## 5 Results
### Virtual Sensor Fault-Correction Effect
#### 5.2.2 Energy Consumption  
Monthly chiller, circulation pump, and fan energy consumptions after the correction of faults in a SCWT sensor were evaluated for each simulation in August, as shown in Figure 11. The sensor faults had a limited impact on the energy consumption in Cases A-1 and A-2, where the frequency of sensor faults was low. Consequently, the circulation pump, fan, and chiller energy consumptions were similar to those of the normal case (Figure 11). Additionally, the energy consumption in Cases A-1 and A-2 varied based on the fault frequency and offset, as observed in the evaluation of the indoor thermal comfort. The fixed-offset cases (Cases B-1 and B-2) experienced faults with negative offsets in the SCWT sensor, resulting in reductions of approximately 1.3% and 0.8% in chiller energy consumption, respectively, compared with that of the normal case. This was because the compressor workload was reduced as the SCWT did not reach the set value (Figure 11a). To compensate for this, the circulation pump energy consumption increased by approximately 19.2% and 7.1% (Figure 11b), and the fan energy consumption increased by 11.8% and 0.9% for Cases B-1 and B-2, respectively (Figure 11c). However, Cases B-3 and B-4, with positive offsets in the sensor faults, resulted in increases of approximately 1.3% and 2.1% in chiller energy consumption, respectively, owing to the increased compressor workload (Figure 11a). The circulation pump energy consumption decreased by approximately 5.7% and 14.3% for Cases B-3 and B-4, respectively, as the supply chilled water flow rate decreased (Figure 11b). This was because the SCWT value was lower than the set value. In this case, the chilled water still supplied the heat required for air conditioning; thus, the fan energy consumption remained the same as that in the normal case (Figure 11c). Case C involved random sensor fault offsets, which resulted in increases of approximately 0.6%, 2.9%, and 1.5% in the chiller, circulation pump, and fan energy consumptions, respectively, compared with those of the normal case (Figure 11). Among the drift offset cases, the negative sensor fault offset worsened over time in Case D-1, resulting in a decrease of approximately 10.5% in the chiller energy consumption compared with that of the normal case (Figure 11a). To compensate for this, the circulation pump and fan energy consumptions increased by approximately 23.6% (Figure 11b) and 42.6% (Figure 11c), respectively. Case D-2 had a positive sensor fault offset, which led to an increase of approximately 1.8% in the chiller energy consumption compared with that of the normal case (Figure 11a). The circulation pump energy consumption decreased by approximately 17.1% owing to the lower SCWT (Figure 11b). However, the fan energy consumption remained the same as that in the normal case (Figure 11c). The evaluation results demonstrated that the impact of sensor faults on energy consumption varied depending on the offset value and frequency of fault occurrence in the cases of point and random offsets. In the cases of fixed and drift offsets, faults with a positive offset led to an increase in the chiller energy consumption and a decrease in circulation pump consumption. Conversely, faults with a negative offset resulted in a decrease in circulation pump and fan energy consumptions and an increase in the chiller energy consumption (Table 7). \begin{table}
\begin{tabular}{c c c} \hline
**Offset** & **Negative Offset** & **Positive Offset** \\ \hline Point & Depended on offset value and frequency \\ Fixed & Increase & Negligible \\ Random & Depended on offset value and frequency \\ Drift & Increase & Decrease \\ \hline \end{tabular}
\end{table} 
Table 6: Effects on indoor set-point temperature unmet hours for various fault types and offsets. Figure 11: Monthly energy consumptions for various fault types: (**a**) chiller energy consumption; (**b**) circulation pump energy consumption; and (**c**) fan energy consumption.