## 4 Discussion
The three air conditioning systems were different in the air conditioning thermal load. Furthermore, the dew point temperature in the conventional HVAC system cannot be lower than the temperature of the chilled coils unit, limiting the system's efficiency. However, RDAC systems can successfully break this barrier as they are integrated into a solid dehumidification system. In general, RDAC systems need to be installed with regenerative heating equipment [34; 35; 36]. The system studied here was made of activated alumina, a hygroscopic material that can be regenerated even if the temperature is reduced to 23.9 \({}^{\circ}\)C and has a strong affinity for water vapor in a high RH environment. The efficiency of the moisture-absorbing material in this system can also be regeneratedby the return air of the air conditioning system and it is more energy efficient (20%-25% energy reduction) with regard to regeneration than other materials that generally need to be heated above 60 \({}^{\circ}\)C [16]. In our study, the ambient temperature had a significant influence on the total energy consumption of conventional HVAC, LDAC, and RDAC systems. Therefore, choosing an energy-saving dehumidification air conditioning system for ORs is very important, especially in the subtropical region of Taiwan. In this study, the median concentration of PM\({}_{\geq 0.5}\) in all three dehumidification air conditioning systems met the ISO 14644-1 Class 7 standard (median concentration of PM\({}_{\geq 0.5}\) lower than \(3.52\times 10^{5}\) particles/m\({}^{3}\), or 352 particles/L) [37]. Meanwhile, the airborne bacterial concentration in the operating areas and surrounding areas met China's GB50333-2013 standard (concentrations in operating areas of \(<\)75 CFU/m\({}^{3}\) and in surrounding areas of \(<\)150 CFU/m\({}^{3}\)) [29], but it did not meet the UK standards for an OR at rest (35 CFU/m\({}^{3}\)) [38]. Therefore, more studies are necessary to assess the concentration distribution and influencing factors of airborne bacteria in Taiwanese ORs. We observed no correlation between indoor temperature and airborne bacterial concentration, differing from [PERSON] et al. We found no significant correlation between RH and airborne bacterial concentration, but according to the suggestion of the ASHRAE/ASHE Standard 170, the RH level should be carefully controlled to prevent the risk of microbial growth [5]. The RH levels in the LDAC and RDAC systems were positively correlated with the suspended particulate concentrations, while no correlation was found for the conventional HVAC system. According to [PERSON]'s findings, this shows that the air-handling processors with LiCl solution had an obvious filtration efficiency for PM\({}_{5}\)[39]. This study found that there was no correlation between airborne bacterial concentration and particle concentration in ORs using HVAC systems. This result was similar to a French study [40]. This study dealt with a limited number of ORs with different dehumidification air conditioning systems; thus, increasing the sample size should be considered in further studies. Overall, our results suggest that hospitals should regularly assess the efficiency of their dehumidification air conditioning systems to maintain satisfactory indoor thermal-hygrometric conditions and air quality and achieve energy conservation.