Introduction IPCC (The Intergovernmental Panel on Climate Change) recommends a 50% reduction of manmade CO2 emissions before 2050 to avoid severe problems of global warming. The IEA report “Energy Technology Perspective 2008” has presented the Blue Map scenar- io on how to achieve this emission reduction (IEA re- port, 2008). A consequence for the building sector is that a wide- spread conversion of buildings to very low energy con- sumption and even zero energy buildings is necessary. The EU Parliament approved in 2010 a directive (EPBD Recast) that requires member states to implement am- bitious plans to upgrade much of the existing building stock to nearly zero energy buildings (NZEB) by 2020, with intermediate goals to be set for 2015. Ventilation constitutes a major share of the total en- ergy use buildings of existing non-commercial build- ings in the Nordic countries, typically 35-50% for of- fice buildings (Wigenstad and Grini, 2010). Existing office buildings in Norway have an average energy use of 245 kWh/m² according to Enova (2010). Most non-residential buildings have Constant Air Volume (CAV) ventilation leading to over-ventilation in periods with low or no occupancy. Comparison of perceived indoor climate in schools with CAV-systems and DCV-systems does not indicate that CAV-systems add extra quality to the indoor climate (Mysen Doctoral Theses 2005). The purpose of extra ventilation with CAV-systems is therefore questionable as it leads to ad- ditional energy use. Demand controlled ventilation (DCV) considerably reduces the ventilation airflow rates and energy use compared to CAV systems. This conclusion is based on an inspection of 157 classrooms in primary schools (Mysen et al. 2005). Installation of variable air vol- ume systems (VAV) can reduce the need for air heat- ing by more than 90% and electrical energy for air distribution by 60% (Maripuu and Jagemar 2004, Maripuu 2009). DCV is probably a prerequisite to achieve the ambitious energy-goal for existing com- mercial buildings. However, evaluation of real energy use demonstrates that this potential is seldom met. DCV-based ven- tilation systems must become more reliable to close the gap between theoretical and real energy-perform- ance. This unfortunate experience with DCV seems to have many causes. Identified key factors for im- provement so far are: to avoid wasted energy use be- cause of unnecessary throttling, inadequate specifi- cations, hand-over documentation and balancing re- port for DCV, and a clearly defined and placed re- sponsibility for the overall functionality. This paper presents energy related differences between DCV-sys- tems and recommends requirements for improved en- ergy functionality. Alternative DCV-systems Figures 1 to 3 show the supply ductwork of in prin- ciple different DCV-systems: “Pressure Controlled DCV” (PC-DCV) and “Static Pressure Reset DCV”, and “Variable Air Supply Diffusor”. The exhaust sys- tem is similar in principle, or based on a master-slave concept related to the supply air flow. Requirements for well functioning Demand Controlled Ventilation Peter G. Schild Senior Scientist SINTEF peter.schild@sintef.no Mads Mysen Senior Scientist Oslo University College SINTEF Mads.Mysen@sintef.no REHVA Journal – October 2011 14 articles