CFM ↔ Air Changes per Hour Converter

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Mechanical, Civil & Structural Engineering — Statics/Dynamics, Strength of Materials, Machine Design, Civil, HVAC, Vibration

Tranche

tranche-5

Evidence ID

t5-155

Ledger rows

1

No ledger note is attached.

Review findings

The ACH formula is standard under the stated imperial-unit assumptions, but the catalog claim is bidirectional while only the forward formula is supplied. The honest label should explicitly state the supported directions, CFM, cubic feet, and ACH units.

Formula and scope findings

• The supplied formula ACH=CFM×60/Volume(ft³) is correct only for calculating ACH when airflow is in CFM and volume is in cubic feet.
• The instrument claims conversion in both directions, but the required inverse formula CFM=ACH×Volume(ft³)/60 is missing.
• The input and output modes are not explicitly defined, so it is unclear whether a given numeric airflow value is CFM or an ACH target.

Unit assumptions

• CFM means cubic feet per minute.
• Room volume must be expressed in cubic feet for the supplied formula.
• The factor 60 converts minutes to hours.
• ACH is expressed as air changes per hour.
• Metric volumes such as cubic metres must be converted to cubic feet before using the supplied formula.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

A zero room volume causes division by zero and must be rejected. Negative CFM also exposes an unresolved sign convention: signed arithmetic returns negative ACH, whereas normal HVAC usage generally expects a nonnegative airflow magnitude.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "mode": "ach_from_cfm",
    "cfm": 250,
    "room_volume_ft3": 15000
  },
  "expected_outputs": {
    "ach": 1
  },
  "working": "ACH = CFM × 60 / Volume = 250 × 60 / 15000 = 15000 / 15000 = 1 ACH."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche5/tranche5-results.json
• BOUNDARY_HAZARD_CATALOG.json