*Analysis of Experimental Trends*

The data acquired during normal and faulty operation tests (and reported in previous section) highlight that the percentages of time with values of indoor air temperature within the given deadband (1 ◦C) around the user-defined target (setpoint 26/20 ◦C for summer/winter season) are equal to 69.8%, 57.0%, 71.3%, 69.1%, 0%, 36.1%, 13.4%, 0%,86.6%, 68.3%, 69.6%, 72.5%, 71.4%, 75.4%, 68.7%, 0.0%, 15.7%, and 64.9% for the tests 1–18, respectively. Furthermore, the percentages of time with values of air relative humidity inside the test room within the deadband (5%) around the target (50%) are equal to 98.4%, 84.9%, 83.5%, 88.3%, 16.2%, 80.6%, 88.1%, 90.6%, 65.4%, 84.7%, 80.7%, 87.3%, 81.2%, 49.4%, 82.3%, 99.6%, 80.5%, and 76.0%, during the tests 1–18, respectively. The results of calculation highlight a good capability of the HVAC unit under healthy operation (tests n. 1–4 and 10–13) to accurately control indoor conditions. The previously mentioned percentages are lower than 100% because (a) the initial values of return air temperature and return air relative humidity are in some cases far from target values and (b) during the start-up phases the AHU operates under transient conditions trying to approach the steady-state conditions to achieve the desired targets.

In more detail, Figure 3a–e (associated to the faulty tests performed during summer) highlights the different trends/patterns associated to key operating parameters with respect to the scenarios without faults:


• In Figure 3e (corresponding to the fault 5, i.e., steam humidifier valve kept fully closed), return air relative humidity varies in a narrower range (in this case between 43.0% and 55.5%), highlighting a significantly reduced number of oscillations (as it would be presumed in the case of the humidifier is not active).

Figure 5a–e (associated to the faulty tests performed during winter) allows to underline the different trends/patterns of key operating parameters with respect to the cases without faults:

