# Control System Modification of a 5-kW Pellet Stove: Study and Analysis
## 2 Materials and Methods
### Experimental Facility  
The experimental facility used for this experience was a commercial combustion stove for heating purposes (Extraflame, Montecchio Precalcino, Italy), with a nominal power of 5-kW (see Figure 7a). The main components of this facility are the following (apart from the temperature probe for room temperature measurement):  
* Container. This is the place where pellets are stored before their combustion.
* Combustion chamber (Figure 7b). This is the inner area where combustion takes place, with the corresponding grid where the pellets are placed from the container (previously filled, as observed in Figure 7c) through the screw conveyor, burning on it with air.
* Ash container. Once ash is generated during combustion and accumulated in the ash container, with the subsequent removal (Figure 7d).
* Fuel feeding system. The system consists of a screw conveyor, which will be regulated by using the programmable logic controller (PLC).
* Control system. As previously mentioned, pellet supply to the combustion chamber will be controlled by utilizing a PLC system, including temperature probes to control the whole process.
* Fan. The combustion chamber is equipped with a fan to provide air to the room. The power of this fan can be modified.
* Chimney (Figure 7e), for the removal of flue gas.  
Figure 7: Combustion stove (**a**) and different parts/stages of this equipment: (**b**) combustion chamber; (**c**) feeding the container; (**d**) ash removal; (**e**) chimney for flue gas.  
Thus, the operating conditions of some of these components (such as the fuel feeding system) will be optimized, as explained in the following subsections. Figure 8 shows the general overview of the experimental facility, including the position of different temperature probes and the gas analyzer to obtain different results during combustion. The gas analyzer (Testo 335, Baden-Wurttemberg, Germany) was used to indicate the room temperature and outlet temperature (in \({}^{\circ}\)C), oxygen (%), NO (ppm), and CO (ppm), subsequently calculating the excess air coefficient (n), thermal efficiency (n), and loss through sensitive enthalpy in the flue gas (q\({}_{\mathrm{a}}\)). The temperature probes (expressing temperature values in \({}^{\circ}\)C) were connected to a digital display (Elitech STC-1000, London, UK).  
In this method, there are two kinds of elements in this facility, such as the following:  
* Actuators: These are components that, on the contrary of sensors, can transform an electric input into a physical output (position, rotation, solenoid activation, etc.). Thus, a programmable logic controller (PLC) can manipulate the operation mode of different components to adjust the optimum working regime of the equipment. In this case, the actuators are the screw conveyor and the fans.
* Sensors: These are devices that can detect physical (or chemical) inputs, called instrumentation variables, which are converted to electric signals. These variables can be temperature, light intensity, distance, acceleration, etc. These electric signals are sent to the PLC (motherboard), which interprets them and corrects the working mode of actuators. In this case, the sensors are the temperature probes, the oxygen probe (to measure flue gas), and the depressometer/manometer.