- Email: [email protected]
Performance of “ductless” personalized ventilation in conjunction with displacement ventilation: Impact of disturbances due to walking person(s)
Building and Environment 45 (2010) 427–436
Contents lists available at ScienceDirect
Building and Environment journal homepage: www.elsevier.com/locate/buildenv
Performance of ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation: Impact of disturbances due to walking person(s) 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 12 March 2009 Received in revised form 16 June 2009 Accepted 27 June 2009
The performance of the novel ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation (DV) was compared with the performance of DV alone under realistic conditions involving disturbances due to walking of one or two persons. An office room with two workstations was arranged in a full-scale test room. Two thermal manikins were used as sedentary occupants at the workstations. Two pollution sources, namely exhaled air by one of the manikins and passive pollution on the table in front of the same manikin were simulated. The performance of the ventilation systems was evaluated with regard to the quality of inhaled air and thermal comfort of the seated ‘‘occupants’’. The walking person(s) caused mixing of the clean and cool air near the floor with the polluted and warmer air at higher levels and disturbed the displacement principle which resulted in a decrease of the inhaled air quality. The performance of the ‘‘ductless’’ PV under the tested conditions was better as opposed to DV alone. Thus in practice the ‘‘ductless’’ PV will be superior to DV alone as regards perceived quality of inhaled air. The location of a walking person was found to be important. Person(s) walking close to the displacement diffuser will cause greater disturbance. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: ‘‘Ductless’’ personalized ventilation Displacement ventilation Inhaled air quality Thermal comfort Movement of occupant
1. Introduction Personalized ventilation (PV) is a new principle of clean air distribution. It aims to supply clean air direct to the breathing zone of occupants and provides the possibility for individual control of the microenvironment at each workstation [1,2]. The occupants may control the flow rate, the direction and temperature of the supplied personalized air so as to achieve the preferred thermal comfort conditions at their workstations [3,4]. It is possible that some occupants may turn off the PV system. Therefore it is recommended in practice to use PV in conjunction with a background total volume ventilation system. Recently a novel ‘‘ductless’’ personalized ventilation system was introduced, which utilizes the clean and cool air supplied over the floor by the displacement ventilation (DV) principle [5]. The ‘‘ductless’’ PV sucks, transports and supplies the clean and cool air distributed over the floor area by the DV, to the breathing zone of the occupant. In this way, clean and cool air can be better utilized and the flexibility of desk layout is not
* Corresponding author. Department of Building Services, Slovak University of Technology in Bratislava, 813 68 Bratislava, Slovakia. Tel.: þ421 903 904 484; fax: þ421 252 961 137. 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.2009.06.023
affected. Previously, it has been shown that under steady-state conditions the ‘‘ductless’’ PV coupled with DV is able to provide clean and cool air to the breathing zone of seated occupant [5]. Displacement ventilation is in comparison with traditional mixing ventilation more sensitive to disturbances caused by physical activities of occupants [6] such as opening and closing a door, moving, walking, etc. Mattson and Sandberg [7] used a human simulator of cylindrical shape and Mattson et al. [8] a simulator of more human-like shape to study the impact of a moving person on the airflow pattern in rooms with DV. Bjørn et al. [9] used breathing thermal manikins in order to study the impact of movement on personal exposure to exhaled air. A real person was used in the study by Brohus et al. [6], in which the impact of several typical ‘‘movements’’ on the performance of DV was investigated. Mundt [10] studied particle re-suspension due to a walking person in a room with DV and their entrainment by thermal flows generated by heat sources (including occupants). Full-scale experiments combined with CFD simulation reported by Matsumoto et al. [11] revealed that the object’s moving mode and speed significantly influence the temperature and contaminant distribution in the room. The findings of these studies reveal that movement of a person has a substantial impact on the air distribution in rooms with displacement ventilation and may lead to a decrease of its ventilation performance.
428
´ , A.K. Melikov / Building and Environment 45 (2010) 427–436 B. Halvonˇova
The impact of walking person(s) in different walking scenarios on the performance of ‘‘ductless’’ PV in conjunction with displacement ventilation was studied with regard to concentration of pollution generated by active (heated) and passive (non-heated) pollution sources in the inhaled air. The effect of different walking scenarios on the heat loss from an occupant’s body and temperature distribution were examined as well. Some of the results are presented in this paper. 2. Methods The experiments were conducted in a full-scale test room (4.8 5.4 2.6 m3) located in a laboratory hall. An office room with two workstations; each consisting of a table with ‘‘ductless’’ PV (Fig. 1), a breathing thermal manikin and typical office heat sources were arranged in the room. Prior to the experiments the whole room was sealed. The ‘‘ductless’’ PV installed at each desk consisted of an air terminal device (ATD) mounted on a movable arm and a small axial fan incorporated in a short duct system (positions 1, 4 and 5 in Fig.1). The treated outdoor air supplied to the room near the floor by the DV spread in a relatively thin layer over the floor. The ‘‘ductless’’ PV sucked the clean air direct from this layer at the locations of the desks (position 6 in Fig. 1) and transported it to the breathing zone of the manikins. The ATD used during the experiments, named round movable panel (RMP), is described in Ref. [12]. The movable arm, to which the RMP was attached, allowed for free positioning of the RMP. During the present experiments the RMPs were positioned in front (0.4 m) and slightly above the faces of the manikins. This positioning was most often preferred by people [3,4]. The workstations were positioned behind each other as shown in Fig. 2. A semicircular wall unit with a radius of planar projection of 0.25 m and a height of 1 m, installed on the floor and attached to the middle of one of the walls, was used to supply outdoor treated air. The unit was fitted with nozzles that ensured the spread of the air mainly along the adjacent wall. The air was exhausted from the room by a square unit installed in the middle of the ceiling area. The recirculation of exhaust air to the supply air was not utilized in order to increase sensitivity of the tracer gas measurements.
2.1. Heat and contaminant sources The total heat load generated in the room, i.e. the heat generated by the desk lights, the PC (tower plus monitor), the breathing thermal manikins and the six fluorescent lighting fixtures (6 W each) evenly distributed over the ceiling, was 22.6 W/m2. The two breathing thermal manikins, each seated at one of the workstations on an upholstered office chair, were used to simulate two occupants. The manikins’ bodies are shaped as a 1.7 m tall average size Scandinavian woman and are divided into several individually heated segments (17 or 23 segments). During the measurements the surface temperature of the manikins was controlled to be the same as the skin temperature of an average person in a state of thermal neutrality [13]. Since the experiments simulated summer conditions, the clothing insulation of the manikins together with upholstered office chair insulation, was 0.59 clo in total [14]. Pollution from two sources with different behaviors, namely warm exhaled air (active pollution) and passive (unheated) point pollution source on the table, was simulated by using a constant emission of tracer gases. One of the manikins (referred to in the following as a polluting manikin, seated at workstation WS1) was equipped with an artificial lung. The simulated breathing cycle consisted of 2.5 s inhalation, 2.5 s exhalation and 1.0 s pause. The breathing frequency was 10 cycles per minute and the pulmonary ventilation was 0.6 L per breath. The exhaled air was traced with a constant dose of 0.135 mL/s sulphur hexafluoride (SF6). To ensure the density of air exhaled by people (1.144 kg/m3) the air exhaled by the polluting manikin was heated. The air was exhaled from the nose of the polluting manikin and inhaled through the mouth. The pollution from the passive point pollution source in front of the polluting manikin was simulated by tracer gas Freon. This tracer gas was released from a small perforated ball to ensure a uniform dispersion. The second manikin was used in all experiments as an exposed manikin and was seated at workstation WS2 (Fig. 2). 2.2. Experimental conditions The walking person(s) with natural body movement and wake behind their body generated more realistic disturbances in comparison with the regular and monotonous movement of the human simulators used in previous studies [7,9]. During all experiments 80 L/s of treated outdoor air at 20 C was supplied to the room by the DV, aiming at an exhaust air temperature of 26 C. The temperature in the tall hall was controlled to be 25 C. Experiments with displacement ventilation only, i.e. the reference case (RF), and displacement ventilation together with the ‘‘ductless’’ PV at the two desks supplying each 15 L/s personalized air (PV_15_15) were performed. These are listed in Table 1. Three walking scenarios were simulated (Fig. 3): scenario 1 (W1_1P) – one person walking along the room between the displacement diffuser and the two workstations; scenario 2 (W2_1P) – one person walking along the room far from the displacement diffuser; scenario 3 (W_2P) – two persons walking at the same time along the room on the two sides of the workstations (the paths of scenarios 1 and 2). In order to avoid errors due to differences in the walking pattern and the behavior, the same person walked during the experiments of the three scenarios. In scenario 3 a second person joined the experiments. 2.3. Experimental procedure
Fig. 1. ‘‘Ductless’’ PV system: (1) air terminal device, (2) heat sources, (3) table, (4) installed fan, (5) short duct system, (6) intake of ‘‘ductless’’ PV, (7) floor level.
The procedure applied during the experiments with the three walking scenarios was identical. After steady-state conditions were achieved, measurements were performed without a walking person. The results obtained are referred to in the following as
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 427–436
429
Fig. 2. Set-up of test room: (1) polluting manikin, (2) exposed manikin, (3) air terminal device of ‘‘ductless’’ PV, (4) movable arm of ‘‘ductless’’ PV, (5)–(7) heat sources, (8) displacement diffuser, (9) exhaust unit, (10) ceiling illumination, (T) measuring point for temperature distribution.
‘‘Before’’. The person was then asked to enter the room, to close the door and to start walking normally (measured walking speed of approximately 1.3 m/s) on the side of the workstations (at a distance of approximately 1 m) defined by the scenario 1 (Fig. 3). The tracer gas measurements were initiated after 20 min and lasted for approximately 40 min. The air temperature and the manikins’ heat loss measurements from the last 15 min of the hour were used in the analyses. The results obtained are referred as W1_1P. After 1 h the person was asked to leave the room. Measurements without a walking person were initiated again when steady-state conditions were reached in the test room. The results of these measurements are referred in the following as ‘‘Between’’. The person was then asked to enter the room again and to walk for 1 h according to the scenario 2 (Fig. 3). The measurement procedure had the same timing as for W1_1P. The results of these measurements are referred to in the following as W2_1P. The experimental procedure with two persons was shorter. After steady-state conditions were achieved, measurements were performed without walking persons. The results obtained are referred to in the following as ‘‘Before’’. The two persons were then asked to enter the room, to close the door and to start walking normally (measured walking speed of approximately 1.3 m/s) on the two sides of the workstations defined by the scenarios 1 and 2 (Fig. 3). The measurement results obtained when following the same procedure as one walking person are referred to as W_2P.
2.4. Measured parameters and measuring equipment The vertical temperature distribution was measured at the location ‘‘T’’ (Fig. 2), i.e. close to the exposed manikin. The air temperature was measured at 12 heights above the floor: 0.05, 0.1, 0.2, 0.3, 0.5, 0.6, 0.85, 1.1, 1.4, 1.7, 2.1 and 2.4 m. The concentrations of tracer gases and air temperature were measured in the supply and the exhaust, in the intakes of both ‘‘ductless’’ PV systems and in the tall hall. The tracer gas concentration was measured in the air
Table 1 Studied experimental cases, personalized airflows at workstations in L/s. Cases Before W1_1P Between W1_1P Before W_2P
Reference case (RF) Polluting/exposed manikin No walking – 0/0 L/s Walking – 0/0 L/s No walking – 0/0 L/s Walking – 0/0 L/s No walking – 0/0 L/s Walking – 0/0 L/s
PV_15_15 Polluting/exposed manikin No walking – 15/15 L/s Walking – 15/15 L/s No walking – 15/15 L/s Walking – 15/15 L/s No walking – 15/15 L/s Walking – 15/15 L/s
inhaled by both manikins but the temperature of inhaled air was recorded only for the exposed manikin. The temperature distribution at the location T was measured by thermocouples. All other temperature measurements were performed with medical thermistors. The concentration of tracer gases was measured with a multi-gas monitor based on the photoacoustic infrared detection method of measurement. The dry heat loss from the whole body and the body segments of the manikins was measured together with the surface temperature. The thermal environment of the seated occupant at both workstations in the room was evaluated in terms of the manikin-based equivalent temperature (MBET) determined for each of the body segments and the whole body of thermal manikins [13]. MBET is defined as the uniform temperature of an imaginary enclosure with air velocity equal to zero in which a person will exchange the same dry heat by radiation and convection as in the actual non-uniform environment. It is assumed that the body posture, the activity level and the clothing design and thermal insulation are the same in both environments. For each body segment the manikin-based equivalent temperature, MBETi, is calculated using the following equation:
MBETi ¼ tsk;i
Qt;i hcal;i
(1)
where tsk,i [ C] is the surface temperature measured for the i-th segment, Qt,i [W/m2] is the sensible heat loss (power consumption) of the i-th segment and hcal,i [W/Km2] is a dry heat transfer coefficient, determined during calibration of the manikin in a uniform thermal environment. The MBETbody for the whole body is obtained by computing the area-weighted average over all the body segments. The manikins were calibrated before the start of the measurements.
2.5. Criteria for assessment The performance of the ‘‘ductless’’ PV was evaluated in regard to the inhaled air quality and thermal comfort of a seated occupant by using both thermal manikins. In this paper, the concentrations of tracer gases measured in the inhaled air are expressed in terms of normalized concentration defined by the following equation (2):
Normalized concentration ¼
CI Cs Ce Cs
(2)
where CI is the tracer gas concentration in the inhaled air, Ce is tracer gas concentration in the exhaust air and Cs is tracer gas concentration in the supply air. The lower the value of the
´ , A.K. Melikov / Building and Environment 45 (2010) 427–436 B. Halvonˇova
430
loss from both thermal manikins were recorded for 15 min at the end of each measurement interval. The duration and sampling frequency of each measurement were considered in order to estimate each quantity with high accuracy. The data were analyzed in accordance with ISO guidelines for the expression of uncertainty [15]. 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. 3. Results 3.1. Temperature distribution
Fig. 3. Walking scenarios, i.e. scenario 1 (W1_1P) and scenario 2 (W2_1P).
normalized concentration, the less pollution is inhaled by the manikin. The inhaled and room air temperatures were expressed in terms of normalized temperature by using the following equation (3):
Normalized temperature ¼
XI XS Xe XS
(3)
where XI is the temperature in the inhaled air or in the point, Xe is temperature measured in the exhaust unit and XS is the temperature measured in the displacement diffuser. The lower the value of the normalized temperature, the cooler is the inhaled or room air. The body cooling effect of the ‘‘ductless’’ PV was quantified by the change in the whole body and the segmental MBET from the condition when only displacement ventilation was used i.e. DMBET1 ¼ MBETDV MBET‘‘ductless’’ PV. DMBET1 was determined for all three walking scenarios as well as separately in the case with no disturbances caused by moving person(s). Positive values of DMBET1 will express the cooling effect of the ‘‘ductless’’ PV and negative values will mean that more cooling was provided when only DV was used. The body cooling effect caused by walking person(s) was quantified by the change in the whole body and the segmental MBET from the condition without walking, i.e. DMBET2 ¼ MBETwalking MBETno walking. DMBET2 was determined separately in the case of DV alone and the case of ‘‘ductless’’ PV in conjunction with DV. Positive values of DMBET2 will mean that the cooling of the manikin with walking is less than without walking and negative values will mean that the walking causes more cooling in compared to without walking. 2.6. Precision of measurement At each of the measured points the tracer gas concentration was determined as an average of eight repeated measurements. The temperature of air inhaled by the exposed manikin, the temperature at ‘‘ductless’’ PV intakes, the vertical temperature distribution and the segmental and whole-body surface temperatures and heat
The vertical distribution of temperature measured at the location T is shown in Fig. 4. The comparison in the figure is made for two cases without walking person(s) marked as ‘‘Before’’ and 4 scenarios with walking person(s): one when only DV was used (RF) and three when ‘‘ductless’’ PV was used in conjunction with DV (PV_15_15). The present results show some impact of ‘‘ductless’’ PV on temperature distribution between 0.3 and 1.1 m above the floor. Nevertheless, without walking, the vertical temperature difference between head and ankles of a seated occupant was identical. It was within the range recommended in ISO Standard 7730 [14] for a thermal environment of category B. The temperature increased near the floor level and the vertical temperature gradient in the room decreased when walking took place. The temperature distribution was disturbed by the walking person(s) in the same way, regardless of the applied ventilation system (case with one person walking far from the displacement diffuser – W2_1P is shown as an example in Fig. 4 for both DV alone and for ‘‘ductless’’ PV). On the other hand the location of the walking person with regard to the displacement diffuser was important. The disturbance caused by a person walking on the side of the displacement diffuser W1_1P (Fig. 3) was much stronger than the disturbance caused by a person walking on the opposite side of the workstations W2_1P (Fig. 3). The person walking on the side of the displacement diffuser almost destroyed the temperature stratification, i.e. the temperature distribution became close to that in a room with mixing ventilation. In this case, the second person walking on the opposite side of the workstations (W_2P) did not add to the disturbance. The temperature distribution was less affected in the case W2_1P. In this case, the temperature stratification was preserved though substantial mixing also occurred, especially at heights above 0.3 m due the air movement caused by the body of the walking person. The results in the figure show that the disturbance of the walking person on the vertical temperature distribution in the case of DV alone and ‘‘ductless’’ PV in conjunction with DV was the same. As previously suggested [5], the DV design procedure can be applied also when ‘‘ductless’’ PV is used in conjunction with DV. 3.2. Concentration in inhaled air – one walking person Figs. 5 and 6 show the normalized concentration of the two simulated pollutions in the air inhaled by the polluting and the
Table 2 Sampling frequency, duration of data acquisition, and typical values of expanded absolute uncertainty with a 95% level of confidence. Quantity
Frequency of date acquisition
Duration of measurement period
Uncertainty (conf. level 96%)
Concentrations (inhaled) Temperature (inhaled and room) MBET
5 min 5 Hz 20 s
35–45 min 1 min 2 min
See Result 0.3 C 0.23 C
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 427–436
Fig. 4. Temperature distribution obtained at location T (Fig. 2).
exposed manikins, respectively. The disturbance caused by a person walking according to scenarios 1 (W1_1P) and 2 (W2_1P) is compared in the figures. The uncertainty of the results obtained is indicated. In comparison with displacement ventilation alone, the ‘‘ductless’’ PV was able to protect better the polluting manikin from re-inhalation of its exhaled air in the case of a walking person (Fig. 5 – W1_1P, W2_1P), while in a calm environment, better protection was ensured by the DV alone (Fig. 5 – Before and Between). In a calm environment, the personalized flow supplied from front/above against the manikin’s face mixed with the exhaled air. Therefore more exhaled air was re-inhaled by the polluting manikin. As expected, the walking person introduced mixing in the room and therefore the concentration of the exhaled air inhaled by the polluting manikin increased in both cases, DV alone (RF) and ‘‘ductless’’ PV in conjunction with the DV (PV_15_15). It was closer to 1, i.e. mixing ventilation, in the scenario 1 (W1_1P). The mixing caused by the person walking on the opposite side of the workstation (W2_1P) was less. The results obtained for the passive pollution source were quite different. In a calm environment the pollution without any initial momentum and generated close to the polluting manikin’s body was entrained by the free convection flow around his body and transported upward. As a result, the pollution concentration in the air inhaled by the polluting manikin increased considerably with
431
DV alone. The flow of clean air supplied by the ‘‘ductless’’ PV penetrated the polluted free convection flow and provided clean air for inhalation. The walking person caused mixing of the room air, resulting in less pollution in the inhaled air in the case of DV alone. In this case, the normalized concentration of passive pollution inhaled by the polluting manikin decreased because the air in the vicinity of its body was more diluted. The decrease was greater when the person was walking near the displacement diffuser (W1_1P), than when walking on the opposite side of the workstations (W2_1P). The impact of a walking person on the passive pollution concentration in air inhaled by the polluting manikin in the case with ‘‘ductless’’ PV was observed only with a person walking close to the displacement diffuser (W1_1P). In this case the flow disturbance due to the walking increased the concentration of passive pollution inhaled by the polluting manikin almost twice from 0.49 to 0.94. The results obtained reveal that with regard to the passive pollution the ‘‘ductless’’ PV was superior to the displacement ventilation alone. The results obtained with the exposed manikin show that in general DV alone performed better than the ‘‘ductless’’ PV in conjunction with DV in the absence of a walking person and the opposite was true in the presence of a walking person (Fig. 6). The walking person introduced substantial mixing in the room which greatly increased the concentration of pollution inhaled by the exposed manikin. The distance of the walking person from the displacement diffuser was important: the concentration of the air exhaled by the polluting manikin and of the passive pollution in the air inhaled by the exposed manikin was higher when the person was walking close to the displacement diffuser (W1_1P) than when the same person was walking along the opposite side of the workstations (W2_1P). The reason is that the stratified flow of clean and fresh air supplied by the displacement diffuser was less disturbed on its way to the intake of the ‘‘ductless’’ PV when the person was walking away from displacement unit (W2_1P). 3.3. Concentration in inhaled air – two walking persons The impact of the airflow disturbance due to walking of two persons on the quality of air inhaled by the polluting manikin and the exposed manikin is shown in Fig. 7. The normalized concentration of both pollution sources is compared in the figure between the reference case of DV alone (RF) and the case of ‘‘ductless’’ PV in conjunction with DV (PV_15_15). The results obtained ‘‘Before’’ the two persons started to walk and when the two persons were walking are included in the figure. The uncertainty of the measurements is indicated.
Fig. 5. Normalized concentrations of both pollutions in air inhaled by the polluting manikin. Comparison between the case when only DV was applied (RF) and the case when the ‘‘ductless’’ PV was used in conjunction with DV (PV_15_15).
432
´ , A.K. Melikov / Building and Environment 45 (2010) 427–436 B. Halvonˇova
Fig. 6. Normalized concentrations of both pollutions in air inhaled by the exposed manikin. Comparison between the case when only DV was applied (RF) and the case when the ‘‘ductless’’ PV was used in conjunction with DV (PV_15_15).
As expected, the walking of two persons caused substantial disturbance of the airflow in the room resulting in an increase of personal exposure. In general, the increase of personal exposure was greater in the case of DV alone than in the case of ‘‘ductless’’ PV. The only exception was observed with regard to the passive pollution inhaled by the polluting manikin in the case of DV alone. In this case the mixing introduced due to the walking persons diluted the pollution at the breathing zone more in comparison with a calm environment, which resulted in an improvement of inhaled air quality. The normalized concentration decreased from 6.8 without walking (Before) to 1.4 with walking persons (W_2P). The walking of the two persons had less impact on the quality of air inhaled by the exposed manikin than by the polluting manikin which was located closer to the pollution sources. The inhaled air quality of both manikins was affected by two walking persons similar to the case when only one person was walking according to scenario 1 (W1_1P). The comparison between those two scenarios is shown in Fig. 8. The uncertainty of measurement is indicated. The results in the figure show that the presence of a second walking person in the room had a slight impact on quality of the air inhaled by the two seated manikins. The normalized concentration obtained with one walking person and two walking persons did not differ much. The only exception was
observed with the polluting manikin for the concentration of the passive pollution with DV alone (Fig. 8, left). Here the walking of the second person increased the mixing of the passive pollution generated in front of the polluting manikin with the surrounding room air, leading to increased dilution and better inhaled air quality. The normalized concentration decreased from 3.1 to 1.4. The comparison of the results in the figure reveals that the inhaled air quality obtained with the ‘‘ductless’’ PV was equal to or even better than with DV alone. 3.4. Inhaled air temperature Table 3 lists the temperatures of the air inhaled by the exposed manikin obtained in a calm environment and with the three walking scenarios. The air mixing introduced by the walking person(s) resulted in an increase of the inhaled air temperature. This increase was small with DV alone, around or less than 0.3 C with one walking person (comparable with the uncertainty of the temperature measurement which is 0.3 C) and 0.5 C with two walking persons. The impact of walking on the inhaled air temperature was greater in the case of ‘‘ductless’’ PV. The disturbance introduced by the walking person between the displacement diffuser and the workstations (W1_1P) increased the temperature
Fig. 7. Normalized concentrations of both pollutions in air inhaled by the polluting (left) and the exposed (right) manikins.
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 427–436
433
Fig. 8. Normalized concentrations of both pollutions in air inhaled by the polluting (left) and the exposed (right) manikins.
of the air inhaled by the exposed manikin by 1.7 C. The increase of the inhaled temperature was less (0.7 C) when the person was walking on the opposite side of the workstations (W2_1P). However, in all studied cases the inhaled air temperature with the ‘‘ductless’’ PV remained 2.9–4.5 C lower than with DV used alone. Fig. 9 compares the air temperature measured at a height of approximately 0.1 m above the floor (‘‘ductless’’ PV intake) at the exposed workstation (WS2) with and without walking person(s) in the case of DV alone and in the case of the ‘‘ductless’’ PV in conjunction with DV. Similar temperatures were measured at the polluting workstation (WS1). The results in the figure show that the disturbance of the displacement flow due to the walking of the person(s) resulted in a substantial temperature increase at a height of approximately 0.1 m. The temperature increase was between 0.5 C and 2.1 C. The person walking near the displacement diffuser (W1_1P) caused a greater increase of the air temperature than did a person walking far away from the displacement diffuser (W2_1P). The walking of the second person (W_2P) did not change the air temperature at the intake when the ‘‘ductless’’ PV was used. Some increase was observed only for the case of displacement ventilation used alone. The results in Fig. 9 reveal that the air temperature measured at the location of the ‘‘ductless’’ PV intake in the case of DV alone and the case of ‘‘ductless’’ PV were rather similar. However, as already discussed, the differences in the inhaled air temperature were substantial (Table 3). The analyses of the results in Table 3 and Fig. 9 reveal that in the case of DV alone the change of the air temperature at approximately 0.1 m due to walking had only a slight effect on the inhaled air temperature. The inhaled air was heated mainly by the manikin’s body. In the case of ‘‘ductless’’ PV, the walking of a person had a much greater impact on the inhaled air temperature. The increase of the air temperature at the intake
Table 3 Values of air temperature inhaled by the exposed manikin expressed in C.
Before (without walking) W1_1P (with walking) Between (without walking) W1_1P (with walking) Before (without walking) W_2P (with walking)
RF ( C)
PV_15_15 ( C)
30.3 30.6 30.4 30.6 30.3 30.8
26.0 27.7 25.9 26.6 26.0 27.9
immediately increased the temperature of the inhaled air which in fact was mainly personalized air. Due to the heat exchange between the environment and the components of the ‘‘ductless’’ PV and the heating from the fan, the supplied personalized air was warmer. 3.5. Thermal comfort In Fig. 10 the cooling effect provided by the ‘‘ductless’’ PV for the body segments exposed to the personalized airflow and for the whole body of the exposed manikin is shown. The difference in MBET determined with DV alone and with the ‘‘ductless’’ PV (DMBET1 – defined in Criteria for assessment) is shown. The cooling effect of the ‘‘ductless’’ PV for the segments not shown in the figure was negligible. The results obtained with the two manikins were rather similar; therefore only the results obtained with the exposed manikin are shown. DMBET1 determined for the case without walking person(s) – named as ‘‘No walking’’ is in Fig. 10 (left) compared with the cases with one walking person either close to the displacement diffuser (W1_1P) or on the opposite side of the workstations (W2_1P) and in Fig. 10 (right) with the case with two walking persons (W_2P). The results in the figure reveal a substantial local cooling effect of the ‘‘ductless’’ PV compared to the DV alone. The maximum cooling is obtained for the body segments directly exposed to the personalized airflow. The cooling effect for the segments at the head region is equivalent to the decrease in the room air temperature in the range 2–10 C. The results also reveal that the whole-body cooling effect of the ‘‘ductless’’ PV was around 0.5 C. The results in Fig. 10 identify that the walking had smaller impact on the cooling effect than the personalized flow itself. The change in the whole-body and the segmental MBET due to the walking, DMBET2, (defined in Criteria for assessment) was used to assess the impact of the flow disturbances due to walking on occupants’ thermal comfort. DMBET2 obtained for the case of DV alone and for the case of ‘‘ductless’’ PV when the person was walking close to the displacement diffuser (W1_1P) is compared in Fig. 11. The same comparison but with a person walking on the opposite side of the workstations (W2_1P) is shown in Fig. 12. Positive values of DMBET2 mean that the walking decreases the heat loss from the manikin’s body, and negative values mean that the walking increases the heat loss.
434
´ , A.K. Melikov / Building and Environment 45 (2010) 427–436 B. Halvonˇova
higher changes in the whole-body heat loss due to the walking person were measured with the scenario 2 (W2_1P). For this walking scenario it was also observed that the decreases of heat loss between body segments were less pronounced. 4. Discussion
Fig. 9. Comparison between temperatures measured at intake of the ‘‘ductless’’ PV at the exposed manikin workstation (WS2).
In general, the results in Figs. 11 and 12 show that the air mixing due to walking decreased the heat loss from the manikin’s body (with few exception DMBET2 values were positive). The impact of the walking on DMBET2 differs for the different body segments. It was also different in the RF (DV alone) and in the case of ‘‘ductless’’ PV. For both, the walking caused mixing of the cool air near the floor with the warmer air from the higher levels and increased the air temperature at the lower heights in the room (see Figs. 4 and 9). This resulted in a decrease of the heat loss corresponding to the effect of an approximately 1 C and 0.5 C increase of the MBET measured for the lower body segments (foot, lower leg, etc.) when the person was walking according to scenarios 1 (W1_1P) and 2 (W2_1P) respectively. With the ‘‘ductless’’ PV the walking of the person decreased the heat loss from the head region (face, neck), i.e. the body segments exposed to the personalized flow. The decrease of the heat loss corresponded to the effect of an increase of air temperature of up to 2.6 C (for the left face) when the person was walking according to the scenario 1 (W1_1P). This means that the air movement generated by a walking occupant will affect the performance of the personalized ventilation used, not only with regard to the inhaled air quality but also with regard to the body cooling. As already discussed, this is mainly a result of the increase of the air temperature at the ‘‘ductless’’ PV intake (Table 3, Fig. 9). Comparison of the results in Figs. 11 and 12 shows also that the change in the heat loss from the manikin’s body due to walking of the person depends on the location of that person. For some of the body segments (feet, lower legs, head, etc.) the DMBET2 values were higher with the scenario 1 (W1_1P) and for the other body segments (hands, forearms, chest) they were higher for the scenario 2 (W2_1P). Slightly
It has been documented that personalized ventilation can provide people with cleaner air and better thermal comfort than the total volume ventilation systems [1,3,4,16]. It has also been shown that PV can protect occupants from airborne transmission of infectious agents [17]. In practice, PV can be easily implemented in rooms with under floor ventilation. However, its implementation in rooms with mixing or displacement ventilation is less acceptable because the required additional ducting affects the indoor environment aesthetically. The ‘‘ductless’’ PV introduced in conjunction with DV overcomes the above disadvantage. Halvonova and Melikov [5] documented that under steady-state conditions the inhaled air with the ‘‘ductless’’ PV was as clean as the air inhaled with DV alone and even cleaner depending on the layout of the workstations (the definition of the normalized concentration in their study is different from that used in the present study and therefore the results cannot be directly compared). They also reported that in comparison with DV alone the use of the ‘‘ductless’’ PV decreased substantially the temperature of the inhaled air and increased the body cooling, i.e. it had also the potential for improving perceived air quality (PAQ) and occupants’ thermal comfort. In the present study the performance of the ‘‘ductless’’ PV in conjunction with DV was compared with the performance of DV alone under dynamic and realistic conditions in practice. As expected, the walking person(s) disturbed the boundary layer of clean air supplied over the floor from the displacement diffuser and caused mixing of the simulated pollution with the room air. This resulted in a substantial decrease of the vertical temperature gradient and an increase of the pollution concentration in the inhaled air. The only exception was the decrease of the passive pollution in the air inhaled by the polluting manikin, because the intensified air mixing (due to walking) increased the dilution of this pollution generated in front of the breathing zone of the manikin. The DV, when used alone, was more vulnerable to the disturbance introduced by the walking person(s) than when it was combined with the ‘‘ductless’’ PV. The concentration of the generated pollution in the air inhaled by the manikins was lower with ‘‘ductless’’ PV than when the DV was used alone.
Fig. 10. Cooling effect caused by ‘‘ductless’’ PV on exposed manikin’s body segments and whole body.
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 427–436
435
Fig. 11. Change in the heat loss from the manikin’s body as a result of a person walking according to scenario 1 (W1_1P).
It has been well documented that the PAQ depends on the temperature and humidity of the inhaled air as well as on the pollution level [18]. Cool and dry air is perceived to be of a higher quality than warm and humid air. The air mixing caused by the walking person(s) diminished the vertical temperature gradient in the vicinity of the workstations and increased the air temperature at floor level. In the case of DV alone, this had no substantial effect on the temperature of the inhaled air that was heated mainly by the manikin’s body. However, disturbances due to walking increased the air temperature at the ‘‘ductless’’ PV intakes and thus the inhaled air temperature which depended only on the temperature of the personalized flow since it was relatively high (15 L/s). Under all the conditions studied the temperature of the air inhaled by the manikins with the ‘‘ductless’’ PV was lower than the inhaled air temperature with DV alone. In practice, occupants provided with control may select a personalized flow rate lower than 15 L/s. In this case, the inhaled air temperature will be higher due to the interaction of the personalized flow with the free convection flow. Nevertheless, it will be lower than the inhaled air temperature with DV alone. Recent studies [19,20] reveal that elevated facial velocity improves PAQ and diminishes the negative impact of increased temperature and humidity of the inhaled air. Thus in practice the ‘‘ductless’’ PV combined with DV will be superior to DV alone as regards perceived inhaled air quality by occupants, because it will provide cleaner and cooler air at elevated velocity. The air mixing due to the person(s) walking decreased the heat loss from the manikins, especially the local heat loss from the body
segments directly exposed to the flow near the floor (feet, lower legs) or the personalized flow (head). In practice, this may be beneficial because the main problem with DV is draught at the feet, which are exposed to cool air with relatively high velocity. The combination of the ‘‘ductless’’ PV and DV can be operated at elevated supply air temperatures (e.g. 23 C), which will increase the air temperature in the room (e.g. 28 C). In this case, risk of draught at the feet level will be diminished while the convection cooling of the body provided by the personalized flow of cooler air under the control of the occupant will ensure preferred thermal comfort conditions. This strategy has the potential for energy saving because less cooling of the supplied displacement air is required and the free cooling during several months of the year can be utilized. Three walking scenarios were applied in the present study. In this way, the impact of the distance between the walking person and the displacement diffuser as well as the strength of the disturbance caused by one or two persons was studied. The person walking between the displacement diffuser and the workstations had the greatest impact on the vertical temperature distribution, temperature and pollution concentration in the inhaled air and the heat loss from the manikin’s body. This impact changed little when the second person was included in the experiments. Therefore in practice, it may be recommended to design furniture arrangements that will limit walking of occupants between displacement diffuser and workstations. In the present study the distance between the displacement diffuser and the workstations was not changed. It
Fig. 12. Change in the heat loss from the manikin’s body as a result of a person walking according to scenario 2 (W2_1P).
436
´ , A.K. Melikov / Building and Environment 45 (2010) 427–436 B. Halvonˇova
may be expected that it could also be important for the impact of the walking on the performance of the DV and the ‘‘ductless’’ PV. 5. Conclusions The performance of ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation was compared with the performance of displacement ventilation alone under realistic conditions comprising airflow disturbances due to walking of the person(s) under different scenarios. The walking person(s) increased the mixing of the clean air near the floor with the polluted air at a higher level and disturbed the displacement principle, resulting in a decrease of the quality of air inhaled by manikins. Under these conditions, the performance of the ‘‘ductless’’ personalized ventilation was better than the performance of the displacement ventilation used alone. The walking person(s) diminished the vertical temperature gradient in the vicinity of the workplaces and increased the inhaled air temperature. Under all the conditions (with and without walking) the temperature of the air inhaled by the manikins with the ‘‘ductless’’ personalized ventilation was lower than with displacement ventilation alone. Thus in practice the ‘‘ductless’’ personalized ventilation will be superior to displacement ventilation alone with regard to the perceived air quality. The air mixing due to walking of occupant(s) decreased the heat loss from the thermal manikins, especially the local heat loss from the body segments directly exposed to the flow near the floor or to the personalized flow. At elevated room temperatures the ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation will provide occupants with better thermal comfort than displacement ventilation alone because of the increased local body cooling by the personalized flow. Under these conditions, draught discomfort at the feet can be avoided and energy savings may be achieved. The location of walking persons is important for the performance of both the displacement ventilation alone and the ‘‘ductless’’ personalized ventilation. Person walking close to the displacement diffuser will cause greater disturbance. Acknowledgement This research was partly supported by the Danish Technical Research Council (STVF).
References [1] Melikov A, Cermak R, Mayer M. Personalized ventilation: evaluation of different air terminal devices. Energy and Buildings 2002;34(8):829–36. [2] Melikov AK. Personalized ventilation. Indoor Air 2004;14(7):157–67. [3] Kaczmarczyk J, Melikov A, Fanger PO. Human response to personalized and mixing ventilation. Indoor Air 2004;14(8):1–13. [4] Kaczmarczyk J, Melikov A, Bolashikov Z, Nikolaev L, Fanger PO. Human response to five designs of personalized ventilation. International Journal of Heating, Ventilation and Refrigeration Research 2006;12(2):367–84. [5] Halvonova B, Melikov AK. ‘‘Ductless’’ personalized ventilation in conjunction with displacement ventilation. In: Proceedings of Indoor Air, Copenhagen, Denmark, 2008. [6] Brohus H, Hyldig ML, Kamper S, Vachek UM. Influence of persons’ movements on ventilation effectiveness. In: Proceedings of Indoor Air, Copenhagen, Denmark, 2008. [7] Mattson M, Sandberg M. Displacement ventilation – influence of physical activity. In: Proceedings of Roomvent, Krakow, Poland, Vol. 1, 1994, 78–92. [8] Mattson M, Bjørn E, Sandberg M, Nielsen PV. Simulating people moving in displacement ventilated rooms. In: Proceedings of Healthy Buildings, Washington, USA, Vol. 1, 1997, 495–500. [9] Bjørn E, Mattson M, Sandberg M, Nielsen PV. Displacement ventilation – effects of movement and exhalation. In: Proceedings of Healthy Buildings, Washington, USA, Vol. 2, 1997, 163–168. [10] Mundt E. Non-buoyant pollutant sources and particles in displacement ventilation. Building and Environment 2001;36:829–36. [11] Matsumoto H, Kozaka T, Nakao T. Study on air distribution and ventilation effectiveness in displacement ventilated rooms with a moving object. In: Proceedings of Indoor Air, Copenhagen, Denmark, 2008. [12] Bolashikov Z, Nikolaev L, Melikov A, Kaczmarczyk J, Fanger PO. New air terminal devices with high efficiency for personalized ventilation application. In: Proceedings of Healthy Buildings, Singapore, 2003, 850–855. [13] Tanabe S, Arens EA, Bauman FS, Zhang H, Madsen TL. Evaluating thermal environments by using a thermal manikin with controlled skin surface temperature. ASHRAE Translation 1994;100(1):39–48. [14] ISO. ISO 7730 Moderate thermal environments – Determination of the PMV and PPD indices and specification of the conditions for thermal comfort, International Organization for Standardization, Gene´ve, Switzerland, 2005. [15] ISO. Guide to the expression of uncertainty in measurement, International Organization for Standardization, Gene´ve, Switzerland, 1993. [16] 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. [17] Cermak R, Melikov A. Protection of occupants from exhaled infectious agents and floor material emissions in rooms with personalized and underfloor ventilation. HVAC & R Research 2007;13(1):23–38. [18] Fang L, Clausen G, Fanger PO. Impact of temperature and humidity on the perception of indoor air quality during immediate and longer whole-body exposures. Indoor Air 1998;8:276–84. [19] Melikov A, Kaczmarczyk J, Silva D. Impact of air movement on perceived air quality at different level of relative humidity. In: Proceedings of Indoor Air, Copenhagen, Denmark, 2008. [20] Melikov A, Kaczmarczyk J. Impact of air movement on perceived air quality at different level of air pollution and temperature. In: Proceedings of Indoor Air, Copenhagen, Denmark, 2008.
Contents lists available at ScienceDirect
Building and Environment journal homepage: www.elsevier.com/locate/buildenv
Performance of ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation: Impact of disturbances due to walking person(s) 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 12 March 2009 Received in revised form 16 June 2009 Accepted 27 June 2009
The performance of the novel ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation (DV) was compared with the performance of DV alone under realistic conditions involving disturbances due to walking of one or two persons. An office room with two workstations was arranged in a full-scale test room. Two thermal manikins were used as sedentary occupants at the workstations. Two pollution sources, namely exhaled air by one of the manikins and passive pollution on the table in front of the same manikin were simulated. The performance of the ventilation systems was evaluated with regard to the quality of inhaled air and thermal comfort of the seated ‘‘occupants’’. The walking person(s) caused mixing of the clean and cool air near the floor with the polluted and warmer air at higher levels and disturbed the displacement principle which resulted in a decrease of the inhaled air quality. The performance of the ‘‘ductless’’ PV under the tested conditions was better as opposed to DV alone. Thus in practice the ‘‘ductless’’ PV will be superior to DV alone as regards perceived quality of inhaled air. The location of a walking person was found to be important. Person(s) walking close to the displacement diffuser will cause greater disturbance. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: ‘‘Ductless’’ personalized ventilation Displacement ventilation Inhaled air quality Thermal comfort Movement of occupant
1. Introduction Personalized ventilation (PV) is a new principle of clean air distribution. It aims to supply clean air direct to the breathing zone of occupants and provides the possibility for individual control of the microenvironment at each workstation [1,2]. The occupants may control the flow rate, the direction and temperature of the supplied personalized air so as to achieve the preferred thermal comfort conditions at their workstations [3,4]. It is possible that some occupants may turn off the PV system. Therefore it is recommended in practice to use PV in conjunction with a background total volume ventilation system. Recently a novel ‘‘ductless’’ personalized ventilation system was introduced, which utilizes the clean and cool air supplied over the floor by the displacement ventilation (DV) principle [5]. The ‘‘ductless’’ PV sucks, transports and supplies the clean and cool air distributed over the floor area by the DV, to the breathing zone of the occupant. In this way, clean and cool air can be better utilized and the flexibility of desk layout is not
* Corresponding author. Department of Building Services, Slovak University of Technology in Bratislava, 813 68 Bratislava, Slovakia. Tel.: þ421 903 904 484; fax: þ421 252 961 137. 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.2009.06.023
affected. Previously, it has been shown that under steady-state conditions the ‘‘ductless’’ PV coupled with DV is able to provide clean and cool air to the breathing zone of seated occupant [5]. Displacement ventilation is in comparison with traditional mixing ventilation more sensitive to disturbances caused by physical activities of occupants [6] such as opening and closing a door, moving, walking, etc. Mattson and Sandberg [7] used a human simulator of cylindrical shape and Mattson et al. [8] a simulator of more human-like shape to study the impact of a moving person on the airflow pattern in rooms with DV. Bjørn et al. [9] used breathing thermal manikins in order to study the impact of movement on personal exposure to exhaled air. A real person was used in the study by Brohus et al. [6], in which the impact of several typical ‘‘movements’’ on the performance of DV was investigated. Mundt [10] studied particle re-suspension due to a walking person in a room with DV and their entrainment by thermal flows generated by heat sources (including occupants). Full-scale experiments combined with CFD simulation reported by Matsumoto et al. [11] revealed that the object’s moving mode and speed significantly influence the temperature and contaminant distribution in the room. The findings of these studies reveal that movement of a person has a substantial impact on the air distribution in rooms with displacement ventilation and may lead to a decrease of its ventilation performance.
428
´ , A.K. Melikov / Building and Environment 45 (2010) 427–436 B. Halvonˇova
The impact of walking person(s) in different walking scenarios on the performance of ‘‘ductless’’ PV in conjunction with displacement ventilation was studied with regard to concentration of pollution generated by active (heated) and passive (non-heated) pollution sources in the inhaled air. The effect of different walking scenarios on the heat loss from an occupant’s body and temperature distribution were examined as well. Some of the results are presented in this paper. 2. Methods The experiments were conducted in a full-scale test room (4.8 5.4 2.6 m3) located in a laboratory hall. An office room with two workstations; each consisting of a table with ‘‘ductless’’ PV (Fig. 1), a breathing thermal manikin and typical office heat sources were arranged in the room. Prior to the experiments the whole room was sealed. The ‘‘ductless’’ PV installed at each desk consisted of an air terminal device (ATD) mounted on a movable arm and a small axial fan incorporated in a short duct system (positions 1, 4 and 5 in Fig.1). The treated outdoor air supplied to the room near the floor by the DV spread in a relatively thin layer over the floor. The ‘‘ductless’’ PV sucked the clean air direct from this layer at the locations of the desks (position 6 in Fig. 1) and transported it to the breathing zone of the manikins. The ATD used during the experiments, named round movable panel (RMP), is described in Ref. [12]. The movable arm, to which the RMP was attached, allowed for free positioning of the RMP. During the present experiments the RMPs were positioned in front (0.4 m) and slightly above the faces of the manikins. This positioning was most often preferred by people [3,4]. The workstations were positioned behind each other as shown in Fig. 2. A semicircular wall unit with a radius of planar projection of 0.25 m and a height of 1 m, installed on the floor and attached to the middle of one of the walls, was used to supply outdoor treated air. The unit was fitted with nozzles that ensured the spread of the air mainly along the adjacent wall. The air was exhausted from the room by a square unit installed in the middle of the ceiling area. The recirculation of exhaust air to the supply air was not utilized in order to increase sensitivity of the tracer gas measurements.
2.1. Heat and contaminant sources The total heat load generated in the room, i.e. the heat generated by the desk lights, the PC (tower plus monitor), the breathing thermal manikins and the six fluorescent lighting fixtures (6 W each) evenly distributed over the ceiling, was 22.6 W/m2. The two breathing thermal manikins, each seated at one of the workstations on an upholstered office chair, were used to simulate two occupants. The manikins’ bodies are shaped as a 1.7 m tall average size Scandinavian woman and are divided into several individually heated segments (17 or 23 segments). During the measurements the surface temperature of the manikins was controlled to be the same as the skin temperature of an average person in a state of thermal neutrality [13]. Since the experiments simulated summer conditions, the clothing insulation of the manikins together with upholstered office chair insulation, was 0.59 clo in total [14]. Pollution from two sources with different behaviors, namely warm exhaled air (active pollution) and passive (unheated) point pollution source on the table, was simulated by using a constant emission of tracer gases. One of the manikins (referred to in the following as a polluting manikin, seated at workstation WS1) was equipped with an artificial lung. The simulated breathing cycle consisted of 2.5 s inhalation, 2.5 s exhalation and 1.0 s pause. The breathing frequency was 10 cycles per minute and the pulmonary ventilation was 0.6 L per breath. The exhaled air was traced with a constant dose of 0.135 mL/s sulphur hexafluoride (SF6). To ensure the density of air exhaled by people (1.144 kg/m3) the air exhaled by the polluting manikin was heated. The air was exhaled from the nose of the polluting manikin and inhaled through the mouth. The pollution from the passive point pollution source in front of the polluting manikin was simulated by tracer gas Freon. This tracer gas was released from a small perforated ball to ensure a uniform dispersion. The second manikin was used in all experiments as an exposed manikin and was seated at workstation WS2 (Fig. 2). 2.2. Experimental conditions The walking person(s) with natural body movement and wake behind their body generated more realistic disturbances in comparison with the regular and monotonous movement of the human simulators used in previous studies [7,9]. During all experiments 80 L/s of treated outdoor air at 20 C was supplied to the room by the DV, aiming at an exhaust air temperature of 26 C. The temperature in the tall hall was controlled to be 25 C. Experiments with displacement ventilation only, i.e. the reference case (RF), and displacement ventilation together with the ‘‘ductless’’ PV at the two desks supplying each 15 L/s personalized air (PV_15_15) were performed. These are listed in Table 1. Three walking scenarios were simulated (Fig. 3): scenario 1 (W1_1P) – one person walking along the room between the displacement diffuser and the two workstations; scenario 2 (W2_1P) – one person walking along the room far from the displacement diffuser; scenario 3 (W_2P) – two persons walking at the same time along the room on the two sides of the workstations (the paths of scenarios 1 and 2). In order to avoid errors due to differences in the walking pattern and the behavior, the same person walked during the experiments of the three scenarios. In scenario 3 a second person joined the experiments. 2.3. Experimental procedure
Fig. 1. ‘‘Ductless’’ PV system: (1) air terminal device, (2) heat sources, (3) table, (4) installed fan, (5) short duct system, (6) intake of ‘‘ductless’’ PV, (7) floor level.
The procedure applied during the experiments with the three walking scenarios was identical. After steady-state conditions were achieved, measurements were performed without a walking person. The results obtained are referred to in the following as
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 427–436
429
Fig. 2. Set-up of test room: (1) polluting manikin, (2) exposed manikin, (3) air terminal device of ‘‘ductless’’ PV, (4) movable arm of ‘‘ductless’’ PV, (5)–(7) heat sources, (8) displacement diffuser, (9) exhaust unit, (10) ceiling illumination, (T) measuring point for temperature distribution.
‘‘Before’’. The person was then asked to enter the room, to close the door and to start walking normally (measured walking speed of approximately 1.3 m/s) on the side of the workstations (at a distance of approximately 1 m) defined by the scenario 1 (Fig. 3). The tracer gas measurements were initiated after 20 min and lasted for approximately 40 min. The air temperature and the manikins’ heat loss measurements from the last 15 min of the hour were used in the analyses. The results obtained are referred as W1_1P. After 1 h the person was asked to leave the room. Measurements without a walking person were initiated again when steady-state conditions were reached in the test room. The results of these measurements are referred in the following as ‘‘Between’’. The person was then asked to enter the room again and to walk for 1 h according to the scenario 2 (Fig. 3). The measurement procedure had the same timing as for W1_1P. The results of these measurements are referred to in the following as W2_1P. The experimental procedure with two persons was shorter. After steady-state conditions were achieved, measurements were performed without walking persons. The results obtained are referred to in the following as ‘‘Before’’. The two persons were then asked to enter the room, to close the door and to start walking normally (measured walking speed of approximately 1.3 m/s) on the two sides of the workstations defined by the scenarios 1 and 2 (Fig. 3). The measurement results obtained when following the same procedure as one walking person are referred to as W_2P.
2.4. Measured parameters and measuring equipment The vertical temperature distribution was measured at the location ‘‘T’’ (Fig. 2), i.e. close to the exposed manikin. The air temperature was measured at 12 heights above the floor: 0.05, 0.1, 0.2, 0.3, 0.5, 0.6, 0.85, 1.1, 1.4, 1.7, 2.1 and 2.4 m. The concentrations of tracer gases and air temperature were measured in the supply and the exhaust, in the intakes of both ‘‘ductless’’ PV systems and in the tall hall. The tracer gas concentration was measured in the air
Table 1 Studied experimental cases, personalized airflows at workstations in L/s. Cases Before W1_1P Between W1_1P Before W_2P
Reference case (RF) Polluting/exposed manikin No walking – 0/0 L/s Walking – 0/0 L/s No walking – 0/0 L/s Walking – 0/0 L/s No walking – 0/0 L/s Walking – 0/0 L/s
PV_15_15 Polluting/exposed manikin No walking – 15/15 L/s Walking – 15/15 L/s No walking – 15/15 L/s Walking – 15/15 L/s No walking – 15/15 L/s Walking – 15/15 L/s
inhaled by both manikins but the temperature of inhaled air was recorded only for the exposed manikin. The temperature distribution at the location T was measured by thermocouples. All other temperature measurements were performed with medical thermistors. The concentration of tracer gases was measured with a multi-gas monitor based on the photoacoustic infrared detection method of measurement. The dry heat loss from the whole body and the body segments of the manikins was measured together with the surface temperature. The thermal environment of the seated occupant at both workstations in the room was evaluated in terms of the manikin-based equivalent temperature (MBET) determined for each of the body segments and the whole body of thermal manikins [13]. MBET is defined as the uniform temperature of an imaginary enclosure with air velocity equal to zero in which a person will exchange the same dry heat by radiation and convection as in the actual non-uniform environment. It is assumed that the body posture, the activity level and the clothing design and thermal insulation are the same in both environments. For each body segment the manikin-based equivalent temperature, MBETi, is calculated using the following equation:
MBETi ¼ tsk;i
Qt;i hcal;i
(1)
where tsk,i [ C] is the surface temperature measured for the i-th segment, Qt,i [W/m2] is the sensible heat loss (power consumption) of the i-th segment and hcal,i [W/Km2] is a dry heat transfer coefficient, determined during calibration of the manikin in a uniform thermal environment. The MBETbody for the whole body is obtained by computing the area-weighted average over all the body segments. The manikins were calibrated before the start of the measurements.
2.5. Criteria for assessment The performance of the ‘‘ductless’’ PV was evaluated in regard to the inhaled air quality and thermal comfort of a seated occupant by using both thermal manikins. In this paper, the concentrations of tracer gases measured in the inhaled air are expressed in terms of normalized concentration defined by the following equation (2):
Normalized concentration ¼
CI Cs Ce Cs
(2)
where CI is the tracer gas concentration in the inhaled air, Ce is tracer gas concentration in the exhaust air and Cs is tracer gas concentration in the supply air. The lower the value of the
´ , A.K. Melikov / Building and Environment 45 (2010) 427–436 B. Halvonˇova
430
loss from both thermal manikins were recorded for 15 min at the end of each measurement interval. The duration and sampling frequency of each measurement were considered in order to estimate each quantity with high accuracy. The data were analyzed in accordance with ISO guidelines for the expression of uncertainty [15]. 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. 3. Results 3.1. Temperature distribution
Fig. 3. Walking scenarios, i.e. scenario 1 (W1_1P) and scenario 2 (W2_1P).
normalized concentration, the less pollution is inhaled by the manikin. The inhaled and room air temperatures were expressed in terms of normalized temperature by using the following equation (3):
Normalized temperature ¼
XI XS Xe XS
(3)
where XI is the temperature in the inhaled air or in the point, Xe is temperature measured in the exhaust unit and XS is the temperature measured in the displacement diffuser. The lower the value of the normalized temperature, the cooler is the inhaled or room air. The body cooling effect of the ‘‘ductless’’ PV was quantified by the change in the whole body and the segmental MBET from the condition when only displacement ventilation was used i.e. DMBET1 ¼ MBETDV MBET‘‘ductless’’ PV. DMBET1 was determined for all three walking scenarios as well as separately in the case with no disturbances caused by moving person(s). Positive values of DMBET1 will express the cooling effect of the ‘‘ductless’’ PV and negative values will mean that more cooling was provided when only DV was used. The body cooling effect caused by walking person(s) was quantified by the change in the whole body and the segmental MBET from the condition without walking, i.e. DMBET2 ¼ MBETwalking MBETno walking. DMBET2 was determined separately in the case of DV alone and the case of ‘‘ductless’’ PV in conjunction with DV. Positive values of DMBET2 will mean that the cooling of the manikin with walking is less than without walking and negative values will mean that the walking causes more cooling in compared to without walking. 2.6. Precision of measurement At each of the measured points the tracer gas concentration was determined as an average of eight repeated measurements. The temperature of air inhaled by the exposed manikin, the temperature at ‘‘ductless’’ PV intakes, the vertical temperature distribution and the segmental and whole-body surface temperatures and heat
The vertical distribution of temperature measured at the location T is shown in Fig. 4. The comparison in the figure is made for two cases without walking person(s) marked as ‘‘Before’’ and 4 scenarios with walking person(s): one when only DV was used (RF) and three when ‘‘ductless’’ PV was used in conjunction with DV (PV_15_15). The present results show some impact of ‘‘ductless’’ PV on temperature distribution between 0.3 and 1.1 m above the floor. Nevertheless, without walking, the vertical temperature difference between head and ankles of a seated occupant was identical. It was within the range recommended in ISO Standard 7730 [14] for a thermal environment of category B. The temperature increased near the floor level and the vertical temperature gradient in the room decreased when walking took place. The temperature distribution was disturbed by the walking person(s) in the same way, regardless of the applied ventilation system (case with one person walking far from the displacement diffuser – W2_1P is shown as an example in Fig. 4 for both DV alone and for ‘‘ductless’’ PV). On the other hand the location of the walking person with regard to the displacement diffuser was important. The disturbance caused by a person walking on the side of the displacement diffuser W1_1P (Fig. 3) was much stronger than the disturbance caused by a person walking on the opposite side of the workstations W2_1P (Fig. 3). The person walking on the side of the displacement diffuser almost destroyed the temperature stratification, i.e. the temperature distribution became close to that in a room with mixing ventilation. In this case, the second person walking on the opposite side of the workstations (W_2P) did not add to the disturbance. The temperature distribution was less affected in the case W2_1P. In this case, the temperature stratification was preserved though substantial mixing also occurred, especially at heights above 0.3 m due the air movement caused by the body of the walking person. The results in the figure show that the disturbance of the walking person on the vertical temperature distribution in the case of DV alone and ‘‘ductless’’ PV in conjunction with DV was the same. As previously suggested [5], the DV design procedure can be applied also when ‘‘ductless’’ PV is used in conjunction with DV. 3.2. Concentration in inhaled air – one walking person Figs. 5 and 6 show the normalized concentration of the two simulated pollutions in the air inhaled by the polluting and the
Table 2 Sampling frequency, duration of data acquisition, and typical values of expanded absolute uncertainty with a 95% level of confidence. Quantity
Frequency of date acquisition
Duration of measurement period
Uncertainty (conf. level 96%)
Concentrations (inhaled) Temperature (inhaled and room) MBET
5 min 5 Hz 20 s
35–45 min 1 min 2 min
See Result 0.3 C 0.23 C
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 427–436
Fig. 4. Temperature distribution obtained at location T (Fig. 2).
exposed manikins, respectively. The disturbance caused by a person walking according to scenarios 1 (W1_1P) and 2 (W2_1P) is compared in the figures. The uncertainty of the results obtained is indicated. In comparison with displacement ventilation alone, the ‘‘ductless’’ PV was able to protect better the polluting manikin from re-inhalation of its exhaled air in the case of a walking person (Fig. 5 – W1_1P, W2_1P), while in a calm environment, better protection was ensured by the DV alone (Fig. 5 – Before and Between). In a calm environment, the personalized flow supplied from front/above against the manikin’s face mixed with the exhaled air. Therefore more exhaled air was re-inhaled by the polluting manikin. As expected, the walking person introduced mixing in the room and therefore the concentration of the exhaled air inhaled by the polluting manikin increased in both cases, DV alone (RF) and ‘‘ductless’’ PV in conjunction with the DV (PV_15_15). It was closer to 1, i.e. mixing ventilation, in the scenario 1 (W1_1P). The mixing caused by the person walking on the opposite side of the workstation (W2_1P) was less. The results obtained for the passive pollution source were quite different. In a calm environment the pollution without any initial momentum and generated close to the polluting manikin’s body was entrained by the free convection flow around his body and transported upward. As a result, the pollution concentration in the air inhaled by the polluting manikin increased considerably with
431
DV alone. The flow of clean air supplied by the ‘‘ductless’’ PV penetrated the polluted free convection flow and provided clean air for inhalation. The walking person caused mixing of the room air, resulting in less pollution in the inhaled air in the case of DV alone. In this case, the normalized concentration of passive pollution inhaled by the polluting manikin decreased because the air in the vicinity of its body was more diluted. The decrease was greater when the person was walking near the displacement diffuser (W1_1P), than when walking on the opposite side of the workstations (W2_1P). The impact of a walking person on the passive pollution concentration in air inhaled by the polluting manikin in the case with ‘‘ductless’’ PV was observed only with a person walking close to the displacement diffuser (W1_1P). In this case the flow disturbance due to the walking increased the concentration of passive pollution inhaled by the polluting manikin almost twice from 0.49 to 0.94. The results obtained reveal that with regard to the passive pollution the ‘‘ductless’’ PV was superior to the displacement ventilation alone. The results obtained with the exposed manikin show that in general DV alone performed better than the ‘‘ductless’’ PV in conjunction with DV in the absence of a walking person and the opposite was true in the presence of a walking person (Fig. 6). The walking person introduced substantial mixing in the room which greatly increased the concentration of pollution inhaled by the exposed manikin. The distance of the walking person from the displacement diffuser was important: the concentration of the air exhaled by the polluting manikin and of the passive pollution in the air inhaled by the exposed manikin was higher when the person was walking close to the displacement diffuser (W1_1P) than when the same person was walking along the opposite side of the workstations (W2_1P). The reason is that the stratified flow of clean and fresh air supplied by the displacement diffuser was less disturbed on its way to the intake of the ‘‘ductless’’ PV when the person was walking away from displacement unit (W2_1P). 3.3. Concentration in inhaled air – two walking persons The impact of the airflow disturbance due to walking of two persons on the quality of air inhaled by the polluting manikin and the exposed manikin is shown in Fig. 7. The normalized concentration of both pollution sources is compared in the figure between the reference case of DV alone (RF) and the case of ‘‘ductless’’ PV in conjunction with DV (PV_15_15). The results obtained ‘‘Before’’ the two persons started to walk and when the two persons were walking are included in the figure. The uncertainty of the measurements is indicated.
Fig. 5. Normalized concentrations of both pollutions in air inhaled by the polluting manikin. Comparison between the case when only DV was applied (RF) and the case when the ‘‘ductless’’ PV was used in conjunction with DV (PV_15_15).
432
´ , A.K. Melikov / Building and Environment 45 (2010) 427–436 B. Halvonˇova
Fig. 6. Normalized concentrations of both pollutions in air inhaled by the exposed manikin. Comparison between the case when only DV was applied (RF) and the case when the ‘‘ductless’’ PV was used in conjunction with DV (PV_15_15).
As expected, the walking of two persons caused substantial disturbance of the airflow in the room resulting in an increase of personal exposure. In general, the increase of personal exposure was greater in the case of DV alone than in the case of ‘‘ductless’’ PV. The only exception was observed with regard to the passive pollution inhaled by the polluting manikin in the case of DV alone. In this case the mixing introduced due to the walking persons diluted the pollution at the breathing zone more in comparison with a calm environment, which resulted in an improvement of inhaled air quality. The normalized concentration decreased from 6.8 without walking (Before) to 1.4 with walking persons (W_2P). The walking of the two persons had less impact on the quality of air inhaled by the exposed manikin than by the polluting manikin which was located closer to the pollution sources. The inhaled air quality of both manikins was affected by two walking persons similar to the case when only one person was walking according to scenario 1 (W1_1P). The comparison between those two scenarios is shown in Fig. 8. The uncertainty of measurement is indicated. The results in the figure show that the presence of a second walking person in the room had a slight impact on quality of the air inhaled by the two seated manikins. The normalized concentration obtained with one walking person and two walking persons did not differ much. The only exception was
observed with the polluting manikin for the concentration of the passive pollution with DV alone (Fig. 8, left). Here the walking of the second person increased the mixing of the passive pollution generated in front of the polluting manikin with the surrounding room air, leading to increased dilution and better inhaled air quality. The normalized concentration decreased from 3.1 to 1.4. The comparison of the results in the figure reveals that the inhaled air quality obtained with the ‘‘ductless’’ PV was equal to or even better than with DV alone. 3.4. Inhaled air temperature Table 3 lists the temperatures of the air inhaled by the exposed manikin obtained in a calm environment and with the three walking scenarios. The air mixing introduced by the walking person(s) resulted in an increase of the inhaled air temperature. This increase was small with DV alone, around or less than 0.3 C with one walking person (comparable with the uncertainty of the temperature measurement which is 0.3 C) and 0.5 C with two walking persons. The impact of walking on the inhaled air temperature was greater in the case of ‘‘ductless’’ PV. The disturbance introduced by the walking person between the displacement diffuser and the workstations (W1_1P) increased the temperature
Fig. 7. Normalized concentrations of both pollutions in air inhaled by the polluting (left) and the exposed (right) manikins.
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 427–436
433
Fig. 8. Normalized concentrations of both pollutions in air inhaled by the polluting (left) and the exposed (right) manikins.
of the air inhaled by the exposed manikin by 1.7 C. The increase of the inhaled temperature was less (0.7 C) when the person was walking on the opposite side of the workstations (W2_1P). However, in all studied cases the inhaled air temperature with the ‘‘ductless’’ PV remained 2.9–4.5 C lower than with DV used alone. Fig. 9 compares the air temperature measured at a height of approximately 0.1 m above the floor (‘‘ductless’’ PV intake) at the exposed workstation (WS2) with and without walking person(s) in the case of DV alone and in the case of the ‘‘ductless’’ PV in conjunction with DV. Similar temperatures were measured at the polluting workstation (WS1). The results in the figure show that the disturbance of the displacement flow due to the walking of the person(s) resulted in a substantial temperature increase at a height of approximately 0.1 m. The temperature increase was between 0.5 C and 2.1 C. The person walking near the displacement diffuser (W1_1P) caused a greater increase of the air temperature than did a person walking far away from the displacement diffuser (W2_1P). The walking of the second person (W_2P) did not change the air temperature at the intake when the ‘‘ductless’’ PV was used. Some increase was observed only for the case of displacement ventilation used alone. The results in Fig. 9 reveal that the air temperature measured at the location of the ‘‘ductless’’ PV intake in the case of DV alone and the case of ‘‘ductless’’ PV were rather similar. However, as already discussed, the differences in the inhaled air temperature were substantial (Table 3). The analyses of the results in Table 3 and Fig. 9 reveal that in the case of DV alone the change of the air temperature at approximately 0.1 m due to walking had only a slight effect on the inhaled air temperature. The inhaled air was heated mainly by the manikin’s body. In the case of ‘‘ductless’’ PV, the walking of a person had a much greater impact on the inhaled air temperature. The increase of the air temperature at the intake
Table 3 Values of air temperature inhaled by the exposed manikin expressed in C.
Before (without walking) W1_1P (with walking) Between (without walking) W1_1P (with walking) Before (without walking) W_2P (with walking)
RF ( C)
PV_15_15 ( C)
30.3 30.6 30.4 30.6 30.3 30.8
26.0 27.7 25.9 26.6 26.0 27.9
immediately increased the temperature of the inhaled air which in fact was mainly personalized air. Due to the heat exchange between the environment and the components of the ‘‘ductless’’ PV and the heating from the fan, the supplied personalized air was warmer. 3.5. Thermal comfort In Fig. 10 the cooling effect provided by the ‘‘ductless’’ PV for the body segments exposed to the personalized airflow and for the whole body of the exposed manikin is shown. The difference in MBET determined with DV alone and with the ‘‘ductless’’ PV (DMBET1 – defined in Criteria for assessment) is shown. The cooling effect of the ‘‘ductless’’ PV for the segments not shown in the figure was negligible. The results obtained with the two manikins were rather similar; therefore only the results obtained with the exposed manikin are shown. DMBET1 determined for the case without walking person(s) – named as ‘‘No walking’’ is in Fig. 10 (left) compared with the cases with one walking person either close to the displacement diffuser (W1_1P) or on the opposite side of the workstations (W2_1P) and in Fig. 10 (right) with the case with two walking persons (W_2P). The results in the figure reveal a substantial local cooling effect of the ‘‘ductless’’ PV compared to the DV alone. The maximum cooling is obtained for the body segments directly exposed to the personalized airflow. The cooling effect for the segments at the head region is equivalent to the decrease in the room air temperature in the range 2–10 C. The results also reveal that the whole-body cooling effect of the ‘‘ductless’’ PV was around 0.5 C. The results in Fig. 10 identify that the walking had smaller impact on the cooling effect than the personalized flow itself. The change in the whole-body and the segmental MBET due to the walking, DMBET2, (defined in Criteria for assessment) was used to assess the impact of the flow disturbances due to walking on occupants’ thermal comfort. DMBET2 obtained for the case of DV alone and for the case of ‘‘ductless’’ PV when the person was walking close to the displacement diffuser (W1_1P) is compared in Fig. 11. The same comparison but with a person walking on the opposite side of the workstations (W2_1P) is shown in Fig. 12. Positive values of DMBET2 mean that the walking decreases the heat loss from the manikin’s body, and negative values mean that the walking increases the heat loss.
434
´ , A.K. Melikov / Building and Environment 45 (2010) 427–436 B. Halvonˇova
higher changes in the whole-body heat loss due to the walking person were measured with the scenario 2 (W2_1P). For this walking scenario it was also observed that the decreases of heat loss between body segments were less pronounced. 4. Discussion
Fig. 9. Comparison between temperatures measured at intake of the ‘‘ductless’’ PV at the exposed manikin workstation (WS2).
In general, the results in Figs. 11 and 12 show that the air mixing due to walking decreased the heat loss from the manikin’s body (with few exception DMBET2 values were positive). The impact of the walking on DMBET2 differs for the different body segments. It was also different in the RF (DV alone) and in the case of ‘‘ductless’’ PV. For both, the walking caused mixing of the cool air near the floor with the warmer air from the higher levels and increased the air temperature at the lower heights in the room (see Figs. 4 and 9). This resulted in a decrease of the heat loss corresponding to the effect of an approximately 1 C and 0.5 C increase of the MBET measured for the lower body segments (foot, lower leg, etc.) when the person was walking according to scenarios 1 (W1_1P) and 2 (W2_1P) respectively. With the ‘‘ductless’’ PV the walking of the person decreased the heat loss from the head region (face, neck), i.e. the body segments exposed to the personalized flow. The decrease of the heat loss corresponded to the effect of an increase of air temperature of up to 2.6 C (for the left face) when the person was walking according to the scenario 1 (W1_1P). This means that the air movement generated by a walking occupant will affect the performance of the personalized ventilation used, not only with regard to the inhaled air quality but also with regard to the body cooling. As already discussed, this is mainly a result of the increase of the air temperature at the ‘‘ductless’’ PV intake (Table 3, Fig. 9). Comparison of the results in Figs. 11 and 12 shows also that the change in the heat loss from the manikin’s body due to walking of the person depends on the location of that person. For some of the body segments (feet, lower legs, head, etc.) the DMBET2 values were higher with the scenario 1 (W1_1P) and for the other body segments (hands, forearms, chest) they were higher for the scenario 2 (W2_1P). Slightly
It has been documented that personalized ventilation can provide people with cleaner air and better thermal comfort than the total volume ventilation systems [1,3,4,16]. It has also been shown that PV can protect occupants from airborne transmission of infectious agents [17]. In practice, PV can be easily implemented in rooms with under floor ventilation. However, its implementation in rooms with mixing or displacement ventilation is less acceptable because the required additional ducting affects the indoor environment aesthetically. The ‘‘ductless’’ PV introduced in conjunction with DV overcomes the above disadvantage. Halvonova and Melikov [5] documented that under steady-state conditions the inhaled air with the ‘‘ductless’’ PV was as clean as the air inhaled with DV alone and even cleaner depending on the layout of the workstations (the definition of the normalized concentration in their study is different from that used in the present study and therefore the results cannot be directly compared). They also reported that in comparison with DV alone the use of the ‘‘ductless’’ PV decreased substantially the temperature of the inhaled air and increased the body cooling, i.e. it had also the potential for improving perceived air quality (PAQ) and occupants’ thermal comfort. In the present study the performance of the ‘‘ductless’’ PV in conjunction with DV was compared with the performance of DV alone under dynamic and realistic conditions in practice. As expected, the walking person(s) disturbed the boundary layer of clean air supplied over the floor from the displacement diffuser and caused mixing of the simulated pollution with the room air. This resulted in a substantial decrease of the vertical temperature gradient and an increase of the pollution concentration in the inhaled air. The only exception was the decrease of the passive pollution in the air inhaled by the polluting manikin, because the intensified air mixing (due to walking) increased the dilution of this pollution generated in front of the breathing zone of the manikin. The DV, when used alone, was more vulnerable to the disturbance introduced by the walking person(s) than when it was combined with the ‘‘ductless’’ PV. The concentration of the generated pollution in the air inhaled by the manikins was lower with ‘‘ductless’’ PV than when the DV was used alone.
Fig. 10. Cooling effect caused by ‘‘ductless’’ PV on exposed manikin’s body segments and whole body.
B. Halvonˇova´, A.K. Melikov / Building and Environment 45 (2010) 427–436
435
Fig. 11. Change in the heat loss from the manikin’s body as a result of a person walking according to scenario 1 (W1_1P).
It has been well documented that the PAQ depends on the temperature and humidity of the inhaled air as well as on the pollution level [18]. Cool and dry air is perceived to be of a higher quality than warm and humid air. The air mixing caused by the walking person(s) diminished the vertical temperature gradient in the vicinity of the workstations and increased the air temperature at floor level. In the case of DV alone, this had no substantial effect on the temperature of the inhaled air that was heated mainly by the manikin’s body. However, disturbances due to walking increased the air temperature at the ‘‘ductless’’ PV intakes and thus the inhaled air temperature which depended only on the temperature of the personalized flow since it was relatively high (15 L/s). Under all the conditions studied the temperature of the air inhaled by the manikins with the ‘‘ductless’’ PV was lower than the inhaled air temperature with DV alone. In practice, occupants provided with control may select a personalized flow rate lower than 15 L/s. In this case, the inhaled air temperature will be higher due to the interaction of the personalized flow with the free convection flow. Nevertheless, it will be lower than the inhaled air temperature with DV alone. Recent studies [19,20] reveal that elevated facial velocity improves PAQ and diminishes the negative impact of increased temperature and humidity of the inhaled air. Thus in practice the ‘‘ductless’’ PV combined with DV will be superior to DV alone as regards perceived inhaled air quality by occupants, because it will provide cleaner and cooler air at elevated velocity. The air mixing due to the person(s) walking decreased the heat loss from the manikins, especially the local heat loss from the body
segments directly exposed to the flow near the floor (feet, lower legs) or the personalized flow (head). In practice, this may be beneficial because the main problem with DV is draught at the feet, which are exposed to cool air with relatively high velocity. The combination of the ‘‘ductless’’ PV and DV can be operated at elevated supply air temperatures (e.g. 23 C), which will increase the air temperature in the room (e.g. 28 C). In this case, risk of draught at the feet level will be diminished while the convection cooling of the body provided by the personalized flow of cooler air under the control of the occupant will ensure preferred thermal comfort conditions. This strategy has the potential for energy saving because less cooling of the supplied displacement air is required and the free cooling during several months of the year can be utilized. Three walking scenarios were applied in the present study. In this way, the impact of the distance between the walking person and the displacement diffuser as well as the strength of the disturbance caused by one or two persons was studied. The person walking between the displacement diffuser and the workstations had the greatest impact on the vertical temperature distribution, temperature and pollution concentration in the inhaled air and the heat loss from the manikin’s body. This impact changed little when the second person was included in the experiments. Therefore in practice, it may be recommended to design furniture arrangements that will limit walking of occupants between displacement diffuser and workstations. In the present study the distance between the displacement diffuser and the workstations was not changed. It
Fig. 12. Change in the heat loss from the manikin’s body as a result of a person walking according to scenario 2 (W2_1P).
436
´ , A.K. Melikov / Building and Environment 45 (2010) 427–436 B. Halvonˇova
may be expected that it could also be important for the impact of the walking on the performance of the DV and the ‘‘ductless’’ PV. 5. Conclusions The performance of ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation was compared with the performance of displacement ventilation alone under realistic conditions comprising airflow disturbances due to walking of the person(s) under different scenarios. The walking person(s) increased the mixing of the clean air near the floor with the polluted air at a higher level and disturbed the displacement principle, resulting in a decrease of the quality of air inhaled by manikins. Under these conditions, the performance of the ‘‘ductless’’ personalized ventilation was better than the performance of the displacement ventilation used alone. The walking person(s) diminished the vertical temperature gradient in the vicinity of the workplaces and increased the inhaled air temperature. Under all the conditions (with and without walking) the temperature of the air inhaled by the manikins with the ‘‘ductless’’ personalized ventilation was lower than with displacement ventilation alone. Thus in practice the ‘‘ductless’’ personalized ventilation will be superior to displacement ventilation alone with regard to the perceived air quality. The air mixing due to walking of occupant(s) decreased the heat loss from the thermal manikins, especially the local heat loss from the body segments directly exposed to the flow near the floor or to the personalized flow. At elevated room temperatures the ‘‘ductless’’ personalized ventilation in conjunction with displacement ventilation will provide occupants with better thermal comfort than displacement ventilation alone because of the increased local body cooling by the personalized flow. Under these conditions, draught discomfort at the feet can be avoided and energy savings may be achieved. The location of walking persons is important for the performance of both the displacement ventilation alone and the ‘‘ductless’’ personalized ventilation. Person walking close to the displacement diffuser will cause greater disturbance. Acknowledgement This research was partly supported by the Danish Technical Research Council (STVF).
References [1] Melikov A, Cermak R, Mayer M. Personalized ventilation: evaluation of different air terminal devices. Energy and Buildings 2002;34(8):829–36. [2] Melikov AK. Personalized ventilation. Indoor Air 2004;14(7):157–67. [3] Kaczmarczyk J, Melikov A, Fanger PO. Human response to personalized and mixing ventilation. Indoor Air 2004;14(8):1–13. [4] Kaczmarczyk J, Melikov A, Bolashikov Z, Nikolaev L, Fanger PO. Human response to five designs of personalized ventilation. International Journal of Heating, Ventilation and Refrigeration Research 2006;12(2):367–84. [5] Halvonova B, Melikov AK. ‘‘Ductless’’ personalized ventilation in conjunction with displacement ventilation. In: Proceedings of Indoor Air, Copenhagen, Denmark, 2008. [6] Brohus H, Hyldig ML, Kamper S, Vachek UM. Influence of persons’ movements on ventilation effectiveness. In: Proceedings of Indoor Air, Copenhagen, Denmark, 2008. [7] Mattson M, Sandberg M. Displacement ventilation – influence of physical activity. In: Proceedings of Roomvent, Krakow, Poland, Vol. 1, 1994, 78–92. [8] Mattson M, Bjørn E, Sandberg M, Nielsen PV. Simulating people moving in displacement ventilated rooms. In: Proceedings of Healthy Buildings, Washington, USA, Vol. 1, 1997, 495–500. [9] Bjørn E, Mattson M, Sandberg M, Nielsen PV. Displacement ventilation – effects of movement and exhalation. In: Proceedings of Healthy Buildings, Washington, USA, Vol. 2, 1997, 163–168. [10] Mundt E. Non-buoyant pollutant sources and particles in displacement ventilation. Building and Environment 2001;36:829–36. [11] Matsumoto H, Kozaka T, Nakao T. Study on air distribution and ventilation effectiveness in displacement ventilated rooms with a moving object. In: Proceedings of Indoor Air, Copenhagen, Denmark, 2008. [12] Bolashikov Z, Nikolaev L, Melikov A, Kaczmarczyk J, Fanger PO. New air terminal devices with high efficiency for personalized ventilation application. In: Proceedings of Healthy Buildings, Singapore, 2003, 850–855. [13] Tanabe S, Arens EA, Bauman FS, Zhang H, Madsen TL. Evaluating thermal environments by using a thermal manikin with controlled skin surface temperature. ASHRAE Translation 1994;100(1):39–48. [14] ISO. ISO 7730 Moderate thermal environments – Determination of the PMV and PPD indices and specification of the conditions for thermal comfort, International Organization for Standardization, Gene´ve, Switzerland, 2005. [15] ISO. Guide to the expression of uncertainty in measurement, International Organization for Standardization, Gene´ve, Switzerland, 1993. [16] 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. [17] Cermak R, Melikov A. Protection of occupants from exhaled infectious agents and floor material emissions in rooms with personalized and underfloor ventilation. HVAC & R Research 2007;13(1):23–38. [18] Fang L, Clausen G, Fanger PO. Impact of temperature and humidity on the perception of indoor air quality during immediate and longer whole-body exposures. Indoor Air 1998;8:276–84. [19] Melikov A, Kaczmarczyk J, Silva D. Impact of air movement on perceived air quality at different level of relative humidity. In: Proceedings of Indoor Air, Copenhagen, Denmark, 2008. [20] Melikov A, Kaczmarczyk J. Impact of air movement on perceived air quality at different level of air pollution and temperature. In: Proceedings of Indoor Air, Copenhagen, Denmark, 2008.