When Is a Short Audit Record Sufficient? An Audit-to-Decision Procedure for Industrial Compressed Air Systems

Abstract

Short industrial compressed-air audits can contain thousands of samples while representing only a few dependent operating episodes. Autocorrelation therefore makes nominal sample count an unreliable basis for deciding whether a low-flow regime is sufficiently supported for an energy-efficiency or maintenance action. This paper proposes an audit-to-decision procedure separating three claims: that a low-flow regime exists, that it is measured reliably enough, and that its relative scale justifies action. hv-block selection and minimum-dwell reconstruction are combined with episode repeatability, effective intra-regime size, resampling uncertainty, metrological distinguishability, and relative non-productive consumption in a six-level action scale (D1–D6). The procedure was applied to 29 records from three operating plants. Five PLC-labeled records provided a limited external evaluation of the operational meaning of the identified low-flow state. Nominal BIC and hv-block selection differed in 20 of 24 audit records. Median deviation fell from 32.2–33.9% for nominal-selection baselines to 2.9% when the HMM used the hv-block-selected regime count. Outcomes were 3 × D1, 15 × D2, 7 × D3, and 4 × D4. D-codes were unchanged in 23/24 threshold-tested and 14/16 pressure-augmented records. In the five-record PLC-labeled evaluation, no action unsupported by the labels was triggered. The strongest time-series-only outcome is a mandatory diagnostic work order, not an automatic repair decision.