Energy conservation, Optimized outside air flow rate, Indoor air quality, Air cleaner
*1 Introduction* A technical combination of the operation of heating, cooling and mechanical ventilation provides at the same time thermal comfort and indoor air quality in office buildings, where occupants usually stay day long for work. The indoor air quality in buildings is ensured by mechanical ventilation with a sufficient outside air flow rate according to national or European regulations. However the outside air flow rate increases the heat demand of buildings; the higher the air flow rate the higher is the energy demand. Referring to the demand of oxygen the required outside air flow rate could be reduced to less than a one-tenth of rates that are common today. Therefore, the consideration of this point is that mechanical ventilation systems with constant volume rate are replaced by ones with variable volume rates. These variable volume rates should be an optimal air flow rate in view of energy conservation. The goal of this optimization is to minimize the total energy demand for heating, cooling and ventilation including the energy demand for the transport of the air. The declining indoor air quality due to the reduction of the air flow rate must be compensated by a pollutant sink (air cleaner). A room of an office building is used as model for the case study. A self-developed program combined with the software TRNSYS (TRaNsient SYstems Simulation) is used as a tool for this investigation. *2 Methods* An objective function is used to find that optimal air flow rate. The demand of energy is calculated as the sum of heating, cooling, ventilation and the electricity for the air transport. In a first step a typical ventilation system with a constant volume rate with outside air rates according to EN 13779 is examined as case 1 (reference) and the annual primary energy demand is calculated. In a second step the ventilation system is operated with the optimized air flow rate (i.e. variable volume rate) (case 2) and the annual energy demand is calculated as well. In a third step the two cases are compared and the energy conservation potential is investigated. *3 Results* The results will show the potential of primary energy conservation of a ventilation system with variable optimized volume rates in combination with a pollutant sink against that with a constant volume rate. Furthermore the results shall show in detail the optimal outside flow rate for each period of the day as well as of the year. Results are not yet available but will be presented in the paper. *4 Conclusions* Conclusions are not yet available but will be presented in the paper.