Convertion from CAV to VAV - A Key To Upgrade Ventilation And Reach Energy Targets In The Existing Building Stock

Demand controlled ventilation (DCV) can considerably reduce the ventilation airflow rate and energy use for fans, heating and cooling compared to constant air volume (CAV) ventilation. Based on the new EPBD Recast directive from the EU Parliament, there is a potentially enormous upcoming marked for converting from CAV to efficient DCV in existing commercial buildings. However, several DCV-solutions are not very suitable for upgrading applications because they require redesign of airflow paths or introduction of several new components that are difficult to integrate into existing CAV-systems. A normal consequence is that ventilation upgrading is postponed, or the existing ventilation system is completely discarded and replaced. Such complete replacement of existing systems is probably not environmentally friendly, and has considerable additional costs like loss of estate rental income during the rebuilding period. This paper presents DCV-systems that seem particularly promising for upgrading ventilation in existing commercial buildings. At the moment, DCV with variable supply air diffusers seems generally most suitable for upgrading from CAV to VAV, but project-specific requirements and circumstances must be emphasized before the final choice in each project is taken.