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Alternative personalized ventilation
Energy and Buildings 65 (2013) 37–44
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Alternative personalized ventilation Ferenc Kalmár ∗ , Tünde Kalmár University of Debrecen, Faculty of Engineering, Ótemeto˝ u. 2-4, 4028 Debrecen, Hungary
a r t i c l e
i n f o
Article history: Received 20 October 2012 Received in revised form 10 April 2013 Accepted 4 May 2013 Keywords: Personalized ventilation Draught Turbulence intensity ALTAIR
a b s t r a c t Draught is usually avoidable if proper thermal comfort is to be obtained. Nevertheless in hot environments people try to improve their thermal comfort increasing artificially the air movement around the head using fans. Using personalized ventilation systems extreme high values of air or mean radiant temperatures, or even high relative humidity values can be compensated by air flow velocity. Taking into account that the number of cold receptors in the skin exceeds the number of warm receptors and the velocity of cold information exceeds around ten times the velocity of warm information an innovative personalized ventilation system was developed. The air flow is coming alternatively from three different directions and the frequency of direction changing might be set on request. Experiments have shown that in high temperature environments using the developed equipment neutral or even slightly cold sensations might be obtained. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Experiments related to personalized ventilation (PV) were performed in years ‘70 when Givoni [1], Watson and Labs [2] and others developed a new idea for ventilation, respectively Arens [3] created the bioclimatic charts. The aim of their research was to analyze the compensation of extreme values of some microclimate parameters giving extreme values in opposite sense to other microclimate parameters (especially air temperature, radiation, humidity). Arens and his colleagues [4] proved that in closed spaces when the operative temperature exceeds 22.5 ◦ C people need higher air velocities than that prescribed in different standards [5,6]. They conclude that when temperature is higher than the mentioned value the risk of draught is minimal. Based on their measurements they published the diagram of comfort zone depending on the operative temperature and air velocity. For personalized ventilation systems the ventilation effectiveness is considered to be better than at traditional ventilation systems [7]. Besides Fanger and Olesen at the Danish Technical University, Melikov performed a series experiments and measurements related to personalized ventilation systems [8–11]. Based on their research new PV equipments were developed. Zhang et al. [12] shown that in closed spaces characterized by high temperatures the vertical temperature difference can be higher than the values prescribed in standards. They conclude that in rooms with 26.8 ◦ C ambient temperatures, assuming personalized ventilation the vertical temperature difference can be
∗ Corresponding author. Tel.: +36 52 415155; fax: +36 52 418643. E-mail addresses: [email protected] (F. Kalmár), kalmar [email protected] (T. Kalmár). 0378-7788/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.enbuild.2013.05.010
even 6 ◦ C. In closed spaces even at smaller net floor areas it is impossible to assure the neutral thermal comfort in each section of the room because the needs of the occupants are different. The assurance of similar microclimate parameters in each section of the room can lead in this way to local discomfort. Generally, the different microclimate parameters are needed because of the different view factor between a surface with critical temperature and occupants. Huizenga et al. [13] analyzed the effects of large glazed surfaces on the indoor microclimate and developed methods to reduce the negative effects of radiant heat transfer. The asymmetric radiation can be reduced using properly the personalized ventilation systems. One of the most important questions of personalized ventilation systems is related to draught. Fanger et al. [11] performed measurements related to draught and sensation of discomfort and based on these measurements the draught risk-air temperature–air velocity diagrams were developed [5]. To describe the turbulence intensity of air flow different mathematical models were developed and numerous experiments performed [14,15]. Using CFD methods the values of turbulence intensity were determined [16,17]. Griefahn et al. [18] analyzed the draught risk in case of 23 ◦ C air temperatures depending on the air velocity and turbulence intensity. They conclude that in case of 30% turbulence intensity the maximal value of air velocity is 0.2 m/s. Toftum and Nielsen proved that the draught risk is in relation with the general thermal comfort sensation [19]. They had shown that subjects who appreciate colder a microclimate than the average, sensible react to draught. Ruegg et al. showed that in case of persons sitting close to windows the frame of the windows is the critical surface which can have influence on the draught sensation. Griefahn et al. [20] performed experiments to determine the effects of turbulence intensity on work performance. They conclude that the turbulence has different
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effects on the active and passive parts of the human body. Wang et al. [21] analyzed the relation between turbulence intensity and local discomfort. Their research results shown that the skin temperature can be lower even with 2 ◦ C in spaces with similar temperatures if the turbulence intensity increases from 15% to 30%. Sun et al. [22] analyzed the performance of a personalized ventilation system at two different turbulence intensities. They conclude that increasing the turbulence intensity the skin temperature can be easily decreased. The fresh air can be made available at occupants using different air distribution systems installed in ceilings, floors, tables, chairs or partitions. Zhang et al. [23] based on measurements performed in 200 offices had shown that more than 50% of the occupants need higher air movement than existing and only 4% of the occupants need lower air movement in the closed space. Based on the existing research results we conclude that in closed spaces with high ambient temperatures personalized ventilation can be used even for cooling if the air turbulence intensity is correlated properly with the air temperature. The aim of our research was the development of an innovative personalized ventilation equipment where the occupants are exposed to an air flow controlled directly by the occupant but the direction of the air flow is continuously changing. The air flow comes in an alternate way from the left side, front and right side of the occupant. The frequency of the airflow direction changing can be chosen by the occupants. In the following the results of research work are presented.
2. Sensation of warm and cold The skin is the sensory organ for touch and is also the largest organ in the human body. Changes in temperature, pain, touch, and pressure can be detected by the skin. A thermoreceptor is a sensory receptor, or more accurately the receptive portion of a sensory neuron, that codes absolute and relative changes in temperature, primarily within the innocuous range. In the mammalian peripheral nervous system warmth receptors are thought to be unmyelinated C-fibers (low conduction velocity), while those responding to cold have both C-fibers and thinly myelinated A delta fibers (faster conduction velocity) [24]. According to Lynette Jones “the thermal sensory system is extremely sensitive to very small changes in temperature and on the hairless skin at the base of the thumb, people can perceive a difference of 0.02–0.07 ◦ C in the amplitudes of two cooling pulses or 0.03–0.09 ◦ C of two warming pulses delivered to the hand. The threshold for detecting a change in skin temperature is larger than the threshold for discriminating between two cooling or warming pulses delivered to the skin. When the skin at the base of the thumb is at 33 ◦ C, the threshold for detecting an increase in temperature is 0.20 ◦ C and is 0.11 ◦ C for detecting a decrease in temperature. The rate that skin temperature changes influences how readily people can detect the change in temperature. If the temperature changes very slowly, for example at a rate of less than 0.5 ◦ C/min, then a person can be unaware of a 4–5 ◦ C change in temperature, provided that the temperature of the skin remains within the neutral thermal region of 30–36 ◦ C. If the temperature changes more rapidly, such as at 0.1 ◦ C/s, then small decreases and increases in skin temperature are detected. However, warm and cold thresholds do not decrease any further, if the rate at which temperature changes is faster than 0.1 ◦ C/s” [25]. In hot environments people try to reduce the sensation of discomfort creating an artificial air movement around the head (using fan). The temperature receptors in the skin after a certain period of time due to the adaptation process will send other information about the environment to temperature center than the information sent initially. It would be very important to obtain the same sensation during the whole cooling process. To obtain a high efficiency of the cooling process using air movement around
the head we developed an innovative PV system, which introduce the air alternative from three directions around the head. The variation frequency of air flow direction can be chosen on request. 3. Alternative PV system In closed spaces with high ambient temperatures the PMV values cannot be reduced to values around 0 without cooling even at extremely high ACH values. Measurements have proven that using traditional ventilation systems (air introduced under the ceiling and evacuated under the ceiling (C–C ventilation), air introduced under the ceiling and evacuated above the floor (C–F ventilation), air introduced above the floor and evacuated under the ceiling) in a 3.0 m × 3.0 m × 2.5 m closed space with 28 ◦ C ambient temperature at ACH = 8 h−1 the PMV obtained in the middle of the room is around +1.3, [30]. Using personalized ventilation systems even in extreme conditions neutral thermal sensation can be obtained. Even though there is a strong relation between room geometry and obtained mean radiant temperature [31] at 28–30 ◦ C the ambient temperature (the same mean radiant and air temperature) is obtained. Melikov [27] discussed the existing knowledge on performance of personalized ventilation and human response to it. His review contains the description of airflow interaction with human body and its impact on thermal comfort and inhaled air quality. Tham and Pantelic [28] analyzed the performance of the coupling of a desktop personalized ventilation air terminal device and desk mounted fans. They used the personal exposure effectiveness as an indicator of ventilation effectiveness. They found that coupling of a desktop personalized ventilation air terminal device and desk mounted fans distributes cooling more uniformly across the body. Melikov et al. [29] evaluated different air terminal devices used for personalized ventilation. A breathing manikin was used to simulate human being. They obtained the highest personal exposure effectiveness in case of a vertical desk grill followed by an air terminal device designed as a movable panel. Their conclusion was that personalized ventilation may decrease significantly the number of occupants dissatisfied with the air quality. Khalifa et al. [26] developed a nozzle that achieves high breathing zone air quality. They have obtained a ventilation effectiveness close to 7. At the University of Debrecen, Laboratory of Building Physics an innovative PV system was tested from thermal comfort point of view. The main idea was to introduce the air alternatively from different directions constantly stimulating in this way the cooling sensation. We assumed that the reaction of the occupants is different in this case comparing with traditional PV systems, where the air is coming from a single direction. At first a simple air distribution equipment (Fig. 1 a and b) was developed which gives the possibility to introduce the fresh air from three directions around the subject (left, front, right). The variation of fresh air direction was obtained using a special air distribution device (ADD). The ADD has one opening for air flow which after entering in the ADD can be sent to one of air terminal devices (ATD) fixed on the working desk. The main elements of this device were two disks (Fig. 2). The first disk is fixed in the ADD box and has three orifices. On these orifices the air ducts (AD) are directly connected. The second disk is in rotation during the operation of ventilation system, but this rotation movement is programmed with a certain time step. This disk has only one orifice and is placed under the first disk. The air distribution device is installed on the main ventilation air duct and the air is sent to one of the ATD. The air terminal devices were fixed at certain distances from the head of the occupant. The time step for changing fresh air direction can be chosen between 1 s and 60 s. The distance between air terminal devices and occupants head was changeable but finally we found that for used air flow and velocity 0.6 m was accepted by all subjects.
F. Kalmár, T. Kalmár / Energy and Buildings 65 (2013) 37–44
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Fig. 4. Arrangement of measuring points in the room.
Fig. 1. (a) Arrangement of ATD on the sdesc (section). (b) Arrangement of ATD on the desk (view). D – desk; DT – desktop; AF – air flow; ATD – air terminal device; S – support; AD – air duct; ADD – air distribution device; RA – recirculated air flow; FA – fresh air flow.
Fig. 2. Main elements of ADD.
Based on this idea an office desk with self ALTAIR PV system was developed and patented. 4. Experiments The new PV system was compared with “traditional” ventilation systems (air introduced and evacuated under the ceiling and air introduced under the ceiling and evacuated above the floor). In the test room the ventilation system is equipped with double
heat recovery so the fresh air temperature obtained was lower only with 0.4 ◦ C, then the air temperature in the room. We have been working with 100% fresh air, but ALTAIR can work even with 100% recirculated air. Based on previous experiments carried out without occupants in the room [30] an ACH = 6 h−1 was chosen for C–C and C–F ventilation systems. The aim was to obtain in the occupancy zone as high air velocities as possible (to neutralize the high ambient temperature), but we wanted to avoid draught. The arrangement of air terminal devices in the room can be seen in Fig. 3. The air velocities had been measured at three different heights around the occupant (0.1 m, 0.6 m and 1.1 m) according to Fig. 4. The period of time during which the air flow is coming from a certain direction was set to 10 s. During experiments the following equipments had been used: - mean radiant temperature: TESTO SAVERIS, Globe probe Ø 150 mm, TC Type K, accuracy: ±1 ◦ C; - air temperature: TESTO SAVERIS, probe accuracy: ±0.4 ◦ C; - relative humidity: TESTO 435, probe accuracy: ±2%RH (+2 to +98%RH); - skin temperature: Testo 905-T2, accuracy: ±(1 ◦ C ± 1% of mv); - air velocity: TESTO 425, probe accuracy: ±(0.03 m/s +5% of mv); - air turbulence: TESTO 435, Comfort level probe for degree of turbulence measurement with telescopic handle (max. 820 mm) and stand, meets EN 13779 requirements, accuracy: ±(0.03 m/s +4% of mv); - CO2 concentration: TESTO 435, IAQ probe to assess indoor air quality, CO2 , humidity, temperature and absolute pressure mea-
Fig. 3. Arrangement of C–C and C–F ventilation in the test room.
F. Kalmár, T. Kalmár / Energy and Buildings 65 (2013) 37–44
0.06 0.05
0.04 0.03 0.02 0.01
0 0,1 m
1,1 m
Fig. 5. Air velocities (measurement 1).
occupants in summer in educational institutions or offices). The duration of a measurement was 2 h. In Fig. 5 the average air velocity values are presented in case of analyzed ventilation systems. The measured skin temperatures are shown in Fig. 6a and b. The differences between skin temperatures are presented in Fig. 7. It can be observed that in spite of higher mean air velocities of the air the skin temperatures are higher in case of traditional C–C systems. The first 15–30 min can be considered as adaptation period. The answers related to general thermal comfort sensation are presented in Fig. 8a and b.
36 35.5 35 34.5 34 33.5 33 32.5 32 31.5 31
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4.1. First series of measurements
Time, [min]
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b Temperature, oC
First we compared the new PV system with the traditional ventilation system when the air is introduced and evacuated under the ceiling (C–C ventilation). The ambient temperature was fixed to 30 ◦ C (because of the hysteresis, the variation of temperature values during measurements was between −0.58 ◦ C and +0.49 ◦ C). In case of C–C ventilation system an ACH = 6.0 h−1 was assured (135 m3 /h) while for PV system we used only 20 m3 /h. The measurements were performed involving 19 subjects (10 boys and 9 girls). During measurements we measured the skin surface temperatures of left hand, brow and nose, turbulence intensity and black globe temperature at 1.1 m, CO2 concentration on the desktop. We choose to measure the skin temperature of left hand, brow and nose because at these body segments the number of cold receptors in the skin is high and we assumed that the influence of ALTAIR on the thermal response of subjects is the highest. The activity level of the subjects was 1.2 met (students have been solving problems or writing during measurements) and the clothing thermal resistance was 0.5 clo, which can be assumed to be the thermal resistance of clothing worn by
0,6 m Measuring heights
0:30
The subjects involved were Hungarian students. Before experiments all data related to age, height and weight had been collected, the blood pressure was measured before and after each measurement using OMRON M10-IT equipment. Also subjects had to give answers related to smoking, coffee consumption, preferred temperatures in summer, preferred temperatures in winter, diseases. In order to perform all these preparation activities subjects arrived in the Laboratory before each experiment 30 min earlier and this period was used also for acclimatization to indoor microclimate. The subjects had filled in questionnaires from 15 to 15 min. The aim of measurements was to test the obtained thermal comfort sensation at high temperatures which may occur during summer in closed spaces if air conditioning systems are not installed. We have chosen temperatures between 28 and 30 ◦ C because on this interval of temperatures the heat loss of human body by convection, conduction and radiation is getting small and heat loss by evaporation is getting higher. We assumed that in this case the developed alternative PV (ALTAIR) will give very good results. The answers related to thermal comfort sensation had been assessed statistically using the box plot method. In descriptive statistics, a box plot or is a convenient way of graphically depicting groups of numerical data through their five-number summaries: the smallest observation (sample minimum), lower quartile, median, upper quartile and largest observation (sample maximum).
PV venlaon
0.07
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4. 5.
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3.
Mark on the 7 points thermal comfort scale your thermal comfort sensation Is the air velocity acceptable? Yes No If not, what should do with it? Increase Decrease Do you feel draught? Yes No If yes, please specify the body segment(s) you feel draught Neck Arms Back Legs Ankles Head Are you contented with indoor air quality? Yes No Are you contended with surface temperatures? No Yes If not, what to do? Floor temperature: Increase Decrease Increase Decrease Ceiling temperature: Increase Decrease Internal walls temperature: External walls temperature: Increase Decrease
C-C venlaon
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During measurements subjects had to fill in a short questionnaire. We asked subjects to give answers to following questions:
0.1 Air flow velocity,, [m/s]
surement, with desk-top stand, accuracy: ±(50 ppm CO2 ± 2% of mv) (0 to +5000 ppm CO2 ); - air flow in the ventilation system: DBM 700 flowmeter, accuracy: ±3% of mv.
Temperature, oC
40
Time, [min] Fig. 6. (a) Mean skin temperatures in case of C–C ventilation (tair = 30 ◦ C). (b) Mean skin temperatures in case of ALTAIR PV (tair = 30 ◦ C).
F. Kalmár, T. Kalmár / Energy and Buildings 65 (2013) 37–44
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b 100
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The subjective thermal comfort values are lower in case of ALTAIR PV system with 0.1–0.4 which can be assumed to be significant taking into account that in case of the I. class building comfort category PMV should be kept between −0.2 and +0.2. In case of C–C ventilation system 24.24% reported the sensation of draught while in case of PV system this value was 79.8%! The answers of subjects related to air velocity might be seen in Fig. 9a and b. The occupants
Neutral
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Fig. 7. Differences between skin temperatures (C–C system–PV system).
Increase
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Time, [min] Fig. 9. (a) Acceptance of air velocities (C–C ventilation). (b) Acceptance of air velocities (ALTAIR PV).
are contented or need a higher air velocity in case of traditional ventilation system. It is interesting that in spite of lower air velocities a higher number of occupants need lower air velocities in case of personal ventilation. This is a consequence of higher turbulence intensity. If we add the number of subjects contented with air velocity and the number of subjects who want a higher air velocity, it can be seen that the majority of subjects do not need to decrease the air velocity. This percents do not correlate with the answers related to draught. The answers related to air velocity have proven that the draught in this case is not definitely a negative phenomenon. In case of hot environments draught might be even desirable. 4.2. Second series of measurements
Fig. 8. (a) Subjective thermal comfort sensation, C–C ventilation (tair = 30 ◦ C). (b) Subjective thermal comfort sensation, ALTAIR ventilation (tair = 30 ◦ C).
Similar measurements had been performed in the same test room involving 15 subjects (8 boys and 7 girls), aiming the comparison between alternative personalized ventilation system with traditional C–F ventilation system (air inlet elements under the ceiling and air evacuation above the floor). In this case the ambient temperature was fixed to 28.5 ◦ C. This value was kept during measurement with −0.67 ◦ C, . . ., +0.43 ◦ C. The fresh air quantities were similar with the previous measurements (135 m3 /h in case of C–F system and 20 m3 /h in case of PV system). The obtained mean values of air velocities in the room can be seen in Fig. 10. In this case the air velocities of PV system are similar to previous measurement, but comparing with C–F system these values are higher in case of ALTAIR at 0.1 m and 0.6 m height from the floor and lower at 1.1 m. During these measurements we registered again the skin temperatures of left hand, brow and nose, the CO2 concentration above the desk. The subjects evaluate the general thermal comfort sensation, indoor air quality and draught. The activity level was 1.2 met and the clothing thermal insulation was 0.5 clo. In Fig. 11a and b the mean skin temperature values are presented. The skin temperatures are higher in case of traditional ventilation systems and the differences are increasing during measurement (Fig. 12). The average values of the answers related to general thermal comfort are presented in Fig. 13 a and b.
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1.6
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Fig. 12. Differences between skin temperatures (C–F system–PV system).
Fig. 10. Air velocities (measurement 2).
It can be stated that the differences between subjective thermal comfort values are higher than in previous case. Because the thermal comfort values obtained for traditional ventilation systems are almost similar it can be stated that in case of ta = 28 ◦ C the cooling effect obtained with ALTAIR is more intensive. This is proven even by the answers given. One of them appreciate that the thermal comfort is neutral during the whole measurement period, three of them gave answers lower than 0 (slightly cold!). Also the answers related to draught stand for the intensive cooling process. 24.24% of the subjects felt draught in case of C–F ventilation system (exactly
a
1.4
00:15:00
Air velocity,, [m/s]
0.1
the same percent than at previous measurement) and 83.84% of the subjects felt draught in case of ALTAIR ventilation system. Analyzing the answers related to the air velocity (Fig. 14 a and b) it can be stated, that there is no person who would like to reduce the air velocity in case of C–F system and there is no person who would like to rise the air velocity in case of ALTAIR system. Even in
36 35.5
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31
Time, [min] 36 35.5 35 34.5 34 33.5 33 32.5 32 31.5 31
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Temperature, oC
b
Time, [min] Fig. 11. (a) Mean skin temperatures in case of C–F ventilation (tair = 28 ◦ C). (b) Mean skin temperatures in case of ALTAIR PV (tair = 28 ◦ C).
Fig. 13. (a) Subjective thermal comfort sensation, CF ventilation (tair = 28 ◦ C). (b) Subjective thermal comfort sensation, ALTAIR ventilation (tair = 28 ◦ C).
F. Kalmár, T. Kalmár / Energy and Buildings 65 (2013) 37–44 Table 1 Uncertainties of measured values.
100 90 80 70 60 50 40 30 20 10 0
Increase
Neutral
2:00
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Increase Neutral
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1:00
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0:30
Decrease
0:00
Acceptance, [%]
100 90 80 70 60 50 40 30 20 10 0
Standard uncertainties Type A
Air velocity Air temperature Mean radiant temperature Skin temperature CO2 concentration Air flow (C–C and C–F) Air flow PV
Time, [min]
b
Measured parameter
Decrease
0:00
Acceptance, [%]
a
43
0.00136 0.023 0.0394
Combined uncertainties
Expanded uncertainties
Type B 0.01583 0.2 0.5
0.01588 0.2014 0.5015
±0.03177 ±0.4028 ±1.003
0.1463 17.577 0.394
0.6693 34.259 1.826
0.6851 38.5 1.868
±1.3703 ±77.011 ±3.736
0.199
0.309
0.368
±0.736
4.3. Uncertainties We have analyzed the uncertainties occurred during measurements: uncertainties from repeated reading (Type A) and uncertainties from calibration certificates of instruments (Type B). These uncertainties should be combined and then the expanded uncertainty should be determined. We used a coverage factor k = 2, so the level of confidence of expanded uncertainties is 95%. The uncertainties are presented in Table 1.
Time, [min] Fig. 14. (a) Acceptance of air velocities (C–F ventilation). (b) Acceptance of air velocities (ALTAIR ventilation).
this situation the majority of subjects are contented with the air velocity in case of ALTAIR system. The variation of CO2 concentration at 20 cm above the desk is presented in Fig. 15. It can be stated that in case of traditional C–C and C–F ventilation system in spite of the ACH = 6 h−1 the CO2 concentration cannot be kept constant, while in case of ALTAIR system the CO2 concentration was almost constant during measurements. This fact suggests that the ventilation effectiveness is higher in case of ALTAIR system. In case of C–C and C–F systems it is possible that because of high ACH rate (high velocities of air flow at air inlet elements) the fresh air flow practically follows the surfaces of closing elements without a significant mixing with the air in occupancy/breathing zone (see the air velocities). It is possible that with a lower ACH a better air quality in the breathing zone would be obtained, but the aim of measurements was the analysis of thermal sensation, which theoretically needs higher ACH at such ambient temperatures.
Analysing the traditional ventilation systems and performing thermal comfort measurements at high air change rates it was demonstrated that neutral subjective thermal comfort values cannot be obtained. The thermal receptors responsible for cold sensation are sending the information to brain more rapidly than the receptors responsible for warm sensation and the temperature variation is identified even for variations of 0.1 ◦ C/s. Taking into account on these information a new personalized ventilation method was developed. The idea was to change the direction of the introduced fresh air after a certain period of time. The performed measurements have proven that using this method not only the required fresh air is assured but as a side effect cooling sensation is obtained. Based on the developed method an innovative working desk was developed with integrated ALTAIR system. Acknowledgements The work is supported by the TÁMOP-4.2.2.A-11/1/KONV-20120041 project. The project is co-financed by the European Union and the European Social Fund. References
1050
C-F system
1000
C-C system
950
PV system
900 850
800
Time, [min] Fig. 15. Variation of CO2 concentration during measurements.
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5. Conclusions
[1] B. Givoni, Man, Climate and Architecture, second ed., Van Nostrand Reinhold Company, New York, 1976. [2] D. Watson, K. Labs, Climatic Design, McGraw-Hill Book Company, New York, 1983. [3] E. Arens, S. Turner, H. Zhang, G. Paliaga, Moving air for comfort, ASHRAE Journal (2009) 18–29. [4] E. Arens, R. Gonzalez, L. Berglund, Thermal comfort under an extended range of environmental conditions, ASHRAE Journal 92 (Part 1B) (1986) 18–26. [5] ISO 7730-2005: Ergonomics of the thermal environment—Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria. [6] CR 1752: Ventilation for buildings – Design criteria for the indoor environment, 1998. [7] Olesen, B.W.: EN 15251: Indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics, Technical University of Denmark, International Centre for Indoor Environment and Energy. [8] J. Kaczmarczyk, A. Melikov, D. Sliva, Avoiding draught discomfort with personalized ventilation used at the low range of comfortable room air temperature, in: Indoor Air 2008, August 17–22, Copenhagen, 2008.
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[9] A. Melikov, J. Kaczmarczyk, Sliva D., Impact of air movement on perceived air quality at different level of relative humidity, in: Indoor Air 2008, 17–22 August, Copenhagen, 2008. [10] B. Yang, A. Melikov, C. Sekhar, Cooling effect of ceiling mounted personalized ventilation system, in: Indoor Air 2008, 17–22 August, Copenhagen, 2008. [11] P.O. Fanger, A.K. Melikov, H. Hanzawa, J. Ring, Air turbulence and sensation of draught, Energy and Buildings 12 (1988) 21–39. [12] H. Zhang, C. Huizenga, E. Arens, T. Yu, Modeling thermal comfort in stratified environments, in: Proceedings of Indoor Air 2005, Beijing, 2005, pp. 133–137. [13] C. Huizenga, H. Zhang, E. Arens, A model of human physiology and comfort for assessing complex thermal environments, Building and Environment 36 (2001) 691–699. [14] Q. Chen, W. Xu, A zero-equation turbulence model for indoor airflow simulation, Energy and Buildings 28 (1998) 137–144. [15] C. Li, X. Li, Y. Su, Y. Zhu, A new zero-equation turbulence model for micro-scale climate simulation, Building and Environment 47 (2012) p.243–p.255. [16] W. Xu, Q. Chen, A two-layer turbulence model for simulating indoor airflow Part I. Model development, Energy and Buildings 33 (2001) 613–625. [17] W. Xu, Q. Chen, A two-layer turbulence model for simulating indoor airflow Part II. Applications, Energy and Buildings 33 (2001) 627–639. [18] B. Griefahn, C. Künemund, U. Gehring, The significance of air velocity and turbulence intensity for responses to horizontal drafts in a constant air temperature of 23 ◦ C, International Journal of Industrial Ergonomics 26 (2000) 639–649. [19] J. Toftum, R. Nielsen, Draught sensitivity is influenced by thermal sensation, International Journal of Industrial Ergonomics 18 (1996) 295–305. [20] B. Griefahn, C. Künemund, U. Gehring, The impact of draught related to air velocity, air temperature and workload, Applied Ergonomics 32 (2001) 407–417.
[21] Z. Wang, Modeling thermal comfort with radiant floors and ceilings, in: 4th International Building Physics Conference 2009, June 15–18, Istanbul, 2009, pp. 1–8. [22] W. Sun, K.W. Tham, W. Zhou, N. Gong, Thermal performance of a personalized ventilation air terminal device at two different turbulence intensities, Building and Environment 42 (2007) 3974–3983. [23] H. Zhang, et al., Air movement preferences observed in office buildings, International Journal of Biometeorology 51 (2007) 349–360. [24] D.-S. Ian, K.O. Johnson, C. LaMotte, Y. Shigenaga, P. Kenins, Champness P, Warm fibers innervating palmar and digital skin of the monkey: responses to thermal stimuli, Journal of Neurophysiology 42 (5) (1979) 1297–1315. [25] Lynette, Jones, Thermal touch, Scholarpedia 4 (5) (2009) 7955. [26] H. Ezzat Khalifa, M.I. Janos, J.F. Dannenhoffer III, Experimental investigation of reduced-mixing personal ventilation jets, Buildings and Environment 44 (2009) 1551–1558. [27] A.K. Melikov, Personalized ventilation, Indoor Air 14 (Suppl. 7) (2004) 157–167. [28] K.W. Tham, J. Pantelic, Performance evaluation of the coupling of a desktop personalized ventilation air terminal device and desk mounted fans, Building and Environment 45 (2010) 1941–1950. [29] A.K. Melikov, R. Cermak, M. Majer, Personalized ventilation: evaluation of different air terminal devices, Energy and Buildings 34 (2002) 829–836. [30] F. Kalmár, T. Kalmár, I. Csáki, G. Husi, Interrelation between ACH and air temperature distribution in a room, in: ROOMVENT 2009, 24–27 May, Busan, Korea, 2009. [31] F. Kalmár, T. Kalmár, Interrelation between room geometry and mean radiant temperature, Energy and Buildings 55 (2012 Dec) 414–421.
Contents lists available at ScienceDirect
Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Alternative personalized ventilation Ferenc Kalmár ∗ , Tünde Kalmár University of Debrecen, Faculty of Engineering, Ótemeto˝ u. 2-4, 4028 Debrecen, Hungary
a r t i c l e
i n f o
Article history: Received 20 October 2012 Received in revised form 10 April 2013 Accepted 4 May 2013 Keywords: Personalized ventilation Draught Turbulence intensity ALTAIR
a b s t r a c t Draught is usually avoidable if proper thermal comfort is to be obtained. Nevertheless in hot environments people try to improve their thermal comfort increasing artificially the air movement around the head using fans. Using personalized ventilation systems extreme high values of air or mean radiant temperatures, or even high relative humidity values can be compensated by air flow velocity. Taking into account that the number of cold receptors in the skin exceeds the number of warm receptors and the velocity of cold information exceeds around ten times the velocity of warm information an innovative personalized ventilation system was developed. The air flow is coming alternatively from three different directions and the frequency of direction changing might be set on request. Experiments have shown that in high temperature environments using the developed equipment neutral or even slightly cold sensations might be obtained. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Experiments related to personalized ventilation (PV) were performed in years ‘70 when Givoni [1], Watson and Labs [2] and others developed a new idea for ventilation, respectively Arens [3] created the bioclimatic charts. The aim of their research was to analyze the compensation of extreme values of some microclimate parameters giving extreme values in opposite sense to other microclimate parameters (especially air temperature, radiation, humidity). Arens and his colleagues [4] proved that in closed spaces when the operative temperature exceeds 22.5 ◦ C people need higher air velocities than that prescribed in different standards [5,6]. They conclude that when temperature is higher than the mentioned value the risk of draught is minimal. Based on their measurements they published the diagram of comfort zone depending on the operative temperature and air velocity. For personalized ventilation systems the ventilation effectiveness is considered to be better than at traditional ventilation systems [7]. Besides Fanger and Olesen at the Danish Technical University, Melikov performed a series experiments and measurements related to personalized ventilation systems [8–11]. Based on their research new PV equipments were developed. Zhang et al. [12] shown that in closed spaces characterized by high temperatures the vertical temperature difference can be higher than the values prescribed in standards. They conclude that in rooms with 26.8 ◦ C ambient temperatures, assuming personalized ventilation the vertical temperature difference can be
∗ Corresponding author. Tel.: +36 52 415155; fax: +36 52 418643. E-mail addresses: [email protected] (F. Kalmár), kalmar [email protected] (T. Kalmár). 0378-7788/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.enbuild.2013.05.010
even 6 ◦ C. In closed spaces even at smaller net floor areas it is impossible to assure the neutral thermal comfort in each section of the room because the needs of the occupants are different. The assurance of similar microclimate parameters in each section of the room can lead in this way to local discomfort. Generally, the different microclimate parameters are needed because of the different view factor between a surface with critical temperature and occupants. Huizenga et al. [13] analyzed the effects of large glazed surfaces on the indoor microclimate and developed methods to reduce the negative effects of radiant heat transfer. The asymmetric radiation can be reduced using properly the personalized ventilation systems. One of the most important questions of personalized ventilation systems is related to draught. Fanger et al. [11] performed measurements related to draught and sensation of discomfort and based on these measurements the draught risk-air temperature–air velocity diagrams were developed [5]. To describe the turbulence intensity of air flow different mathematical models were developed and numerous experiments performed [14,15]. Using CFD methods the values of turbulence intensity were determined [16,17]. Griefahn et al. [18] analyzed the draught risk in case of 23 ◦ C air temperatures depending on the air velocity and turbulence intensity. They conclude that in case of 30% turbulence intensity the maximal value of air velocity is 0.2 m/s. Toftum and Nielsen proved that the draught risk is in relation with the general thermal comfort sensation [19]. They had shown that subjects who appreciate colder a microclimate than the average, sensible react to draught. Ruegg et al. showed that in case of persons sitting close to windows the frame of the windows is the critical surface which can have influence on the draught sensation. Griefahn et al. [20] performed experiments to determine the effects of turbulence intensity on work performance. They conclude that the turbulence has different
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effects on the active and passive parts of the human body. Wang et al. [21] analyzed the relation between turbulence intensity and local discomfort. Their research results shown that the skin temperature can be lower even with 2 ◦ C in spaces with similar temperatures if the turbulence intensity increases from 15% to 30%. Sun et al. [22] analyzed the performance of a personalized ventilation system at two different turbulence intensities. They conclude that increasing the turbulence intensity the skin temperature can be easily decreased. The fresh air can be made available at occupants using different air distribution systems installed in ceilings, floors, tables, chairs or partitions. Zhang et al. [23] based on measurements performed in 200 offices had shown that more than 50% of the occupants need higher air movement than existing and only 4% of the occupants need lower air movement in the closed space. Based on the existing research results we conclude that in closed spaces with high ambient temperatures personalized ventilation can be used even for cooling if the air turbulence intensity is correlated properly with the air temperature. The aim of our research was the development of an innovative personalized ventilation equipment where the occupants are exposed to an air flow controlled directly by the occupant but the direction of the air flow is continuously changing. The air flow comes in an alternate way from the left side, front and right side of the occupant. The frequency of the airflow direction changing can be chosen by the occupants. In the following the results of research work are presented.
2. Sensation of warm and cold The skin is the sensory organ for touch and is also the largest organ in the human body. Changes in temperature, pain, touch, and pressure can be detected by the skin. A thermoreceptor is a sensory receptor, or more accurately the receptive portion of a sensory neuron, that codes absolute and relative changes in temperature, primarily within the innocuous range. In the mammalian peripheral nervous system warmth receptors are thought to be unmyelinated C-fibers (low conduction velocity), while those responding to cold have both C-fibers and thinly myelinated A delta fibers (faster conduction velocity) [24]. According to Lynette Jones “the thermal sensory system is extremely sensitive to very small changes in temperature and on the hairless skin at the base of the thumb, people can perceive a difference of 0.02–0.07 ◦ C in the amplitudes of two cooling pulses or 0.03–0.09 ◦ C of two warming pulses delivered to the hand. The threshold for detecting a change in skin temperature is larger than the threshold for discriminating between two cooling or warming pulses delivered to the skin. When the skin at the base of the thumb is at 33 ◦ C, the threshold for detecting an increase in temperature is 0.20 ◦ C and is 0.11 ◦ C for detecting a decrease in temperature. The rate that skin temperature changes influences how readily people can detect the change in temperature. If the temperature changes very slowly, for example at a rate of less than 0.5 ◦ C/min, then a person can be unaware of a 4–5 ◦ C change in temperature, provided that the temperature of the skin remains within the neutral thermal region of 30–36 ◦ C. If the temperature changes more rapidly, such as at 0.1 ◦ C/s, then small decreases and increases in skin temperature are detected. However, warm and cold thresholds do not decrease any further, if the rate at which temperature changes is faster than 0.1 ◦ C/s” [25]. In hot environments people try to reduce the sensation of discomfort creating an artificial air movement around the head (using fan). The temperature receptors in the skin after a certain period of time due to the adaptation process will send other information about the environment to temperature center than the information sent initially. It would be very important to obtain the same sensation during the whole cooling process. To obtain a high efficiency of the cooling process using air movement around
the head we developed an innovative PV system, which introduce the air alternative from three directions around the head. The variation frequency of air flow direction can be chosen on request. 3. Alternative PV system In closed spaces with high ambient temperatures the PMV values cannot be reduced to values around 0 without cooling even at extremely high ACH values. Measurements have proven that using traditional ventilation systems (air introduced under the ceiling and evacuated under the ceiling (C–C ventilation), air introduced under the ceiling and evacuated above the floor (C–F ventilation), air introduced above the floor and evacuated under the ceiling) in a 3.0 m × 3.0 m × 2.5 m closed space with 28 ◦ C ambient temperature at ACH = 8 h−1 the PMV obtained in the middle of the room is around +1.3, [30]. Using personalized ventilation systems even in extreme conditions neutral thermal sensation can be obtained. Even though there is a strong relation between room geometry and obtained mean radiant temperature [31] at 28–30 ◦ C the ambient temperature (the same mean radiant and air temperature) is obtained. Melikov [27] discussed the existing knowledge on performance of personalized ventilation and human response to it. His review contains the description of airflow interaction with human body and its impact on thermal comfort and inhaled air quality. Tham and Pantelic [28] analyzed the performance of the coupling of a desktop personalized ventilation air terminal device and desk mounted fans. They used the personal exposure effectiveness as an indicator of ventilation effectiveness. They found that coupling of a desktop personalized ventilation air terminal device and desk mounted fans distributes cooling more uniformly across the body. Melikov et al. [29] evaluated different air terminal devices used for personalized ventilation. A breathing manikin was used to simulate human being. They obtained the highest personal exposure effectiveness in case of a vertical desk grill followed by an air terminal device designed as a movable panel. Their conclusion was that personalized ventilation may decrease significantly the number of occupants dissatisfied with the air quality. Khalifa et al. [26] developed a nozzle that achieves high breathing zone air quality. They have obtained a ventilation effectiveness close to 7. At the University of Debrecen, Laboratory of Building Physics an innovative PV system was tested from thermal comfort point of view. The main idea was to introduce the air alternatively from different directions constantly stimulating in this way the cooling sensation. We assumed that the reaction of the occupants is different in this case comparing with traditional PV systems, where the air is coming from a single direction. At first a simple air distribution equipment (Fig. 1 a and b) was developed which gives the possibility to introduce the fresh air from three directions around the subject (left, front, right). The variation of fresh air direction was obtained using a special air distribution device (ADD). The ADD has one opening for air flow which after entering in the ADD can be sent to one of air terminal devices (ATD) fixed on the working desk. The main elements of this device were two disks (Fig. 2). The first disk is fixed in the ADD box and has three orifices. On these orifices the air ducts (AD) are directly connected. The second disk is in rotation during the operation of ventilation system, but this rotation movement is programmed with a certain time step. This disk has only one orifice and is placed under the first disk. The air distribution device is installed on the main ventilation air duct and the air is sent to one of the ATD. The air terminal devices were fixed at certain distances from the head of the occupant. The time step for changing fresh air direction can be chosen between 1 s and 60 s. The distance between air terminal devices and occupants head was changeable but finally we found that for used air flow and velocity 0.6 m was accepted by all subjects.
F. Kalmár, T. Kalmár / Energy and Buildings 65 (2013) 37–44
39
Fig. 4. Arrangement of measuring points in the room.
Fig. 1. (a) Arrangement of ATD on the sdesc (section). (b) Arrangement of ATD on the desk (view). D – desk; DT – desktop; AF – air flow; ATD – air terminal device; S – support; AD – air duct; ADD – air distribution device; RA – recirculated air flow; FA – fresh air flow.
Fig. 2. Main elements of ADD.
Based on this idea an office desk with self ALTAIR PV system was developed and patented. 4. Experiments The new PV system was compared with “traditional” ventilation systems (air introduced and evacuated under the ceiling and air introduced under the ceiling and evacuated above the floor). In the test room the ventilation system is equipped with double
heat recovery so the fresh air temperature obtained was lower only with 0.4 ◦ C, then the air temperature in the room. We have been working with 100% fresh air, but ALTAIR can work even with 100% recirculated air. Based on previous experiments carried out without occupants in the room [30] an ACH = 6 h−1 was chosen for C–C and C–F ventilation systems. The aim was to obtain in the occupancy zone as high air velocities as possible (to neutralize the high ambient temperature), but we wanted to avoid draught. The arrangement of air terminal devices in the room can be seen in Fig. 3. The air velocities had been measured at three different heights around the occupant (0.1 m, 0.6 m and 1.1 m) according to Fig. 4. The period of time during which the air flow is coming from a certain direction was set to 10 s. During experiments the following equipments had been used: - mean radiant temperature: TESTO SAVERIS, Globe probe Ø 150 mm, TC Type K, accuracy: ±1 ◦ C; - air temperature: TESTO SAVERIS, probe accuracy: ±0.4 ◦ C; - relative humidity: TESTO 435, probe accuracy: ±2%RH (+2 to +98%RH); - skin temperature: Testo 905-T2, accuracy: ±(1 ◦ C ± 1% of mv); - air velocity: TESTO 425, probe accuracy: ±(0.03 m/s +5% of mv); - air turbulence: TESTO 435, Comfort level probe for degree of turbulence measurement with telescopic handle (max. 820 mm) and stand, meets EN 13779 requirements, accuracy: ±(0.03 m/s +4% of mv); - CO2 concentration: TESTO 435, IAQ probe to assess indoor air quality, CO2 , humidity, temperature and absolute pressure mea-
Fig. 3. Arrangement of C–C and C–F ventilation in the test room.
F. Kalmár, T. Kalmár / Energy and Buildings 65 (2013) 37–44
0.06 0.05
0.04 0.03 0.02 0.01
0 0,1 m
1,1 m
Fig. 5. Air velocities (measurement 1).
occupants in summer in educational institutions or offices). The duration of a measurement was 2 h. In Fig. 5 the average air velocity values are presented in case of analyzed ventilation systems. The measured skin temperatures are shown in Fig. 6a and b. The differences between skin temperatures are presented in Fig. 7. It can be observed that in spite of higher mean air velocities of the air the skin temperatures are higher in case of traditional C–C systems. The first 15–30 min can be considered as adaptation period. The answers related to general thermal comfort sensation are presented in Fig. 8a and b.
36 35.5 35 34.5 34 33.5 33 32.5 32 31.5 31
1:45
2:00
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le hand brow nose 0:45
a
4.1. First series of measurements
Time, [min]
36 35.5 35 34.5 34 33.5 33 32.5 32 31.5 31 30.5 30
1:30
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1:00
0:00
le hand brow nose 0:45
b Temperature, oC
First we compared the new PV system with the traditional ventilation system when the air is introduced and evacuated under the ceiling (C–C ventilation). The ambient temperature was fixed to 30 ◦ C (because of the hysteresis, the variation of temperature values during measurements was between −0.58 ◦ C and +0.49 ◦ C). In case of C–C ventilation system an ACH = 6.0 h−1 was assured (135 m3 /h) while for PV system we used only 20 m3 /h. The measurements were performed involving 19 subjects (10 boys and 9 girls). During measurements we measured the skin surface temperatures of left hand, brow and nose, turbulence intensity and black globe temperature at 1.1 m, CO2 concentration on the desktop. We choose to measure the skin temperature of left hand, brow and nose because at these body segments the number of cold receptors in the skin is high and we assumed that the influence of ALTAIR on the thermal response of subjects is the highest. The activity level of the subjects was 1.2 met (students have been solving problems or writing during measurements) and the clothing thermal resistance was 0.5 clo, which can be assumed to be the thermal resistance of clothing worn by
0,6 m Measuring heights
0:30
The subjects involved were Hungarian students. Before experiments all data related to age, height and weight had been collected, the blood pressure was measured before and after each measurement using OMRON M10-IT equipment. Also subjects had to give answers related to smoking, coffee consumption, preferred temperatures in summer, preferred temperatures in winter, diseases. In order to perform all these preparation activities subjects arrived in the Laboratory before each experiment 30 min earlier and this period was used also for acclimatization to indoor microclimate. The subjects had filled in questionnaires from 15 to 15 min. The aim of measurements was to test the obtained thermal comfort sensation at high temperatures which may occur during summer in closed spaces if air conditioning systems are not installed. We have chosen temperatures between 28 and 30 ◦ C because on this interval of temperatures the heat loss of human body by convection, conduction and radiation is getting small and heat loss by evaporation is getting higher. We assumed that in this case the developed alternative PV (ALTAIR) will give very good results. The answers related to thermal comfort sensation had been assessed statistically using the box plot method. In descriptive statistics, a box plot or is a convenient way of graphically depicting groups of numerical data through their five-number summaries: the smallest observation (sample minimum), lower quartile, median, upper quartile and largest observation (sample maximum).
PV venlaon
0.07
0:30
4. 5.
0.08
0:15
3.
Mark on the 7 points thermal comfort scale your thermal comfort sensation Is the air velocity acceptable? Yes No If not, what should do with it? Increase Decrease Do you feel draught? Yes No If yes, please specify the body segment(s) you feel draught Neck Arms Back Legs Ankles Head Are you contented with indoor air quality? Yes No Are you contended with surface temperatures? No Yes If not, what to do? Floor temperature: Increase Decrease Increase Decrease Ceiling temperature: Increase Decrease Internal walls temperature: External walls temperature: Increase Decrease
C-C venlaon
0:15
1. 2.
0.09
0:00
During measurements subjects had to fill in a short questionnaire. We asked subjects to give answers to following questions:
0.1 Air flow velocity,, [m/s]
surement, with desk-top stand, accuracy: ±(50 ppm CO2 ± 2% of mv) (0 to +5000 ppm CO2 ); - air flow in the ventilation system: DBM 700 flowmeter, accuracy: ±3% of mv.
Temperature, oC
40
Time, [min] Fig. 6. (a) Mean skin temperatures in case of C–C ventilation (tair = 30 ◦ C). (b) Mean skin temperatures in case of ALTAIR PV (tair = 30 ◦ C).
F. Kalmár, T. Kalmár / Energy and Buildings 65 (2013) 37–44
2:00
1:45
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0
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neutral
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Increase
0:45
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1 0.8
Time, [hh:mm]
-0.4
b 100
2:00
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1:00
Decrease
0:45
The subjective thermal comfort values are lower in case of ALTAIR PV system with 0.1–0.4 which can be assumed to be significant taking into account that in case of the I. class building comfort category PMV should be kept between −0.2 and +0.2. In case of C–C ventilation system 24.24% reported the sensation of draught while in case of PV system this value was 79.8%! The answers of subjects related to air velocity might be seen in Fig. 9a and b. The occupants
Neutral
0:30
Fig. 7. Differences between skin temperatures (C–C system–PV system).
Increase
0:00
Time, [min]
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Acceptance, [%]
Temperature difference, oC
le hand brow nose
0:15
a
1.2
41
Time, [min] Fig. 9. (a) Acceptance of air velocities (C–C ventilation). (b) Acceptance of air velocities (ALTAIR PV).
are contented or need a higher air velocity in case of traditional ventilation system. It is interesting that in spite of lower air velocities a higher number of occupants need lower air velocities in case of personal ventilation. This is a consequence of higher turbulence intensity. If we add the number of subjects contented with air velocity and the number of subjects who want a higher air velocity, it can be seen that the majority of subjects do not need to decrease the air velocity. This percents do not correlate with the answers related to draught. The answers related to air velocity have proven that the draught in this case is not definitely a negative phenomenon. In case of hot environments draught might be even desirable. 4.2. Second series of measurements
Fig. 8. (a) Subjective thermal comfort sensation, C–C ventilation (tair = 30 ◦ C). (b) Subjective thermal comfort sensation, ALTAIR ventilation (tair = 30 ◦ C).
Similar measurements had been performed in the same test room involving 15 subjects (8 boys and 7 girls), aiming the comparison between alternative personalized ventilation system with traditional C–F ventilation system (air inlet elements under the ceiling and air evacuation above the floor). In this case the ambient temperature was fixed to 28.5 ◦ C. This value was kept during measurement with −0.67 ◦ C, . . ., +0.43 ◦ C. The fresh air quantities were similar with the previous measurements (135 m3 /h in case of C–F system and 20 m3 /h in case of PV system). The obtained mean values of air velocities in the room can be seen in Fig. 10. In this case the air velocities of PV system are similar to previous measurement, but comparing with C–F system these values are higher in case of ALTAIR at 0.1 m and 0.6 m height from the floor and lower at 1.1 m. During these measurements we registered again the skin temperatures of left hand, brow and nose, the CO2 concentration above the desk. The subjects evaluate the general thermal comfort sensation, indoor air quality and draught. The activity level was 1.2 met and the clothing thermal insulation was 0.5 clo. In Fig. 11a and b the mean skin temperature values are presented. The skin temperatures are higher in case of traditional ventilation systems and the differences are increasing during measurement (Fig. 12). The average values of the answers related to general thermal comfort are presented in Fig. 13 a and b.
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1.6
0.09
C-F venlaon
0.08
PV venlaon
Temperature difference, oC
0.07 0.06 0.05
0.04 0.03
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1
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0,6 m
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0
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Time, [min]
1,1m
Measurement heights
Fig. 12. Differences between skin temperatures (C–F system–PV system).
Fig. 10. Air velocities (measurement 2).
It can be stated that the differences between subjective thermal comfort values are higher than in previous case. Because the thermal comfort values obtained for traditional ventilation systems are almost similar it can be stated that in case of ta = 28 ◦ C the cooling effect obtained with ALTAIR is more intensive. This is proven even by the answers given. One of them appreciate that the thermal comfort is neutral during the whole measurement period, three of them gave answers lower than 0 (slightly cold!). Also the answers related to draught stand for the intensive cooling process. 24.24% of the subjects felt draught in case of C–F ventilation system (exactly
a
1.4
00:15:00
Air velocity,, [m/s]
0.1
the same percent than at previous measurement) and 83.84% of the subjects felt draught in case of ALTAIR ventilation system. Analyzing the answers related to the air velocity (Fig. 14 a and b) it can be stated, that there is no person who would like to reduce the air velocity in case of C–F system and there is no person who would like to rise the air velocity in case of ALTAIR system. Even in
36 35.5
Temperature, oC
35 34.5 34 33.5 33 le hand
32.5 32
brow
31.5
nose
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31
Time, [min] 36 35.5 35 34.5 34 33.5 33 32.5 32 31.5 31
le hand
brow
1:00
0:45
0:30
0:15
nose
0:00
Temperature, oC
b
Time, [min] Fig. 11. (a) Mean skin temperatures in case of C–F ventilation (tair = 28 ◦ C). (b) Mean skin temperatures in case of ALTAIR PV (tair = 28 ◦ C).
Fig. 13. (a) Subjective thermal comfort sensation, CF ventilation (tair = 28 ◦ C). (b) Subjective thermal comfort sensation, ALTAIR ventilation (tair = 28 ◦ C).
F. Kalmár, T. Kalmár / Energy and Buildings 65 (2013) 37–44 Table 1 Uncertainties of measured values.
100 90 80 70 60 50 40 30 20 10 0
Increase
Neutral
2:00
1:45
1:30
1:15
1:00
0:45
0:30
0:15
Increase Neutral
2:00
1:45
1:30
1:15
1:00
0:45
0:15
0:30
Decrease
0:00
Acceptance, [%]
100 90 80 70 60 50 40 30 20 10 0
Standard uncertainties Type A
Air velocity Air temperature Mean radiant temperature Skin temperature CO2 concentration Air flow (C–C and C–F) Air flow PV
Time, [min]
b
Measured parameter
Decrease
0:00
Acceptance, [%]
a
43
0.00136 0.023 0.0394
Combined uncertainties
Expanded uncertainties
Type B 0.01583 0.2 0.5
0.01588 0.2014 0.5015
±0.03177 ±0.4028 ±1.003
0.1463 17.577 0.394
0.6693 34.259 1.826
0.6851 38.5 1.868
±1.3703 ±77.011 ±3.736
0.199
0.309
0.368
±0.736
4.3. Uncertainties We have analyzed the uncertainties occurred during measurements: uncertainties from repeated reading (Type A) and uncertainties from calibration certificates of instruments (Type B). These uncertainties should be combined and then the expanded uncertainty should be determined. We used a coverage factor k = 2, so the level of confidence of expanded uncertainties is 95%. The uncertainties are presented in Table 1.
Time, [min] Fig. 14. (a) Acceptance of air velocities (C–F ventilation). (b) Acceptance of air velocities (ALTAIR ventilation).
this situation the majority of subjects are contented with the air velocity in case of ALTAIR system. The variation of CO2 concentration at 20 cm above the desk is presented in Fig. 15. It can be stated that in case of traditional C–C and C–F ventilation system in spite of the ACH = 6 h−1 the CO2 concentration cannot be kept constant, while in case of ALTAIR system the CO2 concentration was almost constant during measurements. This fact suggests that the ventilation effectiveness is higher in case of ALTAIR system. In case of C–C and C–F systems it is possible that because of high ACH rate (high velocities of air flow at air inlet elements) the fresh air flow practically follows the surfaces of closing elements without a significant mixing with the air in occupancy/breathing zone (see the air velocities). It is possible that with a lower ACH a better air quality in the breathing zone would be obtained, but the aim of measurements was the analysis of thermal sensation, which theoretically needs higher ACH at such ambient temperatures.
Analysing the traditional ventilation systems and performing thermal comfort measurements at high air change rates it was demonstrated that neutral subjective thermal comfort values cannot be obtained. The thermal receptors responsible for cold sensation are sending the information to brain more rapidly than the receptors responsible for warm sensation and the temperature variation is identified even for variations of 0.1 ◦ C/s. Taking into account on these information a new personalized ventilation method was developed. The idea was to change the direction of the introduced fresh air after a certain period of time. The performed measurements have proven that using this method not only the required fresh air is assured but as a side effect cooling sensation is obtained. Based on the developed method an innovative working desk was developed with integrated ALTAIR system. Acknowledgements The work is supported by the TÁMOP-4.2.2.A-11/1/KONV-20120041 project. The project is co-financed by the European Union and the European Social Fund. References
1050
C-F system
1000
C-C system
950
PV system
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800
Time, [min] Fig. 15. Variation of CO2 concentration during measurements.
02:00:00
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5. Conclusions
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