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Project Snapshot
| Category | Details |
|---|---|
| Client | Religious Institution in Australia |
| Sector | Public & Community Facilities |
| Platform / Software | FDS – Fire Dynamic Simulator |
| Standards | Building Code of Australia (BCA), AS 1668.2 |
| Key Outcome | CO concentration levels were maintained within life-safety limits. Areas with poor airflow and CO accumulation were identified and resolved during the design stage, reducing design changes and avoiding additional costs. |
Problem Statement
“We were designing the mechanical ventilation system for a large multi-level basement car park and needed to confirm that our extract fan sizing would keep CO levels below the statutory limits across all basement levels, including during peak entry and exit traffic events.
Hand calculations were used to size the system, but we had no confidence that the CO dispersion behaviour in our specific geometry – with its ramps, columns, low headroom zones, and uneven traffic flows, would match the theoretical assumptions.”
Impact of Challenges
Life-Safety Compliance Risk | CO is a colourless, odourless toxic gas. Accumulation above 25 ppm creates an immediate occupational health hazard for car park users and staff. Failure to demonstrate compliance with statutory CO limits risks authority rejection at building permit or occupancy certificate stage |
Peak Traffic Load Scenario | CO emission rates are highly non-uniform — concentrated at entry ramps, payment stations, and peak-hour queue zones. A ventilation design sized on average traffic assumptions may be wholly inadequate during the 15-minute peak entry or exit surge, when CO generation is highest and exposure duration risk is greatest |
Dead Zone & Low Headroom Risk | Basement car parks contain structural columns, low-headroom soffit zones, ramp throat areas, and dead-end bays that interrupt jet fan airflow paths, creating pockets of stagnant air where CO accumulates undetected. These cannot be identified through design drawings alone |
Equipment Oversizing or Under sizing | Without validated CO dispersion data, the MEP team faced a binary choice: oversize the ventilation system (increasing capital cost and energy consumption) or accept unquantified risk of under sizing (life-safety compliance failure). CFD removes this uncertainty and enables right-sized equipment procurement |
Conserve Solutions - How We Solved It
a. Thinking (Strategy)
The study was carried out as a life-safety validation assessment rather than a normal airflow analysis. The main objective was to demonstrate, using CFD simulations, that CO levels remained within allowable safety limits across all occupied basement areas under the worst operating conditions — before installation of the ventilation system.
Two operating scenarios were analysed to evaluate the performance of the extract ventilation system:
- Normal operation under design traffic conditions.
- Peak traffic condition with maximum CO generation during vehicle entry and exit.
Each scenario was evaluated against AS 1668.2 CO concentration limits and the local Civil Defence authority threshold.
b. Solution Approach/ Execution:
- Developed a full-geometry 3D CFD model of all basement levels in FDS, incorporating structural columns, ramp connections between levels, soffit height variations, extract shaft positions, and discharge angles, vehicle entry and exit ramp portals, and boundary walls.
- Applied species transport modelling with CO as a passive scalar contaminant — defining CO source terms at each parking bay based on vehicle emission factors, weighted by occupancy probability distribution across peak and off-peak traffic periods.
- Simulated 2 operating scenarios: (1) normal traffic flow — design baseline CO concentration mapping, (2) peak 15-minute surge scenario —maximumCO generation rate with concentrated source loading at entry ramp throat and payment station queue zones.
- Mapped CO concentration contours at breathing zone height (1.5m above finished floor level) across all basement levels for each scenario — providing zone-by-zone compliance evidence.
- Quantified air change rates (ACH) achieved in each basement level under all scenarios.
- Assessed cross-level CO migration through open ramp connections — tracking CO transport from lower to upper basement levels and quantifying the cumulative concentration impact on upper-level occupant exposure.
c. Integration
The simulation identified three critical dead zones – in the Basement Level 3, at the low-headroom ramp throat of Level 2, and adjacent to the mechanical plant room wall on Level 2 — where CO concentrations exceeded 50 ppm under the peak surge scenario. All basements were resolved through extending ducts and one additional extract point, implemented in the mechanical coordination drawing before the contractor commenced equipment procurement. This eliminated the risk of post-installation rework and authority rejection.
Project Timeline: 2 weeks
Phase 1 -Week 1 | Develop 3D Model, CFD meshing, vehicle CO emission factor database setup, traffic flow data processing (peak hour counts from transport study, boundary condition definition for all three scenarios. |
Phase 2 – Week 2 | Meshing in FDS as structural mesh, Scenario simulation runs, post-processing, client report preparation and design recommendation matrix delivery. |
What we Delivered
- Full 3D CFD model (FDS) — normal operation, peak 15-minute surge, across all basement levels.
- CO concentration contour maps — breathing zone height (1.5m AFF), all basement levels, all scenarios — colour-mapped against regulatory thresholds.
- Air Change Rate (ACH) compliance summary — level-by-level verification against BCA (Building Code of Australia) requirements.
- Cross-level CO migration pathway analysis — ramp connection transport quantification and upper-level cumulative exposure assessment.
- Dead zone resolution report — three identified zones with corrective action, revised fan positioning coordinates, and additional extract point recommendation.
- Client-ready technical report with executive summary, regulatory compliance matrix, commissioning readiness statement, and CO monitoring system placement recommendations.
Software and Technology Used:
FDS | Fire Dynamics Simulator – CFD Solver works by dividing a space into small 3D cells and calculating how air, smoke, heat, and gases move over time using CFD equations. |
AS 1668.2 | Ventilation and Airconditioning in Buildings — Mechanical ventilation requirements, including minimum outdoor air rates, exhaust ventilation, airflow distribution, contaminant control, and indoor air quality provisions for occupied spaces. |
Measurable Difference:
Metric | Before (Risk) | After Validated | Improvement |
CO Concentration — All Occupied Zones (Normal Operation) | Assumed compliant based on average ACH calculation — no spatial distribution evidence | Confirmed ≤20 ppm across 98.6% of occupied breathing zone area on all three levels | Compliant |
Peak CO Concentration (Basement Levels) | Not assessed — dead zone undetected by hand calculation; CO assumed uniformly diluted | Peak CO identified at 68 ppm under surge scenario pre-optimisation; reduced to 19 ppm post duct extending | Risk Eliminated |
Peak Traffic Surge — Ramp Throat CO | Unquantified — surge emission rate not modelled; design sized on average traffic only | Peak surge CO at ramp throat: 44 ppm — within limit; resolved by directed duct extract at ramp inlet | Within Limits |
Air Change Rate — All Levels (Occupied Mode) | Calculated at 7.2 ACH average — not spatially verified; low-headroom zones unconfirmed | Spatially confirmed ≥6 ACH across all basement levels including low-headroom soffit zones | Compliant |
Why Conserve Solutions
Client Outcome
“Conserve’s CO dispersion analysis gave our MEP team the spatial evidence we didn’t have from hand calculations. The three dead zones they identified would never have shown up in our design review – we would have found them during commissioning, or worse, after handover. This was exactly the kind of design validation we needed before committing to equipment procurement.“
Results:
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