The demands for both thermal comfort and reduced energy consumption in buildings have become a major driving force for the increased use of advanced building automation and control systems (BACS). In the on-going development of Zero Emission Buildings (ZEBs), it seems to be a common understanding that such systems are needed in order to save energy and reach the zero emission goals, and that energy consumption for their operation is negligible compared to the building needs and the energy saving potential BACS causes. However, sensors and actuators in automation and control systems require electricity to operate, and both the environmental impact related to this operation, and the manufacturing and maintenance of electronic components (including wiring) is not well understood in a Life Cycle Assessment (LCA) perspective, even though different standards give framework and methods for energy calculations and LCA of buildings. These standards unfortunately do not include or suggest default values for the auxiliary energy from different levels of BACS. Usually, in building simulation, these values are only assumed to be a part of a fixed internal gain, e.g. as in the Norwegian passive house standard, with no further considerations on the actual operating energy or the environmental impact it represents.

In this paper, auxiliary energy to operate a KNX-bus system for a planned passive house office building with demand control on room/zone level, is measured in a laboratory test. For typical room zones, as for a single office and a meeting room, the electrical standby power counts for respectively 0.91 and 2.00 kWh/m2∙y solely for operating the automatic system on room level. E.g., based on the electricity mix UCPTE, components needed to achieve automatic zone control equals 2.86 and 6.28 kWh/m2∙y of non-renewable primary energy (PEFnon-ren). For the whole building; 0.85 kWh/m2∙y and PEFnon-ren = 2.67 kWh/m2∙y. Other PEF production factors will give different results which can have decisive implications on the development of the ZEB concept and the use of BACS in future buildings. The auxiliary energy for BACS should therefore be included when conducting energy simulations and evaluations of the environmental performance of Zero Emission Buildings.