Greenhouses and vertical farms allow growers to extend seasons, stabilise yields, and protect crops from contamination. Among the many environmental variables that can be controlled, carbon dioxide concentration is one of the most influential for plant growth.

Ambient CO₂ levels of ~400 ppm are rarely sufficient for high-density cultivation. By enriching to several thousand ppm, photosynthesis efficiency increases and crops develop faster with improved yields. However, enrichment only works when concentrations are measured and regulated accurately.

Unmeasured enrichment risks three outcomes:

• Underdosing, which leaves potential yield untapped.
• Overdosing, which wastes CO₂ and energy.
• Instability, which disrupts the balance between ventilation, humidity, and temperature control.

Accurate, continuous CO₂ monitoring is therefore a foundation for successful greenhouse management.

Challenges in the greenhouse environment

Measuring CO₂ in greenhouses is not trivial. Sensors must withstand conditions that are highly variable and often extreme compared to typical indoor applications:

• Relative humidity above 90 %, often close to condensation.
• Wide CO₂ ranges, from ambient background levels to enrichment levels above 10 000 ppm.
• Temperature swings, driven by season, diurnal cycles, and HVAC activity.

These conditions quickly expose the weaknesses of general-purpose sensors, leading to drift, shortened lifespan, or outright failure.

Why NDIR is the right sensing principle

Non-Dispersive Infrared (NDIR) measurement has become the preferred technology for greenhouse CO₂ monitoring because it directly addresses these challenges.

• Direct selectivity — NDIR detects CO₂ by its characteristic infrared absorption, avoiding interference from oxygen or most other gases.
• Long-term stability — With no consumable chemical components, NDIR sensors provide consistent accuracy over many years.
• Wide dynamic range — Capable of covering both ambient conditions and heavily enriched atmospheres.
• Resilience to humidity and temperature — With suitable engineering, NDIR modules maintain accuracy in near-saturated air and fluctuating thermal environments.

For growers, this translates into dependable data for climate control and enrichment systems, ensuring that CO₂ dosing strategies are both effective and efficient.

Purpose-built for greenhouse applications

While NDIR is the principle of choice, not every NDIR sensor is equal. Many were originally designed for indoor air quality or safety applications, not continuous operation at 95 % RH or in fast-changing greenhouse conditions.

The Senseair S88 GH is a great example of an NDIR sensor developed specifically for greenhouses. Based on the proven S88 platform, it incorporates rapid sampling, robust humidity tolerance, and stability across the full greenhouse operating range. Unlike adapted designs, it is engineered from the outset to perform reliably under high humidity and elevated CO₂, providing a dependable basis for enrichment control.

Closing thoughts

For controlled-environment agriculture, CO₂ measurement is not optional — it is critical. The greenhouse climate places unusual demands on sensors, and only NDIR has proven to deliver long-term stability, accuracy, and robustness under these conditions.

With purpose-built sensors such as the Senseair S88 GH, growers and system integrators have access to technology that matches the reality of the greenhouse environment — enabling more precise enrichment, improved yields, and more sustainable operations.