# Context-Based Energy Disaggregation in Smart Homes
## 2 Background  
This section provides background information on load monitoring and appliance profiling. Appliance Profiling refers to the observation of an electronic device's consumption behavior in order to extract all the features that could characterize it in detail. It consists of defining a set of relations between the working states of an appliance and the energy that it consumes [11]. Thanks to the knowledge of these characterizing features, a monitoring system would be able to analyze the output of a meter and recognize the appliance(s) in use. As suggested by [PERSON] [6] and [PERSON] and [PERSON] [12], depending on their power profile, home appliances can be divided into four main categories:  
1. _Permanent consumer devices_. Devices that are permanently on and are characterized by an almost constant power trace (e.g., smoke alarms, telephones, _etc._). 2. _On-off appliances_. Appliances that can be modeled with on/off states (e.g., lamp, toaster, _etc._). 3. _Finite State Machines (FSM) or Multistate devices_. Devices that pass through several switching states. An operation cycle can thus be represented through a Finite State Machine and can be repeated on a daily or weekly basis. Examples are a washing machine, a dishwasher, a clothes dryer, _etc._
4. _Continuously variable consumer devices_. Devices that are characterized by a variable non-periodic power trace. Examples of such appliances include notebook and vacuum cleaners. Furthermore, in order to characterize the behavior of an appliance, a minimal set of three power mode states can be defined [13]:  
* _Active_: the appliance is fully operational; the trend of the power consumption trace depends on the specific appliance. * _Stand by_: the appliance is turned off, but some activities continue to run. The power consumption trace is zero, except for some sporadic low consumption samples. * _Disconnected_: the device is disconnected from the electric network. A further classification can be made by considering the type of device load: resistive, inductive or capacitive load. This differentiation is related to the typology of device internal circuits and strongly influences its power consumption profile. The Active Power is the real part of the Apparent Power complex equation; it represents the amount of energy consumed by an appliance during its ON period. Since the Apparent Power is the product between the current and voltage effective values, then a current/voltage shifting causes a variation in the power transferred to the appliance. This variation can be detected through the analysis of the Reactive Power, the imaginary part of the Apparent Power equation, which represents the amount of power absorbed by inductive/capacitive elements and therefore not exploited by the load. As stated in [13] \"the larger the current/voltage shift the grater the imaginary component\" and, consequently, the lower the active power is transferred to the appliance. Therefore, the types of component that can be found in a device can be distinguished as follows:  
* Inductive type: affects the power consumption by shifting the alternate voltage with respect to the alternate current (e.g., washing machine). * Capacitive type: affects the power consumption by shifting the alternate current with respect to the alternate voltage (e.g., rechargeable battery). * Resistive type: shows no shift of current and voltage; if the appliance is a pure resistive type, the current and voltage waveforms will always be in phase and the imaginary part (reactive power) of the complex apparent power is zero (e.g., toaster). An appliance profile, also mentioned as \"appliance signature\" or \"appliance fingerprint\", is thus composed by several characteristics which can help to identify that specific device (e.g., real power, maximum power value, waveform shape, ON period duration, _etc._). A refrigerator power trace, for example, presents a periodic pattern whose periods depend on the overcoming of an internal temperature threshold manually or automatically set.