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Impact of individually controlled facially applied air movement on perceived air quality at high humidity
Building and Environment 45 (2010) 2170e2176
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Impact of individually controlled facially applied air movement on perceived air quality at high humidity M.A. Skwarczynski a, b, *, A.K. Melikov b, J. Kaczmarczyk c, V. Lyubenova b a
Faculty of Environmental Engineering, Institute of Environmental Protection Engineering, Department of Indoor Environment Engineering, Lublin University of Technology, Lublin, Poland b International Centre for Indoor Environment and Energy, Department of Civil Engineering, Technical University of Denmark, Copenhagen, Denmark c Faculty of Energy and Environmental Engineering, Department of Heating, Ventilation and Dust Removal Technology, Silesian University of Technology, Gliwice, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 March 2010 Received in revised form 25 March 2010 Accepted 27 March 2010
The effect of facially applied air movement on perceived air quality (PAQ) at high humidity was studied. Thirty subjects (21 males and 9 females) participated in three, 3-h experiments performed in a climate chamber. The experimental conditions covered three combinations of relative humidity and local air velocity under a constant air temperature of 26 C, namely: 70% relative humidity without air movement, 30% relative humidity without air movement and 70% relative humidity with air movement under isothermal conditions. Personalized ventilation was used to supply room air from the front toward the upper part of the body (upper chest, head). The subjects could control the flow rate (velocity) of the supplied air in the vicinity of their bodies. The results indicate an airflow with elevated velocity applied to the face significantly improves the acceptability of the air quality at the room air temperature of 26 C and relative humidity of 70%. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Air movement Humidity Perceived air quality Personalized ventilation
1. Introduction The purpose of ventilation is to provide clean, fresh air to occupied space, to remove or dilute pollution and to ensure optimal thermal conditions for the occupants. Present standards [1,9,21,22] specify requirements for ventilation rates and the thermal environment. The European Standard EN 15251 [1] recommends ventilation rates for buildings when taking into account pollutant emissions from the building materials and the occupants. At the low range of comfortable room temperatures (19e24 C) recommended in the present standards [1] relative humidity has little impact on people’s thermal comfort. At the high range of recommended temperatures (25e27 C) high relative humidity increases occupants’ thermal discomfort. In hot and humid climates as well as in temperate climates during summer relative humidity should be considered also from energy point of view. Dehumidification and humidification of the air used for ventilation of buildings may increase substantially the energy consumption of HVAC
* Corresponding author. Faculty of Environmental Engineering, Institute of Environmental Protection Engineering, Department of Indoor Environment Engineering, Lublin University of Technology, Nadbystrzycka 40B, 20-618 Lublin, Poland. Tel.: þ48 815384411; fax: þ48 815381997. E-mail address: [email protected] (M.A. Skwarczynski). 0360-1323/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2010.03.017
systems. EN 15251 [1] specifies design values for indoor relative humidity when humidification and dehumidification are needed: in case of dehumidification e 50%, 60% and 70%, and in case of humidification e 40%, 30% and 20% respectively for categories I, II and III of indoor environment. The absolute humidity can also be specified as a second parameter to be adjusted in rooms [2]. The winter minimum value for the absolute humidity is equal to 6 g kg1. This corresponds to 40% relative humidity at 22 C. The summer maximum value is specified as 12 g kg1, corresponding to 60% relative humidity at 26 C. The negative effect of high temperature and high humidity on air quality and odour intensity perception have been demonstrated in several studies. Berglund and Cain [3] showed that air was perceived as fresher and less stuffy with decreasing temperature and humidity. The effect of humidity on freshness, stuffiness and the acceptability of air quality was smaller when the dew point was below 11 C than when it was above 11 C, which corresponds to 49.7% relative humidity at 22 C and 39.1% relative humidity at 26 C [3,4,20]. The cooling of the mucous membranes at the surface of the nasal passages is presumed to be decisive in people’s thermal perception of the inhaled air [7]. Inhaled air cools the mucosa if the temperature of the inhaled air is below the mucosal temperature, which is normally 30e32 C [4e6]. The cooling of the mucous membranes is proportional to the temperature and water vapour
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gradients between the surface of the respiratory tract and the inhaled air. Keck et al. [8] suggested that, despite the high airstream velocity in the centre of the inspired air, high thermal pressure gradients in the anterior part of the nose can cause a high heating capacity, especially in this region, and this can be assumed to be decisive in people’s perceptions of inhaled air. Room air movement is an important factor to be considered for occupants’ thermal comfort. At high room temperatures elevated air movement improves occupants’ thermal comfort. However at the lower range of room air temperatures air movement may cause draught discomfort (draught is defined as unwanted local cooling of the body due to air movement). When people sense a draught they often demand higher room air temperatures or even that the ventilation system is stopped. To be consistent with the EN 15251 [1] criteria, the maximum mean air velocities for a landscaped office (open-plan office) for summer (the cooling season) are 0.18, 0.22, 0.25 m s1 in categories I, II and III, respectively, and for winter (the heating season) these air velocities are 0.15, 0.18, 0.21 m s1. The cooling power of air movement increases with the increase of its velocity and the decrease of its temperature. At high room air temperature flow of cool air will improve the thermal comfort for majority of the occupants while at low room air temperature warm air will have the same positive effect [10]. Present standards [1,9,21] recommend individual control of the speed of the local air movement at the vicinity of each occupant in order to achieve preferred thermal environment. The control of air movement in the breathing zone can be achieved using a personalized ventilation system [25] or a table fan. The strategy of increasing the upper limit of operative temperature in rooms and improving occupants’ thermal comfort by individually controlled air movement may lead to energy savings [12,26]. Further energy savings can be achieved if dehumidification of the supplied air can be avoided. In this respect, the effect of increased air movement on perceived air quality (PAQ) is important. It has been reported in the literature that air is perceived as more fresh at higher velocity [11,13,23,28]. The elevated velocity of airflow supplied by personalized ventilation against the face diminishes the negative impact of increased relative humidity on PAQ [11]. In the referred human subject study [11] the air velocity was set at a constant level of either 0.3 m s1 or 0.6 m s1 and the subjects could not adjust their local conditions. However, earlier studies [14,15] have reported that the possibility of controlling the micro-environment can play a substantial role in the occupants’ responses, leading to a more positive evaluation of the same environment. The objective of the present study was to investigate the effect of individually controlled elevated facial air velocity on perceived air quality (PAQ), air freshness, air dryness and odour intensity at high level of relative humidity.
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constant at the set conditions. The measurement point was located at the centre of chamber at the height 1.1 m. Eight workstations were arranged in the chamber. Four of them had personalized ventilation systems (PVSs) installed. The layout of the chamber is shown in Fig. 1. The desks were positioned and used in pairs, i.e. four pairs 1, 2, 3, 4. Each desk pair had one desk without a PVS (1A, 2A, 3A, 4A) and one desk with a PVS (1B, 2B, 3B, 4B). The supply air terminal device (ATD) of the PVS, named the round movable panel (RMP), has been described by Bolashikov et al. (2003) [16]. The RMP generated a personalized flow with uniform velocity distribution and low initial turbulence intensity. The ATD was mounted on a movable arm-duct attached to the desk-top, allowing changes to be made in its distance from, and position relative to, the occupant. The movable arm was connected by duct to the AC circular fan. The maximum airflow generated by each fan was 20 L s1 which corresponded to the air velocity of 1.8 m s1. Turbulence intensity on the centre of the generated flow was measured to be 4% at distance 0.5 m from the RMP. The turbulence intensity increased with the decrease of the air velocity. Subjects’ could control individually the supplied personalized flow, i.e. airflow velocity, at each desk. During the experiment, individuals were allowed to control the flow rate of the PVS at their desk but not to change the positioning of the ATD. Silencers were installed in each of the PVSs in order to decrease the noise. Partitions were placed between the desks to avoid eye contact between the subjects during the experiment. All materials and equipment (including desks and computers) used during the experiment were low polluting. Thirty subjects participated in the experiment. They were nonsmoking, Danish students without chronic diseases, such as asthma, hay fever or other allergies. The anthropological data of the subjects are listed in Table 1. The subjects were divided into eight groups. Each group participated in experiments in the afternoons and was assigned to a specific weekday and the same time of the day in order to diminish possible influence of day and time. The minimum time between two successive experiments for each group was one week. The subjects were paid for participating in the experiment. The experimental conditions covered three combinations of relative humidity and local velocity under a constant room air temperature of 26 C. The three combinations were 70% humidity with air movement (condition 1), 70% humidity without air movement (condition 2) and 30% humidity without air movement (condition 3). The experimental conditions are listed in Table 2. In condition 1, the subjects could individually control the personalized flow velocity within the range of 0e1.8 m s1. The air supplied by the PVS was measured from the chamber at a height of 0.2 m above the floor. Thus, the temperature of the air supplied was the same as that of the room, 26 C. In conditions 2 and 3, the subjects did not use the PVS. The subject groups were exposed to each of the three conditions in a randomized order.
2. Method 2.2. Questionnaires 2.1. Experimental facilities The experiments were performed in a climate chamber 4.7 m wide, 5.9 m long and 2.5 m high. The air temperature in the chamber was kept constant using piston flow ventilation. The air was supplied to the chamber through the perforated floor and was exhausted from the ceiling. In total 60 L s1 (40 L s1 of fresh air and 20 L s1 of recirculated air) was supplied to the chamber (air change rate 3 h1). The surface temperature of the walls inside the chamber was kept equal to the room air temperature; radiant temperature asymmetry was less than 0.1 C. The air velocity generated in the chamber by the ventilation system was lower than 0.05 m s1. The temperature and relative humidity were kept
Remote Performance Measurement (RPM) software [17], was used to collect subjects’ response to the environment. Based on standard [1] acceptability of air quality was measured using a continuous acceptability scale where 1 equal to clearly unacceptable, 0 to just unacceptable,þ0 to just acceptable and þ1 to clearly acceptable was used. The assessment of odour intensity was measured on a five point scale: 0 equal to no odour, 1 to slight odour, 2 to moderate odour, 3 to strong odour, 4 to very strong odour and 5 to overwhelming odour. The freshness and dryness of the air were measured on a continuous scale where 0 equal to air fresh and 100 to air stuffy. The subjects also reported any adjustments to their clothes made during the experiment.
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Fig. 1. The layout of the climate chamber.
2.3. Experimental procedure The subjects participated in a 1 h training session before the main experiments. During this 1 h the experimental procedure was explained to them and they were trained on how to fill in the questionnaire. The main experiments were conducted over three weeks in February 2008, each ‘week’ e from Monday to Thursday. Two groups participated in the experiments each day. Upon arrival, and before each experiment, the subjects stayed in an adjacent chamber where they were acclimatized for 15 min to the thermal conditions (a temperature of 26 C and 30% of relative humidity) they would experience during the experiment. The air change rate was 56 h1 of clean outdoor air and was much higher than in experimental chamber. The subjects were encouraged to modify their clothing in order to feel thermally comfortable. Air quality in this chamber was high due to the high outdoor airflow rate supply. At the end of the 15th minute period, the subjects were asked to report on the clothing they were wearing at that moment. They entered the experimental chamber. In this chamber the experimental time was divided into two parts. In the first part, the subjects were acclimatized to thermal conditions from the 15th to the 60th minute. In the second part of the experiment, (from the 60th to the 180th minute) the subjects performed typical office work: addition exercises and typing blocks of text. The experimental time schedule is shown in Fig. 2. At the beginning of each experiment, immediately upon entering the experimental chamber, the subjects assessed the acceptability of the air, odour intensity, air freshness and air dryness. The subjects sat at their desks without the personalized
ventilation system: Desks 1A, 2A, 3A and 4A as shown in Fig. 1 for 15 min. After that time the subjects were moved to a desk with an installed PVS, i.e. desks 1B, 2B, 3B and 4B (Fig. 1). The ATD of the PVS was adjusted to supply a personalized flow to the subject’s face/ chest. The subjects were encouraged to adjust the personalized flow rate according to their needs during the following 15 min. After 15 min’ exposure to the personalized flow the procedure was repeated; the subjects moved to the desks without PVS where they stayed for 15 min and then returned to the desks with PVS. The second part of the experiment, including the performance tasks, was then started. Questionnaires about the acceptability of the air quality were completed every 5 min during the first part of the experiment. The questionnaires about odour intensity, air freshness and air dryness were obtained at the end of each stage of the experiment. The subjects were allowed to adjust their clothing as they preferred during the experiment. 2.4. Statistical analysis The results obtained at the different environmental conditions were statistically analyzed. The ShapiroeWilk test was used to test the normality of the distribution with the level of significance of p < 0.05. Data that were normally distributed were analyzed with an ANOVA test for repeated measures and the NewmaneKeuls multi-stage test. For non-normally distributed data the FriedmanANOVA test and the Wilcoxon-matched-pair test were used and the results. All of the presented data are median values.
Table 2 Experimental conditions. Chamber parameters Table 1 Anthropological data of the subjects. Subjects (female/male)
30 (9/21)
Age (mean SD) Weight (mean SD) Height (mean SD)
22 2.2 years 76.27 12.4 kg 179.33 9 cm
Personalized ventilation
Condition number
Room air temperature [ C]
Room air humidity, RH [%]
Air temperature [ C]
Air humidity, RH [%]
Air velocity [m s1]
1 2 3
26 26 26
70 70 30
26 Without Without
70
Regulated
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Fig. 2. Procedure of the experiment.
3. Results and discussion This paper focuses on the perceived air quality. Fig. 3 shows the acceptability of the inhaled air quality reported over time under the three conditions studied. Room air at a high humidity of 70% was significantly less acceptable than room air at lower humidity of 30%. The facially applied air movement significantly (p < 0.01) improved the acceptability of the inhaled air in comparison with the condition at a relative humidity of 70% without the facially applied personalized flow. The improvement resulting from the elevated velocity was, however, not large enough to result in the same acceptability level as that rated for 30% relative humidity. The improvement was persistent and was constant under the two occasions at the desk with the PVS during intermittent occupation. However, it can be seen from the results in Fig. 3 that during the first part, when the occupants used personalized ventilation, 30the43rd min, the acceptability of the air quality gradually increased to a level which correlated with the level in the second part of the experiment. The reason for the observed change in the perception was that, during the first part of the experiment, the subjects tried to regulate the PVS and to establish a personalized flow with the preferred velocity required for optimal thermal sensation acceptability. This could also be correlated with the cooling effect of the respiratory tract. The difference in acceptability of the PAQ under the condition with the PVS was significant between the two experimental parts.
Fig. 3. Acceptability of the air quality during exposure under three experimental conditions (varying in temperature, humidity and air movement).
This also confirms that there is no impact of a ‘remembering effect’ in the responses of the subjects. The results in Fig. 3 also show small (insignificant) change in the air quality perception in time. The average of odour intensity ratings by the subjects at the end of each step of the experiment are presented in Fig. 4. The odour intensity was significantly lower at 30% relative humidity than at 70% relative humidity. No significant difference was observed between 70% relative humidity with and without PVS (except during one of the votes, 43 min after the start of the experiment). Under these two conditions odour intensity was rated as between ‘moderate odour’ and ‘slight odour’. It was observed that, over time, the subjects became more adjusted to the odour intensity. Generally the local air movement did not compensate for the negative impact of high humidity on odour intensity sensation. Fig. 5 presents the results of the air freshness ratings by the subjects at the end of each step of the experiment. The air was perceived to be fresher in the case with low humidity (30%) than in the case with high humidity without air movement. The statistical analysis showed that, during the first part of the experiment, significant differences in the rating of air freshness at low and high humidity without personalized flow as well as between the cases of high humidity with and without air movement were observed. This implies that, the air was felt to be much fresher at high humidity with the personalized flow. Only at the beginning of the exposure was the air felt to be significantly fresher
Fig. 4. Odour intensity e average for 30 subjects under three temperature, humidity and air-movement conditions.
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Fig. 7. Percentage of subjects dissatisfied with air quality, averaged for all 30 subjects under the three temperature, humidity and air-movement conditions. Fig. 5. Air freshness under three temperature, humidity and air-movement conditions.
at 30% relative humidity than at 70% relative humidity with personalized flow. The average rating for air dryness obtained for the three experimental conditions is compared in Fig. 6. The air was perceived to be drier in the condition with low humidity as compared with the high humidity condition (with and without air movement). At high humidity without personalized flow, the air was felt to be more humid than with personalized flow. The current results confirm previous findings of Melikov et al. [11,24] on the positive effect of the increased velocity on reported air acceptability. The percentage of persons dissatisfied (PD) was calculated from the mean acceptability of the assessed air using a log curve fitted to the relation obtained by Gunnarsen and Fanger [18]:
PD ¼
expð0:18 5:28 ACCÞ 100: 1 þ expð0:18 5:28 ACCÞ
(1)
where: PD is the percentage of persons dissatisfied with the air quality (%); ACC is the mean acceptability of assessed air. The calculated PD, shown in Fig. 7, clearly indicates that facially applied, elevated velocity air significantly improved PAQ. The percentage dissatisfied subjects at 70% relative humidity was significantly lower with the personalized ventilation than without it. The PVS significantly decreased the dissatisfaction with PAQ from almost 60% to between 30% and 20%. According to EN 15251,
rooms with such air quality belong to category III, which is recommended for existing buildings without requirement for high air quality standards. The relatively high percentage of dissatisfied subjects (between 20% and 30%) identified at high humidity with personalized ventilation was a consequence of the locally supplied air not being clean outdoor air but recirculated polluted, warm and humid room air. The improvement indicated was solely due to the increased air movement. Providing clean and cool personalized air would have further enhanced the perceived air quality [19]. Although the increased velocity cannot compensate entirely for the negative impact of increased relative humidity on PAQ the analysis of the results indicate that it may still be more beneficial to use a PVS instead of dehumidifying the total volume of the room air supplied through the background ventilation. This strategy may lead to a decrease in the energy used for ventilation. The demonstrated improvement in the perceived air quality with personalized ventilation used at higher temperature and humidity was obtained without increasing the flow rate of clean outdoor air into the room. Another advantage of the controlled locally applied air movement identified in the present study was the effect of the individual control itself. The perceived air quality results were compared with those reported by Melikov et al. [11] and obtained at constant air velocity, namely 0.6 m s1 without individual control. In the present study the preferable air velocity ranged between 0.6 and 1.5 m s1. All subjects selected velocity higher than 0.8 m s1 for some period of time during the exposure. No significant difference between male and female subjects with regard to the average exposure velocity (male 1 m s1 0.15 m s1; female 0.95 0.14 m s1) as well as minimum (0.6 m s1) and maximum velocity (close to 1.5 m s1) was found. A direct comparison was not possible since different groups of subjects were used in the two studies. The overall experimental procedures for both studies were also different (the previous study did not include the performance tests). However the procedure used in both studies during the first 60 min after the start was identical. For the purpose of comparison it was necessary to define an index R, which describes the decrease in dissatisfaction with air quality due to local air movement relative to the dissatisfaction expressed with air quality in a calm environment without air movement. The relative improvement is obtained from equation (2) shown below:
R ¼
Fig. 6. Air dryness under three temperature, humidity and air-movement conditions.
PD26 70 : PD26 70 pv
(2)
where: PD26_70 is the percentage dissatisfied under conditions of 26 C and 70% relative humidity; PD26_70_pv is the percentage dissatisfied under conditions of 26 C and 70% relative humidity with facially applied air movement.
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savings as was already discussed. However this approach has to be carefully considered because high relative humidity in the building construction can degrade building materials, creating favourable conditions for microbial growth [27]. Moisture in indoor air may cause condensation on cold interior surfaces or in the construction that also increases the risk of microbial growth. For example, the dew point corresponding to 26 C with 70% RH of indoor air is 20 C. 4. Conclusions
Fig. 8. Relative reduction of percentage dissatisfied (PD) in present and previous study [11].
Fig. 8 shows the differences between data from the present study and that from a previous one performed by Melikov et al. [11]. The comparison of the results shows a substantial reduction in the percentage dissatisfied with PAQ after a 10-min exposure when subjects were provided with individual control of a personalized flow (the present experiment) compared with when they did not have individual control [11]. The main reason for the difference could be that the individual control used in the present study gave subjects the opportunity to control the velocity of the personalized airflow to obtain their preferred conditions. The results of this study reveal that humidity have a strong impact on the perception of indoor air quality and confirm the previous findings [20] that, at low velocity and constant pollution levels, PAQ decreases with increasing air humidity. One of the reasons could be that, at high air humidity, cooling of the mucous membranes in the upper respiratory tract during inhalation is decreased, causing the air to be perceived as stuffy and unacceptable. The effect is assumed to be related to warm discomfort in the respiratory tract caused by an insufficient evaporative and convective cooling of the mucous membranes [7]. As shown by comparing this study with a previous study by Melikov et al. [11], enhanced cooling due to the elevated velocity of air directed at the face through personalized flow improved the PAQ. The personalized flow with high velocity improved the sensation of air freshness at 26 C and 70% relative humidity over that experienced at the level of 26 C and 30% relative humidity and was rated as being much better than at 26 C and 70% relative humidity without personalized flow. However, it had no impact on the odour intensity; this agrees with the results of a previous study [20] that temperature and humidity, especially with polluted air, have little influence on the perception of the odour intensity. Experiments performed in tropics with tropically acclimatized subjects confirmed present findings that elevated air movement improve the perceived air quality [24]. The applied personalized flow made subjects feel the air less humid than without air movement. The air was perceived as being more fresh and acceptable when the face and anterior part of the nose were cooled by the personalized flow. Insufficient cooling may be interpreted as a local, warm discomfort in the respiratory tract and may lead to the inhaled air being perceived as unacceptable. The positive impact of facially applied air movement in decreasing the negative impact of high relative humidity on perceived air quality may be applied in practice to achieve energy
A facially applied airflow with individually controlled velocity significantly improves the acceptability of the air quality at an indoor air temperature of 26 C and relative humidity of 70%, and partly compensates for the negative impact of relative humidity on perceived air quality at low velocity levels. Facially applied, personalized flow makes the air feel fresher and less humid. No effect of facially applied air movement with elevated velocity on odour intensity was identified. It is recommended that the effect of a facially applied airflow of clean air with humidity lower than the humidity of the surroundings be studied. The positive impact of increased facially applied air movement at high relative humidity may be considered for energy savings strategy. However this strategy should be carefully considered because long-term high humidity may cause microbial growth. References [1] EN 15251. Criteria for indoor environment including thermal, indoor air quality, light and noise. Brussels: European Committee for Standardization; 2007. [2] EN 13779. Ventilation for non-residential buildings d performance requirements for ventilation and room-conditioning systems. Brussels: European Committee for Standardization; 2007. [3] Berglund LG, Cain W. Perceived air quality and thermal environment. In: Proceedings of Indoor Air Quality, San Diego, 1989. p. 93e9. [4] Fang L, Clausen G, Fanger PO. Impact of temperature and humidity on the perception of indoor air quality. Indoor Air 1998;8(2):80e90. [5] Mcfadden J. Respiratory heat and water exchange: physiological and clinical implications. Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology 1993;54(2):331e6. [6] Andersen I, Proctor DF. The fate and effects of inhaled materials. In: Proctor DF, Andersen I, editors. The nose upper airway physiology and the atmospheric environment. Elsevier Biomedical Press; 1982. p. 423e55. [7] Toftum J, Jorgensen AS, Fanger PO. Upper limits of air humidity for preventing warm respiratory discomfort. Energy and Buildings 1998;28(3):1e13. [8] Keck T, Leiacker R, Riechelmann H, Rettinger G. Temperature profile in the nasal cavity. Laryngoscope 2000;110:651e4. [9] ANSI/ASHRAE Standard 55-2004. Thermal environmental conditions for human occupancy. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc; 2004. [10] Kaczmarczyk J, Melikov A, Sliva D. Effect of warm air supplied facially on occupants’ comfort. Building and Environment 2010;45(4):848e55. [11] Melikov AK, Kaczmarczyk J, Sliva D. Impact of air movement on perceived air quality at different level of relative humidity. In: Proceedings of the 11th international conference on indoor air quality and climate e Indoor Air 2008, Copenhagen; 17e22 August 2008, Paper ID: 1037. [12] Schiavon S, Melikov A. Energy saving and improved comfort by increasing air movement. Energy and Buildings 2008;40(10):1954e60. [13] Bedford T. Basic principles of ventilation and heating. 2nd ed. London: Lewis; 1974. [14] Menzies RI, Tamblyn RM, Tamblyn RT, Farant JP, Hanley J, Spitzner WO. The effect of varying levels of outdoor air ventilation on symptoms of sick building syndrome. In: Proceedings of indoor air quality, Healthy Buildings, Atlanta; 1991. p. 90e6. [15] Bauman FS, Carter TG, Baughman AV, Arens EA. Field study of the impact of a desktop task/ambient conditioning system in an office buildings. ASHRAE Transactions 1998;104(1):125e42. [16] Bolashikov Z, Nikolaev L, Melikov A, Kaczmarczyk J, Fanger PO. New air terminal devices with high efficiency for personalized ventilation application. In: Proceedings of Healthy Buildings, Singapore, 7-1 National University of Singapore, Department of Building, vol. 2; 2003. p. 850e5. [17] Toftum J, Wyon DP, Svanekjær H, Lantner A. Remote performance measurement (RPM) e a new, internet-based method for the measurement of occupant performance in office buildings. In: Proceedings of Indoor Air, 10th
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M.A. Skwarczynski et al. / Building and Environment 45 (2010) 2170e2176 international conference on indoor air quality and climate, vol. 1, Beijing, 2e9 September 2005. p. 357e361. Gunnarsen L, Fanger PO. Adaptation to indoor air pollution. Energy and Buildings 1992;18:43e54. Kaczmarczyk J, Melikov A, Fanger PO. Human response to personalized ventilation and mixing ventilation. Indoor Air 2004;14(8):17e29. Fang L, Clausen G, Fanger PO. Impact of temperature and humidity on perception of indoor air quality during immediate and longer whole-body exposures. Indoor Air 1998;8(4):276e84. ISO 7730. Moderate thermal environment e determination of the PMV and PPD indices and specification of the conditions for thermal comfort. International Organization for Standardization; 2005. ANSI/ASHRAE Standard 62.1-2007. Ventilation for acceptable indoor air quality. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc; 2007. Melikov AK, Kaczmarczyk J. Impact of air movement on perceived air quality at different level of air pollution and temperature. In: Proceedings of the 11th
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Impact of individually controlled facially applied air movement on perceived air quality at high humidity M.A. Skwarczynski a, b, *, A.K. Melikov b, J. Kaczmarczyk c, V. Lyubenova b a
Faculty of Environmental Engineering, Institute of Environmental Protection Engineering, Department of Indoor Environment Engineering, Lublin University of Technology, Lublin, Poland b International Centre for Indoor Environment and Energy, Department of Civil Engineering, Technical University of Denmark, Copenhagen, Denmark c Faculty of Energy and Environmental Engineering, Department of Heating, Ventilation and Dust Removal Technology, Silesian University of Technology, Gliwice, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 March 2010 Received in revised form 25 March 2010 Accepted 27 March 2010
The effect of facially applied air movement on perceived air quality (PAQ) at high humidity was studied. Thirty subjects (21 males and 9 females) participated in three, 3-h experiments performed in a climate chamber. The experimental conditions covered three combinations of relative humidity and local air velocity under a constant air temperature of 26 C, namely: 70% relative humidity without air movement, 30% relative humidity without air movement and 70% relative humidity with air movement under isothermal conditions. Personalized ventilation was used to supply room air from the front toward the upper part of the body (upper chest, head). The subjects could control the flow rate (velocity) of the supplied air in the vicinity of their bodies. The results indicate an airflow with elevated velocity applied to the face significantly improves the acceptability of the air quality at the room air temperature of 26 C and relative humidity of 70%. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Air movement Humidity Perceived air quality Personalized ventilation
1. Introduction The purpose of ventilation is to provide clean, fresh air to occupied space, to remove or dilute pollution and to ensure optimal thermal conditions for the occupants. Present standards [1,9,21,22] specify requirements for ventilation rates and the thermal environment. The European Standard EN 15251 [1] recommends ventilation rates for buildings when taking into account pollutant emissions from the building materials and the occupants. At the low range of comfortable room temperatures (19e24 C) recommended in the present standards [1] relative humidity has little impact on people’s thermal comfort. At the high range of recommended temperatures (25e27 C) high relative humidity increases occupants’ thermal discomfort. In hot and humid climates as well as in temperate climates during summer relative humidity should be considered also from energy point of view. Dehumidification and humidification of the air used for ventilation of buildings may increase substantially the energy consumption of HVAC
* Corresponding author. Faculty of Environmental Engineering, Institute of Environmental Protection Engineering, Department of Indoor Environment Engineering, Lublin University of Technology, Nadbystrzycka 40B, 20-618 Lublin, Poland. Tel.: þ48 815384411; fax: þ48 815381997. E-mail address: [email protected] (M.A. Skwarczynski). 0360-1323/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2010.03.017
systems. EN 15251 [1] specifies design values for indoor relative humidity when humidification and dehumidification are needed: in case of dehumidification e 50%, 60% and 70%, and in case of humidification e 40%, 30% and 20% respectively for categories I, II and III of indoor environment. The absolute humidity can also be specified as a second parameter to be adjusted in rooms [2]. The winter minimum value for the absolute humidity is equal to 6 g kg1. This corresponds to 40% relative humidity at 22 C. The summer maximum value is specified as 12 g kg1, corresponding to 60% relative humidity at 26 C. The negative effect of high temperature and high humidity on air quality and odour intensity perception have been demonstrated in several studies. Berglund and Cain [3] showed that air was perceived as fresher and less stuffy with decreasing temperature and humidity. The effect of humidity on freshness, stuffiness and the acceptability of air quality was smaller when the dew point was below 11 C than when it was above 11 C, which corresponds to 49.7% relative humidity at 22 C and 39.1% relative humidity at 26 C [3,4,20]. The cooling of the mucous membranes at the surface of the nasal passages is presumed to be decisive in people’s thermal perception of the inhaled air [7]. Inhaled air cools the mucosa if the temperature of the inhaled air is below the mucosal temperature, which is normally 30e32 C [4e6]. The cooling of the mucous membranes is proportional to the temperature and water vapour
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gradients between the surface of the respiratory tract and the inhaled air. Keck et al. [8] suggested that, despite the high airstream velocity in the centre of the inspired air, high thermal pressure gradients in the anterior part of the nose can cause a high heating capacity, especially in this region, and this can be assumed to be decisive in people’s perceptions of inhaled air. Room air movement is an important factor to be considered for occupants’ thermal comfort. At high room temperatures elevated air movement improves occupants’ thermal comfort. However at the lower range of room air temperatures air movement may cause draught discomfort (draught is defined as unwanted local cooling of the body due to air movement). When people sense a draught they often demand higher room air temperatures or even that the ventilation system is stopped. To be consistent with the EN 15251 [1] criteria, the maximum mean air velocities for a landscaped office (open-plan office) for summer (the cooling season) are 0.18, 0.22, 0.25 m s1 in categories I, II and III, respectively, and for winter (the heating season) these air velocities are 0.15, 0.18, 0.21 m s1. The cooling power of air movement increases with the increase of its velocity and the decrease of its temperature. At high room air temperature flow of cool air will improve the thermal comfort for majority of the occupants while at low room air temperature warm air will have the same positive effect [10]. Present standards [1,9,21] recommend individual control of the speed of the local air movement at the vicinity of each occupant in order to achieve preferred thermal environment. The control of air movement in the breathing zone can be achieved using a personalized ventilation system [25] or a table fan. The strategy of increasing the upper limit of operative temperature in rooms and improving occupants’ thermal comfort by individually controlled air movement may lead to energy savings [12,26]. Further energy savings can be achieved if dehumidification of the supplied air can be avoided. In this respect, the effect of increased air movement on perceived air quality (PAQ) is important. It has been reported in the literature that air is perceived as more fresh at higher velocity [11,13,23,28]. The elevated velocity of airflow supplied by personalized ventilation against the face diminishes the negative impact of increased relative humidity on PAQ [11]. In the referred human subject study [11] the air velocity was set at a constant level of either 0.3 m s1 or 0.6 m s1 and the subjects could not adjust their local conditions. However, earlier studies [14,15] have reported that the possibility of controlling the micro-environment can play a substantial role in the occupants’ responses, leading to a more positive evaluation of the same environment. The objective of the present study was to investigate the effect of individually controlled elevated facial air velocity on perceived air quality (PAQ), air freshness, air dryness and odour intensity at high level of relative humidity.
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constant at the set conditions. The measurement point was located at the centre of chamber at the height 1.1 m. Eight workstations were arranged in the chamber. Four of them had personalized ventilation systems (PVSs) installed. The layout of the chamber is shown in Fig. 1. The desks were positioned and used in pairs, i.e. four pairs 1, 2, 3, 4. Each desk pair had one desk without a PVS (1A, 2A, 3A, 4A) and one desk with a PVS (1B, 2B, 3B, 4B). The supply air terminal device (ATD) of the PVS, named the round movable panel (RMP), has been described by Bolashikov et al. (2003) [16]. The RMP generated a personalized flow with uniform velocity distribution and low initial turbulence intensity. The ATD was mounted on a movable arm-duct attached to the desk-top, allowing changes to be made in its distance from, and position relative to, the occupant. The movable arm was connected by duct to the AC circular fan. The maximum airflow generated by each fan was 20 L s1 which corresponded to the air velocity of 1.8 m s1. Turbulence intensity on the centre of the generated flow was measured to be 4% at distance 0.5 m from the RMP. The turbulence intensity increased with the decrease of the air velocity. Subjects’ could control individually the supplied personalized flow, i.e. airflow velocity, at each desk. During the experiment, individuals were allowed to control the flow rate of the PVS at their desk but not to change the positioning of the ATD. Silencers were installed in each of the PVSs in order to decrease the noise. Partitions were placed between the desks to avoid eye contact between the subjects during the experiment. All materials and equipment (including desks and computers) used during the experiment were low polluting. Thirty subjects participated in the experiment. They were nonsmoking, Danish students without chronic diseases, such as asthma, hay fever or other allergies. The anthropological data of the subjects are listed in Table 1. The subjects were divided into eight groups. Each group participated in experiments in the afternoons and was assigned to a specific weekday and the same time of the day in order to diminish possible influence of day and time. The minimum time between two successive experiments for each group was one week. The subjects were paid for participating in the experiment. The experimental conditions covered three combinations of relative humidity and local velocity under a constant room air temperature of 26 C. The three combinations were 70% humidity with air movement (condition 1), 70% humidity without air movement (condition 2) and 30% humidity without air movement (condition 3). The experimental conditions are listed in Table 2. In condition 1, the subjects could individually control the personalized flow velocity within the range of 0e1.8 m s1. The air supplied by the PVS was measured from the chamber at a height of 0.2 m above the floor. Thus, the temperature of the air supplied was the same as that of the room, 26 C. In conditions 2 and 3, the subjects did not use the PVS. The subject groups were exposed to each of the three conditions in a randomized order.
2. Method 2.2. Questionnaires 2.1. Experimental facilities The experiments were performed in a climate chamber 4.7 m wide, 5.9 m long and 2.5 m high. The air temperature in the chamber was kept constant using piston flow ventilation. The air was supplied to the chamber through the perforated floor and was exhausted from the ceiling. In total 60 L s1 (40 L s1 of fresh air and 20 L s1 of recirculated air) was supplied to the chamber (air change rate 3 h1). The surface temperature of the walls inside the chamber was kept equal to the room air temperature; radiant temperature asymmetry was less than 0.1 C. The air velocity generated in the chamber by the ventilation system was lower than 0.05 m s1. The temperature and relative humidity were kept
Remote Performance Measurement (RPM) software [17], was used to collect subjects’ response to the environment. Based on standard [1] acceptability of air quality was measured using a continuous acceptability scale where 1 equal to clearly unacceptable, 0 to just unacceptable,þ0 to just acceptable and þ1 to clearly acceptable was used. The assessment of odour intensity was measured on a five point scale: 0 equal to no odour, 1 to slight odour, 2 to moderate odour, 3 to strong odour, 4 to very strong odour and 5 to overwhelming odour. The freshness and dryness of the air were measured on a continuous scale where 0 equal to air fresh and 100 to air stuffy. The subjects also reported any adjustments to their clothes made during the experiment.
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Fig. 1. The layout of the climate chamber.
2.3. Experimental procedure The subjects participated in a 1 h training session before the main experiments. During this 1 h the experimental procedure was explained to them and they were trained on how to fill in the questionnaire. The main experiments were conducted over three weeks in February 2008, each ‘week’ e from Monday to Thursday. Two groups participated in the experiments each day. Upon arrival, and before each experiment, the subjects stayed in an adjacent chamber where they were acclimatized for 15 min to the thermal conditions (a temperature of 26 C and 30% of relative humidity) they would experience during the experiment. The air change rate was 56 h1 of clean outdoor air and was much higher than in experimental chamber. The subjects were encouraged to modify their clothing in order to feel thermally comfortable. Air quality in this chamber was high due to the high outdoor airflow rate supply. At the end of the 15th minute period, the subjects were asked to report on the clothing they were wearing at that moment. They entered the experimental chamber. In this chamber the experimental time was divided into two parts. In the first part, the subjects were acclimatized to thermal conditions from the 15th to the 60th minute. In the second part of the experiment, (from the 60th to the 180th minute) the subjects performed typical office work: addition exercises and typing blocks of text. The experimental time schedule is shown in Fig. 2. At the beginning of each experiment, immediately upon entering the experimental chamber, the subjects assessed the acceptability of the air, odour intensity, air freshness and air dryness. The subjects sat at their desks without the personalized
ventilation system: Desks 1A, 2A, 3A and 4A as shown in Fig. 1 for 15 min. After that time the subjects were moved to a desk with an installed PVS, i.e. desks 1B, 2B, 3B and 4B (Fig. 1). The ATD of the PVS was adjusted to supply a personalized flow to the subject’s face/ chest. The subjects were encouraged to adjust the personalized flow rate according to their needs during the following 15 min. After 15 min’ exposure to the personalized flow the procedure was repeated; the subjects moved to the desks without PVS where they stayed for 15 min and then returned to the desks with PVS. The second part of the experiment, including the performance tasks, was then started. Questionnaires about the acceptability of the air quality were completed every 5 min during the first part of the experiment. The questionnaires about odour intensity, air freshness and air dryness were obtained at the end of each stage of the experiment. The subjects were allowed to adjust their clothing as they preferred during the experiment. 2.4. Statistical analysis The results obtained at the different environmental conditions were statistically analyzed. The ShapiroeWilk test was used to test the normality of the distribution with the level of significance of p < 0.05. Data that were normally distributed were analyzed with an ANOVA test for repeated measures and the NewmaneKeuls multi-stage test. For non-normally distributed data the FriedmanANOVA test and the Wilcoxon-matched-pair test were used and the results. All of the presented data are median values.
Table 2 Experimental conditions. Chamber parameters Table 1 Anthropological data of the subjects. Subjects (female/male)
30 (9/21)
Age (mean SD) Weight (mean SD) Height (mean SD)
22 2.2 years 76.27 12.4 kg 179.33 9 cm
Personalized ventilation
Condition number
Room air temperature [ C]
Room air humidity, RH [%]
Air temperature [ C]
Air humidity, RH [%]
Air velocity [m s1]
1 2 3
26 26 26
70 70 30
26 Without Without
70
Regulated
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Fig. 2. Procedure of the experiment.
3. Results and discussion This paper focuses on the perceived air quality. Fig. 3 shows the acceptability of the inhaled air quality reported over time under the three conditions studied. Room air at a high humidity of 70% was significantly less acceptable than room air at lower humidity of 30%. The facially applied air movement significantly (p < 0.01) improved the acceptability of the inhaled air in comparison with the condition at a relative humidity of 70% without the facially applied personalized flow. The improvement resulting from the elevated velocity was, however, not large enough to result in the same acceptability level as that rated for 30% relative humidity. The improvement was persistent and was constant under the two occasions at the desk with the PVS during intermittent occupation. However, it can be seen from the results in Fig. 3 that during the first part, when the occupants used personalized ventilation, 30the43rd min, the acceptability of the air quality gradually increased to a level which correlated with the level in the second part of the experiment. The reason for the observed change in the perception was that, during the first part of the experiment, the subjects tried to regulate the PVS and to establish a personalized flow with the preferred velocity required for optimal thermal sensation acceptability. This could also be correlated with the cooling effect of the respiratory tract. The difference in acceptability of the PAQ under the condition with the PVS was significant between the two experimental parts.
Fig. 3. Acceptability of the air quality during exposure under three experimental conditions (varying in temperature, humidity and air movement).
This also confirms that there is no impact of a ‘remembering effect’ in the responses of the subjects. The results in Fig. 3 also show small (insignificant) change in the air quality perception in time. The average of odour intensity ratings by the subjects at the end of each step of the experiment are presented in Fig. 4. The odour intensity was significantly lower at 30% relative humidity than at 70% relative humidity. No significant difference was observed between 70% relative humidity with and without PVS (except during one of the votes, 43 min after the start of the experiment). Under these two conditions odour intensity was rated as between ‘moderate odour’ and ‘slight odour’. It was observed that, over time, the subjects became more adjusted to the odour intensity. Generally the local air movement did not compensate for the negative impact of high humidity on odour intensity sensation. Fig. 5 presents the results of the air freshness ratings by the subjects at the end of each step of the experiment. The air was perceived to be fresher in the case with low humidity (30%) than in the case with high humidity without air movement. The statistical analysis showed that, during the first part of the experiment, significant differences in the rating of air freshness at low and high humidity without personalized flow as well as between the cases of high humidity with and without air movement were observed. This implies that, the air was felt to be much fresher at high humidity with the personalized flow. Only at the beginning of the exposure was the air felt to be significantly fresher
Fig. 4. Odour intensity e average for 30 subjects under three temperature, humidity and air-movement conditions.
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Fig. 7. Percentage of subjects dissatisfied with air quality, averaged for all 30 subjects under the three temperature, humidity and air-movement conditions. Fig. 5. Air freshness under three temperature, humidity and air-movement conditions.
at 30% relative humidity than at 70% relative humidity with personalized flow. The average rating for air dryness obtained for the three experimental conditions is compared in Fig. 6. The air was perceived to be drier in the condition with low humidity as compared with the high humidity condition (with and without air movement). At high humidity without personalized flow, the air was felt to be more humid than with personalized flow. The current results confirm previous findings of Melikov et al. [11,24] on the positive effect of the increased velocity on reported air acceptability. The percentage of persons dissatisfied (PD) was calculated from the mean acceptability of the assessed air using a log curve fitted to the relation obtained by Gunnarsen and Fanger [18]:
PD ¼
expð0:18 5:28 ACCÞ 100: 1 þ expð0:18 5:28 ACCÞ
(1)
where: PD is the percentage of persons dissatisfied with the air quality (%); ACC is the mean acceptability of assessed air. The calculated PD, shown in Fig. 7, clearly indicates that facially applied, elevated velocity air significantly improved PAQ. The percentage dissatisfied subjects at 70% relative humidity was significantly lower with the personalized ventilation than without it. The PVS significantly decreased the dissatisfaction with PAQ from almost 60% to between 30% and 20%. According to EN 15251,
rooms with such air quality belong to category III, which is recommended for existing buildings without requirement for high air quality standards. The relatively high percentage of dissatisfied subjects (between 20% and 30%) identified at high humidity with personalized ventilation was a consequence of the locally supplied air not being clean outdoor air but recirculated polluted, warm and humid room air. The improvement indicated was solely due to the increased air movement. Providing clean and cool personalized air would have further enhanced the perceived air quality [19]. Although the increased velocity cannot compensate entirely for the negative impact of increased relative humidity on PAQ the analysis of the results indicate that it may still be more beneficial to use a PVS instead of dehumidifying the total volume of the room air supplied through the background ventilation. This strategy may lead to a decrease in the energy used for ventilation. The demonstrated improvement in the perceived air quality with personalized ventilation used at higher temperature and humidity was obtained without increasing the flow rate of clean outdoor air into the room. Another advantage of the controlled locally applied air movement identified in the present study was the effect of the individual control itself. The perceived air quality results were compared with those reported by Melikov et al. [11] and obtained at constant air velocity, namely 0.6 m s1 without individual control. In the present study the preferable air velocity ranged between 0.6 and 1.5 m s1. All subjects selected velocity higher than 0.8 m s1 for some period of time during the exposure. No significant difference between male and female subjects with regard to the average exposure velocity (male 1 m s1 0.15 m s1; female 0.95 0.14 m s1) as well as minimum (0.6 m s1) and maximum velocity (close to 1.5 m s1) was found. A direct comparison was not possible since different groups of subjects were used in the two studies. The overall experimental procedures for both studies were also different (the previous study did not include the performance tests). However the procedure used in both studies during the first 60 min after the start was identical. For the purpose of comparison it was necessary to define an index R, which describes the decrease in dissatisfaction with air quality due to local air movement relative to the dissatisfaction expressed with air quality in a calm environment without air movement. The relative improvement is obtained from equation (2) shown below:
R ¼
Fig. 6. Air dryness under three temperature, humidity and air-movement conditions.
PD26 70 : PD26 70 pv
(2)
where: PD26_70 is the percentage dissatisfied under conditions of 26 C and 70% relative humidity; PD26_70_pv is the percentage dissatisfied under conditions of 26 C and 70% relative humidity with facially applied air movement.
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savings as was already discussed. However this approach has to be carefully considered because high relative humidity in the building construction can degrade building materials, creating favourable conditions for microbial growth [27]. Moisture in indoor air may cause condensation on cold interior surfaces or in the construction that also increases the risk of microbial growth. For example, the dew point corresponding to 26 C with 70% RH of indoor air is 20 C. 4. Conclusions
Fig. 8. Relative reduction of percentage dissatisfied (PD) in present and previous study [11].
Fig. 8 shows the differences between data from the present study and that from a previous one performed by Melikov et al. [11]. The comparison of the results shows a substantial reduction in the percentage dissatisfied with PAQ after a 10-min exposure when subjects were provided with individual control of a personalized flow (the present experiment) compared with when they did not have individual control [11]. The main reason for the difference could be that the individual control used in the present study gave subjects the opportunity to control the velocity of the personalized airflow to obtain their preferred conditions. The results of this study reveal that humidity have a strong impact on the perception of indoor air quality and confirm the previous findings [20] that, at low velocity and constant pollution levels, PAQ decreases with increasing air humidity. One of the reasons could be that, at high air humidity, cooling of the mucous membranes in the upper respiratory tract during inhalation is decreased, causing the air to be perceived as stuffy and unacceptable. The effect is assumed to be related to warm discomfort in the respiratory tract caused by an insufficient evaporative and convective cooling of the mucous membranes [7]. As shown by comparing this study with a previous study by Melikov et al. [11], enhanced cooling due to the elevated velocity of air directed at the face through personalized flow improved the PAQ. The personalized flow with high velocity improved the sensation of air freshness at 26 C and 70% relative humidity over that experienced at the level of 26 C and 30% relative humidity and was rated as being much better than at 26 C and 70% relative humidity without personalized flow. However, it had no impact on the odour intensity; this agrees with the results of a previous study [20] that temperature and humidity, especially with polluted air, have little influence on the perception of the odour intensity. Experiments performed in tropics with tropically acclimatized subjects confirmed present findings that elevated air movement improve the perceived air quality [24]. The applied personalized flow made subjects feel the air less humid than without air movement. The air was perceived as being more fresh and acceptable when the face and anterior part of the nose were cooled by the personalized flow. Insufficient cooling may be interpreted as a local, warm discomfort in the respiratory tract and may lead to the inhaled air being perceived as unacceptable. The positive impact of facially applied air movement in decreasing the negative impact of high relative humidity on perceived air quality may be applied in practice to achieve energy
A facially applied airflow with individually controlled velocity significantly improves the acceptability of the air quality at an indoor air temperature of 26 C and relative humidity of 70%, and partly compensates for the negative impact of relative humidity on perceived air quality at low velocity levels. Facially applied, personalized flow makes the air feel fresher and less humid. No effect of facially applied air movement with elevated velocity on odour intensity was identified. It is recommended that the effect of a facially applied airflow of clean air with humidity lower than the humidity of the surroundings be studied. The positive impact of increased facially applied air movement at high relative humidity may be considered for energy savings strategy. However this strategy should be carefully considered because long-term high humidity may cause microbial growth. References [1] EN 15251. Criteria for indoor environment including thermal, indoor air quality, light and noise. Brussels: European Committee for Standardization; 2007. [2] EN 13779. Ventilation for non-residential buildings d performance requirements for ventilation and room-conditioning systems. Brussels: European Committee for Standardization; 2007. [3] Berglund LG, Cain W. Perceived air quality and thermal environment. In: Proceedings of Indoor Air Quality, San Diego, 1989. p. 93e9. [4] Fang L, Clausen G, Fanger PO. Impact of temperature and humidity on the perception of indoor air quality. Indoor Air 1998;8(2):80e90. [5] Mcfadden J. Respiratory heat and water exchange: physiological and clinical implications. Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology 1993;54(2):331e6. [6] Andersen I, Proctor DF. The fate and effects of inhaled materials. In: Proctor DF, Andersen I, editors. The nose upper airway physiology and the atmospheric environment. Elsevier Biomedical Press; 1982. p. 423e55. [7] Toftum J, Jorgensen AS, Fanger PO. Upper limits of air humidity for preventing warm respiratory discomfort. Energy and Buildings 1998;28(3):1e13. [8] Keck T, Leiacker R, Riechelmann H, Rettinger G. Temperature profile in the nasal cavity. Laryngoscope 2000;110:651e4. [9] ANSI/ASHRAE Standard 55-2004. Thermal environmental conditions for human occupancy. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc; 2004. [10] Kaczmarczyk J, Melikov A, Sliva D. Effect of warm air supplied facially on occupants’ comfort. Building and Environment 2010;45(4):848e55. [11] Melikov AK, Kaczmarczyk J, Sliva D. Impact of air movement on perceived air quality at different level of relative humidity. In: Proceedings of the 11th international conference on indoor air quality and climate e Indoor Air 2008, Copenhagen; 17e22 August 2008, Paper ID: 1037. [12] Schiavon S, Melikov A. Energy saving and improved comfort by increasing air movement. Energy and Buildings 2008;40(10):1954e60. [13] Bedford T. Basic principles of ventilation and heating. 2nd ed. London: Lewis; 1974. [14] Menzies RI, Tamblyn RM, Tamblyn RT, Farant JP, Hanley J, Spitzner WO. The effect of varying levels of outdoor air ventilation on symptoms of sick building syndrome. In: Proceedings of indoor air quality, Healthy Buildings, Atlanta; 1991. p. 90e6. [15] Bauman FS, Carter TG, Baughman AV, Arens EA. Field study of the impact of a desktop task/ambient conditioning system in an office buildings. ASHRAE Transactions 1998;104(1):125e42. [16] Bolashikov Z, Nikolaev L, Melikov A, Kaczmarczyk J, Fanger PO. New air terminal devices with high efficiency for personalized ventilation application. In: Proceedings of Healthy Buildings, Singapore, 7-1 National University of Singapore, Department of Building, vol. 2; 2003. p. 850e5. [17] Toftum J, Wyon DP, Svanekjær H, Lantner A. Remote performance measurement (RPM) e a new, internet-based method for the measurement of occupant performance in office buildings. In: Proceedings of Indoor Air, 10th
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