Environmental sensing
Temperature, humidity and the supporting cast
A building rarely fails on a single number. Environmental sensors — temperature, humidity, occupancy and pressure — provide the context that makes air quality data interpretable, and the comfort signals occupants actually feel.
The toolkit
What environmental sensors cover
Temperature
Resistance (PT100, PT1000) and thermistor sensors are dominant. Accuracy of ±0.2 to ±0.5 °C is typical in commercial use.
Relative humidity
Capacitive elements measure %RH. Drift, condensation exposure and contamination affect long-term accuracy more than headline spec.
Occupancy
PIR, counting and time-of-flight sensors inform demand-controlled ventilation, lighting and space utilisation without identifying individuals.
Differential pressure
Across filters, doors and zones, pressure trends reveal loading, leakage and containment performance.
Placement matters more than spec
Where sensors live shapes the data
A high-specification sensor in the wrong location produces low-quality data. Sun on a wall raises a temperature reading by several degrees; a sensor in the supply-air path measures the system, not the occupants; a humidity sensor next to a kettle has a story of its own.
Placement principles are simple: in the occupied zone, on internal partitions where possible, away from heat sources, supply diffusers and external glazing. Where placement compromises are unavoidable, the data interpretation must acknowledge them.
For ventilation control, the sensor's job is to represent the breathing zone. For comfort, it is to represent what occupants experience. Those are not always the same point.
Performance
What to expect — and what to ignore
| Parameter | Realistic accuracy | Notes |
|---|---|---|
| Temperature | ±0.2–0.5 °C | Manufacturer spec only meaningful with sensible placement |
| Relative humidity | ±2–5 %RH | Drift and contamination dominate over time |
| CO2 (NDIR) | ±50 ppm + 3% of reading | Auto-baseline calibration assumes regular fresh-air exposure |
| Occupancy (PIR) | Presence only, latency dependent | Counting requires different sensor types |
| Differential pressure | ±2–5 Pa typical commercial | Low-range applications need higher-grade transducers |
Limits
Common misinterpretations
Comfort is not air quality
Pleasant temperature and humidity can coexist with high CO2 or particulates. Comfort and IAQ are related but distinct.
Response time
Sensors lag. Fast events — door openings, ventilation switching — may not appear at the reported resolution.
Wireless reliability
LoRaWAN, Zigbee and BLE each have range, battery and interference characteristics. Network design is part of sensor design.
Condensation risk
Humidity and surface temperature together predict condensation risk. Either alone is insufficient.
Integration
From sensor to system
Environmental sensors rarely sit alone. They feed BMS controllers, IoT platforms, demand-controlled ventilation logic and occupant-facing displays. The integration path — wired BACnet/Modbus, wireless LoRaWAN, cloud API — should be chosen for the building's existing infrastructure, not the other way round.
Suitable for
Where environmental sensing earns its place
Smart buildings
Occupancy- and condition-aware control across HVAC, lighting and space management.
Schools and offices
Comfort assurance and demand-controlled ventilation across variable use patterns.
Healthcare and labs
Tight temperature, humidity and pressure tolerances with documented performance.
FAQ
Environmental sensor questions
Discuss an Air Quality Monitoring Project
Environmental sensor specification, placement and integration for UK commercial, educational and healthcare estates.
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Connected systems