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**Figure 7.** Reference (August and September) and monitoring samples corresponding to November.

Given that the process has changed, a new reference sample should be obtained and studied. The stabilization and monitoring process should begin for the next year, starting December. Figure **??** shows the rank control chart for the calibration (August and September) and monitoring samples of November. In practice, monitoring can be efficiently performed using the proposed control charts because you do not need to estimate the LCL through resampling procedures. Additionally, the rank control chart can be adapted for monitoring multivariate functional data, that is, when there are different types of curves that define the quality of a specific system or process simultaneously. For example, a direct case of application considers their first derivative along with the original curves.

The application of rank control charts also allows us to monitor the process by studying more than one functional variable. Particularly, it not only allows us to study the energy consumption curves but also the curves of daily temperature, daily relative humidity, daily CO2 concentration, among others; they completely characterize the energy efficiency of the facilities and their thermal comfort and ambient air quality. Precisely, this procedure would allow us to perform a functional multivariate monitoring.

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**Figure 8.** Rank control chart for Phase II of quality control. Both reference (corresponding to August and September) and monitoring (corresponding to November) samples are shown.
