Demand controlled ventilation strategies for high indoor air quality and low heating energy demand

In this study several demand controlled ventilation (DCV) strategies are compared with regard to indoor air quality, thermal comfort, and heating energy demand. In order to appropriately model the office room equipped with a PID controlled floor heating system and 4 commonly used bottom-hinged tilted windows located in our low-energy research house (SmartHOME), the thermal time constants and air exchange rates including the infiltration rate and natural ventilation rate were measured. Simulations were then performed for 2 typical winter days in Munich in the accordingly modeled office room with 2 adults working from 8 a.m. to 6 p.m. The DCV strategies ensure that the CO₂ concentration of the indoor air stays within the preset range. The Pettenkofer limit of 1000 ppm is a hygienically approved limit value for long-term occupied spaces. The results show that the combination of appropriate DCV and floor heating control strategies can greatly reduce the heating energy consumption and at the same time guarantees high indoor air quality and low room temperature variations. It can decrease the total heating energy demand of the office room during working hours by approximately 27% and save 4.4 kWh per typical winter day compared with the usually recommended “brief and intensive airing” method. Moreover, based on our measurements we performed CFD (Computational Fluid Dynamics) simulations in order to determine the temporally resolved 3D distributions of the indoor CO₂ concentration. These results help determine the best location in the room for a single sensor inside the room to representatively measure the CO₂ concentration.