2.2 Ventilation Design (A03), Enhanced Ventilation Design (A06) & Air Quality Monitoring (A08)

2.2 Ventilation Design (A03), Enhanced Ventilation Design (A06) & Air Quality Monitoring (A08)

Core Exam Takeaway: Get the feature numbering right — A03 Ventilation Design is the precondition, A06 Enhanced Ventilation Design is the 30%/60% and demand-controlled-ventilation optimization (3 pt WELL Certification / 5 pt WELL Core), and A08 Air Quality Monitoring and Awareness is the sensing-and-display optimization (2 pt / 1.5 pt). A05 is Enhanced Air Quality, not enhanced ventilation — a distinction candidates lose points on constantly.

Ventilation is the process of introducing outdoor air while displacing stale indoor air. A03's engineering premise is that adequate dilution prevents accumulation of metabolic $CO_2$, human bioeffluents, moisture and background emissions.

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Feature A03: Ventilation Design — Precondition

+-----------------------------------------------------------------------------+
|                  ASHRAE 62.1 VENTILATION RATE PROCEDURE                     |
|                                                                             |
|             V_bz = (R_p * P_z) + (R_a * A_z)                                |
|             V_ot = V_bz / E_z                                               |
|                                                                             |
|   V_bz = Breathing zone outdoor airflow rate (cfm or L/s)                   |
|   R_p  = Outdoor airflow rate required per person (cfm/person)              |
|   P_z  = Zone population (number of occupants)                              |
|   R_a  = Outdoor airflow rate required per unit floor area (cfm/sq ft)       |
|   A_z  = Zone floor area (sq ft)                                            |
|   E_z  = Zone air distribution effectiveness factor                          |
|   V_ot = Outdoor air intake flow rate delivered to terminal zone             |
+-----------------------------------------------------------------------------+

A03 Part 1 Option 1 — Mechanically ventilated spaces

One of the following, and note that the chosen guideline must describe ventilation rates for at least 90% of the project area:

• (a) Newly installed systems designed to meet the supply and exhaust rates of one or more of:

  1. ASHRAE 62.1-2010 or any more recent version (Ventilation Rate Procedure or IAQ Procedure)
  2. ASHRAE 62.2-2016 (the residential standard)
  3. EN 16798-1 — for Category IV buildings
  4. AS 1668.2-2012 or any more recent version
  5. CIBSE Guide A: Environmental Design, 2007 or any more recent version

  The system must be scheduled to be tested and balanced after project occupancy.

• (b) Existing systems that have been tested and balanced within the last five years to meet the rates in one of the guidelines above.

[!WARNING] Two traps here. First, EN 16798-1 is accepted for Category IV buildings — not Category I or II. Second, WELL sets no numeric air-balance tolerance such as "within ±10% of design"; it requires that balancing be scheduled (new systems) or performed within five years (existing systems). Do not invent a tolerance.

Compliance methodologies within ASHRAE 62.1.

1. Ventilation Rate Procedure (VRP): prescriptive mass-flow calculation summing the people component ($R_p \times P_z$) and the area component ($R_a \times A_z$), then adjusting by Zone Air Distribution Effectiveness ($E_z$) — ceiling supply of cool air with ceiling return $E_z = 1.0$; warm air supplied from ceiling diffusers $E_z = 0.8$ (buoyant warm air short-circuits to the return); underfloor or displacement supply of cool air at floor level $E_z = 1.2$.
2. Indoor Air Quality Procedure (IAQP): performance-based mass-balance approach using contaminant emission rates, sensory evaluation and air cleaning.

A03 Part 1 Option 2 — Naturally ventilated spaces (no mechanical ventilation)

• (a) Use one or more design criteria covering at least 90% of project area: the Natural Ventilation Procedure in ASHRAE 62.1-2010 or newer; CIBSE AM10 (2005 or newer), Section 2.4 and Chapter 4; AS 1668.4-2012 or newer; or any Option 1 reference that describes natural ventilation procedures.
• (b) Vents and windows used in the ventilation calculations must be permanently open or have controls preventing closure during occupancy. Operable windows not used in the calculations may be user-operated.
• (c) Outdoor air must meet, as an average for the previous year: $PM_{2.5} < 15\ \mu\text{g/m}^3$ and $PM_{10} < 30\ \mu\text{g/m}^3$.

A03 Part 1 Option 3 — Naturally ventilated spaces in elevated-particulate areas

Same design criteria and window-control rules, but the outdoor air thresholds relax to $PM_{2.5} < 35\ \mu\text{g/m}^3$ and $PM_{10} < 70\ \mu\text{g/m}^3$ — and the project is limited to Silver regardless of total points achieved.

The mixed-mode rule (high-yield)

Mixed-mode projects must meet the natural-ventilation requirements when the mechanical system is off and the mechanical requirements when it is on. Critically: the project must use mechanical ventilation whenever outdoor $PM_{2.5}$ exceeds $15\ \mu\text{g/m}^3$, based on a measuring device within 2.5 mi (4 km) of the project.

WELL Core guidance: meet A03 in the whole building. A mechanical or mixed-mode project must provide leased spaces with sufficient outdoor air but is not required to install ducts and diffusers within leased spaces.

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Feature A06: Enhanced Ventilation Design — Optimization (3 pt / WELL Core 5 pt)

A06's premise is that codes deliver merely "acceptable" air. WELL cites research that airflow significantly exceeding standards is needed to minimize SBS symptoms, and that SBS risk drops significantly when $CO_2$ stays under about 800 ppm — which is why the compliance thresholds sit where they do, not what they are.

A06 Part 1 — Increase Outdoor Air Supply (2 pt / Core 3 pt)

$CO_2$ sensor placement rules (Option 2b): measure at return air diffusers or in the breathing zone at least 3.3 ft (1 m) away from doors, windows, air supply diffusers or occupants. At least one sensor per occupancy zone (or per air handling unit where multiple AHUs serve one zone). Adjacent areas with substantially different occupancy density, pattern or usage count as separate zones.

[!WARNING] 800 ppm is not a WELL v2 compliance threshold. It appears in A06's research narrative. The scored thresholds are 900/750 ppm absolute or 500/350 ppm above outdoor. Mixed-mode projects select the option matching whichever ventilation mode operates for the majority of annual operating hours.

A06 Part 2 — Improve Ventilation Effectiveness (1 pt / Core 2 pt)

Use a displacement ventilation system in at least 90% of regularly occupied spaces, designed on the basis of ASHRAE Guidelines RP-949, ASHRAE 62.1-2019 "Stratified Air Distribution Systems" (Section 6.2.1.2.1), or REHVA Guidebook No. 01 (Displacement Ventilation in non-industrial premises). Displacement ventilation delivers fresh air at floor level and lets warmer, polluted air — including exhaled $CO_2$ — be extracted above the ventilation zone.

   OUTDOOR AIR DELIVERY (A06 Part 1 Option 1, relative to ASHRAE 62.1-2010)

   ASHRAE 62.1-2010 baseline: [==========] 100%   (A03 precondition)
   +30% enhanced rate:        [=============] 130%  (A06: 1 pt / Core 2 pt)
   +60% enhanced rate:        [================] 160%  (A06: 2 pt / Core 3 pt)

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Feature A08: Air Quality Monitoring and Awareness — Optimization (2 pt / WELL Core 1.5 pt)

A08 Part 1 — Install Indoor Air Monitors (1 pt / Core 0.5 pt)

Option 1 — Sensor requirements. Deploy monitors measuring at least three of the following, at the stated accuracies:

• Siting and density: monitors sited per the Performance Verification Guidebook, at a density of at least one sensor per 3,500 ft² (325 m²).
• Sampling intervals: no longer than 10 minutes for carbon dioxide and no longer than one hour for other pollutants.

Option 2 — Reporting and maintenance. Data submitted annually through the WELL digital platform, and monitors recalibrated or replaced annually with documentation submitted annually.

A08 Part 2 — Promote Air Quality Awareness (1 pt / Core 1 pt)

Only claimable if Part 1 is also achieved. Make the Part 1 data available to occupants:

• (a) Either display screens positioned at a height of 3.6–5.6 ft (1.1–1.7 m) with at least one display per 3,500 ft² (325 m²) of regularly occupied space, or hosting on a website or phone application accessible to occupants with signs at least one per 3,500 ft² (325 m²) indicating where the data may be accessed.
• (b) The data presented must include either the measured concentrations or qualitative results such as color-coded levels.

WELL Core guidance: meet A08 in non-leased spaces; an additional point is available for also measuring environmental parameters in all leased spaces. Data displays must be in tenant-accessible areas or otherwise made available to tenants.

[!TIP] The 3,500 ft² (325 m²) module recurs three times in the Air concept — A01 Part 2 Option 2 VOC sensor density, A08 Part 1 monitor density, and A08 Part 2 display or sign density. Learn it once, use it three times. Note the 3.6–5.6 ft (1.1–1.7 m) height applies to A08 Part 2 display screens, not to the sensors themselves; sensor siting defers to the Performance Verification Guidebook.