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Click on the following link to see a DCV system at work:

The Demand Controlled Ventilation (DCV) group has been set up to gain recognition for control as a sustainable ventilation strategy for new and existing buildings.

Demand Controlled Ventilation (DCV): an introduction

As buildings become more air tight and well insulated, purpose provided ventilation is required to create a safe, healthy and comfortable indoor climate and protect the building against damage that may be caused by moisture.

Enough is enough

The minimum required ventilation rate is often based on maximum occupancy. However, dwellings are not always fully or continually occupied and if we can control the ventilation rate based upon actual occupancy and activity, then we have the potential to reduce the ventilation rate and therefore reduce the annual energy required to power the fan(s) and save energy without compromising indoor air quality. Additionally, if a DCV allows home owners or tenants to ventilate less during the heating season and more during the hot summer nights, then the annual energy required to heat or cool the outdoor air also decreases.

Sensor technology

Demand Controlled Ventilation (DCV) systems employ sensors to detect the level of occupancy and activity by measuring water vapour, CO2 or other pollutants and adjust the ventilation rate accordingly (both dynamically and automatically) and by doing so avoid excessive ventilation and reduce the energy consumption of systems which run continuously at fixed ventilation rates.

NB Although water vapour and CO2 levels correlate well with human occupancy and human-generated pollutants, they do not reflect the buildup of pollutants not related to occupancy. Therefore, DCV needs to ensure that all potential contaminants remain at the specified safe levels when occupied.

More is sometimes better

It is widely believed that actual occupancy levels in private housing are lower than the conventional ventilation systems are designed to handle. It is also believed that the actual occupancy levels in social housing is higher than the conventional ventilation systems are designed to handle. In both cases, DCV offers a strategy to optimize the balance between the necessity of creating and sustaining a healthy and comfortable indoor climate and using as little energy as possible in the process.

It’s science, but not rocket science

Pheat (W) = ρ x c (Wh/m3.K) x qv (m3/h) x ΔT (K)      (EN 15241)

The above formula clearly shows how energy can be saved with ventilation systems, namely:

  • Reduce the uncontrolled flow of fresh air into the building (infiltration).
    • NB Although DCV systems can and do use infiltration air, (theoretical) infiltration rate calculations should not be used for ventilation system design.
  • Reduce the controlled flow of fresh air into the building (ventilation) to the minimum level required without making any concessions to IAQ by:
    • Controlling the volume of fresh air flowing into the building according to occupancy and activity (DCV);
    • Improving ventilation effectiveness/efficiency;
    • Reducing the generation/emission of pollutants as much as possible (e.g. VOCs, formaldehyde, radon, etc) to reduce the minimum ventilation rate when the building or a room is unoccupied;
  • Reduce the temperature difference between the outdoor air temperature and desired indoor air temperature (MVHR);
  • Minimise air leakage and pressure loss in air distribution systems and maintain them periodically;
  • Use fans which have a low SFP in the operating area that they are used the most;
  • Choose suitable filters and maintain them regularly.

Click on the following link to see a DCV system at work:

Last updated 25 June 12