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Performance of “ductless” personalized ventilation in conjunction with displacement ventilation: Impact of intake height
Building and Environment 45 (2010) 996–1005
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Performance of ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation: Impact of intake height ˇ ova´ a, b, *, Arsen K. Melikov b Barbora Halvon a b
Department of Building Services, Slovak University of Technology in Bratislava, 813 68 Bratislava, Slovakia International Centre for Indoor Environment and Energy, Department of Civil Engineering, Technical University of Denmark, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 July 2009 Received in revised form 8 October 2009 Accepted 9 October 2009
The importance of the intake positioning height above the floor level on the performance of ‘‘ductless’’ personalized ventilation (‘‘ductless’’ PV) in conjunction with displacement ventilation (DV) was examined with regard to the quality of inhaled air and of the thermal comfort provided. A typical office room with two workstations positioned one behind the other was arranged in a full-scale room. Each workstation consisted of a table with an installed ‘‘ductless’’ PV system, PC, desk lamp and seated breathing thermal manikin. The ‘‘ductless’’ PV system sucked the clean and cool displacement air supplied over the floor at four different heights, i.e. 2, 5, 10 and 20 cm and transported it direct to the breathing level. Moreover, two displacement airflow rates were used with a supply temperature adjusted in order to maintain an exhaust air temperature of 26 C. Two pollution sources, namely air exhaled by one of the manikins and passive pollution on the table in front of the same manikin were simulated by constant dosing of tracer gases. The results show that the positioning of a ‘‘ductless’’ PV intake height up to 0.2 m above the floor will not significantly influence the quality of inhaled air and thermal comfort. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: ‘‘Ductless’’ personalized ventilation Displacement ventilation Perceived air quality Thermal comfort
1. Introduction Preferences regarding the indoor environment differ between individuals to a large extent. Even for the same person the preferred environment may change from day to day as well as during the same day. In practice it is impossible at the same time to ensure satisfaction for all room occupants by any total-volume ventilation principle since the indoor environment, although designed according to existing standards [1–3], may not be that preferred by all occupants in the room. Some occupants are more sensitive to the quality of inhaled air and others to the thermal environment. Increasing the supplied flow rate to satisfy occupants who like air movement will increase the dissatisfaction of occupants who are sensitive and who are bothered by air movement. At the same pollution level in a room the perceived air quality will improve when the air temperature decreases, but this may cause thermal discomfort for occupants who prefer a warmer environment. One way to overcome the individual differences is to provide each occupant with individual control of the microenvironment at his/
* Corresponding author. Slovak University of Technology in Bratislava, Department of Building Services, 813 68 Bratislava, Slovakia. Tel.: þ421 903 904 484; fax: þ421 2 5296 11 37. ˇ ova´). E-mail address: [email protected] (B. Halvon 0360-1323/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2009.10.007
her workstation. The number of dissatisfied occupants will decrease when each workstation is equipped with personalized ventilation providing clean air to the breathing zone and allowing for individual control of the flow rate, i.e. air velocity, flow direction, temperature and in some designs the distance of the air supply device from the body. The preferred thermal environment can thus be achieved [4]. Recently, a novel air distribution idea, namely ‘‘ductless‘‘ personalized ventilation (‘‘ductless’’ PV) in conjunction with displacement ventilation (DV) was introduced [5,6]. The outdoor treated air supplied to the room by a displacement diffuser spreads over the floor and creates a stratified flow of clean and cool air [7]. The main idea behind the ‘‘ductless’’ PV is to transport the clean air from this layer direct to the breathing zone of each occupant. In this way the air from the floor area can be utilized more efficiently. The performance of the ‘‘ductless’’ PV was studied in regard to the arrangement of workstations, the use of partitions, and disturbances caused by walking person(s) [5,6]. It was found that the performance of ‘‘ductless’’ PV will depend on the type and location of pollution sources, within the room. The performance of the ‘‘ductless’’ PV was found to be better than that of DV used alone for some typical conditions in practice (e.g. presence of walking person(s)). According to REHVA Guidebook [8] the typical height of the stratified flow of clean and cool air above the floor level is
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approximately 20 cm when displacement ventilation is properly designed and correctly operated. The thickness of the layer of clean and cool air depends on many factors such as supply airflow rate and temperature, type of air supply diffuser, etc. and can vary also within the room. Furthermore, vertical temperature gradients are present in the flow of clean and cool air. This non-uniformity may influence the performance of the ‘‘ductless’’ PV. The purpose of the present study was to examine the importance of the intake positioning height above the floor on the performance of ‘‘ductless’’ PV in conjunction with DV. Attention was focused on the impact of the intake positioning height on the quality of inhaled air and of the thermal comfort provided. 2. Methods 2.1. Full-scale room A full-scale room (4.8 5.4 2.6 m3), was arranged as a typical office with two workstations WS1 and WS2 (Fig. 1). The walls and the floor of the room were made of wooden chipboard with 0.05 m insulation. One of the walls was single-glazed and the ceiling was made of gypsum tiles. The room was located in an air-conditioned tall concrete hall. The operative temperature in the tall hall was kept close to the room air temperature in order to reduce the heat transfer through the walls of the test room. Each workstation consisted of a desk with a ‘‘ductless’’ PV system (Fig. 2), personal computer with monitor, desk lamp and a dressed seated breathing thermal manikin simulating an ‘‘occupant’’. 2.2. Ventilation systems Displacement ventilation was used as a total-volume ventilation principle. The outdoor treated air was supplied through a semicircular wall unit with a radius in planar projection of 0.25 m and a height of 1 m (position 7, Fig. 1). The unit was fitted with nozzles, which ensured the spread of the supplied air mainly along the adjacent wall. The used air was exhausted from the room through a rectangular perforated air terminal device installed in the middle of the ceiling (position 8, Fig. 1). Recirculation of room air was not utilized in order to increase sensitivity of the performed tracer gas measurements. The ‘‘ductless’’ PV systems installed at each desk consisted of an air terminal device (ATD) mounted on a moveable arm (diameter 0.08 m) and a small axial fan incorporated in a short duct system (diameter 0.1 m), respectively positions 1, 4 and 5 in Fig. 2. The ‘‘ductless’’ PV sucked the air at the locations of the desks (position 6, Fig. 2) directly from the layer of clean and fresh air and transported it to the breathing zone. In the present study the Round
Fig. 2. ‘‘Ductless’’ PV: (1) Round moveable panel (RMP), (2) heat sources, (3) desk, (4) installed fan, (5) short duct system, (6) intake of ‘‘ductless’’ PV, (7) floor level.
Moveable Panel (RMP) with a diameter of 0.185 m [9] was used as the ATD. During the experiments, the RMPs were positioned in front (0.4 m from the face) and slightly above the face level, the positioning most often preferred by people [10,11], i.e. the personalized flow was directed towards to the manikin face from front and above with supply air velocity of 0.56 m/s. The positioning was identical for both manikins and did not differ between the experimental cases since it has been reported [12,13] that the direction of personalized airflow in relation to the occupant’s head may affect the inhaled air quality to a large extent.
2.3. Breathing thermal manikins The manikins were used to simulate seated occupants performing office work. The bodies of the manikins were shaped as a 1.7 m tall average Scandinavian woman and were divided into several individually controlled and heated body segments. One of the manikins had 17 body segments and the other had 23 segments. The surface temperature of the manikins was controlled to equal the skin temperature of an average person in a state of thermal neutrality while performing light office work [14]. Since the experiments simulated summer conditions the clothing insulation of the manikins, together with the upholstered office chair insulation, was 0.59 clo in total [1].
Fig. 1. Full-scale room: (1) polluting manikin, (2) exposed manikin, (4) – (6) heat sources, (7) displacement diffuser. Locations (I), (II) and (III) – measuring points of contaminant distribution, locations (I) and (IV) – measuring points of temperature distribution.
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Human breathing was simulated by artificial lungs [15]. The breathing cycle consisted of 2.5 s inhalation, 2.5 s exhalation and 1.0 s pause, which is usual for people performing light office work. The breathing frequency was 10 cycles per minute and the pulmonary ventilation was 0.6 L per breath. During the experiments, breathing was simulated only with the manikin seated at the front workstation WS1 (referred to in the following as polluting manikin). The breathing pattern was set to mouth inhalation/nose exhalation [16]. The second manikin positioned at WS2 and referred to henceforth as exposed manikin did not ‘‘breathe’’. As reported [15], air sampled at the upper lip at a distance < 0.01 m from the face of the non-breathing manikin will ensure measurement of temperature and pollution concentration as those measured in the inhaled air (within the uncertainty of the measurement). The air inhaled by the polluting manikin was also analysed. 2.4. Heat and contaminant sources The total heat load generated in the test room by typical office equipment (PCs, monitors, and desk lamps), the breathing thermal manikins and six ceiling fluorescent fixtures was 22.6 W/m2. In the cases when the two ‘‘ductless’’ PV systems were turned on the additional heat produced by incorporated duct fans increased the total heat load to 24.9 W/m2. The set-ups during the experimental cases presented in this paper (Table 1) differed in the number of simulated pollution sources. During the experiments focused on the impact of the airflow rate supplied to the room by the displacement ventilation on the performance of ‘‘ductless’’ PV in conjunction with DV (experimental cases 1.1 – 1.3, Table 1), two pollution sources with different behaviour in the space were simulated: the air exhaled by the polluting manikin (active pollution) was marked with SF6 and a point passive pollution source (not heated) placed on the table in front of the polluting manikin was simulated with Freon. The Freon was discharged from a small perforated ball in order to ensure approximately equal distribution of this tracer gas in its vicinity. During the experiments focused on the importance of ‘‘ductless’’ PV intake positioning height above the floor (experimental cases 2.1 – 2.4, Table 1), the performance of ‘‘ductless’’ PV in conjunction with DV was evaluated only in regard to the air exhaled by the polluting manikin (active pollution). In the experimental cases 2.1 – 2.4 Freon was added to the air exhaled by the polluting manikin instead of SF6 (used in the experimental cases 1.1 – 1.3). To ensure the density of air exhaled by people (1.144 kg/m3) the air exhaled by the polluting manikin was heated. 2.5. Experimental conditions Experiments at two airflow rates of outdoor treated air, 60 L/s and 80 L/s, supplying an supplied air temperature of respectively
Table 1 Studied experimental cases. Displacement ventilation rate
60 L/s
Workstations
WS1
WS2
WS1
WS2
0 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s
0 L/s 0 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s
0 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s
0 L/s 0 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s
Personalized airflow rate
Case Case Case Case Case Case Case
1.1 1.2 1.3 2.1 2.2 2.3 2.4
80 L/s
Intake height positioning of ‘‘ductless’’ PV above floor 5 cm 5 cm 5 cm 2 cm 5 cm 10 cm 20 cm
18 C and 20 C by the displacement ventilation, aiming at an exhaust air temperature of 26 C, were performed. Experimental cases 1.1 – 1.3 (Table 1) cover three different combinations of personalized airflow rate at the two displacement airflows studied. In the following, the studied combinations are referred to in short by identification of the ‘‘ductless’’ PV flow rate at the polluting workstation (WS1) followed by the ‘‘ductless’’ PV flow rate at the exposed workstation (WS2), i.e. PV_15_0 will mean that the results were obtained with the personalized airflow rate at WS1 of 15 L/s and no personalized flow was supplied at WS2. The impact of the positioning height of the ‘‘ductless’’ PV intake, 2, 5, 10 and 20 cm above the floor level, was studied when the ‘‘ductless’’ PV systems at each of the two workstations supplied 15 L/s (experimental cases 2.1 – 2.4, Table 1). At each studied case the intakes of ‘‘ductless’’ PV systems were positioned identically at both workstations. The positioning height of the ‘‘ductless’’ PV intakes was selected in order to completely cover the width of the clean and cool air layer above the floor, i.e. stratified flow created by DV. These experiments were performed at 60 L/s and 80 L/s displacement airflow rates. In the following, the studied cases are referred to according to the intake location above the floor, i.e. 10 cm will mean that the intakes of the ‘‘ductless’’ PV were positioned at 10 cm above the floor. All measurements were performed under steady-state conditions. 2.6. Measured quantities and measuring equipment Tracer gas concentration was measured at three locations diagonally distributed within the test room, as indicated in Fig. 1 as I, II, III. At the location I the concentration measurements were performed at heights of 0.1, 0.6, 1.1, 1.4, 1.7 and 2.2 m above the floor. At the two remaining locations, II and III, concentration measurements were performed at 0.1, 0.6, 1.1 and 1.7 m (due to the limited number of sampling channels of the multipoint sampler unit used). The tracer gas concentration was also measured at the supply and exhaust air, at the intakes of the two ‘‘ductless’’ PV systems (position 6, Fig. 2), in the air inhaled by the manikins and in the tall hall. Similar locations were selected for the temperature measurement – supply and exhaust air, intakes and RMPs of both ‘‘ductless’’ PV systems, air inhaled by exposed manikin and in the tall hall. Furthermore, the vertical temperature distribution was measured at two locations I and IV (Fig. 1) at 13 heights above the floor level: 0.05, 0.1, 0.15, 0.2, 0.3, 0.5, 0.6, 0.85, 1.1, 1.4, 1.7, 2.1 and 2.4 m. The thermal environment was evaluated by the thermal manikins. The airflow rate supplied by the DV was monitored by an orifice plate installed in the duct downstream of the air supply terminal device. The supplied personalized airflow rate was determined based on pressure difference measured by a transducer positioned in the duct. The temperature measurements in the room were performed either by medical thermistors (inhaled air, supply and exhaust air, tall hall, intake of ‘‘ductless’’ PV and air supplied by RMP) or by constantan-copper thermocouples (temperature distribution within the occupied zone). The tracer gas concentration was measured with a multi-gas analyzer based on the photoacoustic infrared detection method. 2.7. Indicators for assessment The tracer gas concentration measured in the air inhaled by the manikins during the experiments focused on studying the impact of the displacement airflow rates on ‘‘ductless’’ PV performance (experimental cases 1.1 - 1.3, Table 1) was normalized according to equation (1):
Normalized concentration 1 ¼
Ci CPV Ce CPV
(1)
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 996–1005
where Ci is the tracer gas concentration (SF6 or Freon) in the air inhaled by a manikin, Ce is the tracer gas concentration (SF6 or Freon) in the exhaust air and CPV is the tracer gas concentration (SF6 or Freon) in the air sucked by the respective ‘‘ductless’’ PV, i.e. when quality of air inhaled by exposed manikin was evaluated the concentration was measured in the ‘‘ductless’’ PV intake at exposed manikin workstation. Concentration measurements at the same locations were performed in order to calculate the normalized concentration for the reference case of displacement ventilation only (in this case the displacement air near the floor at the location of manikin is entrained and moved upward to the breathing zone by the free convection flow around human body). The lower the value of the normalized concentration, the less pollution is inhaled by the manikins. When the importance of the intake positioning height on the ‘‘ductless’’ PV performance was studied (experimental cases 2.1 – 2.4, Table 1), either the measured tracer gas (Freon) concentration (in ppm) was analysed or the measured data were normalized according to equations (2) and (3):
999
measurements. The temperature measurements at two locations (I and IV, Fig. 1) were performed at 15 min intervals. The duration and sampling frequency of each measurement was adequate to enable each quantity to be estimated with high accuracy. The data were analysed in accordance with ISO guidelines [18]. The sample standard uncertainty was calculated as the combination of the maximum uncertainty of measurement (random error) and the uncertainty of the instrument (calibration). The absolute expanded uncertainty with a level of confidence of 95% (coverage factor of 2) is listed in Table 2. Temperature and flow rate of the air supplied by displacement ventilation, personalized airflow rate and temperature of the air in the tall hall were periodically measured during the performed experiments. They remained rather constant (the changes were small and within the accuracy of the measuring instruments). Prior to the experiments the whole room was sealed in order to prevent any possible disturbances from the tall concrete hall.
3. Results
Normalized concentration 2 ¼
Normalized concentration 3 ¼
CPV CPV Ci Ci
(2)
5cm
(3)
5cm
where CPV is the concentration of tracer gas Freon in the air sucked by the respective ‘‘ductless’’ PV, CPV_5cm was selected as a reference intake concentration, i.e. tracer gas concentration in the air sucked by the respective ‘‘ductless’’ PV system with intake positioned at a height of 5 cm above the floor, Ci is the concentration of tracer gas Freon in the air inhaled by the manikin and Ci_5cm was selected as a reference inhaled concentration, i.e. Freon concentration in the inhaled air when the intake of the respective ‘‘ductless’’ PV was located 5 cm above the floor. The concentration measured at 5 cm above the floor was selected as reference intake/inhaled concentration in order to be the same as in previous studies on performance of ‘‘ductless’’ PV in conjunction with DV [5,6]. The contaminant concentration and temperature distribution within the occupied zone was expressed also in terms of normalized values calculated according to equation (4):
Normalized value 4 ¼
XP XS Xe XS
(4)
where Xp is the tracer gas concentration (SF6 or Freon) or temperature at the measured point, Xe and XS is the tracer gas concentration or the temperature in the exhaust air and in the supply air, respectively. The thermal environment at both workstations was evaluated in terms of the manikin-based equivalent temperature (MBET) determined for each of the body segments and for the whole body of both manikins. It is defined as the temperature of a uniform enclosure in which a thermal manikin with realistic skin surface temperatures would lose heat at the same rate as it would in the actual environment [17].
2.8. Precision of measurement At each point 13–15 readings of the measured tracer gas concentration were recorded. The temperature at the intake opening and the air supply terminal device of the ‘‘ductless’’ PV, the inhaled temperature, the segmental and whole body surface temperature and heat loss from the thermal manikins were measured approximately for one hour together with the tracer gas
3.1. Temperature distribution in the room The normalized vertical temperature distribution, averaged for the measurements performed at locations I and IV (Fig. 1), is shown in Fig. 3. Almost identical vertical temperature distribution was measured at the two locations and in order to generalize the results averaging was applied. As expected, a vertical temperature gradient existed in the room. In the reference case (RF) of DV alone, the temperature gradient was affected to some extent up to a height of approximately 1.7 m, i.e. height of the occupied zone (Fig. 3, left) by the airflow rate supplied by DV. Since the heat generated in the room and the exhaust temperature was kept constant, the supply air temperature at 60 L/s was decreased in comparison with the supply air temperature at 80 L/s. The thermal environment in the occupied zone will be affected by the decrease of the temperature and flow rate of the supplied displacement air. The results show that the increase of the normalized temperature gradient up to 1.2 m height, i.e. to the neutral height, was the same for the two airflow rates. However above 1.2 m the normalized temperature gradient at an airflow rate of 80 L/s increased faster to reach the same exhaust air temperature as with a displacement airflow rate of 60 L/s. The personalized flow supplied at each of the two workstations 15 L/s had some impact on the vertical temperature distribution at the measured locations. Fig. 3 (right) compares the normalized vertical temperature profiles obtained as an average from the measurements at locations I and IV when the intake height was changed (experimental cases 2.1–2.4) and the displacement airflow rate was 60 L/s. The average normalized vertical temperature profile obtained with DV alone (RF case) is shown in the figure as well. Difference in the vertical temperature distribution obtained in the cases with ‘‘ductless’’ PV and the reference case of DV alone can be
Table 2 Sampling frequency, duration of data acquisition, and typical values of expanded absolute uncertainty with a 95% level of confidence. Quantity
Frequency of Data Acquisition
Duration of Measurement Period
Uncertainty (Conf. Level 95%)
Concentrations (inhaled and room) Temperature (inhaled and room) MBET
10 min
130–150 min
See result
5 Hz
1 min
0.3 C
20 s
2 min
0.23 C
1000
´ , A.K. Melikov / Building and Environment 45 (2010) 996–1005 B. Halvonˇova
Fig. 3. Normalized vertical temperature distribution; averaged values from locations I and IV. Left: distribution at two displacement airflow rates, right: distribution at RF and four cases with different positioning of ‘‘ductless’’ PV intakes at displacement airflow rate of 60 L/s.
observed between 0.3 and 1.1 m height above the floor. The ‘‘ductless’’ PV caused some airflow mixing in its vicinity and moved the warmer air down to the floor. Therefore the room air temperature was slightly warmer between 0.3 and 1.1 m height. However it may be suggested that this difference will have no significant impact on the occupants’ thermal comfort. The different positioning of the ‘‘ductless’’ PV intake above the floor, up to a level of 0.2 m, had no impact on the temperature distribution in the room. Similar results were observed at a displacement airflow rate of 80 L/s. 3.2. Contaminant distribution in the room The normalized vertical distribution of the simulated pollution sources, i.e. the exhaled air (mixed with SF6) and the passive pollution (simulated by Freon), obtained at location I (Fig. 1) is shown respectively in Fig. 4 (left) and Fig. 4 (right). The distribution
measured with DV alone (RF) and with cases when ‘‘ductless’’ PV was switched on either at the polluting workstation (PV_15_0) or at both workstations (PV_15_15) is compared in the figure for displacement airflow rates of 60 L/s and 80 L/s. The results obtained at the remaining two locations, i.e. locations II and III (Fig. 1) showed approximately the same development. The results in Fig. 4 show the expected vertical stratification in the concentration of the pollution sources. In the reference case of DV alone the increase of the supplied flow rate from 60 L/s to 80 L/s increases the stratification height for the exhaled air (Fig. 4 left) and has only a limited impact on the spread of the passive pollution located at lower level. As expected, a higher concentration is measured at 60 L/s. The use of personalized ventilation causes mixing and increases the concentration of tracer gas at a lower level. The increase is larger when the ‘‘ductless’’ PV systems are used at the two workplaces.
Fig. 4. Distribution of normalized concentration obtained at location I; the comparison is made for RF (DV alone) and two cases with different combinations of personalized airflows under two displacement rates (60 and 80 L/s).
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Table 3 Normalized concentration of simulated pollutions in the inhaled air, experimental cases 1.1–1.3. Pollution source
Condition
Case
Polluting manikin
Exposed manikin
Air supplied by displacement ventilation
Exhaled air (SF6)
Point passive pollution (Freon)
RF PV_15_0 PV_15_15 RF PV_15_0 PV_15_15
1.1 1.2 1.3 1.1 1.2 1.3
3.3. Pollution concentration in inhaled air The normalized concentration (equation (1)) of the tracer gases (SF6 and Freon) in the air inhaled by the manikins at 60 L/s and 80 L/ s displacement airflow rate in the reference case (RF) without ‘‘ductless’’ PV, when only the ‘‘ductless’’ PV of the polluting manikin was used (PV_15_0) and when the two ‘‘ductless’’ PVs were used (PV_15_15), is listed in Table 3. In the RF the difference in the tracer gas concentration in the air inhaled by the two manikins is considerable. Part of the pollution generated in the vicinity of the polluting manikin was entrained by the free convective flow existing around its body. In this way, it was moved to the mouth of the manikin where it was inhaled. The air exhaled by the polluting manikin with high momentum escaped from the free convective flow and therefore its contribution to the inhaled air was much lower than the concentration of the passive pollution generated at very low momentum in front of the manikin and easily moved upward and inhaled. Therefore the concentration of the two pollutions in the air inhaled by the polluting manikin was much higher than in the air inhaled by the exposed manikin. The use of the ‘‘ductless’’ PV caused mixing and transport of pollution between the workstations. The concentration of the two tracer gases in the air inhaled by the exposed manikin increased substantially when only the ‘‘ductless’’ PV of the polluting manikin was used. The increase of the DV supply flow rate increased the stratification height, resulting in a decrease of the pollution in the air inhaled by the exposed manikin. The use of the ‘‘ductless’’ PV at the workstation of the exposed manikin greatly decreased the concentration of the two tracer gases in the air inhaled by this manikin, i.e. the ‘‘ductless’’ PV protected this manikin. In the case of the polluting manikin the greatest benefit in using the ‘‘ductless’’ PV was with regard to the inhaled passive pollution. The
60 L/s
80 L/s
60 L/s
80 L/s
0.34 0.05 0.32 0.00 0.30 0.01 6.91 0.81 0.19 0.02 0.34 0.03
0.52 0.05 0.29 0.01 0.39 0.01 6.95 0.79 0.25 0.03 0.47 0.07
0.07 0.04 1.20 0.09 0.10 0.03 0.18 0.07 0.52 0.05 0.07 0.02
0.01 0.01 0.58 0.13 0.03 0.01 0.04 0.00 0.08 0.02 0.01 0.01
concentration of passive pollution in the air inhaled by the polluting manikin decreased dramatically when its ‘‘ductless’’ PV was in operation. Fig. 5 presents the normalized concentration (equation (2)) (left) and the real concentration (right) of the tracer gas (Freon) present in the exhaled air and present in the exhaled air and measured at the intakes of both ‘‘ductless’’ PV systems when 60 L/s of air was supplied by the DV. The results obtained with the four positioning heights of ‘‘ductless’’ PV intakes above the floor level, i.e. 2, 5, 10 and 20 cm, are compared in the figure. The results show that the normalized concentration at the intake is almost the same for the four heights studied. As the results in Fig. 5 (right) show, the tracer gas concentration at the intake of the ‘‘ductless’’ PV at the workstation of the exposed manikin is slightly higher that at the intake of the ‘‘ductless’’ PV of the polluting manikin Fig. 6 shows the normalized concentration (equation (3)) (left) and real concentration (right) of tracer gas (tracer gas (Freon) present in the air exhaled by the polluting manikin) present in the air exhaled (active pollution) and measured in the air inhaled by the two manikins when 60 L/s of air was supplied by the DV. The results obtained when the intakes of the ‘‘ductless’’ PV systems were positioned at 2, 5, 10 and 20 cm height above the floor are compared in the figure. The differences in the normalized concentration in the inhaled air are larger than the differences in the normalized concentration at the intakes (Fig. 5, left). The concentration of tracer gas tracer gas was substantially higher in the air inhaled by the polluting manikin than in the air inhaled by the exposed manikin. This is the result of the interaction of the personalized flow with the flow of exhalation. The difference in tracer gas concentration in the air inhaled by the polluting manikin and in the air at the intake of its ‘‘ductless’’ PV is much larger than the difference of tracer gas concentration in the air inhaled by the
Fig. 5. Normalized concentration (left) and real concentration in ppm (right) of air exhaled by polluting manikin (Freon) measured at the intakes of ‘‘ductless’’ personalized ventilation at 60 L/s displacement airflow rate.
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Fig. 6. Normalized concentration (left) and real concentration in ppm (right) of air exhaled by polluting manikin (Freon) in the air inhaled by the manikins measured when the ‘‘ductless’’ personalized ventilation was used at displacement airflow rate of 60 L/s.
exposed manikin and at the intake of its ‘‘ductless’’ PV. Furthermore the differences between the tracer gas concentration at the intakes of the ‘‘ductless’’ PV systems at the workstations is much smaller than the tracer gas concentration difference in air inhaled by the manikins. The results obtained at 80 L/s airflow rate supplied from the displacement diffuser were similar. 3.4. Temperature of inhaled air The temperature of air inhaled by the exposed manikin under the different personalized airflow rate combinations is listed in Table 4. The inhaled air temperature with DV alone (RF) was not affected by the increase of the supplied flow rate from 60 to 80 L/s. The cool air at the lower height of the room was heated while being moved upwards by the free convective flow. The use of the ‘‘ductless’’ PV only at the workstation of the polluting manikin (PV_15_0) also did not have any impact on the temperature of the air inhaled be the exposed manikin. In these cases, the observed differences were within the uncertainty of the measurements ( 0.3 C). The use of the ‘‘ductless’’ PV at the workstation of the exposed manikin (PV_15_15), however, decreased the inhaled air temperature dramatically. In this case, the temperature of the supplied displacement air was important; the inhaled air temperature was measured about 0.6 C lower when the displacement air was supplied at 18 C than when it was supplied at 20 C. The air temperature measured at the intake of the ‘‘ductless’’ PV, at its RMP and directly in the air inhaled by the exposed manikin when the intake positioning height of the ‘‘ductless’’ PV was changed, i.e. 2, 5, 10 and 20 cm is listed in Table 5. The temperatures measured at the displacement flow rate of 60 L/s and 80 L/s is listed in the table separately. The comparison of the temperature measured at the intake when it is positioned at different heights shows the impact of the vertical air temperature gradient that existed due to the displacement air distribution principle. The temperature measured at the intake when positioned at 20 cm
above the floor is slightly higher than the temperature measured at the remaining positioning heights. However, the observed temperature difference diminishes by the time the sucked air is transported through the ‘‘ductless’’ PV components to the RMP, because of its heating by the walls of the ducting and the fan. The differences in the personalized air temperature at the RMP measured at different positioning heights of the ‘‘ductless’’ PV intake are within the uncertainty of the temperature measurement ( 0.3 C). The temperature difference at the intake and at the RMP at the four intake positioning heights is listed in Table 5 as well. 3.5. Heat loss from manikin’s body The determined manikin-based equivalent temperature (MBET) for each body segment and the whole body of the manikins was used to analyse the performance of the ‘‘ductless’’ PV in regard to thermal comfort. The use of ‘‘ductless’’ PV at the workstation of the exposed manikin cooled the body and hence decreased the MBET for the exposed body segments (back of neck, face), as can be seen from the results in Fig. 7. The results shown in the figure were obtained at a displacement airflow rate of 60 L/s and different combinations of ‘‘ductless’’ PV airflow rates. The greatest cooling effect due to the use of ‘‘ductless’’ PV was obtained for the face region (10.3 C – left side and 6.3 C – right side) and for the back of the neck (5.3 C), i.e. the body segments directly exposed to the personalized airflow. The difference between the left and the right face can be explained by the fact that the manikin was not precisely positioned and the left face was more exposed to the personalized
Table 5 Temperature measured at intake and RMP of ‘‘ductless’’ personalized ventilation at the ‘‘exposed’’ workstation and temperature of air inhaled by the exposed manikin. Airflow rate
Temperature in a point
60 L/s
Temperature at intake ( C), TPV Temperature at RMP ( C), TRMP TRMP-TPV ( C) Temperature at inhalation ( C), Ti Ti-TRMP ( C) Temperature at intake ( C), TPV Temperature at RMP ( C), TRMP TRMP-TPV ( C) Temperature at inhalation ( C), T; Ti-TRMP ( C)
Table 4 Temperature of air inhaled by exposed manikin seated at workstation WS2. Airflow rate
Temperature in a point
60 L/s 80 L/s
Temperature at inhalation ( C) Temperature at inhalation ( C)
‘‘Ductless’’ personalized ventilation RF
PV_15_0
PV_15_15
30.3 30.2
30.1 30.2
25.5 26.1
80 L/s
‘‘Ductless’’ PV intake location above the floor 2 cm
5 cm
10 cm
20 cm
22.4 23.9 1.5 25.3 1.4 22.5 24.0 1.5 25.2 1.2
22.7 24.1 1.4 25.5 1.4 22.6 23.9 1.3 25.1 1.2
22.3 23.7 1.4 25.1 1.4 22.7 24.1 1.4 25.3 1.2
22.9 23.9 1.0 25.2 1.3 23.4 24.3 0.9 25.4 1.1
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Fig. 7. MBET of exposed manikin at a displacement airflow rate of 60 L/s.
flow, i.e. the direction of personalized flow is an important factor for occupants’ thermal comfort. The whole body cooling effect of the personalized air was lower than 1 C. As expected, the use of the ‘‘ductless’’ PV at the workstation of the polluting manikin did not affect the MBET determined for the exposed manikin, whether or not its ‘‘ductless’’ PV was used. Fig. 8 compares the cooling effect provided by the ‘‘ductless’’ PV in comparison with the cooling effect of DV used alone at the two supply flow rates, 60 L/s and 80 L/s. The difference in MBET determined with DV alone and the MBET determined with ‘‘ductless’’ PV in conjunction with DV (case PV_15_15) was calculated for the body segments and the whole body of the exposed manikin. As can be seen from the results in the figure, the cooling effect provided by ‘‘ductless’’ PV was higher at a displacement airflow rate of 60 L/s. This is mainly due to the lower temperature of the supplied personalized air at 60 L/s (already discussed above). The cooling effect of the body segments not directly exposed to personalized airflow was negligible (within the uncertainty of the measurement). No significant impact of the positioning height of the ‘‘ductless’’ PV intake on the cooling effect of the personalized flow was observed in the present study (the small differences obtained were within the measurement uncertainty). Therefore the results are not presented in this paper.
4. Discussion The use of the ‘‘ductless’’ PV makes it possible to transport the cool and clean air supplied from the displacement diffuser over the floor direct to the breathing zone of occupants and thus to ensure a high level of inhaled air quality. The air provided to inhalation by the ‘‘ductless’’ PV can be as clean as the air provided by DV used alone. In fact when the pollution source is located in the vicinity of the human body, the concentration of pollution in the inhaled air is much lower with ‘‘ductless’’ PV than when DV is used alone. Furthermore, the results of the present study document that the temperature of the inhaled air provided by ‘‘ductless’’ PV can be several degrees lower (in the present study up to approx. 5 C) than the temperature of the inhaled air provided with DV alone. The results of human subject experiments with personalized ventilation reveal that personalized air with a temperature lower than the room air temperature and relatively high velocity improves the perceived air quality significantly above the level of improvement due to its cleanness [4,19,20]. Therefore it may be expected that the PAQ with ‘‘ductless’’ PV will be better than with DV used alone. The results of the present study support findings in previous studies [5,6,12,21] that the personalized ventilation may increase mixing and transportation of pollution generated in the vicinity of its supply ATD and in general will decrease the quality of the
Fig. 8. Cooling effect provided by ‘‘ductless’’ PV; difference between MBET measured with DV alone (RF) and with ‘‘ductless’’ PV used at both workstations (PV_15_15).
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inhaled air. However, it must be noted that in this case the superior performance of DV alone is limited only to the case when there are no moving occupants, which in fact occurs seldom in practice (only in single type offices). In the present study the ‘‘ductless’’ PV used at the workstation of the polluting manikin increased the concentration of tracer gas in the air inhaled by the exposed manikin when its ‘‘ductless’’ PV was not used. The use of the ‘‘ductless’’ PV improved the inhaled air quality to the level of DV alone. At a supply flow rate of 80 L/s, inhaled air with ‘‘ductless’’ PV was cleaner but slightly warmer than the air inhaled at 60 L/s. The opposite impact of these two parameters, cleanness and temperature of the inhaled air, on the perceived air quality is difficult to evaluate. An important finding of the present study is that the positioning height of the ‘‘ductless’’ PV intake up to a level of 0.2 m above the floor did not have a significant impact on the cleanness and the temperature of air supplied by its ATD. However, the cleanness of the air at the intake of different workstations may not be the same. The intakes of the ‘‘ductless’’ PV at the two workstations were not symmetrically exposed to the flow of clean displacement air. As already mentioned, the nozzles inside the displacement diffuser were adjusted to supply initially the clean air mainly along the adjacent wall in order to reduce the size of the area near the diffuser with velocity higher than 0.2 m. This may be one of the reasons for the observed differences. Although a vertical temperature gradient exists in the stratified layer of clean air, the temperature of the supplied personalized air at the ATD was almost the same because the heat transfer in the ‘‘ductless’’ PV system diminished the small differences in the air temperature at the intake when it was positioned at different heights. The tracer gas concentration in the air inhaled by the polluting manikin was substantially higher than the concentration in the air inhaled by the exposed manikin regardless of whether DV was used alone or in conjunction with ‘‘ductless’’ PV. In general, the ‘‘polluted’’ air exhaled through the nose of the polluting manikin with high momentum escaped from the free convective flow around its body. The jets of exhalation interacted with the personalized flow from front/above. As a result, the exhaled air was discharged backwards towards the body of the polluting manikin where it was entrained by the free convective flow and moved to its mouth to be inhaled. The discharged exhaled air was also transported further back towards the workstation with the exposed manikin. In this case it was diluted with the room air. Therefore the tracer gas concentration of exhaled air in the air inhaled by the exposed manikin decreased in comparison with the polluting manikin. The tracer gas concentration in the inhaled air depends strongly on the airflow interaction at the breathing zone. This is valid also for the second pollution source tested during the first experimental stage (passive pollution). The impact of the airflow interaction in the case of PV in conjunction with mixing, displacement and underfloor ventilation is discussed in detail [12,13,22]. It can be concluded that ‘‘ductless’’ PV is able to protect the occupant from pollution generated at other workstations on a similar or even better level than with DV used alone. Furthermore, it will protect the occupant from passive pollution located in his/ her vicinity better in comparison with DV alone. The present results showed that ‘‘ductless’’ PV had a rather local effect and did not adversely change the temperature distribution in the vicinity of two workstations and in the occupied zone; the temperatures in the occupied zone measured at the combinations of personalized airflows studied were within the ranges prescribed by the present standards [1,2]. This is an important finding for practice since it means that the methods for prediction of velocity and temperature fields in rooms with DV can equally well be applied for ‘‘ductless’’ PV in conjunction with DV under present conditions. In general it may be concluded that if the DV is designed
properly, the additional application of ‘‘ductless’’ PV under individual control of an occupant will not cause thermal discomfort. Substantial cooling of the manikin’s body segments exposed to the flow from the ‘‘ductless’’ PV, i.e. scull, left and right face and back of the neck, was identified. Previous research [23,24] has documented that airflow from front, like the flow provided by the ‘‘ductless’’ PV in the present study, causes less draught discomfort than airflow from behind. Nevertheless the performance of the ‘‘ductless’’ PV with regard to draught discomfort needs to be studied at the lower range of comfortable temperatures in human subject experiments. Local thermal discomfort due to draught is one of the problems in rooms with DV. In practice, building managers often increase the supply air temperature and thus the temperature in the occupied zone in order to avoid draught complaints. This leads to complaints from too warm air. In such cases the increased inhaled air temperature may increase complaints of unacceptable PAQ as well [25]. Implementation of the ‘‘ductless’’ PV will allow for supplying the displacement air at a relatively high temperature, i.e. keep room air temperature relatively high, and to provide occupants with a preferred thermal environment and a high level of inhaled air quality by use and control of the personalized air. In this way the cool and clean displacement air can be utilized more efficiently and under certain conditions this strategy may lead to energy savings as well. In the real office dust, droplet nuclei as a result of coughing and sneezing (may carry viruses of infected person), etc. may be present at the floor level. These may be transported to the breathing zone by the ‘‘ductless’’ PV. Therefore it is recommended to install a filter at the intake or in the ‘‘ductless’’ PV system. Installation of UVGI lamps will cleanse the air from viruses. 5. Conclusions ‘‘Ductless’’ personalized ventilation in conjunction with displacement ventilation provides air to inhalation as clean as air provided by use of displacement ventilation alone. In the case of pollution located in the vicinity of an occupant’s body, the inhaled air with ‘‘ductless’’ personalized ventilation is considerably cleaner than the air inhaled with displacement ventilation alone. The perceived air quality with ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation will be superior to the PAQ with displacement ventilation alone because of the positive impact of cooler personalized air supplied at elevated velocity. The different positioning of the ‘‘ductless’’ personalized ventilation intake height up to a level of 0.2 m above the floor had no significant impact on the cleanness and temperature of the air supplied by the air terminal device of the ‘‘ductless’’ personalized ventilation. The use of ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation had only a local impact on the temperature distribution in the room. In practice, the use of ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation will allow the room temperature to be kept at a relatively high level while occupants provided with individual control of the personalized flow of clean and cool air will benefit with high quality of the inhaled air and preferred thermal environment. Acknowledgement This research was partially supported by the Danish Technical Research Council (STVF).
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Nomenclature
Abbreviations ATD air terminal device DV displacement ventilation ‘‘ductless’’ PV ‘‘ductless’’ personalized ventilation PAQ perceived air quality PV personalized ventilation RF reference case RMP round moveable panel WS workstation Symbols C X MBET
concentration in inhaled air or in a point (ppm) concentration (ppm) or temperature ( C) in a point manikin-based equivalent temperature ( C)
References [1] Iso. Iso 7730:2005(E) moderate thermal environments – determination of the PMV and PPD indices and specification of the conditions for thermal comfort. Switzerland: International Organization for Standardization; 2005. [2] Ashrae. Ashrae standard 55: thermal environmental conditions for human occupancy. Atlanta: American Society of Heating, Refrigerating and AirConditioning Engineers; 1992. [3] Cen EN. Criteria for the indoor environment including thermal, indoor air quality, light and noise. Brussels: European Committee for Standardization; 2007. 15251-2007. [4] Melikov AK. Personalized ventilation. Indoor Air 2004;14(7):157–67. [5] Halvonova B and Melikov AK. ‘‘Ductless’’ personalized ventilation in conjunction with displacement ventilation. In: Proceedings of indoor air ’08. Copenhagen, Denmark. [6] Halvonova B and Melikov AK. Performance of ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation: impact of disturbances due to walking person(s), Building and Environment, (submitted for publication). [7] Nielsen PV. Displacement ventilation – theory and design. Aalborg University; 1993. 0902-8002 U9306. [8] REHVA. Guidebook: displacement ventilation in non-industrial premises. Federation of European Heating and Air-conditioning Associations, ISBN 82-594-2369-3; 2002.
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[9] Bolashikov Z, Nikolaev L, Melikov A, Kaczmarczyk J and Fanger PO. New air terminal devices with high efficiency for personalized ventilation application. In: Proceedings of healthy buildings ’03. Singapore. p. 850–5. [10] Kaczmarczyk J, Melikov A, Fanger PO. Human response to personalized and mixing ventilation. Indoor Air 2004;14(8):1–13. [11] Kaczmarczyk J, Melikov A, Bolashikov Z, Nikolaev L, Fanger PO. Human response to five designs of personalized ventilation. Ventilation and Refrigeration Research. International Journal of Heating 2006;12(2): 367–84. [12] Cermak R, Melikov A, Forejt L, Kovar O. Performance of personalized ventilation in conjunction with mixing and displacement ventilation. HVAC&R Research 2006;12(2):295–310. [13] Cermak R. Design strategies for personalized ventilation. PhD thesis: international centre for indoor environment and energy, Technical University of Denmark, ISBN 87-7475-318-5, 2004. [14] Tanabe S, Arens EA, Bauman FS, Zhang H, Madsen TL. Evaluating thermal environments by using a thermal manikin with controlled skin surface temperature. ASHRAE Translations 1994;100(1):39–48. [15] Melikov A, Kaczmarczyk J. Indoor air quality assessment by a breathing thermal manikin. Indoor Air 2007;17(1):50–9. [16] Melikov AK. Breathing thermal manikins for indoor environment assessment: important characteristics and requirements. European Journal of Applied Physiology 2004;92(6):710–3. [17] Nilson H, Holmer I, Bohm M and Noren O. Definition and theoretical background of the equivalent temperature. In: Proceedings of the 6th international conference FLORENCE ATA, EQUIV Seminar 2, Firenze, Italy; 1999. [18] ISO. Guide to the expression of uncertainty in measurement. Switzerland: International Organization for Standardization; 1993. [19] Melikov A, Kaczmarczyk J and Silva D. Impact of air movement on perceived air quality at different levels of relative humidity. In: Proceedings of indoor air. Copenhagen, Denmark; 2008. [20] Melikov A and Kaczmarczyk J. Impact of air movement on perceived air quality at different levels of air pollution and temperature. In: Proceedings of indoor air. Copenhagen, Denmark; 2008. [21] Melikov AK, Cermak R, Kovar O and Forejt L. Impact of airflow interaction on inhaled air quality and transport of contaminants in rooms with personalized and total volume ventilation. In: Proceedings of healthy buildings ’03. Singapore. p. 592–7. [22] Cermak R, Melikov A. Protection of occupants from exhaled infectious agents and floor material emissions in rooms with personalized and underfloor ventilation. HVAC & R RResearch 2007;8:23–38. [23] Mayer E, Schwab R. Direction of low turbulent air flow and thermal comfort. In: Proc. Healthy Buildings ’88, vol. 2; 1988. p. 577–81. [24] Toftum J, Zhou G and Melikov AK. Airflow direction and human sensitivity to draught. In: Proceedings of CLIMA 2000. Brussels; 1997. [25] Melikov AK, Pitchurov G, Naidenov K, Langkilde G. Field study of occupants thermal comfort in rooms with displacement ventilation. Indoor Air 2005;15(3):205–14.
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Performance of ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation: Impact of intake height ˇ ova´ a, b, *, Arsen K. Melikov b Barbora Halvon a b
Department of Building Services, Slovak University of Technology in Bratislava, 813 68 Bratislava, Slovakia International Centre for Indoor Environment and Energy, Department of Civil Engineering, Technical University of Denmark, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 July 2009 Received in revised form 8 October 2009 Accepted 9 October 2009
The importance of the intake positioning height above the floor level on the performance of ‘‘ductless’’ personalized ventilation (‘‘ductless’’ PV) in conjunction with displacement ventilation (DV) was examined with regard to the quality of inhaled air and of the thermal comfort provided. A typical office room with two workstations positioned one behind the other was arranged in a full-scale room. Each workstation consisted of a table with an installed ‘‘ductless’’ PV system, PC, desk lamp and seated breathing thermal manikin. The ‘‘ductless’’ PV system sucked the clean and cool displacement air supplied over the floor at four different heights, i.e. 2, 5, 10 and 20 cm and transported it direct to the breathing level. Moreover, two displacement airflow rates were used with a supply temperature adjusted in order to maintain an exhaust air temperature of 26 C. Two pollution sources, namely air exhaled by one of the manikins and passive pollution on the table in front of the same manikin were simulated by constant dosing of tracer gases. The results show that the positioning of a ‘‘ductless’’ PV intake height up to 0.2 m above the floor will not significantly influence the quality of inhaled air and thermal comfort. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: ‘‘Ductless’’ personalized ventilation Displacement ventilation Perceived air quality Thermal comfort
1. Introduction Preferences regarding the indoor environment differ between individuals to a large extent. Even for the same person the preferred environment may change from day to day as well as during the same day. In practice it is impossible at the same time to ensure satisfaction for all room occupants by any total-volume ventilation principle since the indoor environment, although designed according to existing standards [1–3], may not be that preferred by all occupants in the room. Some occupants are more sensitive to the quality of inhaled air and others to the thermal environment. Increasing the supplied flow rate to satisfy occupants who like air movement will increase the dissatisfaction of occupants who are sensitive and who are bothered by air movement. At the same pollution level in a room the perceived air quality will improve when the air temperature decreases, but this may cause thermal discomfort for occupants who prefer a warmer environment. One way to overcome the individual differences is to provide each occupant with individual control of the microenvironment at his/
* Corresponding author. Slovak University of Technology in Bratislava, Department of Building Services, 813 68 Bratislava, Slovakia. Tel.: þ421 903 904 484; fax: þ421 2 5296 11 37. ˇ ova´). E-mail address: [email protected] (B. Halvon 0360-1323/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2009.10.007
her workstation. The number of dissatisfied occupants will decrease when each workstation is equipped with personalized ventilation providing clean air to the breathing zone and allowing for individual control of the flow rate, i.e. air velocity, flow direction, temperature and in some designs the distance of the air supply device from the body. The preferred thermal environment can thus be achieved [4]. Recently, a novel air distribution idea, namely ‘‘ductless‘‘ personalized ventilation (‘‘ductless’’ PV) in conjunction with displacement ventilation (DV) was introduced [5,6]. The outdoor treated air supplied to the room by a displacement diffuser spreads over the floor and creates a stratified flow of clean and cool air [7]. The main idea behind the ‘‘ductless’’ PV is to transport the clean air from this layer direct to the breathing zone of each occupant. In this way the air from the floor area can be utilized more efficiently. The performance of the ‘‘ductless’’ PV was studied in regard to the arrangement of workstations, the use of partitions, and disturbances caused by walking person(s) [5,6]. It was found that the performance of ‘‘ductless’’ PV will depend on the type and location of pollution sources, within the room. The performance of the ‘‘ductless’’ PV was found to be better than that of DV used alone for some typical conditions in practice (e.g. presence of walking person(s)). According to REHVA Guidebook [8] the typical height of the stratified flow of clean and cool air above the floor level is
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approximately 20 cm when displacement ventilation is properly designed and correctly operated. The thickness of the layer of clean and cool air depends on many factors such as supply airflow rate and temperature, type of air supply diffuser, etc. and can vary also within the room. Furthermore, vertical temperature gradients are present in the flow of clean and cool air. This non-uniformity may influence the performance of the ‘‘ductless’’ PV. The purpose of the present study was to examine the importance of the intake positioning height above the floor on the performance of ‘‘ductless’’ PV in conjunction with DV. Attention was focused on the impact of the intake positioning height on the quality of inhaled air and of the thermal comfort provided. 2. Methods 2.1. Full-scale room A full-scale room (4.8 5.4 2.6 m3), was arranged as a typical office with two workstations WS1 and WS2 (Fig. 1). The walls and the floor of the room were made of wooden chipboard with 0.05 m insulation. One of the walls was single-glazed and the ceiling was made of gypsum tiles. The room was located in an air-conditioned tall concrete hall. The operative temperature in the tall hall was kept close to the room air temperature in order to reduce the heat transfer through the walls of the test room. Each workstation consisted of a desk with a ‘‘ductless’’ PV system (Fig. 2), personal computer with monitor, desk lamp and a dressed seated breathing thermal manikin simulating an ‘‘occupant’’. 2.2. Ventilation systems Displacement ventilation was used as a total-volume ventilation principle. The outdoor treated air was supplied through a semicircular wall unit with a radius in planar projection of 0.25 m and a height of 1 m (position 7, Fig. 1). The unit was fitted with nozzles, which ensured the spread of the supplied air mainly along the adjacent wall. The used air was exhausted from the room through a rectangular perforated air terminal device installed in the middle of the ceiling (position 8, Fig. 1). Recirculation of room air was not utilized in order to increase sensitivity of the performed tracer gas measurements. The ‘‘ductless’’ PV systems installed at each desk consisted of an air terminal device (ATD) mounted on a moveable arm (diameter 0.08 m) and a small axial fan incorporated in a short duct system (diameter 0.1 m), respectively positions 1, 4 and 5 in Fig. 2. The ‘‘ductless’’ PV sucked the air at the locations of the desks (position 6, Fig. 2) directly from the layer of clean and fresh air and transported it to the breathing zone. In the present study the Round
Fig. 2. ‘‘Ductless’’ PV: (1) Round moveable panel (RMP), (2) heat sources, (3) desk, (4) installed fan, (5) short duct system, (6) intake of ‘‘ductless’’ PV, (7) floor level.
Moveable Panel (RMP) with a diameter of 0.185 m [9] was used as the ATD. During the experiments, the RMPs were positioned in front (0.4 m from the face) and slightly above the face level, the positioning most often preferred by people [10,11], i.e. the personalized flow was directed towards to the manikin face from front and above with supply air velocity of 0.56 m/s. The positioning was identical for both manikins and did not differ between the experimental cases since it has been reported [12,13] that the direction of personalized airflow in relation to the occupant’s head may affect the inhaled air quality to a large extent.
2.3. Breathing thermal manikins The manikins were used to simulate seated occupants performing office work. The bodies of the manikins were shaped as a 1.7 m tall average Scandinavian woman and were divided into several individually controlled and heated body segments. One of the manikins had 17 body segments and the other had 23 segments. The surface temperature of the manikins was controlled to equal the skin temperature of an average person in a state of thermal neutrality while performing light office work [14]. Since the experiments simulated summer conditions the clothing insulation of the manikins, together with the upholstered office chair insulation, was 0.59 clo in total [1].
Fig. 1. Full-scale room: (1) polluting manikin, (2) exposed manikin, (4) – (6) heat sources, (7) displacement diffuser. Locations (I), (II) and (III) – measuring points of contaminant distribution, locations (I) and (IV) – measuring points of temperature distribution.
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Human breathing was simulated by artificial lungs [15]. The breathing cycle consisted of 2.5 s inhalation, 2.5 s exhalation and 1.0 s pause, which is usual for people performing light office work. The breathing frequency was 10 cycles per minute and the pulmonary ventilation was 0.6 L per breath. During the experiments, breathing was simulated only with the manikin seated at the front workstation WS1 (referred to in the following as polluting manikin). The breathing pattern was set to mouth inhalation/nose exhalation [16]. The second manikin positioned at WS2 and referred to henceforth as exposed manikin did not ‘‘breathe’’. As reported [15], air sampled at the upper lip at a distance < 0.01 m from the face of the non-breathing manikin will ensure measurement of temperature and pollution concentration as those measured in the inhaled air (within the uncertainty of the measurement). The air inhaled by the polluting manikin was also analysed. 2.4. Heat and contaminant sources The total heat load generated in the test room by typical office equipment (PCs, monitors, and desk lamps), the breathing thermal manikins and six ceiling fluorescent fixtures was 22.6 W/m2. In the cases when the two ‘‘ductless’’ PV systems were turned on the additional heat produced by incorporated duct fans increased the total heat load to 24.9 W/m2. The set-ups during the experimental cases presented in this paper (Table 1) differed in the number of simulated pollution sources. During the experiments focused on the impact of the airflow rate supplied to the room by the displacement ventilation on the performance of ‘‘ductless’’ PV in conjunction with DV (experimental cases 1.1 – 1.3, Table 1), two pollution sources with different behaviour in the space were simulated: the air exhaled by the polluting manikin (active pollution) was marked with SF6 and a point passive pollution source (not heated) placed on the table in front of the polluting manikin was simulated with Freon. The Freon was discharged from a small perforated ball in order to ensure approximately equal distribution of this tracer gas in its vicinity. During the experiments focused on the importance of ‘‘ductless’’ PV intake positioning height above the floor (experimental cases 2.1 – 2.4, Table 1), the performance of ‘‘ductless’’ PV in conjunction with DV was evaluated only in regard to the air exhaled by the polluting manikin (active pollution). In the experimental cases 2.1 – 2.4 Freon was added to the air exhaled by the polluting manikin instead of SF6 (used in the experimental cases 1.1 – 1.3). To ensure the density of air exhaled by people (1.144 kg/m3) the air exhaled by the polluting manikin was heated. 2.5. Experimental conditions Experiments at two airflow rates of outdoor treated air, 60 L/s and 80 L/s, supplying an supplied air temperature of respectively
Table 1 Studied experimental cases. Displacement ventilation rate
60 L/s
Workstations
WS1
WS2
WS1
WS2
0 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s
0 L/s 0 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s
0 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s
0 L/s 0 L/s 15 L/s 15 L/s 15 L/s 15 L/s 15 L/s
Personalized airflow rate
Case Case Case Case Case Case Case
1.1 1.2 1.3 2.1 2.2 2.3 2.4
80 L/s
Intake height positioning of ‘‘ductless’’ PV above floor 5 cm 5 cm 5 cm 2 cm 5 cm 10 cm 20 cm
18 C and 20 C by the displacement ventilation, aiming at an exhaust air temperature of 26 C, were performed. Experimental cases 1.1 – 1.3 (Table 1) cover three different combinations of personalized airflow rate at the two displacement airflows studied. In the following, the studied combinations are referred to in short by identification of the ‘‘ductless’’ PV flow rate at the polluting workstation (WS1) followed by the ‘‘ductless’’ PV flow rate at the exposed workstation (WS2), i.e. PV_15_0 will mean that the results were obtained with the personalized airflow rate at WS1 of 15 L/s and no personalized flow was supplied at WS2. The impact of the positioning height of the ‘‘ductless’’ PV intake, 2, 5, 10 and 20 cm above the floor level, was studied when the ‘‘ductless’’ PV systems at each of the two workstations supplied 15 L/s (experimental cases 2.1 – 2.4, Table 1). At each studied case the intakes of ‘‘ductless’’ PV systems were positioned identically at both workstations. The positioning height of the ‘‘ductless’’ PV intakes was selected in order to completely cover the width of the clean and cool air layer above the floor, i.e. stratified flow created by DV. These experiments were performed at 60 L/s and 80 L/s displacement airflow rates. In the following, the studied cases are referred to according to the intake location above the floor, i.e. 10 cm will mean that the intakes of the ‘‘ductless’’ PV were positioned at 10 cm above the floor. All measurements were performed under steady-state conditions. 2.6. Measured quantities and measuring equipment Tracer gas concentration was measured at three locations diagonally distributed within the test room, as indicated in Fig. 1 as I, II, III. At the location I the concentration measurements were performed at heights of 0.1, 0.6, 1.1, 1.4, 1.7 and 2.2 m above the floor. At the two remaining locations, II and III, concentration measurements were performed at 0.1, 0.6, 1.1 and 1.7 m (due to the limited number of sampling channels of the multipoint sampler unit used). The tracer gas concentration was also measured at the supply and exhaust air, at the intakes of the two ‘‘ductless’’ PV systems (position 6, Fig. 2), in the air inhaled by the manikins and in the tall hall. Similar locations were selected for the temperature measurement – supply and exhaust air, intakes and RMPs of both ‘‘ductless’’ PV systems, air inhaled by exposed manikin and in the tall hall. Furthermore, the vertical temperature distribution was measured at two locations I and IV (Fig. 1) at 13 heights above the floor level: 0.05, 0.1, 0.15, 0.2, 0.3, 0.5, 0.6, 0.85, 1.1, 1.4, 1.7, 2.1 and 2.4 m. The thermal environment was evaluated by the thermal manikins. The airflow rate supplied by the DV was monitored by an orifice plate installed in the duct downstream of the air supply terminal device. The supplied personalized airflow rate was determined based on pressure difference measured by a transducer positioned in the duct. The temperature measurements in the room were performed either by medical thermistors (inhaled air, supply and exhaust air, tall hall, intake of ‘‘ductless’’ PV and air supplied by RMP) or by constantan-copper thermocouples (temperature distribution within the occupied zone). The tracer gas concentration was measured with a multi-gas analyzer based on the photoacoustic infrared detection method. 2.7. Indicators for assessment The tracer gas concentration measured in the air inhaled by the manikins during the experiments focused on studying the impact of the displacement airflow rates on ‘‘ductless’’ PV performance (experimental cases 1.1 - 1.3, Table 1) was normalized according to equation (1):
Normalized concentration 1 ¼
Ci CPV Ce CPV
(1)
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 996–1005
where Ci is the tracer gas concentration (SF6 or Freon) in the air inhaled by a manikin, Ce is the tracer gas concentration (SF6 or Freon) in the exhaust air and CPV is the tracer gas concentration (SF6 or Freon) in the air sucked by the respective ‘‘ductless’’ PV, i.e. when quality of air inhaled by exposed manikin was evaluated the concentration was measured in the ‘‘ductless’’ PV intake at exposed manikin workstation. Concentration measurements at the same locations were performed in order to calculate the normalized concentration for the reference case of displacement ventilation only (in this case the displacement air near the floor at the location of manikin is entrained and moved upward to the breathing zone by the free convection flow around human body). The lower the value of the normalized concentration, the less pollution is inhaled by the manikins. When the importance of the intake positioning height on the ‘‘ductless’’ PV performance was studied (experimental cases 2.1 – 2.4, Table 1), either the measured tracer gas (Freon) concentration (in ppm) was analysed or the measured data were normalized according to equations (2) and (3):
999
measurements. The temperature measurements at two locations (I and IV, Fig. 1) were performed at 15 min intervals. The duration and sampling frequency of each measurement was adequate to enable each quantity to be estimated with high accuracy. The data were analysed in accordance with ISO guidelines [18]. The sample standard uncertainty was calculated as the combination of the maximum uncertainty of measurement (random error) and the uncertainty of the instrument (calibration). The absolute expanded uncertainty with a level of confidence of 95% (coverage factor of 2) is listed in Table 2. Temperature and flow rate of the air supplied by displacement ventilation, personalized airflow rate and temperature of the air in the tall hall were periodically measured during the performed experiments. They remained rather constant (the changes were small and within the accuracy of the measuring instruments). Prior to the experiments the whole room was sealed in order to prevent any possible disturbances from the tall concrete hall.
3. Results
Normalized concentration 2 ¼
Normalized concentration 3 ¼
CPV CPV Ci Ci
(2)
5cm
(3)
5cm
where CPV is the concentration of tracer gas Freon in the air sucked by the respective ‘‘ductless’’ PV, CPV_5cm was selected as a reference intake concentration, i.e. tracer gas concentration in the air sucked by the respective ‘‘ductless’’ PV system with intake positioned at a height of 5 cm above the floor, Ci is the concentration of tracer gas Freon in the air inhaled by the manikin and Ci_5cm was selected as a reference inhaled concentration, i.e. Freon concentration in the inhaled air when the intake of the respective ‘‘ductless’’ PV was located 5 cm above the floor. The concentration measured at 5 cm above the floor was selected as reference intake/inhaled concentration in order to be the same as in previous studies on performance of ‘‘ductless’’ PV in conjunction with DV [5,6]. The contaminant concentration and temperature distribution within the occupied zone was expressed also in terms of normalized values calculated according to equation (4):
Normalized value 4 ¼
XP XS Xe XS
(4)
where Xp is the tracer gas concentration (SF6 or Freon) or temperature at the measured point, Xe and XS is the tracer gas concentration or the temperature in the exhaust air and in the supply air, respectively. The thermal environment at both workstations was evaluated in terms of the manikin-based equivalent temperature (MBET) determined for each of the body segments and for the whole body of both manikins. It is defined as the temperature of a uniform enclosure in which a thermal manikin with realistic skin surface temperatures would lose heat at the same rate as it would in the actual environment [17].
2.8. Precision of measurement At each point 13–15 readings of the measured tracer gas concentration were recorded. The temperature at the intake opening and the air supply terminal device of the ‘‘ductless’’ PV, the inhaled temperature, the segmental and whole body surface temperature and heat loss from the thermal manikins were measured approximately for one hour together with the tracer gas
3.1. Temperature distribution in the room The normalized vertical temperature distribution, averaged for the measurements performed at locations I and IV (Fig. 1), is shown in Fig. 3. Almost identical vertical temperature distribution was measured at the two locations and in order to generalize the results averaging was applied. As expected, a vertical temperature gradient existed in the room. In the reference case (RF) of DV alone, the temperature gradient was affected to some extent up to a height of approximately 1.7 m, i.e. height of the occupied zone (Fig. 3, left) by the airflow rate supplied by DV. Since the heat generated in the room and the exhaust temperature was kept constant, the supply air temperature at 60 L/s was decreased in comparison with the supply air temperature at 80 L/s. The thermal environment in the occupied zone will be affected by the decrease of the temperature and flow rate of the supplied displacement air. The results show that the increase of the normalized temperature gradient up to 1.2 m height, i.e. to the neutral height, was the same for the two airflow rates. However above 1.2 m the normalized temperature gradient at an airflow rate of 80 L/s increased faster to reach the same exhaust air temperature as with a displacement airflow rate of 60 L/s. The personalized flow supplied at each of the two workstations 15 L/s had some impact on the vertical temperature distribution at the measured locations. Fig. 3 (right) compares the normalized vertical temperature profiles obtained as an average from the measurements at locations I and IV when the intake height was changed (experimental cases 2.1–2.4) and the displacement airflow rate was 60 L/s. The average normalized vertical temperature profile obtained with DV alone (RF case) is shown in the figure as well. Difference in the vertical temperature distribution obtained in the cases with ‘‘ductless’’ PV and the reference case of DV alone can be
Table 2 Sampling frequency, duration of data acquisition, and typical values of expanded absolute uncertainty with a 95% level of confidence. Quantity
Frequency of Data Acquisition
Duration of Measurement Period
Uncertainty (Conf. Level 95%)
Concentrations (inhaled and room) Temperature (inhaled and room) MBET
10 min
130–150 min
See result
5 Hz
1 min
0.3 C
20 s
2 min
0.23 C
1000
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Fig. 3. Normalized vertical temperature distribution; averaged values from locations I and IV. Left: distribution at two displacement airflow rates, right: distribution at RF and four cases with different positioning of ‘‘ductless’’ PV intakes at displacement airflow rate of 60 L/s.
observed between 0.3 and 1.1 m height above the floor. The ‘‘ductless’’ PV caused some airflow mixing in its vicinity and moved the warmer air down to the floor. Therefore the room air temperature was slightly warmer between 0.3 and 1.1 m height. However it may be suggested that this difference will have no significant impact on the occupants’ thermal comfort. The different positioning of the ‘‘ductless’’ PV intake above the floor, up to a level of 0.2 m, had no impact on the temperature distribution in the room. Similar results were observed at a displacement airflow rate of 80 L/s. 3.2. Contaminant distribution in the room The normalized vertical distribution of the simulated pollution sources, i.e. the exhaled air (mixed with SF6) and the passive pollution (simulated by Freon), obtained at location I (Fig. 1) is shown respectively in Fig. 4 (left) and Fig. 4 (right). The distribution
measured with DV alone (RF) and with cases when ‘‘ductless’’ PV was switched on either at the polluting workstation (PV_15_0) or at both workstations (PV_15_15) is compared in the figure for displacement airflow rates of 60 L/s and 80 L/s. The results obtained at the remaining two locations, i.e. locations II and III (Fig. 1) showed approximately the same development. The results in Fig. 4 show the expected vertical stratification in the concentration of the pollution sources. In the reference case of DV alone the increase of the supplied flow rate from 60 L/s to 80 L/s increases the stratification height for the exhaled air (Fig. 4 left) and has only a limited impact on the spread of the passive pollution located at lower level. As expected, a higher concentration is measured at 60 L/s. The use of personalized ventilation causes mixing and increases the concentration of tracer gas at a lower level. The increase is larger when the ‘‘ductless’’ PV systems are used at the two workplaces.
Fig. 4. Distribution of normalized concentration obtained at location I; the comparison is made for RF (DV alone) and two cases with different combinations of personalized airflows under two displacement rates (60 and 80 L/s).
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 996–1005
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Table 3 Normalized concentration of simulated pollutions in the inhaled air, experimental cases 1.1–1.3. Pollution source
Condition
Case
Polluting manikin
Exposed manikin
Air supplied by displacement ventilation
Exhaled air (SF6)
Point passive pollution (Freon)
RF PV_15_0 PV_15_15 RF PV_15_0 PV_15_15
1.1 1.2 1.3 1.1 1.2 1.3
3.3. Pollution concentration in inhaled air The normalized concentration (equation (1)) of the tracer gases (SF6 and Freon) in the air inhaled by the manikins at 60 L/s and 80 L/ s displacement airflow rate in the reference case (RF) without ‘‘ductless’’ PV, when only the ‘‘ductless’’ PV of the polluting manikin was used (PV_15_0) and when the two ‘‘ductless’’ PVs were used (PV_15_15), is listed in Table 3. In the RF the difference in the tracer gas concentration in the air inhaled by the two manikins is considerable. Part of the pollution generated in the vicinity of the polluting manikin was entrained by the free convective flow existing around its body. In this way, it was moved to the mouth of the manikin where it was inhaled. The air exhaled by the polluting manikin with high momentum escaped from the free convective flow and therefore its contribution to the inhaled air was much lower than the concentration of the passive pollution generated at very low momentum in front of the manikin and easily moved upward and inhaled. Therefore the concentration of the two pollutions in the air inhaled by the polluting manikin was much higher than in the air inhaled by the exposed manikin. The use of the ‘‘ductless’’ PV caused mixing and transport of pollution between the workstations. The concentration of the two tracer gases in the air inhaled by the exposed manikin increased substantially when only the ‘‘ductless’’ PV of the polluting manikin was used. The increase of the DV supply flow rate increased the stratification height, resulting in a decrease of the pollution in the air inhaled by the exposed manikin. The use of the ‘‘ductless’’ PV at the workstation of the exposed manikin greatly decreased the concentration of the two tracer gases in the air inhaled by this manikin, i.e. the ‘‘ductless’’ PV protected this manikin. In the case of the polluting manikin the greatest benefit in using the ‘‘ductless’’ PV was with regard to the inhaled passive pollution. The
60 L/s
80 L/s
60 L/s
80 L/s
0.34 0.05 0.32 0.00 0.30 0.01 6.91 0.81 0.19 0.02 0.34 0.03
0.52 0.05 0.29 0.01 0.39 0.01 6.95 0.79 0.25 0.03 0.47 0.07
0.07 0.04 1.20 0.09 0.10 0.03 0.18 0.07 0.52 0.05 0.07 0.02
0.01 0.01 0.58 0.13 0.03 0.01 0.04 0.00 0.08 0.02 0.01 0.01
concentration of passive pollution in the air inhaled by the polluting manikin decreased dramatically when its ‘‘ductless’’ PV was in operation. Fig. 5 presents the normalized concentration (equation (2)) (left) and the real concentration (right) of the tracer gas (Freon) present in the exhaled air and present in the exhaled air and measured at the intakes of both ‘‘ductless’’ PV systems when 60 L/s of air was supplied by the DV. The results obtained with the four positioning heights of ‘‘ductless’’ PV intakes above the floor level, i.e. 2, 5, 10 and 20 cm, are compared in the figure. The results show that the normalized concentration at the intake is almost the same for the four heights studied. As the results in Fig. 5 (right) show, the tracer gas concentration at the intake of the ‘‘ductless’’ PV at the workstation of the exposed manikin is slightly higher that at the intake of the ‘‘ductless’’ PV of the polluting manikin Fig. 6 shows the normalized concentration (equation (3)) (left) and real concentration (right) of tracer gas (tracer gas (Freon) present in the air exhaled by the polluting manikin) present in the air exhaled (active pollution) and measured in the air inhaled by the two manikins when 60 L/s of air was supplied by the DV. The results obtained when the intakes of the ‘‘ductless’’ PV systems were positioned at 2, 5, 10 and 20 cm height above the floor are compared in the figure. The differences in the normalized concentration in the inhaled air are larger than the differences in the normalized concentration at the intakes (Fig. 5, left). The concentration of tracer gas tracer gas was substantially higher in the air inhaled by the polluting manikin than in the air inhaled by the exposed manikin. This is the result of the interaction of the personalized flow with the flow of exhalation. The difference in tracer gas concentration in the air inhaled by the polluting manikin and in the air at the intake of its ‘‘ductless’’ PV is much larger than the difference of tracer gas concentration in the air inhaled by the
Fig. 5. Normalized concentration (left) and real concentration in ppm (right) of air exhaled by polluting manikin (Freon) measured at the intakes of ‘‘ductless’’ personalized ventilation at 60 L/s displacement airflow rate.
´ , A.K. Melikov / Building and Environment 45 (2010) 996–1005 B. Halvonˇova
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Fig. 6. Normalized concentration (left) and real concentration in ppm (right) of air exhaled by polluting manikin (Freon) in the air inhaled by the manikins measured when the ‘‘ductless’’ personalized ventilation was used at displacement airflow rate of 60 L/s.
exposed manikin and at the intake of its ‘‘ductless’’ PV. Furthermore the differences between the tracer gas concentration at the intakes of the ‘‘ductless’’ PV systems at the workstations is much smaller than the tracer gas concentration difference in air inhaled by the manikins. The results obtained at 80 L/s airflow rate supplied from the displacement diffuser were similar. 3.4. Temperature of inhaled air The temperature of air inhaled by the exposed manikin under the different personalized airflow rate combinations is listed in Table 4. The inhaled air temperature with DV alone (RF) was not affected by the increase of the supplied flow rate from 60 to 80 L/s. The cool air at the lower height of the room was heated while being moved upwards by the free convective flow. The use of the ‘‘ductless’’ PV only at the workstation of the polluting manikin (PV_15_0) also did not have any impact on the temperature of the air inhaled be the exposed manikin. In these cases, the observed differences were within the uncertainty of the measurements ( 0.3 C). The use of the ‘‘ductless’’ PV at the workstation of the exposed manikin (PV_15_15), however, decreased the inhaled air temperature dramatically. In this case, the temperature of the supplied displacement air was important; the inhaled air temperature was measured about 0.6 C lower when the displacement air was supplied at 18 C than when it was supplied at 20 C. The air temperature measured at the intake of the ‘‘ductless’’ PV, at its RMP and directly in the air inhaled by the exposed manikin when the intake positioning height of the ‘‘ductless’’ PV was changed, i.e. 2, 5, 10 and 20 cm is listed in Table 5. The temperatures measured at the displacement flow rate of 60 L/s and 80 L/s is listed in the table separately. The comparison of the temperature measured at the intake when it is positioned at different heights shows the impact of the vertical air temperature gradient that existed due to the displacement air distribution principle. The temperature measured at the intake when positioned at 20 cm
above the floor is slightly higher than the temperature measured at the remaining positioning heights. However, the observed temperature difference diminishes by the time the sucked air is transported through the ‘‘ductless’’ PV components to the RMP, because of its heating by the walls of the ducting and the fan. The differences in the personalized air temperature at the RMP measured at different positioning heights of the ‘‘ductless’’ PV intake are within the uncertainty of the temperature measurement ( 0.3 C). The temperature difference at the intake and at the RMP at the four intake positioning heights is listed in Table 5 as well. 3.5. Heat loss from manikin’s body The determined manikin-based equivalent temperature (MBET) for each body segment and the whole body of the manikins was used to analyse the performance of the ‘‘ductless’’ PV in regard to thermal comfort. The use of ‘‘ductless’’ PV at the workstation of the exposed manikin cooled the body and hence decreased the MBET for the exposed body segments (back of neck, face), as can be seen from the results in Fig. 7. The results shown in the figure were obtained at a displacement airflow rate of 60 L/s and different combinations of ‘‘ductless’’ PV airflow rates. The greatest cooling effect due to the use of ‘‘ductless’’ PV was obtained for the face region (10.3 C – left side and 6.3 C – right side) and for the back of the neck (5.3 C), i.e. the body segments directly exposed to the personalized airflow. The difference between the left and the right face can be explained by the fact that the manikin was not precisely positioned and the left face was more exposed to the personalized
Table 5 Temperature measured at intake and RMP of ‘‘ductless’’ personalized ventilation at the ‘‘exposed’’ workstation and temperature of air inhaled by the exposed manikin. Airflow rate
Temperature in a point
60 L/s
Temperature at intake ( C), TPV Temperature at RMP ( C), TRMP TRMP-TPV ( C) Temperature at inhalation ( C), Ti Ti-TRMP ( C) Temperature at intake ( C), TPV Temperature at RMP ( C), TRMP TRMP-TPV ( C) Temperature at inhalation ( C), T; Ti-TRMP ( C)
Table 4 Temperature of air inhaled by exposed manikin seated at workstation WS2. Airflow rate
Temperature in a point
60 L/s 80 L/s
Temperature at inhalation ( C) Temperature at inhalation ( C)
‘‘Ductless’’ personalized ventilation RF
PV_15_0
PV_15_15
30.3 30.2
30.1 30.2
25.5 26.1
80 L/s
‘‘Ductless’’ PV intake location above the floor 2 cm
5 cm
10 cm
20 cm
22.4 23.9 1.5 25.3 1.4 22.5 24.0 1.5 25.2 1.2
22.7 24.1 1.4 25.5 1.4 22.6 23.9 1.3 25.1 1.2
22.3 23.7 1.4 25.1 1.4 22.7 24.1 1.4 25.3 1.2
22.9 23.9 1.0 25.2 1.3 23.4 24.3 0.9 25.4 1.1
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 996–1005
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Fig. 7. MBET of exposed manikin at a displacement airflow rate of 60 L/s.
flow, i.e. the direction of personalized flow is an important factor for occupants’ thermal comfort. The whole body cooling effect of the personalized air was lower than 1 C. As expected, the use of the ‘‘ductless’’ PV at the workstation of the polluting manikin did not affect the MBET determined for the exposed manikin, whether or not its ‘‘ductless’’ PV was used. Fig. 8 compares the cooling effect provided by the ‘‘ductless’’ PV in comparison with the cooling effect of DV used alone at the two supply flow rates, 60 L/s and 80 L/s. The difference in MBET determined with DV alone and the MBET determined with ‘‘ductless’’ PV in conjunction with DV (case PV_15_15) was calculated for the body segments and the whole body of the exposed manikin. As can be seen from the results in the figure, the cooling effect provided by ‘‘ductless’’ PV was higher at a displacement airflow rate of 60 L/s. This is mainly due to the lower temperature of the supplied personalized air at 60 L/s (already discussed above). The cooling effect of the body segments not directly exposed to personalized airflow was negligible (within the uncertainty of the measurement). No significant impact of the positioning height of the ‘‘ductless’’ PV intake on the cooling effect of the personalized flow was observed in the present study (the small differences obtained were within the measurement uncertainty). Therefore the results are not presented in this paper.
4. Discussion The use of the ‘‘ductless’’ PV makes it possible to transport the cool and clean air supplied from the displacement diffuser over the floor direct to the breathing zone of occupants and thus to ensure a high level of inhaled air quality. The air provided to inhalation by the ‘‘ductless’’ PV can be as clean as the air provided by DV used alone. In fact when the pollution source is located in the vicinity of the human body, the concentration of pollution in the inhaled air is much lower with ‘‘ductless’’ PV than when DV is used alone. Furthermore, the results of the present study document that the temperature of the inhaled air provided by ‘‘ductless’’ PV can be several degrees lower (in the present study up to approx. 5 C) than the temperature of the inhaled air provided with DV alone. The results of human subject experiments with personalized ventilation reveal that personalized air with a temperature lower than the room air temperature and relatively high velocity improves the perceived air quality significantly above the level of improvement due to its cleanness [4,19,20]. Therefore it may be expected that the PAQ with ‘‘ductless’’ PV will be better than with DV used alone. The results of the present study support findings in previous studies [5,6,12,21] that the personalized ventilation may increase mixing and transportation of pollution generated in the vicinity of its supply ATD and in general will decrease the quality of the
Fig. 8. Cooling effect provided by ‘‘ductless’’ PV; difference between MBET measured with DV alone (RF) and with ‘‘ductless’’ PV used at both workstations (PV_15_15).
1004
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inhaled air. However, it must be noted that in this case the superior performance of DV alone is limited only to the case when there are no moving occupants, which in fact occurs seldom in practice (only in single type offices). In the present study the ‘‘ductless’’ PV used at the workstation of the polluting manikin increased the concentration of tracer gas in the air inhaled by the exposed manikin when its ‘‘ductless’’ PV was not used. The use of the ‘‘ductless’’ PV improved the inhaled air quality to the level of DV alone. At a supply flow rate of 80 L/s, inhaled air with ‘‘ductless’’ PV was cleaner but slightly warmer than the air inhaled at 60 L/s. The opposite impact of these two parameters, cleanness and temperature of the inhaled air, on the perceived air quality is difficult to evaluate. An important finding of the present study is that the positioning height of the ‘‘ductless’’ PV intake up to a level of 0.2 m above the floor did not have a significant impact on the cleanness and the temperature of air supplied by its ATD. However, the cleanness of the air at the intake of different workstations may not be the same. The intakes of the ‘‘ductless’’ PV at the two workstations were not symmetrically exposed to the flow of clean displacement air. As already mentioned, the nozzles inside the displacement diffuser were adjusted to supply initially the clean air mainly along the adjacent wall in order to reduce the size of the area near the diffuser with velocity higher than 0.2 m. This may be one of the reasons for the observed differences. Although a vertical temperature gradient exists in the stratified layer of clean air, the temperature of the supplied personalized air at the ATD was almost the same because the heat transfer in the ‘‘ductless’’ PV system diminished the small differences in the air temperature at the intake when it was positioned at different heights. The tracer gas concentration in the air inhaled by the polluting manikin was substantially higher than the concentration in the air inhaled by the exposed manikin regardless of whether DV was used alone or in conjunction with ‘‘ductless’’ PV. In general, the ‘‘polluted’’ air exhaled through the nose of the polluting manikin with high momentum escaped from the free convective flow around its body. The jets of exhalation interacted with the personalized flow from front/above. As a result, the exhaled air was discharged backwards towards the body of the polluting manikin where it was entrained by the free convective flow and moved to its mouth to be inhaled. The discharged exhaled air was also transported further back towards the workstation with the exposed manikin. In this case it was diluted with the room air. Therefore the tracer gas concentration of exhaled air in the air inhaled by the exposed manikin decreased in comparison with the polluting manikin. The tracer gas concentration in the inhaled air depends strongly on the airflow interaction at the breathing zone. This is valid also for the second pollution source tested during the first experimental stage (passive pollution). The impact of the airflow interaction in the case of PV in conjunction with mixing, displacement and underfloor ventilation is discussed in detail [12,13,22]. It can be concluded that ‘‘ductless’’ PV is able to protect the occupant from pollution generated at other workstations on a similar or even better level than with DV used alone. Furthermore, it will protect the occupant from passive pollution located in his/ her vicinity better in comparison with DV alone. The present results showed that ‘‘ductless’’ PV had a rather local effect and did not adversely change the temperature distribution in the vicinity of two workstations and in the occupied zone; the temperatures in the occupied zone measured at the combinations of personalized airflows studied were within the ranges prescribed by the present standards [1,2]. This is an important finding for practice since it means that the methods for prediction of velocity and temperature fields in rooms with DV can equally well be applied for ‘‘ductless’’ PV in conjunction with DV under present conditions. In general it may be concluded that if the DV is designed
properly, the additional application of ‘‘ductless’’ PV under individual control of an occupant will not cause thermal discomfort. Substantial cooling of the manikin’s body segments exposed to the flow from the ‘‘ductless’’ PV, i.e. scull, left and right face and back of the neck, was identified. Previous research [23,24] has documented that airflow from front, like the flow provided by the ‘‘ductless’’ PV in the present study, causes less draught discomfort than airflow from behind. Nevertheless the performance of the ‘‘ductless’’ PV with regard to draught discomfort needs to be studied at the lower range of comfortable temperatures in human subject experiments. Local thermal discomfort due to draught is one of the problems in rooms with DV. In practice, building managers often increase the supply air temperature and thus the temperature in the occupied zone in order to avoid draught complaints. This leads to complaints from too warm air. In such cases the increased inhaled air temperature may increase complaints of unacceptable PAQ as well [25]. Implementation of the ‘‘ductless’’ PV will allow for supplying the displacement air at a relatively high temperature, i.e. keep room air temperature relatively high, and to provide occupants with a preferred thermal environment and a high level of inhaled air quality by use and control of the personalized air. In this way the cool and clean displacement air can be utilized more efficiently and under certain conditions this strategy may lead to energy savings as well. In the real office dust, droplet nuclei as a result of coughing and sneezing (may carry viruses of infected person), etc. may be present at the floor level. These may be transported to the breathing zone by the ‘‘ductless’’ PV. Therefore it is recommended to install a filter at the intake or in the ‘‘ductless’’ PV system. Installation of UVGI lamps will cleanse the air from viruses. 5. Conclusions ‘‘Ductless’’ personalized ventilation in conjunction with displacement ventilation provides air to inhalation as clean as air provided by use of displacement ventilation alone. In the case of pollution located in the vicinity of an occupant’s body, the inhaled air with ‘‘ductless’’ personalized ventilation is considerably cleaner than the air inhaled with displacement ventilation alone. The perceived air quality with ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation will be superior to the PAQ with displacement ventilation alone because of the positive impact of cooler personalized air supplied at elevated velocity. The different positioning of the ‘‘ductless’’ personalized ventilation intake height up to a level of 0.2 m above the floor had no significant impact on the cleanness and temperature of the air supplied by the air terminal device of the ‘‘ductless’’ personalized ventilation. The use of ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation had only a local impact on the temperature distribution in the room. In practice, the use of ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation will allow the room temperature to be kept at a relatively high level while occupants provided with individual control of the personalized flow of clean and cool air will benefit with high quality of the inhaled air and preferred thermal environment. Acknowledgement This research was partially supported by the Danish Technical Research Council (STVF).
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 996–1005
Nomenclature
Abbreviations ATD air terminal device DV displacement ventilation ‘‘ductless’’ PV ‘‘ductless’’ personalized ventilation PAQ perceived air quality PV personalized ventilation RF reference case RMP round moveable panel WS workstation Symbols C X MBET
concentration in inhaled air or in a point (ppm) concentration (ppm) or temperature ( C) in a point manikin-based equivalent temperature ( C)
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