What is Carbon Dioxide (CO₂)?

Carbon Dioxide (CO₂) is a colourless, odourless gas naturally present in Earth’s atmosphere. It is produced by human respiration, combustion of fossil fuels, and organic decomposition. In building ventilation, CO₂ levels are a key indicator of indoor air quality (IAQ). Elevated concentrations can lead to drowsiness, reduced cognitive function, and poor health outcomes.

Context in UK Building & Ventilation

  • Building Regulations (Approved Document F 2021) mandates adequate ventilation to maintain CO₂ levels below 1,500 ppm (parts per million) in occupied spaces.
  • Retrofits & Renovations: Poorly sealed homes (e.g., after insulation upgrades) may trap CO₂, necessitating mechanical ventilation (MVHR) or background trickle vents.
  • Monitoring: CO₂ sensors are increasingly used in Passivhaus and low-energy builds to ensure compliance with health standards.

Practical Example

A UK residential retrofit adding airtightness measures (e.g., triple glazing, insulation) may inadvertently reduce natural air exchange. Installing a demand-controlled ventilation (DCV) system with CO₂ sensors ensures airflow adjusts based on occupancy, maintaining safe levels.

Related Essential Terms

  1. Indoor Air Quality (IAQ): The overall healthiness of air inside buildings, influenced by CO₂, VOCs, humidity, and particulates.
  2. Mechanical Ventilation with Heat Recovery (MVHR): A system that extracts stale air (high in CO₂) while recovering heat, improving energy efficiency and IAQ.
  3. Approved Document F (Ventilation, 2021): UK regulation specifying minimum ventilation rates for dwellings, including CO₂ limits.
  4. Airtightness (Air Permeability): Measured in m³/(h·m²)@50Pa, critical for preventing CO₂ buildup in modern builds.
  5. Passivhaus Standard: Ultra-low-energy buildings requiring CO₂ monitoring to balance airtightness with ventilation.
  6. Volatile Organic Compounds (VOCs): Often co-monitored with CO₂, as both degrade IAQ.
  7. Demand-Controlled Ventilation (DCV): Smart systems using CO₂ sensors to adjust airflow dynamically.