Cleanroom Air Handling Units (AHU) — The Lungs of Your Controlled Environment
The Air Handling Unit is the most mechanically complex and operationally critical component of any cleanroom. It is the engine that filters, conditions, heats, cools, humidifies, dehumidifies, and delivers the precise volumes of treated air that define your ISO class — every second of every day. Metrolabs designs and installs custom-built cleanroom AHUs engineered specifically for pharmaceutical, biotech, hospital, and research facility requirements: not adapted from commercial HVAC catalogues, but purpose-built for cleanroom compliance.
What a Cleanroom AHU Does That Standard HVAC Cannot
A commercial HVAC unit is designed for comfort. A cleanroom AHU is designed for contamination control, pressure precision, and compliance evidence. The engineering differences are fundamental, not incremental.
EN 1886 Class L1/L2 Casing — No Leakage Pathways
Standard HVAC casings leak at panel joints, access doors, and penetrations — allowing unconditioned, unfiltered external air to bypass the filtration train and contaminate the supply air stream. Metrolabs AHU casings are manufactured to EN 1886 Class L1 (most stringent) or L2 leakage classification — tested and certified to prevent any ingress of unconditioned air into the air handling path.
Stainless Steel Aseptic Interior — Sloped Drain, Coved Corners
Standard AHU interiors use galvanized steel or painted surfaces that corrode, delaminate, and harbour microbial growth in the cooling coil section. Metrolabs cleanroom AHU interiors are SS 304 — smooth, non-porous, and resistant to all disinfectants. The cooling coil drain pan is sloped for positive drainage with R20 coved corners — eliminating the standing water and biofilm that forms in flat-bottom drain pans and feeds microbial contamination into the supply air.
EC Plug Fan with VFD — Constant Pressure Under Filter Loading
As HEPA and other filters progressively load with particles, their resistance to airflow increases. A standard fixed-speed fan will deliver less airflow as filters load — reducing air changes per hour and eventually losing the ISO class. The EC plug fan with VFD automatically increases fan speed as filter loading increases, maintaining constant supply airflow — and therefore constant ISO class — throughout the filter service life until filter differential pressure alarms trigger replacement.
CAV / VAV Pressure Logic — Dynamic Response to Door Events
When a door in the cleanroom pressure cascade opens, the pressure differential momentarily collapses. Metrolabs AHUs with Variable Air Volume (VAV) control respond dynamically — the pressure sensor detects the pressure drop and the AHU increases supply airflow within seconds to restore the design differential. This prevents contaminated lower-grade air from flowing into higher-grade zones during normal personnel and material transit events.
Six Engineering Sections Within Every Metrolabs Cleanroom AHU
Each section of the AHU performs a specific air treatment function. Metrolabs custom-configures the section sequence, sizing, and specification for each cleanroom project:
G4 Pre-Filter Section
The first filtration stage in the AHU, the G4 coarse filter section captures large-particle dust, pollen, fibres, and atmospheric particles (efficiency >90% for synthetic dust, EN 779) at the AHU intake. Its primary function is not to clean the supply air for the cleanroom — it is to protect the downstream cooling coil from fouling. A dirty cooling coil loses heat transfer efficiency, grows microbial colonies on its wet surface, and accelerates the particle loading of the expensive F9 and HEPA filters. G4 pre-filters are inexpensive and replaceable without accessing internal AHU sections.
Cooling Coil Section
The cooling coil simultaneously reduces the air temperature and removes moisture (dehumidification) by cooling the air below its dew point. Metrolabs specifies hydrophilic aluminium-fin copper-tube coils — the hydrophilic treatment ensures water forms a continuous film on the fins rather than individual droplets, flowing smoothly into the drain pan rather than being entrained into the supply air stream. The SS 304 drain pan has positive slope to the drain outlet and R20 coved corners that prevent the biofilm formation common in standard flat-bottom, right-angle drain pans.
Humidifier / Dehumidifier Section
Most pharmaceutical and biotech cleanroom specifications require relative humidity within a narrow band — typically 45–55% ±5% RH. The humidifier section (steam injection or ultrasonic) adds moisture when the cooling coil has dehumidified the air below the setpoint. Dehumidification is achieved by the cooling coil itself. The PLC control system coordinates cooling coil temperature, humidifier output, and reheating coil temperature in a cascade control strategy to achieve stable RH without hunting and overshoot.
F7 / F9 Fine Filter Section
The second filtration stage — F7 (80–90% at MPPS) or F9 (95% at MPPS) bag filters — capture sub-micron particles after the cooling coil section, acting as the primary protection for the terminal HEPA filters in the ceiling. The F9 section dramatically extends HEPA filter service life — from 12–24 months in unprotected installations to 5–8 years in well-maintained tiered systems. All fine filter sections include a differential pressure gauge with remote BMS transmitter — trending the filter differential pressure over time to predict replacement before contamination risk arises.
EC Plug Fan with VFD
The fan section is the mechanical heart of the AHU. Metrolabs specifies electronically commutated (EC) plug fans — backwardly curved impellers driven by integrated EC motors that are inherently variable-speed. The Variable Frequency Drive (VFD) modulates the fan speed in response to the supply duct static pressure or the cleanroom differential pressure sensor, maintaining constant airflow as filters load and as cleanroom conditions change. EC plug fans are 30–40% more energy efficient than belt-drive axial fans, generate less vibration, and have no belts to slip or replace.
Reheating Coil Section
After the cooling coil has lowered the air temperature below the room setpoint for dehumidification, the reheating coil raises it back to the supply temperature setpoint before the air enters the duct system. The reheating section — typically a hot-water coil or electric heater — is the primary temperature control mechanism in the AHU. The PLC maintains the supply air temperature within ±0.5°C of setpoint by modulating the reheating coil output in response to the supply air temperature sensor, ensuring the cleanroom temperature remains stable regardless of changes in occupancy, equipment heat load, or external temperature.
Metrolabs AHU — Performance Features & Standards
Every Metrolabs cleanroom AHU is built to the following performance parameters — from the source specification all the way through to the validated performance at commissioning:
| Feature | Metrolabs Standard | Cleanroom Impact |
|---|---|---|
| Casing LeakageAir tightness of AHU body | EN 1886 Class L1 / L2 | Prevents bypass of unconditioned air into supply stream |
| Thermal TransmittanceHeat loss through casing | T2 / T3 (EN 1886) | Eliminates cold spots — no condensation, no mould risk |
| Fan TechnologyType and control | EC Plug Fan + VFD | Constant airflow as filters load — ISO class maintained |
| Cooling / Heating CoilsMaterial and treatment | Hydrophilic Al fin / Cu tube | Moisture film control — no carryover — no biofilm |
| Drain PanMaterial and design | SS 304, sloped, R20 coved | No standing water — zero biofilm accumulation |
| Pre-filterFirst filtration stage | G4 panel / bag (EN 779) | Coil protection — extends F9 and HEPA service life |
| Fine FilterSecond filtration stage | F7 / F9 bag (EN 779) | HEPA protection — 5–8 year terminal HEPA service |
| Air Flow ControlVolume management | CAV / VAV selectable | Dynamic pressure recovery after door events |
| Control SystemAutomation platform | PLC + HMI touchscreen | Real-time T&H control — alarm management |
| BMS IntegrationBuilding management | Modbus / BACnet / dry I/O | Centralised monitoring of all HVAC parameters |
Four AHU Configurations for Every Cleanroom Scale & Requirement
Metrolabs custom-builds each AHU to match the cleanroom’s ISO class, airflow volume, filtration tier, and energy recovery requirements — from a single-zone pharmaceutical lab to a multi-zone GMP manufacturing suite:
Constant Air Volume (CAV) AHU — Single-Zone
The standard configuration for pharmaceutical and research cleanrooms with a single ISO class zone. The CAV AHU delivers a fixed, calculated volume of conditioned air continuously to maintain the design air change rate. The VFD increases fan speed automatically as filters load to maintain constant supply volume. Simple, reliable, and cost-effective for cleanrooms that do not require zone-by-zone pressure management. Used for ISO Class 5–8 single-room pharmaceutical labs, food processing cleanrooms, and hospital cleanroom areas.
Variable Air Volume (VAV) AHU — Multi-Zone Cascade
For multi-room GMP suites with a pressure cascade between Grade A, B, C, and D zones, the VAV AHU modulates the supply air volume to individual zones in response to differential pressure sensors at each zone boundary. When a door opens and the pressure drops, the VAV controller increases supply to that zone to restore the differential within seconds. Critical for pharmaceutical facilities where simultaneous door opening events in personnel airlocks must not cause Grade A contamination from lower-grade zones. PLC-controlled with BMS integration for full audit trail.
Heat Recovery AHU — Energy-Efficient High-ACH
For cleanrooms requiring very high air change rates — ISO Class 5 (240+ ACH), ISO Class 6 (150+ ACH) — the energy cost of heating and cooling large volumes of 100% fresh supply air is substantial. Metrolabs Heat Recovery AHUs incorporate a thermal wheel (rotary heat exchanger) or run-around coil between the exhaust and supply air streams — recovering 60–85% of the thermal energy from exhaust air to pre-condition incoming fresh air. This significantly reduces chiller and boiler loads without any cross-contamination between exhaust and supply streams. Recommended for pharmaceutical GMP facilities with continuous high-ACH requirements.
Negative Pressure AHU — Containment & BSL
For BSL-2 and BSL-3 containment facilities, hospital isolation rooms, and pharmaceutical suites handling potent or hazardous materials, the AHU is configured to maintain negative pressure within the controlled zone — ensuring all airflow is inward, preventing any contaminated air from escaping the boundary. The negative pressure AHU delivers less supply air than it extracts, with the differential monitored continuously by calibrated pressure sensors. HEPA-filtered exhaust is mandatory — Metrolabs configures the exhaust stream with H14 HEPA terminal filters before discharge to atmosphere.
Metrolabs AHUs in Every Regulated Cleanroom Sector
Pharmaceutical GMP Suites
Multi-zone VAV AHUs maintaining Grade A through D pressure cascades — validated T&H control and 21 CFR Part 11 data logging for WHO and US-FDA inspections.
Aseptic Filling & Sterile Manufacturing
High-ACH CAV AHUs with H14 HEPA terminal supply for Grade A laminar flow — VHP-compatible SS 304 interior and drain pan design. ISO Class 5 to Grade A.
Biotech & ATMP Manufacturing
Custom VAV multi-zone AHUs for gene therapy, CAR-T, and mRNA GMP suites — with full BMS integration and validated environmental monitoring logging from Day 1.
Hospital Operating Theatres
Positive pressure CAV AHUs with laminar downflow H14 HEPA ceiling for surgical suite ISO Class 5 — negative pressure AHUs for isolation rooms and infectious disease wards.
BSL-2 & BSL-3 Labs
Negative pressure AHUs with HEPA-filtered exhaust for biosafety containment — inward airflow at all times, alarm on pressure breach, continuous BMS monitoring.
Food & Beverage Cleanrooms
FSSAI and HACCP-compliant AHUs for high-care food production — positive pressure, H13 HEPA terminal, humidity control to prevent condensation and microbial growth.
Electronics & Semiconductor
High-static AHUs for ISO Class 4–7 semiconductor and electronics cleanrooms — precise humidity control (45–55% RH) for ESD prevention, vibration-free EC fan design.
NABL Research Labs
Single-zone CAV AHUs for NABL-accredited testing and research controlled environments — with documented T&H performance for ISO/IEC 17025 accreditation submissions.
Custom-Built AHU Strategy — From Load Calculation to Validated Performance
Metrolabs does not supply catalogue AHUs adapted to cleanroom requirements. Every AHU is engineered from a project-specific load calculation — sized for your cleanroom floor area, ISO class, occupancy, and process heat loads — and tested to validated performance before installation:
Project-Specific Load Calculation
Every AHU design begins with a detailed load calculation — cleanroom sensible and latent heat loads, fresh air quantities, filtration pressure drops, ductwork static pressure, and fan selection — producing a project-specific performance specification before any equipment is ordered.
Factory Performance Testing
Metrolabs AHUs are factory-tested for airflow performance, casing leakage (EN 1886), fan curve verification, coil heat transfer, and control system function before delivery. Factory test reports are included in the IQ documentation package.
VHP-Compatible Throughout
All materials in contact with the AHU supply air path — casing interior, coils, drain pan, fan, filter frames — are selected to withstand VHP (Vaporized Hydrogen Peroxide) sterilization cycles at concentrations up to 1000 ppm without degradation or off-gassing.
Full IQ / OQ at Handover
Installation Qualification (IQ) and Operational Qualification (OQ) documentation at handover — including factory test reports, casing leakage certificate, coil performance test, commissioning data, calibration records, and BMS point list with data log confirmation.
Metrolabs Cleanroom AHU vs. Standard Commercial HVAC
Metrolabs AHU Delivery — Four Stages from Calculation to Validated Performance
Every Metrolabs cleanroom AHU project follows a structured four-stage delivery process — ensuring the AHU is correctly sized, correctly built, correctly installed, and correctly validated:
Load Calculation & AHU Specification
Cleanroom heat load, fresh air volume, filtration pressure drops, duct static pressure, and fan selection calculated from first principles. AHU specification produced detailing every section, size, material, and performance parameter for client approval before manufacture.
AHU Manufacture & Factory Test
AHU fabricated to approved specification. Factory performance tests conducted: airflow, casing leakage (EN 1886), fan curve, coil heat transfer, control system function. Factory test report issued before dispatch to site.
Site Installation & Ductwork
AHU rigged into plant room. Ductwork, plenums, and duct-mounted components connected. All joints sealed and ductwork pressure-tested to SMACNA Class A. Control wiring and BMS integration connected. Filter sections loaded with G4, F9, and HEPA.
Commissioning, Balancing & IQ/OQ
Airflow balancing across all zones. VFD tuned to design static pressure. T&H calibration and control loop tuning. BMS data logging confirmed. HEPA PAO integrity test. IQ/OQ documentation issued including all test records, calibration certs, and as-built drawings.
Metrolabs AHUs Meet Every Major Cleanroom Regulatory Framework
WHO & EU GMP
WHO GMP and EU Annex 1 specify minimum air change rates, pressure differentials, temperature and humidity ranges, and HVAC qualification requirements for pharmaceutical cleanrooms. Metrolabs AHUs with validated T&H control and 21 CFR Part 11 data logging satisfy all these requirements with documented evidence.
WHO GMP · EU Annex 1EN 1886 AHU Standard
EN 1886 is the European standard specifically for air handling units — covering casing leakage (Class L1/L2), thermal transmittance (Class T2/T3), and mechanical strength. Metrolabs AHUs are built and tested to this standard, with factory-issued EN 1886 test certificates supplied at handover.
EN 1886 Class L1/L2ISO 14644 & 21 CFR Part 11
ISO 14644-1 (particle classification) and ISO 14644-2 (ongoing monitoring) requirements are satisfied by the AHU delivering consistent airflow and HEPA filtration. 21 CFR Part 11-compliant electronic records from the PLC/BMS satisfy US-FDA environmental monitoring documentation requirements.
ISO 14644 · 21 CFR Pt11NABL & FSSAI
NABL accreditation (ISO/IEC 17025) and FSSAI licensing both require documented evidence of controlled temperature, humidity, and particle environment in test and production areas. Metrolabs AHU with BMS data logging provides continuous, documented evidence satisfying both accreditation requirements.
NABL · FSSAI · HACCPReady to Engineer Your High-Accuracy Cleanroom AHU?
Contact Metrolabs for a free consultation and load calculation. Our HVAC engineering team will assess your cleanroom ISO class, floor area, process heat loads, filtration requirement, and compliance obligations — and produce a project-specific AHU specification with a factory-tested performance guarantee.
🧱 Request Free AHU Load Calculation & Consultation
Consultation Requested!
Our AHU engineering team will contact you within 24 working hours.
Immediate: 9840931231