## 5 Analysis of the Implementation of Energy Efficiency Measures from the 2018 Audit
### Replacement of the Thermal Insulation of the Continuous Furnace in the Firing Zone  
In the 2018 energy audit, a thermographic analysis revealed relatively high temperatures in the firing zone of the continuous kiln. This fact raised the alarm about the need to act on these temperatures. Figures 7 and 8 show the thermographic images obtained in the energy audit carried out by the company in 2018. In 2018, auditors detected radiation and convection losses and determined the total heat lost through the furnace walls to be 228,298 kJ/h. To mitigate these heat losses, thermal insulation was replaced. With this replacement, the auditors predicted that average wall temperatures would decrease from 105 \({}^{\circ}\)C to 80 \({}^{\circ}\)C and the heat lost through the walls would reduce to 140,440 kJ/h. The total amount of heat lost through the ceiling was calculated to be 120,609 kJ/h. The roof temperature was expected to decrease from 105 \({}^{\circ}\)C to 80 \({}^{\circ}\)C, resulting in a reduction in heat loss through the roof to 74,264 kJ/h. Based on the wall and ceiling audit, the total estimated energy savings would amount to 134,203 kJ/h. The continuous oven operates 24 h per day and 335 days per year. The expected savings was 1079 GJ/year, which represents a saving of 67748.28/year for a unit cost per m\({}^{3}\) of 60.2763/m\({}^{3}\). For an estimated annual investment in thermal insulation of 645,220, the simple payback period would be 5.84 years. The replacement of the thermal insulation of the continuous furnace at manufacturing unit two was carried out in the firing zone in 2018 and consisted of replacing the fiber insulation with brick. Figure 8: Cooling zone of the continuous kiln of unit two before any improvement (source: Energy Audit Report 2018). Figure 7: Firing zone of the continuous kiln of unit two before any improvement (source: Energy Audit Report 2018. A thermographic analysis was performed to assess whether the intended effect of the measure was achieved, using a FLIR A320 Tempscreen fixed thermographic camera (see Figure 9). The temperatures of the walls and ceiling of the continuous furnace were compared before and after the implementation of thermal insulation in the continuous furnace. The continuous oven has an initial zone--the pre-oven--where preheating takes place with heat recovery from the oven itself from the cooling zone through fans. This zone was not considered since the temperatures of the walls are at room temperature. After this pre-heating zone, there is a door that opens to allow the wagons to pass into the kiln pre-heating zone. The kiln walls were divided into four distinct zones for each side (left and right): a firing zone with a lower height, a cooling zone wall, a firing zone wall, and preheating zone. A total of 216 sections were created in the four zones, with a length of 0.66 each. The characteristics of the wall sections for the calculation of thermal losses are shown in Table 11.  
The temperatures of the different sections were obtained through thermographic images captured by the Fixed FLIR A320 Tempscreen thermographic camera. The heat lost by natural convection and radiation on the walls of the continuous oven was calculated using Equations (1)-(3), which refer to heat losses from hot surfaces. The kiln's annual working time of 335 days and 24 h/day were considered. An ambient temperature of 28 \({}^{\circ}\)C (301 K) and a surface emissivity (\(\varepsilon\)) of 0.9 were adopted for the painted sheet. It was assumed that the geometry factor for the vertical planes was 5.22 and the geometry factor for the horizontal planes was 6.12. These values are the same as those adopted by the auditor when carrying out the 2018 audit. Equations (1)-(4) are in line with those assumed by the auditor and in accordance with the energy audit manual in the industry [25]. The thermal input, Q (kJ/h), is given by Equation (1):  
\[\text{Q}=\text{U}\times\text{A} \tag{1}\]