## 3 Results and Discussion
The disadvantage of this system is a slower response to changes in the desired temperature of the supplied air and a less sensitive power regulation. Therefore, there were slight variations in the air temperature during individual measurements. However, this also applies to normal operating conditions of OR ventilation and reflects sudden local changes in comfort near the LAFC. The lower temperature of the supply air through the LAFC also affected the overall velocity and trajectory of the air flow in the operating table area, due to [PERSON]'s law of gravity. If the temperature difference is too large, the area of direct flow may decrease, and the air column may narrow [17]. In addition to the inaccuracy of the measuring device, another limitation of the study, compared to the real situation, is the absence of medical personnel, which partially (200-400 W) reduced the heat load of the OR. Other devices in the OR (lamps, surgical equipment, etc.) that produce heat were turned on. As already mentioned in several studies, the issue is to find a compromise between the requirements of the OR ventilation legislation and the thermal comfort of medical personnel [6; 7; 8; 9; 16; 17; 21; 34; 35]. Even while maintaining a higher air flow rate, it is possible to achieve a low air outlet velocity through the LAFC by using LAFCs with larger dimensions and a larger outlet area. It is necessary to observe the recommended speeds of legislation, standards and the LAFC manufacturer. Several studies have already indicated that lower discharge velocities reduce the risk of contamination by suppressing unwanted turbulence [19; 41; 42]. The PMV and PPD indices indicate that in the summer months, when air is supplied to the OR that is cooler than the desired room temperature, it is more advantageous to choose the dimensions of the LAFC so that the outflow velocity is in the range of 0.15-0.175 m/s. The increasing velocity of air flow through the LAFC causes an unpleasant feeling of coldness for the medical staff (surgeon). This can negatively affect the  
Figure 11: Comparison of PPD indexes for variant 1 to 5.  
work performance and the success of the surgical procedure [43]. At an air flow speed of 0.2 m/s through the LAFC, the PPD index was higher than 30% in the area of the body's center of gravity (1.1 m) and the head (1.7 m). At a speed of 0.25 m/s, which is commonly used, the PPD index was evaluated at 70% in the area of the center of the body. [PERSON] et al. [34] monitored the airflow velocity through the LAFC in the range of 0.1-0.5 m/s. In this range of speeds, a difference of up to 5 \({}^{\circ}\)C was detected on the surface of the protective clothing. Legislation, standards and regulations in different countries do not have the same statement on the appropriate outflow velocity through the LAFC. Standards VDI 2167 [6] and DIN 1946 [7] recommend speeds above 0.23 m/s, while standard ASHRAE 170 [8] recommends speeds in the range of 0.13-0.18 m/s, which was the range identified in our results. The EN ISO 14 644-1 standard recommends, for operating room in cleanliness class ISO 6, outflow velocities in the range of 0.1-0.25 m/s [1]. It can be concluded that during the summer months, the combination of a lower supply temperature and a higher speed of air flow in the area of the operating table results in the local creation of an uncomfortable environment. This conclusion was confirmed, through personal discussion and consultation with several medical professionals (mainly surgeons). [PERSON] et al. [44], in his study, also confirmed the different assessment of thermal comfort between body segments caused by different radiant temperatures. [PERSON] et al. [21] mentioned that decreasing the air flow rate in the OR is one of the options for reducing the feeling of cold in the OR. The results indicate the least comfortable environment is located in the area of the body's center. ASHRAE Standard 55 adopts the P.O. Fanger indexes of PMV and PPD and takes into account the effect of local discomfort by increasing PPD by 10% [45].