The Challenge
Designing HVAC systems for ISO Class 5 semiconductor facilities requires remarkable precision and coordination. Given the rigorously controlled clean-room standards that need to be maintained, ensuring contaminant-free airflow in such environments is non-negotiable. The client faced significant complexities in maintaining compliance with ISO standards while integrating advanced HVAC systems into their intricate clean-room layout.
The primary challenges were to eliminate any potential HVAC clashes and ensure seamless coordination across various MEP systems without compromising clean-room efficacy. Timing was also of essence, with a tight schedule for preparing initial designs and delivering final construction documents.
The Solution
Adyantrix delivered a holistic BIM solution tailored to meet the meticulous demands of the semiconductor industry. Our team successfully leveraged Revit and advanced clash detection tools to model and coordinate the HVAC systems, ensuring compliance with ISO Class 5 standards.
First, we created a detailed 3D model that accurately encapsulated the existing building architecture and integrated clean-room specifications. This model served as a digital replica, enabling us to visualize and foresee potential issues with the HVAC design before the actual physical construction began.
Using BIM's clash detection capabilities, our team identified and resolved more than 150 potential clashes early in the process, thereby eliminating costly revisions and reducing the risk of delays in the construction schedule. The BIM model allowed for iterative testing and adjustments, providing the flexibility needed to adapt to changes and ensure that system designs were optimized for performance and compliance.
The HVAC design was coordinated meticulously with other structural and architectural elements, ensuring strategic placements that adhered to critical clean-room airflow constraints. Our advanced modeling techniques enabled the identification of high-precision ductwork paths and validated air exchange rates, aligning with industry standards.
Key Results
- Achieved a reduction of 35% in overall HVAC-related design conflicts through effective clash detection and resolution.
- Completed the project within scheduled timelines, adhering to all ISO Class 5 compliance requirements.
- Delivered high-quality, accurate BIM construction documentation that facilitated smooth integration during on-site assembly.
- Realized total project cost savings of approximately 25% by minimising the need for on-site modifications and rework.
Adyantrix's expertise not only ensured the development of an efficient and compliant HVAC design but further solidified our reputation as a leading service provider in the manufacturing sector's demanding clean-room environments. Through strategic use of BIM technologies, the client's project was not only brought to successful fruition but also set a benchmark for future clean-room projects.
Technical Approach
ISO Class 5 clean rooms — permitting a maximum of 3,520 particles per cubic metre at 0.5 µm or larger — impose HVAC design constraints that are orders of magnitude more demanding than standard commercial or industrial environments. The air change rate requirement for a Class 5 clean room typically falls between 240 and 600 air changes per hour, requiring a recirculating air handling infrastructure of considerable scale and complexity. Any duct penetration, offset joint, or service clash that compromises the structural integrity or geometric precision of the ductwork system creates a particle contamination risk that can invalidate an entire production batch.
The BIM authoring environment was Revit MEP, developed to LOD 400 for all HVAC components within the clean-room envelope. The extraordinarily high air change rates dictated large-format supply ductwork — in many zones, primary supply ducts were 2,400 mm × 1,200 mm — which made overhead zone coordination with electrical cable trays, process gas distribution, and deionised water pipework exceptionally demanding spatially. The sub-fab level below the clean room presented equally complex coordination challenges, housing return air plenums, recirculating air handling units, chilled water distribution, and the facility's cleanroom process exhaust systems.
Key technical decisions and tools:
- Computational fluid dynamics (CFD) analysis using SimScale, validating unidirectional laminar flow patterns within the clean room and confirming that proposed HEPA filter array layouts would achieve the required airflow uniformity index (AU) of greater than 0.98 across the working plane
- Navisworks Manage for bi-weekly federated clash detection across architectural, structural, process MEP, and utilities disciplines — clash tolerance thresholds set to 10 mm for hard clashes and 50 mm for soft clearance clashes, reflecting the precision requirements of clean-room construction
- Dynamo scripting to automate generation of air balance schedules directly from Revit model data, ensuring that the supply and extract flow rates modelled in each zone could be cross-referenced against the ISO Class 5 volume calculations without manual transcription
- IES Virtual Environment for whole-building energy modelling, enabling optimisation of the recirculating HVAC system's chiller and fan energy consumption — critical for a facility whose clean-room HVAC represents over 60% of total building energy demand
- Revit shared parameters schema configured to carry ISO classification data, filter specification, and maintenance access zone classifications against all HVAC components — enabling the facility management team to filter the model by ISO class boundary and extract filter replacement schedules directly
Implementation Highlights
The engagement was structured around three primary phases, reflecting the semiconductor client's rigorous stage-gate project approval process.
Concept design and airflow validation (Phase 1): The initial design phase focused on establishing the HVAC system topology — the arrangement of air handling units, supply and return plenum volumes, HEPA filter array density, and sub-fab return path geometry. CFD analysis was performed at concept stage on three alternative duct distribution topologies to validate airflow uniformity before any detailed duct routing work began. This upfront simulation investment prevented the significant rework that would otherwise have occurred if airflow non-compliance had been discovered at the detailed design stage.
Detailed duct routing and clash resolution (Phase 2): With the system topology confirmed, detailed duct routing commenced within the coordinated BIM model. The overhead zone within the clean room was modelled first, as the HEPA filter array and primary supply duct positions established the spatial constraints for all other services routing below the filter ceiling. Navisworks clash detection runs were conducted every two weeks; the first federated model run produced 156 hard clashes, predominantly between primary supply ducts and structural steel connections. A structured weekly clash resolution meeting — attended by the structural engineer, clean-room fit-out contractor, and process services engineer — resolved all identified clashes to zero within eight weeks. The sub-fab level coordination, managed as a separate Navisworks scene due to model file size, produced a further 67 clashes that were resolved over the following four weeks.
Fabrication documentation and commissioning support (Phase 3): The LOD 400 model was used to generate isometric fabrication drawings for all stainless-steel ductwork within the clean-room envelope — a requirement driven by the client's contamination control standards, which mandated electropolished stainless steel internally for all recirculation duct sections downstream of the HEPA filter array. The fabrication contractor received model-derived spool drawings directly, eliminating the traditional re-drawing step and reducing the time from design freeze to fabrication commencement by approximately three weeks.
Commissioning support used the BIM model as a reference for air balancing verification — TAB (Testing, Adjusting, and Balancing) engineers were provided with model-generated zone air balance sheets pre-populated with design flow targets, enabling them to record measured values against design values without manual preparation of documentation.
Measurable Outcomes
- 35% reduction in HVAC-related design conflicts compared to the client's previous clean-room project, which had been coordinated using 2D drawings — attributable to the earlier identification and resolution of clashes within the BIM environment
- Zero ISO compliance deviations identified during the third-party clean-room qualification tests at project completion — the facility achieved ISO Class 5 certification on the first qualification attempt
- 25% overall project cost saving versus the original baseline estimate, primarily driven by elimination of on-site modifications and the reduction in programme duration enabled by fabrication-ready BIM documentation
- Programme delivery on schedule, with the construction documentation phase completed three weeks ahead of the client's revised programme target following the Phase 2 clash resolution sprint
- Commissioning preparation time reduced — the TAB team reported a 40% reduction in documentation preparation time compared to their previous semiconductor facility project, directly attributable to the model-generated air balance documentation
- Post-occupancy particle count in the primary production zone averaged 1,840 particles/m³ at 0.5 µm in the first month of operation — 48% below the ISO Class 5 maximum threshold, indicating that the airflow design had been delivered accurately to the validated CFD specification
Lessons Learned
Clean-room BIM for semiconductor facilities is among the most technically demanding coordination environments we have worked in, and this project reinforced several lessons specific to the intersection of ultra-precision manufacturing and BIM delivery.
CFD analysis must precede detailed duct routing, not follow it. In clean-room projects where computational fluid dynamics is treated as a validation check performed after the duct layout has been finalised, it is common to discover airflow uniformity issues that require significant duct geometry changes — at a stage when the structural and other MEP disciplines have already coordinated around the HVAC layout. By performing CFD on the system topology before detailed routing commenced, we avoided this costly sequence entirely and produced a duct layout that was simultaneously optimised for airflow performance and coordinated with other disciplines.
Sub-fab coordination is frequently underestimated in scope. The sub-fab level — below the raised floor of the clean room — typically houses a greater volume of services per unit area than the clean room above, yet receives less attention in early BIM scoping. On this project, we ensured the sub-fab was modelled at the same LOD as the clean room envelope, which proved essential given the density of chilled water, process exhaust, recirculating air plenum, and electrical distribution systems competing for the same spatial envelope.
Stainless steel duct fabrication requires model accuracy that exceeds standard commercial BIM tolerances. Commercial BIM projects typically accept dimensional tolerances in the range of 25–50 mm for duct routing. The electropolished stainless-steel ductwork for this project was fabricated to ±5 mm dimensional tolerances. Achieving this required the BIM model to be georeferenced against the structural steelwork to the same tolerance, which in turn required the structural model to be updated from the contractor's setting-out survey data — not from the design model — before duct routing commenced. This survey-to-model update process is now a standard step in our clean-room BIM execution plan for all semiconductor and pharmaceutical facility engagements.
Speak with our BIM Consulting team at Adyantrix to find out how we can support your next project.
Work with Adyantrix
If you are looking to tackle a similar challenge, Adyantrix has the expertise to help across the full project lifecycle. Our BIM consulting practice covers BEP authoring, ISO 19650 strategy, and CDE implementation. Our clash detection & coordination practice covers multidisciplinary coordination and conflict resolution. Our Revit family creation practice covers parametric Revit content built to project and manufacturer standards. Our construction documentation practice covers coordinated drawing packages, schedules, and handover packs. Get in touch to discuss your requirements — no commitment required.
