br Methodology br Research results br Conclusion

Methodology
Research results
Conclusion
Introduction The goal of the air distribution inside a hospital operating room (OR) is to protect the patient and staff from cross-infection while maintaining occupant comfort and not affecting the facilitation of surgical tasks. However, a source of contamination bypasses HEPA installations in every OR, this source being the surgical staff themselves and the particles stirred up by their movement (Cook and Int-Hout, 2009). Therefore, air motion control must be used to maximize air asepsis. In hospital ORs, using HEPA-filtered air and vertical (downward) laminar airflow is typical. ASHRAE Standard 170-2008 (ASHRAE, 2008) requires that ventilation be provided from the ceiling in a downward direction concentrated over the patient and surgical team. The area of the primary ventilation air diffusers must extend at least 305mm beyond each side of the surgical table. It also requires that air is exhausted from at least two grilles on opposing sides of the room near the floor. It requires the use of non-aspirating, Group E outlets that provide a unidirectional flow pattern in the room (aka laminar flow diffusers). However, previous research has shown that this method does not necessarily achieve the desired unidirectional flow pattern or adequately achieve optimal air asepsis (Zhai et al., 2013). Zhai et al. (2013) used on-site field experiment, full-scale laboratory experiment, and computational modeling to verify and test the current ventilation practices in OR. Both experimental and simulation results showed a strong inward contraction of the supply air jet, instead of a unidirectional downward flow. The buoyancy forces on the downward supply air jet were determined to be the cause of the observed air distribution pattern. This research will build upon the study of Zhai et al. (2013) by testing alternative air supply configurations which may maximize air asepsis. The pattern of the airflow will also be studied to determine if it Human Angiopoietin 4 / ANG4 / ANGPT4 Protein (His Tag) provides a more unidirectional airflow.
Computer model setup A computational fluid dynamics (CFD) tool was used to predict the flow pattern and contaminant transport in a representative OR environment. CFD has been widely used in indoor environment study (Spengler and Chen, 2000; Chen and Zhai, 2004; Zhai et al., 2007 etc.). A same CFD model as that used in Zhai et al. (2013) was rebuilt by this study and validated against the full-scale laboratory experiments. The same diffuser specifications and air change rate per hour (ACH) as tested in the experiment were used in the initial CFD model, as well as the same room and equipment and occupant conditions, as shown in Table 1 and Figure 1. These objects and heat gain values were chosen based on detailed on-site OR studies and measurements (Zhai et al., 2013). The equipment thermal loads as well as temperature of the patient\'s wound and skin can be seen in Table 2. Table 3 indicates the sizes of all of the objects in the room.
Computer model validation
Air distribution simulation with improved air conditioning systems To avoid the in-ward flow under the unidirectional diffuser, a few practical strategies were tested using the validated CFD model. The first was to create vertical downward air curtain around the laminar diffuser. Several commercial products are available which create an “air curtain” barrier between the operating area and the rest of the room, as illustrated in Figure 8. The system attempts to create a physical barrier that separates the surgical area from the recirculating air in the perimeter of the room while directing particulates toward exhaust grilles. This system uses three main components, the laminar flow diffuser, the linear slot diffusers (or “air curtains”), and low-level exhaust grilles. Four air curtain cases were thus created, three followed the manufacturer design specifications, and one did not. The fifth case simply tested the effects of a larger area of laminar flow diffusers without using air curtain.