# Safety and Energy Implications of Setback Control in Operating Rooms during Unoccupied Periods
## 3 Results and Discussion  
### Pressure Relationships  
Table 5 gathers the pressure relationships registered during each test in both ORs. The results are separated for the periods of regular ventilation (occupation) and for the periods  
Figure 2: Systems affected by the ventilation setback and the energy demand and supply.  
under ventilation setback (nonoccupation). Besides the average pressure differences registered, Table 5 shows the \"nonconforming\" cases that occur when the pressure difference registered drops below 6 Pa. This value corresponds to the minimum accepted according to the Spanish regulations, being the strictest among the two standards (Table 4), and the revised literature [15, 25]. The average and the minimum pressure differences registered during these nonconforming periods are also shown.  
It can be seen that no nonconforming pressure relationships are registered during setback operation, with the only exception of test 5 in OR1, while almost all the periods under regular ventilation show nonconforming pressure relationships. This is due to the positive pressure difference loss caused by the door opening, which will only occur during occupation periods. These occupation periods are either for medical use of the ORs or for cleaning and maintenance work. To better illustrate this, Figure 3 represents the percentage of time when nonconforming pressure relationships occur for each test and OR when the average pressure differences are maintained. Consequently, it can be concluded that the ventilation setback does not compromise the pressure relationships required at ORs for safety issues.  
As an example, the results from OR1 during test 1 are graphed in Figure 4. It can clearly be seen that the remarkable variations in the required 15 Pa pressure relationships occur during occupation periods, hence the regular operation of the ventilation system. On the contrary, during the nonoccupation periods when ventilation setback is applied, the pressure relationship is almost stable at 15 Pa. Indeed, punctual losses of this pressure difference only occur during occupation periods due to the door opening.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Test**} & \multirow{2}{*}{**OR**} & \multirow{2}{*}{**Ventilation Mode**} & \multirow{2}{*}{**Total Time**} & \multirow{2}{*}{**Average Pressure Difference (AP)**} & \multicolumn{2}{c}{**Average Values**} & \multicolumn{1}{c}{**Minimum Values**} \\  & & & & & **Nonconforming Pressure Differences 1** & **Nonconforming Pressure Differences 1** \\  & & & & & **(Pa)** & **(Pa)** \\ \hline
1 & OR1 & Regular & 26.5 & 15.7 & 1.4 & 0.0 \\  & & Setback & 52.2 & 15.5 & na & na \\  & OR2 & Regular & 0.8 & 17.2 & na & na \\  & & Setback & 77.9 & 14.9 & na & na \\
2 & OR1 & Regular & 24.1 & 15.7 & 1.3 & 0.0 \\  & & Setback & 59.2 & 15.1 & na & na \\  & OR2 & Regular & 8.7 & 15.4 & na & na \\  & & Setback & 74.6 & 14.9 & na & na \\
3 & OR1 & Regular & 13.6 & 15.1 & 1.7 & 0.0 \\  & & Setback & 0.0 & na & na & na \\  & OR2 & Regular & 5.9 & 14.6 & na & na \\  & & Setback & 7.2 & 15.4 & na & na \\
4 & OR1 & Regular & 20.0 & 15.0 & 1.1 & 0.0 \\  & & Setback & 45.5 & 15.1 & na & na \\  & OR2 & Regular & 4.5 & 16.7 & na & na \\  & & Setback & 60.9 & 14.8 & na & na \\
5 & OR1 & Regular & 40.7 & 15.2 & 1.3 & 0.0 \\  & & Setback & 42.3 & 15.1 & 0.0 & 0.0 \\  & OR2 & Regular & 8.3 & 15.2 & 0.9 & 0.1 \\  & & Setback & 74.7 & 14.8 & na & na \\ \hline \hline \end{tabular}  
* Total time when the pressure differences registered are below 6 Pa. na: not applicable/no cases registered.  
\end{table}
Table 5: Results for the pressure relationships registered during the tests.