# An IoT-Based Encapsulated Design System for Rapid Model Identification of Plant Development
## 3 Encapsulated Design Plant Growth Devices
### Climate Parameter Regulation
#### 3.1.1 Air Temperature  
Proper distribution of temperature values is extremely important for the vernalization stage. In wheat, this stage coincides with the phenological stages of germination and sowing, as well as the first and second stages of organogenesis. During the vernalization stage, crops produce only vegetative organs. Plants at this stage must be exposed to low temperatures in order to pass into the reproductive period. Temperature control is achieved using temperature sensors, positive temperature coefficient (PTC) ceramic insulated heaters, a ventilation system, and the influence of disturbances such as LED lights, solar irradiance through the glass cabinet, or the electronic device's residual heating. The heating element is used in combination with fans to control the air flow, as depicted in Figure 2. The role of the heating element is to reach the maximum temperature in the operating mode and to heat until the set reference is reached. This type of heater was chosen primarily due to its relatively large heating surface, compared with the tile of the same dimensions, and the property that a certain level of air flow will dissipate heat into the encapsulated design. The control system design scheme is presented in Figure 3a, together with an exemplary temperature response in four different zones, as in Figure 3b. The fan speed (air flow) is controlled by pulse-width modulation (PWM) to enable wide air flow span. The speed, as well as the heater's on and off periods, are regulated within a closed control loop with an individual proportional-integral (PI) controller for each zone. The four zones share the same encapsulated air in the upper compartment of the device (see Figure 1), but the airflow imposed by the fans, solar irradiance, and artificial lighting intensity can ensure the individual temperature-setting of the zone, with cross-coupled dependency in the remaining zones. In particular, up to 7 \({}^{\circ}\)C difference may be achieved between the coolest and warmest zones. The control system is therefore designed with decoupling controllers that compensate for the influence of temperatures from other microclimate zones on the observed ones. Based on obtained open-loop step responses, system identification is carried out, wherein  
Figure 2: Plant growth device construction scheme with general scheme in (**a**) and separate control systems with corresponding sensors and actuators highlighted for temperature and CO\({}_{2}\) concentration in (**b**), lighting in (**c**), and soil irrigation and air moisture in (**d**). the zone temperature dynamics are described as a first-order lag system with a time delay. The transfer function of the exemplary zone 1 \"\(G_{21}\)\" describes the influence of the heater from zone 2 (\(U_{2}\)) on the temperature in zone 1 (\(T_{1}\)):  
\[G_{21}(s)=\frac{T_{1}(s)}{U_{2}(s)}=e^{-65s}\frac{0.009246}{s+0.002333}. \tag{1}\]  
Similarly, the identification process is carried out for all four zones with respect to the two heaters with bottom fans and the four top fans. The heaters with bottom fans are controlled using relay controllers following a hysteresis function with an activation band of 0.2 \"C. The integrated overheating protection of the heater prevents PI fan-speed control beneath the heaters themselves. The hysteresis band can be tuned to reduce temperature deviations from the set-point or to reduce energy consumption. The decoupling (compensation) controllers are designed as:  
\[R_{21}(s)=K\frac{G_{21}(s)}{G_{12}(s)}, \tag{2}\]  
where \(G_{21}\) and \(G_{12}\) are the transfer functions for the temperature dynamics of zone 1 and 2 with respect to the heaters for zone 2 and 1, respectively. The controller gain, \(K\), ranging from [0, 1], is used to attenuate the compensation signals from other zones and fine-tune the response. As shown in Figures 1 and 2, the fan system on the top of the chamber, with the separation of four different zones, directly affects each temperature value, with the capability of reducing it down to the ambient temperature.