## 4 Personal Climatization Systems
### Personal Ventilation with Preconditioned Air  
Personal ventilation enhances the air quality at the workplace via directed fresh air towards the respective breathing area [119]. Such systems use either outdoor air or room air extracted from high quality air layers or combined indoor/outdoor air. Through the separation of the inhaled air from the general room air, the amount of inhaled pathogens decreases [120]. Beyond that, personal ventilation improves thermal comfort, especially in case of high ambient temperatures [120]. If personal ventilation is applied, the indoor climate will be comfortable even at high ambient temperatures, which leads to corresponding energy savings [121]. According to [PERSON] et al. [122], heating the feet improves a global \"cold\" sensation, whereas cool air supply towards the face improves a global \"warm\" thermal sensation. The efficiency of personal ventilation depends on the air source and the related air temperature. At ambient temperatures between 23 \({}^{\circ}\)C and 26 \({}^{\circ}\)C a supply of indoor spaces with outdoor air provides a higher air quality than recirculated indoor air [123; 124]. The application of preconditioned outdoor air through the headrests improves both, the pureness of the inhaled air as well as the expected thermal comfort [103]. [PERSON] et al. [125] confirm the substantial improvement of air quality at ambient temperatures of 24 \({}^{\circ}\)C by applying personal ventilation instead of mixing ventilation. A chilled ceiling extended by personal ventilation systems greatly enhances the air quality compared to a chilled ceiling extended by displacement ventilation [120]. According to [PERSON] et al. [123; 124], supply air whose temperature is below the ambient temperature improves IAQ greatly. [PERSON] et al. [126] showed that the cooling force on the body is strongly depending on the applied personal HVAC system as the cooling impact varies between 3 K and 9 K. Personal ventilation fundamentally enhances the perceived air quality and may also improve thermal comfort at ambient temperatures starting from 26 \({}^{\circ}\)C. This is especially the case, if the supply air temperature is preconditioned to a lower air temperature than the prevailing ambient temperature. [PERSON] et al. [125] revealed that a supply air temperature that is 3 K below the ambient temperature is favorable. [PERSON] et al. [127] moreover stated that at ambient temperatures of 27.5 \({}^{\circ}\)C a supply air temperature of 23 \({}^{\circ}\)C is more comfortable than a supply air temperature of 26 \({}^{\circ}\)C. At ambient temperatures of 20 \({}^{\circ}\)C, preconditioned personal ventilation improves thermal comfort without decreasing air quality (preconditioned supply air temperature: 26 \({}^{\circ}\)C, air temperature after mixing with room air: 24 \({}^{\circ}\)C). Furthermore, unheated horizontal ventilation of the face region decreases thermal sensation [128]. The impact of personal ventilation further depends on the relative humidity. Personal ventilation improves the perceived air quality more considerably at a relative humidity of 70% than at a relative humidity of 30%. Furthermore, a low volume flow rate (3.5 L s\({}^{-1}\)) enhances the inhaled air quality more significantly than a high-volume flow rate (6.5 L s\({}^{-1}\)) [129]. If the occupants have control over the volume flow rate of the personal ventilation system, thermal comfort will be achieved at ambient air temperatures between 20 \({}^{\circ}\)C and 26 \({}^{\circ}\)C [130]. However, the researchers could not determine an optimal volume flow rate, since the occupants had mainly chosen values between 0 L s\({}^{-1}\) and 16 L s\({}^{-1}\). In rooms equipped with displacement ventilation, personal ventilation systems that use air of layers in close distance to the floor, enhance the perceived air quality at ambient temperatures between 26 \({}^{\circ}\)C and 29 \({}^{\circ}\)C (Table 6-49, 6-50). It additionally compensates a 3 K increase of ambient temperature [131; 132; 133; 134].