capacity control capabilities if not expressly designed as such. Regardless of feasibility concerns, systems with centrifugal compressors should not be exempt from other non-trim control measures and systems that have both centrifugal and non-centrifugal compressors should not be granted an exception from trim-controls. 

Regarding feasibility concerns, there are products that allow for effective capacity control of centrifugal compressors such as inlet guide vanes and control packages. There is also another exception for the trim control measure for systems of any type that have minimal load variation. This other exception may further pre-empt concerns with centrifugal compressor control effectiveness and allow for centrifugal compressors to operate as baseload, limited turndown compressors when the system arrangement or load profile warrants it 

None of the proposed changes require any modification to compliance software. Compliance software does not currently include compressed air, and the Statewide CASE Team does not recommend that it should.  

Relevant Documents

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

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Draft CASE Report Now Available (Comments accepted until July 24, 2020)

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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