# An Accident Model with Considering Physical Processes for Indoor Environment Safety
## 3 Accident Model
### Stamp-Pp
#### 3.2.2 Service  
In this section, we discuss the behaviors of the Performers System, and when the behaviors can be taken as Services. **Definition 3** (Behavior of the Performers System). : _The way the Performers System behaves to adjust the indoor environment._  
The Behaviors of the Performers System are the representation of the functions of related Performers. For example, the Performers System in Figure 2 has the ability to cool the temperature down (behavior), which could be achieved by setting a lower temperature level under the cool mode of the air-conditioner (function). The representation of the Behaviors is the physical process, e.g., temperature change. **Definition 4** (Service). : _The Behavior of the Performers System exhibited in order to fulfill occupants' comfort requirement._  
One example of the Service can be the Performers System in Figure 2, which increases the indoor temperature to 22 \({}^{\circ}\)C for thermal comfort. Comfort means psychological and physical satisfaction with the state of the indoor environment, e.g., thermal comfort. It is the way to evaluate the Behaviors of the Performers System, and thus implicitly constrain the Behaviors. The comfort has different contents for different goals of the Performers System, e.g., thermal comfort; comfort in terms of humidity levels. There are two ways to evaluate comfort. Let us take thermal comfort as an example. The first is based on the perception of occupants. If occupants feel uncomfortable, one can manually set a desired temperature level to the Performers System. It is easy and accurate but limited in some scenarios. For example, babies and elderly people may not be sensitive to temperature change due to their nervous system not being well developed or being degenerated. The second way is for comfort to be automatically evaluated by the smart home system core. This depends on various indices [24; 25] for evaluating the physical environment for thermal comfort. For example, the PMV-PPD (Predicted Mean Vote and Predicted Percentage of Dissatisfied) index [25] is used to evaluate thermal comfort with respect to environmental factors and personal factors. PMV and PPD are short for predicted mean vote and predicted percentage of dissatisfaction, respectively, and are calculated based on Formulas (1)  
Figure 2: An example of the Performers System. and (2), where \(TS\) denotes the thermal sensation transfer coefficient and is determined by metabolic rate; \(MV\) means internal heat production in the human body and is determined by the metabolic rate and external work; and \(HL1\), \(HL2\), \(HL3\), \(HL4\), \(HL5\), and \(HL6\) represent heat losses through skin, sweating, latent respiration, dry respiration, radiation and convection, respectively. Then combine with the ASHRAE (American Society of Heating, Regrigerating and Air-Conditioning Engineers) thermal sensation scale as shown in Table 1 to determine the comfortableness. The details are referred to in [25]. \[PMV=TS\times(WM-HL1-HL2-HL3-HL4-HL5-HL6) \tag{1}\]  
\[PPD=100-95\times e^{-0.03353\times PMV^{4}-0.2179\times PMV^{2}} \tag{2}\]  
Environmental factors like humidity can be acquired through humidity sensors. Personal factors like metabolic rate can be roughly evaluated based on the occupant's activities, e.g., sedentary. Another way is to take advantage of wearable devices to measure personal information and send these data to the smart home system core to evaluate comfortableness. However, as far as the author is aware, cloth insulation cannot be evaluated through wearable devices for now. It can only be roughly evaluated through scenarios like in hot summer, where the value of cloth insulation is small, and an average value is assigned for the summer season. **Definition 5** (Service Manner). : _The Service under a specific condition is called a Service Manner._  
The condition can be personal or environmental. For a Service, e.g., adjust the indoor temperature for thermal comfort by an air-conditioner, changes in conditions result in different Service content.