Three unobtrusive domestic occupancy measurement technologies under qualitative review

• Compared three occupancy measurement technologies for domestic energy efficiency.
• Overall occupancy, room occupancy, number of occupants and location were assessed.
• Passive infra-red: only good at occupancy detection, but prone to negative false.
• CO2: highly depends on air circulation, thus only detects overall occupancy reliably.
• Device-free localisation shows clear potential and requires more research.

Almost one third of the UK's total energy is consumed by the domestic sector. Occupancy measurement could have the potential to save significant amounts of that energy, either instantly via a home automation system or retrospectively via post-occupancy evaluation. However, not many localisation technologies are applicable to a domestic environment. In this paper three unobtrusive occupancy measuring technologies, i.e. Passive Infra-Red (PIR), Carbon Dioxide (CO2) and Device-free Localisation (DfL), are compared. Their operation is explained and possible advantages and disadvantages are outlined. A qualitative experimental study then analyses the abilities of each system to detect overall occupancy, detect room level occupancy, count the number of occupants and localise them. It has been found that CO2 and PIR sensors are very limited. The impacts of other factors, such as windows or occupants’ metabolic rates, were significant on the reliability of the measured data. DfL on the other hand has great potential, but requires further research.