# Safety and Energy Implications of Setback Control in Operating Rooms during Unoccupied Periods
## 2 Materials and Methods
### Data Analysis  
The measurements are analyzed with two aims: (1) checking that the pressure relationships are not compromised through the ventilation setback and (2) estimating the energy, emissions, and economics savings achievable. The first objective is directly studied by analyzing the differential pressures registered during the setback (nonoccupation) operating periods during the tests performed (Table 3). The second is approached by extrapolating the achieved results from the Typical Meteorological Year data of the target location. \begin{table}
\begin{tabular}{c c} \hline \hline
**Controlled Variables** & **Set Value** \\ \hline Supply volume airflow & 2500 m\({}^{3}\)/h \\ \hline Indoor overpressure & 15 Pa \\ \hline \multirow{4}{*}{Supply Dry Bulb Temperature} & During occupation: 22.0 \({}^{\circ}\)C \\  & During non-occupation: 19.0 \({}^{\circ}\)C (winter), \\ \cline{1-1}  & 25 \({}^{\circ}\)C (summer) \\ \cline{1-1}  & Min. 14.0 \({}^{\circ}\)C \\ \cline{1-1}  & Max. 28.0 \({}^{\circ}\)C \\ \hline Supply Relative Humidity & Max. 60\% \\ \hline Indoor Relative Humidity & 35\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Controlled parameters in the OR through the SCADA. The energy savings achievable can be distinguished between thermal and electrical savings. In terms of energy supply, the heating thermal savings entail a reduction in the consumption of natural gas of the boilers, while the cooling thermal savings involve electric energy savings in the chillers. The reduction in the energy consumed by fans directly involves electric energy savings. When necessary, humidification is provided through vapor injection fed by the hospital's steam system and, thus, involves natural gas savings in the boilers. However, due to the particular climate of the location, controlled dehumidification during the summer period is not necessary, and it only occasionally occurs in the cooling coil in an uncontrolled way (Figure 2). The ventilation setback operating periods (\(t_{setback}\)) directly imply electric energy savings when using the frequency-controlled fans of the AHU:  
\[Fans\;energy\;savings=\big{(}P_{occupation}-P_{setback}\big{)}\cdot t_{setback} \tag{1}\]  
Energy savings in the cooling coil during the setback derive from the lower ventilation thermal loads due to both the reduced supply airflow and the modification in the set temperature (Table 2). \[Cooling\;coil\;savings=\bigg{(}\dot{V}.\frac{1}{v}.\Delta{h_{tot\;cc}}-\dot{V}_{ setback}.\frac{1}{v}.\Delta{h_{tot\;cc\;stuck}}\bigg{)}.\Delta t \tag{2}\]  
where \(\dot{V}\) is the design supply ventilation rate (see Table 2), \(\dot{V}_{setback}\) is the supplied airflow during the setback operation, \(v\) is the dry air specific volume at the measured supply air conditions, and \(\Delta t\) is the period of the setback operation. The total enthalpy variation achieved in the coil \(\Delta{h_{tot\;cc}}\) is due to both cooling and uncontrolled dehumidification when cooling down the outdoor conditions to the set supply temperature during regular operations or during the setback (Table 2).