targeting on personal healthcare monitoring and telehealth systems[21]. The development of AAL systems is mainly driven by the demo-graphic change. The technology might help to minimize increasingcosts in the healthcare sector. In general, three broad views concerningAAL are differentiated: (i) functionality: smart homes as help for a moreefficient and easy management of the demands of daily living; (ii) in-strumentality: possibility of smart home technology to improve energyefficiency and to lower energy costs and negative environmental in-fluences (e.g. outdoor/indoor pollutants); (iii) socio-technical: com-plement assistance for human healthcare [21,22], as shown in Fig. 3.Concerning healthcare applications, it is important to consider so-cial and ethical problems, such as the handling and acceptance by olderpeople. An important aspect in this regard is that sensor technologiesmust not replace human care but that technologically solutions areprovided in order to complement and support healthcare treatmentsand systems without distracting or attracting attention as realized in theInternet of Things [21,23]. Based on this approach, an IAQ sensorsystem for AAL has been developed incorporating sensors for tem-perature, relative humidity, light intensity and CO 2 [21].Even if there are many technologies available for measuring thermaland air quality parameters in homes, there are significant challenges inapplication of these technologies and in making them useful in con-trolling the indoor environment. One of the reasons is that the indoorenvironment is a complex system, with its elements strongly connectedand affecting each other. For example, when increasing the ventilationrate by opening the window to allow cooler outdoor air to enter thehouse interior, some fraction of the pollutants generated indoors isremoved, for example CO 2 or combustion products generated duringcooking. However, increased ventilation can promote the ingress ofpollutants and particles from outside leading to elevated concentrationsindoors, especially when the indoor environments are close to busyroadsides [24,25]. Different studies targeting on indoor air qualitywithin low energy buildings and passive houses have shown that airexchange rates are mostly too low (< 0.2 h−1) due to an inadequatesetting or missing knowledge in operation and management of occu-pants leading to increased CO 2 levels indoors [26,27]. Increased CO 2 -concentrations were also found during night-times as residents swit-ched off the mechanical ventilation system due to uncomfortable airflows. Otherwise, facing the high area/resident ratio in newly built low-energy houses, CO 2 values can stay unintentionally low because of di-lution effects