Most commercial ventilation systems run at a fixed rate whenever the building is occupied, moving the same volume of air whether a space is full or nearly empty. That is simple, but it is wasteful — you are conditioning and moving air nobody needs. Demand-controlled ventilation fixes that by matching airflow to actual occupancy, and the savings can be substantial.
How it works
The principle is straightforward. CO2 levels in a space rise as more people occupy it, because people exhale CO2. A CO2 sensor therefore gives a reliable, real-time proxy for how busy a space is. Demand-controlled ventilation feeds those sensor readings to the air handling system, which increases airflow when CO2 rises and reduces it when the space empties.
Instead of running flat out all day, the system ramps up for a full meeting room and eases off for a quiet afternoon — automatically, without anyone touching a control.
Where the savings come from
Two places. First, fan energy: moving less air means the fans draw less power, and because fan power rises sharply with airflow, even modest reductions in volume produce meaningful energy savings. Second, conditioning energy: every cubic metre of outdoor air brought in has to be heated or cooled to the right temperature. Ventilate only to demand and you heat and cool far less air. In buildings with variable occupancy — offices, schools, conference facilities, retail — the combined saving is often significant.
Without compromising air quality
The obvious worry is that reducing airflow means worse air. It is the opposite. Demand-controlled ventilation is driven by air quality — it responds to CO2, the very thing you are trying to keep down. When a space fills and CO2 climbs, the system delivers more air, not less. Occupants get better-matched ventilation than a fixed system provides, because a fixed system is a compromise: too much air when quiet, sometimes too little when packed.
Is it right for your building?
Demand-controlled ventilation makes most sense where occupancy varies through the day and across spaces. A building that is uniformly full from nine to five has less to gain than one with meeting rooms, flexible areas or fluctuating footfall. Many existing air handling systems can be adapted to demand control rather than replaced — it is often a matter of adding sensing and updating controls.
We assess whether demand-controlled ventilation fits your building, and we design and install the sensing and control changes to make it work with your existing air handling equipment where possible.
If your ventilation runs at a fixed rate regardless of how busy the building is, there is almost certainly energy being wasted.
