# Safety and Energy Implications of Setback Control in Operating Rooms during Unoccupied Periods
## 4 Conclusions  
The setback controls of Heating, ventilation and Air Conditioning systems in Operating Rooms can yield large energy savings in hospitals, but they must comply with the safety regulations.  
A ventilation setback requires air terminal units (pressure-independent) in both the supply and return ductworks; otherwise, the pressure relationship cannot be guaranteed. The supply airflow and pressure difference must be continuously measured and controlled.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Monday** & **Tuesday** & **Wednesday** & **Thursday** & **Friday** & **Saturday** & **Sunday** \\ \hline Average (h) & 8 & 8 & 9 & 9 & 7 & 1 & 2 \\ Standard deviation (h) & 1.5 & 2.1 & 2.1 & 1.9 & 1.7 & 0.9 & 2.8 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Average OR occupation periods registered in 1 week (general use ORs).  
This work uses occupancy sensors to control the nonoccupation periods. These sensors must cover the whole OR.  
It is accepted that there are no indoor sources of pollutants during the nonoccupation periods. The setback must be applied after a certain period since the last occupation of the OR to ensure the remaining contaminants from the occupants are properly removed. In this work, a 20-min lag was applied, which complied with the standards.  
During the ventilation setback, there is no loss of the positive pressure difference required at the ORs, which is nonetheless caused by the door opening during the occupation periods. Consequently, the ventilation setback does not compromise the pressure relationships required for safety issues.  
Since the ventilation setback must be controlled to maintain the required positive pressure inside the OR, the reduced supply airflow may be different for each space. Consequently, the energy savings will vary among different ORs, even in the same hospital.  
The expected annual energy savings for one OR reach 15,884 kWh of natural gas and 5498 kWh of electricity. The extrapolation for the 18 ORs yields conservative results due to the actual short operating periods and accounts for 1.12% of the total natural gas and 0.64% of the electric energy consumed at the hospital during 2021.  
Conceptualization, J.F.S.-A.; methodology, A.T.-G.; formal analysis, H.L.-P. and A.T.-G.; investigation, F.E.-G. and L.M.N.-G.; data curation, H.L.-P.; writing--original draft preparation, A.T.-G.; and supervision, J.F.S.-A. All authors have read and agreed to the published version of the manuscript.  
This research was funded by ENTE REGIONAL DE LA ENERGIA of the Regional Government of Castile and Leon (grant number EREN_2019_L2_UVA) and by the European Union through the LIFE Programme, LIFE SMART HOSPITAL project (grant number ENV/ES/001013). The APC was funded by the Institute of Advanced Production Technologies (ITAP) of the University of Valladolid.  
Not applicable.  
The data presented in this study are openly available in [[https://uvadoc.uva.es/handle/10324/52820](https://uvadoc.uva.es/handle/10324/52820)]([https://uvadoc.uva.es/handle/10324/52820](https://uvadoc.uva.es/handle/10324/52820)).  
The authors would like to acknowledge the managers and maintenance staff of the University Hospital Rio Hortega for their permission and assistance when developing the study.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of the data; in the writing of the manuscript; or in the decision to publish the results.