Cleanroom Temperature & Humidity Controllers — Climate Stability for Sensitive Research
Temperature and humidity are the two environmental parameters most directly responsible for product stability, microbial growth, static electricity, and personnel safety in a cleanroom. A ±2°C temperature excursion in a biological manufacturing suite can invalidate a production batch. A 10% RH spike in a powder handling area can cause clumping, flowability failure, and microbial contamination. Metrolabs T&H Controllers are the central nervous system of your AHU — PID-controlled precision instruments that maintain temperature to ±0.3°C and relative humidity to ±2% RH, continuously, automatically, and with 21 CFR Part 11-compliant electronic data logging.
Climate Is Not a Comfort Parameter — It Is a Process Critical Variable
In pharmaceutical and research cleanrooms, temperature and humidity are not set for personnel comfort — they are set because the product or process specification requires them. Deviating outside the specified range is a GMP deviation that requires investigation, batch disposition review, and potentially product rejection.
Temperature — Product Stability and Assay Validity
Biological products — monoclonal antibodies, vaccines, cell therapy products, blood products — are temperature-sensitive to a degree that a ±2°C temperature excursion above specification can reduce potency, cause precipitation, or invalidate a stability study. Even in non-biological pharmaceutical manufacturing, temperature control at ±0.3°C ensures that viscosity, crystallisation, and chemical reaction rates in API synthesis remain within validated process parameters. The PLC-PID controller maintains the supply air temperature at setpoint with no overshoot — the pharmaceutical process sees the room temperature it was validated at, not a cycling approximation.
Relative Humidity — Microbial Risk and Product Integrity
Relative humidity above 60% creates conditions that support microbial growth on surfaces, packaging materials, and product — a critical contamination risk in pharmaceutical and food cleanrooms. Below 40% RH, static electricity builds up rapidly, creating product loss in powder handling and electronic component damage in electronics cleanrooms. The pharmaceutical GMP specification (typically 45–55% RH) is set precisely within the window that minimises both microbial risk and static risk — the T&H controller must maintain the room within this narrow band continuously and automatically.
PID Algorithm — Eliminating Hunting and Energy Waste
Standard on/off controllers — or simple proportional controllers without integral and derivative terms — cause the cleanroom temperature and humidity to oscillate continuously around the setpoint — a phenomenon called “hunting.” Every overshoot cycles the compressor and heater, accelerating wear and consuming more energy. The PID algorithm uses the error (P), the accumulated error over time (I), and the rate of change of error (D) together to calculate a smooth, precisely calibrated output that drives the system to setpoint and holds it there without oscillation. The derivative term in particular prevents overshoot — anticipating the approach to setpoint and reducing output before the setpoint is reached.
GMP Compliance — Continuous Documented Environmental Data
WHO GMP, EU Annex 1, and US-FDA 21 CFR Part 11 require continuous monitoring of temperature and humidity in all classified cleanroom zones, with documented alarm limits, timestamped data records, and SOP response to excursions. The Metrolabs T&H controller BMS data feed provides this compliance evidence automatically — eliminating manual paper temperature logs that are incomplete, falsifiable, and inadmissible as GMP evidence.
Six T&H Controller & Sensor Configurations
Metrolabs supplies T&H monitoring and control systems in six configurations — from standalone room indicators to fully integrated multi-zone PLC systems:
Wall-Flush Room T&H Display — Personnel Status
A flush-mounted wall display unit showing live temperature and relative humidity with large, high-visibility digital readout visible from across the room. The display housing sits flush with the modular panel surface — zero protrusion, smooth VHP-resistant glass or membrane front face, zero-ledge installation. The display shows current T and RH values alongside the setpoint — allowing personnel to verify conditions immediately on entering the zone, a key part of the entry SOP. Integrated alarm LEDs (green = within setpoint, red = outside dead-band) provide instant visual status without requiring personnel to read the numeric value. The display unit includes an internal PT100 sensor element and capacitive RH element — positioned within the unit housing to measure representative room air temperature and humidity, not wall surface temperature.
PLC-Based AHU T&H Controller — Dual-Channel PID
The core control system for the cleanroom AHU — a PLC (Programmable Logic Controller) with HMI touchscreen, running dual-channel PID algorithms for simultaneous, coordinated temperature and humidity control. Channel 1 controls the cooling coil chilled water valve and the reheating coil output to achieve the supply air temperature setpoint. Channel 2 controls the humidifier output and the dehumidifier (via cooling coil temperature setpoint modulation) to achieve the supply air humidity setpoint. The two channels interact in a coordinated cascade — the controller knows that increasing humidity through the humidifier will also raise the supply air temperature, and pre-compensates the reheating coil accordingly — preventing the hunting and overshoot that plague dual-channel on/off control systems. The PLC connects to the BMS via Modbus RTU, BACnet, or 4–20mA outputs.
PT100 / PT1000 RTD Temperature Sensor
Platinum Resistance Temperature Detectors (RTDs) are the industry standard for pharmaceutical cleanroom temperature measurement — providing better accuracy, stability, and linearity than thermistors or thermocouples over the 15–25°C cleanroom temperature range. The PT100 (100Ω at 0°C) and PT1000 (1000Ω at 0°C) sensors follow a precise, internationally standardised resistance-temperature relationship (IEC 60751) that allows high-accuracy measurement without individual calibration of each sensor — any compliant PT100 reads the same temperature for the same resistance. Low drift over extended periods means recalibration intervals are long. Metrolabs uses 4-wire PT100 connection to eliminate lead resistance errors in long cable runs — critical for sensor elements installed in the AHU air stream at distances from the controller panel.
Capacitive Polymer Humidity Sensor
The standard RH sensor for pharmaceutical cleanroom applications — a thin-film capacitive polymer element whose capacitance changes proportionally with relative humidity. Capacitive sensors provide excellent linearity across the 20–80% RH range (the pharmaceutical cleanroom operating range), fast response time, and stable performance over extended operation without the drift and hysteresis that characterise resistive humidity sensors. The polymer element is protected by a stainless steel sintered metal filter cover — preventing dust and particulate contamination from reaching the sensing surface while allowing full gas-phase humidity measurement. Metrolabs specifies NIST-traceable calibrated humidity sensors — supplied with a calibration certificate showing the measured accuracy at three reference humidity points across the measurement range.
Multi-Zone Centralised T&H Management System
For pharmaceutical suites, hospital complexes, and research facilities with multiple independently controlled cleanroom zones, Metrolabs designs a centralised T&H management system — a single PLC/SCADA hub monitoring and controlling T&H in all zones simultaneously. Each zone has its own room-mounted sensors feeding the central PLC, which runs independent PID loops for each zone’s AHU. The central HMI displays all zone T&H values on a single mimic diagram — facility managers can see the environmental status of every room from one location. Zone-specific alarm setpoints, dead-bands, and logging intervals are independently configurable. All zone data is logged to a central data logger for unified GMP environmental monitoring records. Supports up to 64 zones on a single Modbus network.
Standalone Validated Data Logger — 21 CFR Part 11
For facilities requiring environmental monitoring evidence independent of the AHU control system — providing a second, redundant data trail that cannot be affected by AHU control system faults — Metrolabs supplies standalone validated data loggers with their own independent T&H sensor elements, local storage of timestamped records, and USB/Ethernet export to validated data management software. The standalone logger satisfies the 21 CFR Part 11 requirement for audit trail integrity — all records are electronically signed, tamper-evident, and access-controlled by user role. The logger continues recording even when BMS communication is lost — ensuring continuous environmental monitoring data during system maintenance or communication failures. Calibration certificates for all sensor elements supplied. Recommended for all pharmaceutical GMP facilities with US-FDA or PMDA submission requirements.
Metrolabs T&H Controller — Technical Standards & Accuracy
Every Metrolabs T&H controller system is commissioned and documented to the following performance parameters:
| Feature | Metrolabs Standard | Benefit |
|---|---|---|
| Temperature Accuracy | ±0.3°C of setpoint | Precise enough for biological & chemical process validation |
| Humidity Accuracy✓ GMP Spec | ±2.0% RH of setpoint | Within pharmaceutical 45–55% RH specification range |
| Control Algorithm | PID (P + I + D terms) | No hunting, no overshoot — energy efficient |
| Temperature Sensor | PT100 / PT1000 RTD (IEC 60751) | Long-term stable — minimal recalibration |
| Humidity Sensor | Capacitive polymer element | Accurate 20–80% RH — fast response |
| Communication | Modbus RTU / BACnet / 4–20mA | Integrates with any BMS platform |
| Display | Flush-mounted digital HMI | Zero-ledge — VHP resistant — GMP hygienic |
| Data Logging | 21 CFR Part 11 compliant | Audit-ready — tamper-evident — WHO/FDA accepted |
Placing Sensors in Representative Zones — Data That Reflects Reality
A T&H sensor installed in the wrong location produces data that misrepresents the actual cleanroom conditions — potentially masking excursions in the critical work zone while showing compliant values at the sensor position. Metrolabs follows ISO 14644-2 sensor positioning principles:
Representative Zone Placement — Away from Disturbances
Sensors are positioned in the representative zone of the cleanroom — the area most affected by the process and most representative of the conditions to which the product or personnel is exposed. This means away from door draughts (which create localised cool or warm air pockets), away from heat-generating equipment (centrifuges, incubators, process vessels), and away from HEPA supply diffusers (which create locally cool, low-humidity microclimates directly below the filter). Typically 1.2–1.5m above floor level, in the room quadrant opposite the primary HEPA supply.
AHU Supply Air Sensor — Control Reference
A dedicated supply air T&H sensor is installed in the AHU supply duct downstream of the reheating coil and humidifier — this is the sensor the PID controller uses as its control feedback. The supply air setpoint is typically calibrated so that the room sensor (at representative zone) reads the specified room conditions — the supply air temperature and humidity are slightly different from the room values due to mixing with return air in the plenum.
Audit-Ready Data Logging — Batch Environmental Records
Every T&H reading is timestamped and stored in the BMS data logger with the sensor ID, room ID, value, alarm status (normal / warning / alarm), and operator acknowledgement for any alarm event. The data record supports a complete batch environmental monitoring review — demonstrating that temperature and humidity remained within the validated range throughout the production batch from start to finish. Data is exportable in CSV and PDF format with an electronic audit trail of all access and modifications.
Alarm Dead-Band — Preventing Nuisance Alarms
A configurable dead-band (typically ±0.5°C for temperature, ±3% for RH beyond the control setpoint) prevents alarms from triggering during normal transient fluctuations — door openings, occupancy changes, process heat load variations — while still alarming promptly on genuine out-of-specification excursions that require investigation and documentation. The dead-band is set wider than the control accuracy specification to prevent the alarm from triggering every time the PID makes a minor control correction.
T&H Controllers Across Every Regulated Cleanroom Sector
Pharmaceutical GMP
PLC-PID dual-channel control for Grade A through D AHUs — ±0.3°C and ±2% RH with 21 CFR Part 11 logging for WHO, US-FDA, and EU regulatory batch records.
Aseptic & Biologicals
High-accuracy T&H control for Grade A/B aseptic manufacturing — temperature stability critical for biological product potency and sterility assurance throughout filling.
Biotech & Cell Culture
Multi-zone centralised T&H management for cell therapy and ATMP GMP suites — each culture room independently controlled with unified batch environmental records.
Hospital & Healthcare
T&H control for hospital cleanrooms, OTs, and CSSD — temperature and humidity within NHS/NABH standards, integrated with hospital BMS for centralised monitoring.
Electronics Cleanrooms
Humidity control at 45–55% RH for semiconductor and electronics cleanrooms — preventing ESD events and ensuring stable process yields in humidity-sensitive manufacturing.
Food & Beverage
T&H control for FSSAI high-care food cleanrooms — humidity maintained below 60% RH to prevent microbial growth on food contact surfaces and packaging.
NABL Research Labs
Standalone validated data loggers for NABL-accredited testing labs — NIST-traceable sensor calibration and 21 CFR Part 11 records for ISO/IEC 17025 submissions.
Long-Term Storage & Stability
T&H monitoring and control for pharmaceutical stability chambers and product storage rooms — continuous logged evidence of storage conditions for stability study data.
Fully Integrated Environmental Strategy — Not Just a Thermostat
Metrolabs does not supply standalone thermostats — we design and commission a complete, validated environmental monitoring and control system, custom-programmed to the specific AHU, zone layout, and regulatory requirements of each project:
Custom-Programmed PID Tuning per AHU
Every AHU has a different thermal mass, cooling coil capacity, humidifier output, and duct length — meaning the PID parameters (gain, integral time, derivative time) that produce stable, hunting-free control are different for every installation. Metrolabs commissions the PID parameters through step-response testing at first commissioning, producing the optimal settings for each specific AHU rather than factory defaults that may produce hunting in that specific system.
Coordinated Dual-Channel — Temperature and Humidity in Balance
The most common T&H control failure is running temperature and humidity as two completely independent control loops — when the humidifier adds moisture to increase RH, the supply air temperature rises, causing the heating controller to reduce output, which then drops the RH back as the air cools. Metrolabs programmes the dual PID channels to run in coordinated cascade — the temperature controller knows about humidifier output changes and pre-compensates the reheating coil, eliminating the interaction-induced hunting entirely.
Audit-Ready from Day 1 — 21 CFR Part 11
The BMS T&H data logging is configured, access-controlled, and validated at commissioning — the GMP environmental monitoring record is active from the first day of cleanroom operation. Each log entry is electronically signed, timestamped, and stored in a tamper-evident format. Alarm event records include operator acknowledgement ID. The system is pre-configured to export the standard environmental monitoring report format required for batch record submission.
VHP-Compatible — No Damage After 500+ Cycles
All sensor housings, display faces, and controller front panels are specified for full VHP exposure — the materials are tested to maintain dimensional stability, sealing performance, and electrical function after 500+ VHP sterilisation cycles at up to 1000 ppm H O concentration. This prevents the material degradation, condensation of VHP residue on sensor elements, and seal failures that cause T&H controller malfunctions in facilities with regular room-wide VHP programmes.
T&H Controller Type Comparison
From Controller Selection to Validated PID Tuning & 21 CFR Logging
Metrolabs manages the complete T&H controller installation from sensor placement through PID tuning, BMS integration, and validated data logging confirmation:
Sensor Position Design
Representative zone positions confirmed per ISO 14644-2. AHU supply duct sensor position agreed for PID feedback. Room display unit positions confirmed for zone entry SOP compliance. Cable route plan produced.
Controller Installation & Wiring
PLC, sensors, and displays flush-installed. PT100 4-wire connections made to eliminate lead resistance errors. 4–20mA or Modbus cable run to BMS. All connections tested for signal integrity before PLC power-on.
PID Tuning & BMS Integration
Step-response test on AHU: temperature step change applied, controller response recorded. PID parameters (Kp, Ti, Td) calculated and programmed. BMS trend logging confirmed active. Alarm setpoints, dead-bands, and delay timers configured per zone.
Calibration Verification & IQ Issue
Sensor output verified against NIST-traceable reference at three temperature and RH points. PID stability confirmed by 24-hour trend run. Alarm response test performed and logged. All calibration certs and tuning records in HVAC IQ documentation.
T&H Monitoring Required by Every Major Cleanroom Regulatory Framework
WHO & EU GMP
WHO GMP and EU Annex 1 require continuous monitoring of temperature and humidity with defined alarm limits and documented SOP response to excursions. The PLC T&H controller BMS log provides the primary environmental monitoring evidence for GMP batch record review and regulatory inspection.
WHO GMP · EU Annex 1ISO 14644-2
ISO 14644-2 specifies temperature and humidity as primary cleanroom monitoring parameters with defined monitoring intervals, alarm limits, and data review frequency. Metrolabs T&H controller BMS logging satisfies the continuous monitoring requirement directly — data reviewed at defined intervals as part of the ISO 14644-2 periodic review programme.
ISO 14644-221 CFR Part 11
US-FDA 21 CFR Part 11 requires that electronic environmental monitoring records are timestamped, tamper-evident, access-controlled, and audit-trailed. Metrolabs BMS T&H data logging is configured to meet all Part 11 electronic record requirements — data is admissible as GMP evidence in US-FDA, PMDA, and MHRA inspection submissions.
21 CFR Part 11NABL & FSSAI
NABL ISO/IEC 17025 accreditation and FSSAI licensing require documented evidence of controlled temperature and humidity conditions in test and production areas. Metrolabs T&H logging with NIST-traceable sensor calibration provides continuous, documented compliance evidence for both accreditation bodies.
NABL · FSSAI · IEC 60751Ready to Achieve ±0.3°C and ±2% RH with 21 CFR Logging?
Contact Metrolabs for a free consultation. Our instrumentation specialists will assess your AHU configuration, zone layout, regulatory requirements, and BMS platform — then specify, supply, install, commission, and tune a complete PLC-PID T&H control system with sensor calibration certificates and 21 CFR Part 11 data logging at handover.
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