Ventilation verification — ASHRAE 62.1 VRP & DCV

camber.ventilation does the explicit code-rate ventilation check that complements the CO₂ proxy in camber.iaq and the OA-fraction diagnostic in camber.oafraction.

Ventilation Rate Procedure (VRP) — is the delivered outdoor air at least the ASHRAE 62.1 requirement for the zone?
Demand-Controlled Ventilation (DCV) — does the outdoor air actually modulate with occupancy/CO₂, or is it static (DCV not working)?

flowchart TD
  frame["role-frame (OA airflow, CO2, occupancy)"] --> vrp["assess_62_1 (VRP)"]
  frame --> dcv["assess_dcv (DCV)"]
  rates["OA_RATES_62_1 (Table 6.1)"] --> req["required_oa_cfm (Voz)"]
  req --> vrp
  vrp --> vstatus["status: under / adequate / over"]
  dcv --> dstatus["status: functioning / static / uncorrelated"]
  vstatus --> rule1["ventilation_rate_62_1 rule"]
  dstatus --> rule2["dcv_verification rule"]
  rule1 --> finding["Finding (warn / fault)"]
  rule2 --> finding

Two independent checks: is enough OA delivered (VRP), and does OA modulate with demand (DCV).

The VRP requirement

ASHRAE 62.1 sets the zone outdoor-air requirement as

Vbz = Rp·Pz + Ra·Az          (people term + area term)
Voz = Vbz / Ez               (corrected for air-distribution effectiveness)

required_oa_cfm(area_sqft, population, *, rp, ra, ez=1.0) computes Voz. The Rp/Ra rates come from OA_RATES_62_1 (62.1 Table 6.1, a public-standard subset) via oa_rates_for(space_type), or you pass them explicitly.

from camber.ventilation import assess_62_1

# a 2,000 ft² office for 10 people, metering ~120 cfm OA over occupied hours
r = assess_62_1(
    oa_cfm_series,
    area_sqft=2000,
    population=10,
    space_type="office",
    occupied_mask=occ,
    aggregate="median",
)
r.required_cfm  # 170.0   (5·10 + 0.06·2000)
r.status  # "under" -> deficit 50 cfm

measured_oa_cfm may be a scalar or a time series; a series is filtered by occupied_mask and reduced by aggregate. Status is under (ratio < under_tol), over (ratio > over_factor, an energy penalty), or adequate.

Option flags — `assess_62_1`

flag	default	effect
`space_type`	—	look up `Rp`/`Ra` from the 62.1 table
`rp`, `ra`	from table	override the people / area rates
`ez`	`1.0`	zone air-distribution effectiveness (raises the requirement when < 1)
`aggregate`	`"median"`	reduce a series: `median`/`mean`/`min`/`p05`/`p95`
`occupied_mask`	`None`	restrict a series to occupied hours
`under_tol`	`0.9`	flag under below this fraction of required
`over_factor`	`1.5`	flag over above this multiple of required

DCV verification

from camber.ventilation import assess_dcv

res = assess_dcv(oa_signal, co2_series, occupied_mask=occ, co2_setpoint=1000)
res.status  # "functioning" | "static" | "uncorrelated" | "insufficient"
res.modulation  # (max-min)/max of the OA signal
res.correlation  # OA vs demand (DCV -> positive)

oa_signal can be OA flow, OA fraction, or OA-damper position; demand_signal is CO₂ or occupancy. static = OA doesn't modulate (fixed OA / DCV off); uncorrelated = it modulates but not with demand. With a co2_setpoint, co2_breach_at_min_pct reports under-ventilation that persists while OA is pinned at its minimum.

Option flags — `assess_dcv`

flag	default	effect
`min_corr`	`0.3`	min OA↔demand correlation to call DCV "functioning"
`min_modulation`	`0.1`	min OA range `(max-min)/max`; below ⇒ "static"
`co2_setpoint`	`None`	also flag CO₂ breaching this while OA is at minimum
`occupied_mask`	`None`	restrict to occupied hours

Rules

dcv_verification (DemandControlledVentilation) — config-free, auto-registered. Uses OA airflow (Role.OA_AIRFLOW) or OA-damper position, and CO₂ or occupancy as demand; warn on static/uncorrelated, fault when CO₂ breaches setpoint at minimum OA. Construction flags: min_corr, min_modulation, co2_setpoint, occupied_only.
ventilation_rate_62_1 (VentilationRateProcedure) — needs the zone's design inputs, so it's instantiated explicitly (not auto-registered):

from camber.rules.ventilation_rule import VentilationRateProcedure

rule = VentilationRateProcedure(area_sqft=2000, population=10, space_type="office")
finding = rule.analyze("AHU-1", role_frame)  # fault on under-ventilation

Scope

This verifies the rate from trends; it is not a substitute for a stamped 62.1 ventilation calculation. The Table 6.1 defaults are a convenience — confirm the zone's category and design population against the project's mechanical schedule.