**3. Experimental Tests**

A set of 18 fault-free and faulty daily experimental tests has been performed in order to examine the HVAC system operation during transient and steady-state operation under both winter and summer conditions. Tables 4 and 5 describe the operating of the experimental tests under summer and winter conditions, respectively.

**Table 4.** Operating conditions of the experimental tests under fault free (tests 1–4) and faulty operation (tests 5–9) during summer.



**Table 5.** Operating conditions of the experimental tests under fault free (tests 10–13) and faulty operation (test 14–18) during winter.

During all the tests, a number of system parameters have been kept constant: DBT = 1 ◦C, DBRH = 5%, OPDRA = 100%, OPDOA = 20%, OPDEA = 20%, and OPDHRS = 100. In more detail, 8 tests have been performed under fault free conditions (tests n. 1, 2, 3, 4 in Table 4 carried out during summer and tests n. 10, 11, 12, 13 in Table 5 carried out during winter). The remaining 10 tests have been carried out while artificially introducing specific faults (tests n. 5, 6, 7, 8, 9 in Table 4 carried out during summer and tests n. 14, 15, 16, 17, 18 in Table 5 carried out during winter). The experiments have been performed by measuring every minute all the parameters indicated in Table 2. In this study, the recording time step of measured data has been defined according to the experimental approaches adopted in similar works available in the scientific literature. For example, the ASHRAE RP-1312 data set [24] developed for AFDD purposes consists of experimental data recorded every minute from a facility comprising two AHUs; recently, Piscitelli et al. [5], Yun et al. [27], as well as Fan et al. [28] proposed novel methodologies for performing AFDD analyses of AHUs based on this ASHRAE RP-1312 database [24]; Cheng et al. [40] developed a new AFDD method for AHUs using experimental data measured every minute. Therefore, a measurement time step of one minute could be reasonably assumed as acceptable in order to take into account the response time of HVAC components.

Only during the faulty tests, the operation of specific AHU components has been forced to assure user-specified positions in order to artificially simulate the following 5 specific typical faults (named fault 1, 2, 3, 4, 5):


In this study, the above-mentioned faults have been introduced at the beginning of the faulty tests and maintained during the entire duration of the experiments (what happens in the case of the faults are shorter has not been investigated).

During the tests n. 1–4 and n. 10–13 (fault free tests), the AHU's components have been operated without any artificial faults.

In both Tables 4 and 5, the parameters characterizing the corresponding faults have been highlighted in red.

Figures 2a–d and 3a–e highlight the experimental trends of return air temperature TRA, supply air temperature TSA, outside air temperature TOA, air temperature around the test room TBEA, return air relative humidity RHRA, supply air relative humidity RHSA, and air relative humidity around the test room RHBEA recorded during the fault free and faulty tests, respectively, performed under summer conditions (detailed in Table 4).

**Figure 2.** Experimental data measured during the fault free tests under summer conditions: test n. 1 (**a**), test n. 2 (**b**), test n. 3 (**c**), and test n. 4 (**d**).

**Figure 3.** *Cont*.

 18 Sep-9:56 18 Sep-10:26 18 Sep-10:56 18 Sep-11:26 18 Sep-11:56 18 Sep-12:26 18 Sep-12:56 TTRA TSA TOA T\_BEA RHRA RHSA RH\_BEA RA TSA TOA TBEA RHRA RHSA RHBEA

**Figure 3.** Experimental data measured during the faulty tests under summer conditions: test n. 5 (**a**), test n. 6 (**b**), test n. 7 (**c**), test n. 8 (**d**), and test n. 9 (**e**).

Figure 2a reports the experimental trends of TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the fault free test n.1; Figure 2b shows the measured parameters TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the fault free test n.2; Figure 2c indicates the measured data associated to TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the fault free test n.3; Figure 2d highlights the temporal variation of TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the fault free test n.4.

Figure 3a reports the experimental trends of TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the faulty test n.5; Figure 3b shows the measured parameters TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the faulty test n.6; Figure 3c indicates the measured data associated to TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the faulty test n.7; Figure 3d highlight the temporal variation of TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the faulty test n.8; the values of TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA recorded during the faulty test n.9 are depicted in Figure 3e.

Figures 4a–d and 5a–e report the experimental trends of TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA recorded during the fault free and faulty tests, respectively, performed under winter conditions (detailed in Table 5).

**Figure 4.** *Cont*.

**Figure 4.** Experimental data measured during the fault free tests under winter conditions: test n. 10 (**a**), test n. 11 (**b**), test n. 12 (**c**), and test n. 13 (**d**).

**Figure 5.** Experimental data measured during the faulty tests under winter conditions: test n. 14 (**a**), test n. 15 (**b**), test n. 16 (**c**), test n. 17 (**d**), and test n. 18 (**e**).

Figure 4a reports the experimental trends of TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the fault free test n.10; Figure 4b shows the measured parameters TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the fault free test n.11; Figure 4c indicates the measured data associated to TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the fault free test n.12; Figure 4d highlights the temporal variation of TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the fault free test n.13.

Figure 5a reports the experimental trends of TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the faulty test n.14; Figure 5b shows the measured parameters TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the faulty test n.15; Figure 5c indicates the measured data associated to TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the faulty test n.16; Figure 5d highlight the temporal variation of TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA during the faulty test n.17; the values of TRA, TSA, TOA, TBEA, RHRA, RHSA, RHBEA recorded during the faulty test n.18 are depicted in Figure 5e.
