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Environ Model Assess (2008) 13:449–458 DOI 10.1007/s10666-007-9107-5

Numerical Study of the Indoor Environmental Conditions of a Large Athletic Hall Using the CFD Code PHOENICS O. I. Stathopoulou & V. D. Assimakopoulos

Received: 14 March 2006 / Accepted: 18 December 2006 / Published online: 8 June 2007 # Springer Science + Business Media B.V. 2007

Abstract This study investigates, experimentally and numerically, the environmental conditions prevailing in a large mechanically ventilated athletic hall, with the aid of the computational fluid dynamics code PHOENICS. The indoor space of the building was simulated in the PHOENICS environment and the model results were validated against experimental data collected during a 10-day campaign in the hall. The measurements included airflow characteristics and pollutants concentrations at different locations of the indoor space, as well as surface temperatures of the indoor materials. Having obtained good agreement between experimental and numerical results, different scenarios were applied in the model to investigate the environmental conditions prevailing in the hall under different ventilation and occupational conditions. These regard air-conditioning, heating, and cooling modes, as well as empty and full hall during an athletic event. The airflow, temperature, and CO2 concentration fields were studied and results revealed dynamic behavior of the fields, significantly altering with the different considered cases. The airflow patterns were characterized by distinct vortices of various sizes, originating from the ceiling air inlet fans of the heating–ventilating–air conditioning system,

O. I. Stathopoulou (*) Department of Applied Physics, Faculty of Physics, University of Athens, Building Physics 5, University Campus, Zografou, 157 84 Athens, Greece e-mail: [email protected] V. D. Assimakopoulos Institute for Environmental Research and Sustainable Development, National Observatory of Athens, I.Metaxa and V.Pavlou Str., P.Penteli, 152 36 Athens, Greece

while temperature and pollution stratification were evident, indicating ineffective performance of the ventilation system. Keyword Large enclosure . Athletic halls . CFD model . Indoor conditions . IAQ

1 Introduction In the past few decades, indoor air quality has become a public health concern because people spend more than 80% of their time indoors. Studies have concentrated on the measurement of pollutants concentrations in indoor environments, such as residences, offices, shopping malls, and restaurants, giving a comparison of their pollution status and identifying indoor pollutants sources [6–8]. Other studies have examined the relation of indoor contaminants concentrations to the ventilation characteristics of the room [4]. At the same time, computational fluid dynamics (CFD) codes have become an important tool in the research field of air quality, in both the indoor and outdoor environments. They are currently applied for investigations of indoor airflow fields for building design and optimum ventilation purposes [14] and for pollutants dispersion in working areas for health and safety reasons [2, 3]. However, few studies combine theoretical and experimental methods to investigate air quality in stadiums and athletic halls [5, 9, 13], where a large number of people are present during events and athletes train and compete. Proper ventilation and supply of fresh air play a significant role in the control of indoor air quality [11] and thermal comfort given that metabolism is intense due to the overcrowding of people. Therefore, this study investigates experimentally and numerically the environmental conditions prevailing in a

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large indoor basketball hall under different mechanical ventilation schemes and occupation conditions.

O.I. Stathopoulou, V.D. Assimakopoulos

chemical species in steady three-dimensional flows: @ ðρFÞ þ divfðρυF Γ F gradF Þg ¼ SF @t

ð1Þ

2 Methodology 2.1 Experimental Procedure A 10-day experimental campaign in the frame of a national research project took place in an indoor basketball hall built in 2000 and situated in the eastern suburbs of Thessaloniki, Greece. Parking areas and auxiliary athletic facilities surround the hall. The close vicinity includes heavy-traffic roads at about 500 m and the sea at about 1 km to the southwest. The height of the indoor space is 22 m, the arena is 1,125 m2, and the capacity of the hall is 8,000 people. The windows are normally closed and the heating–ventilating–air conditioning (HVAC) system operates according to the needs. Measurements were taken at different locations in the hall with the HVAC system in operation. Instrumentation included DANTEC FlowMasters giving spot mean air velocity, temperature, and turbulence intensity measurements at 1-min sets. Surface temperatures of indoor materials were measured with an infrared thermometer (Cole & Parmer) and CO2 concentration measurements were taken using portable instrumentation (BACHARACH CO2 analyzer, IAQRAE—indoor air quality monitor). 2.2 Theoretical Model—Initial and Boundary Conditions The PHOENICS CFD code [12] solves the time-averaged conservation equations of mass, momentum, energy, and Fig. 1 Geometrical domain of the athletic hall

where ρ; υ; Γ F ; and S F are density, velocity vector, “effective exchange coefficient of Φ,” and source rate per unit volume, respectively, for a solved-for variable Φ. The discretization of the domain is followed by the reduction of the previous equations to their finite domain form using the “hybrid formulation of the coefficients,” and the solution technique employs the SIMPLEST algorithm (an improved version of the well-known SIMPLE algorithm). The standard k–ɛ turbulence model is applied, while buoyancy effects are considered. To improve convergence, underrelaxation was used. A three-dimensional rectangular enclosure was considered in Cartesian coordinate system, as seen in Fig. 1. For symmetry reasons, only one fourth of the indoor space was modeled. The dimensions of the objects are real and geometry is as detailed as possible according to the plans of the building and the blueprints of the mechanical ventilation system, always taking into account computational efficiency. The domain size is 45×45×22 m, and it includes 81 rows of spectators’ seats, 23 circular air-inlet fans at the ceiling, and eight air outlets close to floor level. It should be noted that the model configurations were set so that the best balance is achieved among convergence, grid independency, and runtime saving, due to the high complexity of the domain geometry (Fig. 2). The cases studied are the following and the settings of each case are given in Table 1.

Environmental conditions in athletic halls

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Fig. 2 Plane view of the geometrical grid

&

& & &

Basic case: It corresponds to a selected day from the experimental campaign. The hall is empty and the HVAC system operates in the air-conditioning mode, without heating or cooling. Heating case: This case corresponds to a selected day from the experimental campaign. The hall is empty and the HVAC system operates in the heating mode. Cooling case: This is a hypothetical case; the hall is assumed to be empty and the HVAC system operates in the cooling mode. Event case: The hall is half-full with 4,000 spectators attending an athletic event and ventilation conditions are the same as in the basic case.

Model configurations concerning boundary and initial conditions, as well as settings information of the cases studied, are given below: &

& &

Fresh air comes in the hall via the ceiling circular fans (air inlets of Fig. 1), the diameters of which are either 0.4 or 0.63 m, with mean (axial along −z) velocities and turbulence intensities of 1.18–3.38 m/s and 13–31%, respectively, according to the experimental measurements. The X–Z and Y–Z domain planes have symmetry boundary conditions (Fig. 1). In the event case, people are modeled as heat and scalar sources emitting metabolic CO2, while they are evenly

Table 1 Information and input model data of the cases studied Data

Basic case

Heating case

Cooling case

Event case

Grid cells Min cell size (m) Inlet air temp. (°C) Initial indoor air temp. (°C) Ceiling surface temp. (°C) Floor surface temp. (°C) East wall surface temp. (°C) North wall surface temp. (°C) Pillars surface temp. (°C) Surface temp. of 1st seat level (°C) Surface temp. of 2nd seat level (°C) Surface temp. of 3rd seat level (°C)

71×107×46 0.63×0.42×0.48 20.7–21.3a 20.2a 22a 19a 20a 20a 17–20a 18a 18.5a 19a

71×107×46 0.63×0.42×0.48 28.8a 18.15a 22a 19a 20a 20a 17–20a 18a 18.5a 19a

71×107×46 0.63×0.42×0.48 20 28 31 27 28 28 29 28 29 30

91×142×48 0.49×0.3×0.46 20.7–21.3a 20.2a 22a 19a 20a 20a 17–20a 18a 18.5a 19a

a

Experimentally measured data

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Table 2 Measured and simulated air velocities and temperatures at measurement points of the domain for the basic case Measurement points of domain

Vexp (m/s)

Vth (m/s)

Texp (°C)

Tth (°C)

1 (air-outlet) 2 (air-outlet) 3 (air-outlet) 4 (air-outlet) 5 (air-outlet) 6 (arena level) 7 (arena level) 8 (above 1st seat level) 9 (above 1st seat level) 10 (above 2nd seat level)

0.43 0.41 0.31 0.19 0.42 0.09 0.12 0.35 0.29 0.48

0.35 0.24 0.25 0.36 0.39 0.06 0.09 0.06 0.04 0.43

21.8 21.3 21.5 21.6 21.6 22.2 22.3 22 22 22.2

19.2 19.2 19.3 19.2 19.4 20.6 20.6 19.9 19.5 21

distributed in the hall, i.e., in proportion to the volume of the spectators’ seats. The total heat emissions per person are considered 115 W [1, 10]. The CO2 concentration value given for the interpretation of the model results is 4,023 mg/m3 and corresponds to the value measured very close to spectators attending the event, while a series of measurements collected from several event days of the experimental campaign were taken into account.

3 Results and Discussion 3.1 Basic Case The simulated results of the basic case present a good agreement with the experimental measurements. Table 2 gives the measured and computed air velocities (Vexp and Vth, respectively) and temperatures (Texp and Tth, respectively) at several domain points, including air outlets and points at the arena and the seats levels. The disagreement observed for velocities at points 8 and 9 is probably Fig. 3 Air velocity field (m/s) below air-inlet fans for the basic case

attributed to the geometric complexity of those areas, which could not be modeled in detail and may cause in reality a more complex flow field. Computed and measured temperatures at domain points 6–10 and at points 1–5 close to the air abductors of the HVAC system present a difference of approximately 2°C. Because both theoretical and experimental results are physically plausible giving higher temperatures at the higher levels and lower ones at the lower levels of the hall, the temperature underestimation by the model is attributed to modeling simplifications for reasons of computational efficiency. The airflow field in the hall presents interesting patterns. Figure 3 displays a vector plot of velocity on a Y–Z plane, which extends from a row of ceiling air-inlet fans. Air jets squirt from the circular fans with varying initial velocities between 1.2 and 3.4 m/s, decreasing to 0.2 m/s at approximately 6.5 m above the arena floor. Moving up from the first seat level to the third one, the jets become more intense and velocities increase, ranging at 0.9–1.5 m/s close to the spectators. Above the second- and third-level seats, between the air jets, distinct recirculating vortices are formed, which tend to break down to smaller ones descending to the firstlevel seats. At the area over the arena, weak vortex-like structures prevail, which are disrupted by the operation of the air-outlets. The velocity within these recirculating patterns does not exceed 0.2 m/s. The temperature patterns exhibit smooth vertical stratification. Higher values (21°C) prevail above the height of 14 m from the floor and up to the ceiling (over the second and third seat levels) and in the jet areas, while lower temperatures (19–20°C) appear very close to the arena floor and the first-level seats, as well as near the air-outlets (Fig. 4). These patterns are consistent with the airflow field observed because the incoming air of 21°C (approx.) is well mixed at the upper layers due to intense circulation, while the penetrating depths of the jets above the arena are not deep enough to bring the relatively warmer air to the floor.


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Fig. 4 Temperature field (°C) below air-inlet fans for the basic case

Thus, temperature at the lower layers is considerably influenced by the initial temperature. It is also interesting to note that the average air velocity and temperature at the height of 2 m, where the upper boundary of the athletes’ occupied zone can be determined, are 0.07 m/s and 20.8°C, respectively. The previous value for velocity is considered very low according to ASHRAE standards [1]. 3.2 Heating Case This case corresponds to a certain experimental day, for which measurements of air velocity and temperature are only available for point 2 (air outlet) (Fig. 1). Experimental results give 0.48 m/s and 20.2°C for air velocity and temperature, respectively, while the computed values are 0.2 m/s and 21.37°C. It seems that under heating conditions temperature is overestimated by the model (approx. 1°C), contrary to the basic case, where the opposite was observed. However, this cannot be assumed for the whole indoor space because the available measurement points are insufficient, but the overestimation by the model is expected due to Fig. 5 Air velocity field (m/s) below air-inlet fans for the heating case

modeling simplifications regarding unconsidered heat losses, such as through the building envelope. The air velocity field developed in the hall under heating conditions presents significant differences from those of the basic case, mainly owing to the high temperature of the incoming air (28.8°C) and the low air velocities prevailing in general in the hall (Fig. 5). At the areas above the secondand third-level seats, where the distance from the ceiling air-inlet fans is short, the vortex-like patterns between the air jets are preserved, though they are relatively weaker, and velocities also remain enhanced (0.8–1.5 m/s). However, above the arena and the first-level seats, where the distance from the ceiling fans is longer, the air jets have small penetrating depths (approx. 8 m), and thus, the warm air masses do not reach the lower levels. The air moves horizontally below the height level of approximately 14 m, with no constant direction, while close to the outlets the air is forced towards them. Temperature stratification in the hall is significantly enhanced, especially at the lower levels (above the arena and the first-level seats) (Fig. 6). The warm incoming air (28.8°C) coupled with the low initial indoor temperature

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Fig. 6 Temperature field (°C) below air-inlet fans for the heating case

(18.15°C), as well as the effective mixing of the upper zone and the poor mixing of the lower layers (discussed above) are expected to form such temperature patterns (Fig. 6). The highest temperatures (28°C) appear at the upper half of the indoor space (above the 12-m level), while warm air pockets are formed between the jets. At the area of the third-level seats, high temperatures prevail that lead to discomfort conditions (26.5–28.8°C). The values decrease to 25°C at 0.8 m above the arena floor and become even lower only very close to the surfaces and the air-outlets. Finally, it is interesting to note that under heating conditions the average air velocity at the height level of 2 m (border of playing zone) has not changed considerably (0.05 m/s) compared to the basic case, the mean temperature, though, is increased by approximately 4°C (25.2°C). 3.3 Cooling Case A typical summer day is considered in this case, with an outdoor temperature of 30°C and an initial indoor temperature of 28°C. The velocity field developed in the hall Fig. 7 Air velocity field (m/s) below air-inlet fans for the cooling case

under cooling conditions (Fig. 7) resembles that of the heating case because the temperature difference between the incoming air (20°C) and the existing indoor air is large. The vortex-like patterns are maintained; vortices, however are more distinct and they extend to lower heights, reaching 5 m from the floor. Below that height the flow remains horizontal, moving from the arena towards the seats and the air outlets. Thus, better mixing is achieved, especially above the arena and the first-level seats, because the cold incoming air tends to descend and jets have bigger penetrating depths (10–16 m). At the second-level seats, circulation is more intense than in the heating case, while velocities reach 0.4 m/s close to the spectators. At the thirdlevel seats the velocities remain at the same magnitude (0.9–1.6 m/s). It is also interesting to note that, at the area between the first and second seat levels, a rather intense upward air stream occurs with velocities of 0.25 m/s, which was not evident in the previous cases. Owing to better indoor air mixing and buoyancy effect, temperature stratification is weakened (Fig. 8) and temperature is almost uniform in the hall (approx. 23.5°C) until a


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Fig. 8 Temperature field (°C) below air-inlet fans for the cooling case

height of 17 m. From that level up to the ceiling it increases to 25.5°C, indicating entrapment of relatively warmer air masses at the higher levels between the cold jets. Thus, only the third-level seats maintain high temperatures. Furthermore, at the area between the second and third seat levels, temperature is kept slightly lower (23°C) due to the intense air circulation in that area. Finally, the average air velocity and temperature at the breathing level of athletes (2 m from the floor) are 0.06 m/s and 23.4°C, respectively. 3.4 Event Case The presence of spectators in this case significantly affects the air velocity field prevailing in the hall (Figs. 9 and 10). Compared to the basic case, the vortices developed above the seats among the jets are more intense and they appear at higher levels, extending to the ceiling. This is mainly attributed to the fact that people create a rough and warm surface that enhances air mixing. However, above the arena

Fig. 9 Air velocity field (m/s) below air-inlet fans for the event case

and up to a height of 8–10 m, the flow field resembles more the heating case where the air moves horizontally from the arena towards the seats. At the areas between successive rows of ceiling fans, where jets have less impact on the flow field, a single recirculating vortex-like pattern is formed, with lower velocities at the center area (above the arena) and higher ones close to the ceiling and the seats (especially of the second and third levels). Furthermore, at the middle block of seats, the air velocities reach 0.5 m/s due to the complexity of the geometrical domain in this area coupled with the presence of people and the short distance from the air outlets (point 5, Fig. 1), which favor the airflow acceleration. The vertical temperature stratification observed in the previous cases has turned to diagonal, with the lowest values ranging at 19–22°C at the arena to the highest ones (27–28°C) at the upper seats (Fig. 11). As can be seen, relatively colder air jets with respect to the surrounding air penetrate to a depth of approximately 5 m. However, while

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Fig. 10 Air velocity field (m/s) between rows of air-inlet fans for the event case

the colder air above the arena and the first-level seats is able to reach the lower levels, this is not the case for the area above the second- and third-level seats. Thus, the temperature increases by about 4°C above the arena and until the ceiling (26°C), whereas at the second- and third-level seats the gradient is smaller, with temperature slightly varying in the ranges of 25–26°C and 27–28°C, respectively. In spite of the increase in indoor temperature, the average value at the 2-m level is kept low (19.7°C), while the respective air velocity is 0.1 m/s, not considerably altered with respect to the basic case. In this case, as in the basic case and unlike the heating case, the temperature difference between incoming air and indoor air is small (less than 1°C). Therefore, the temperature and airflow patterns established here are mainly attributed to intense buoyancy effects, heat emitted by the spectators coupled with the low velocities prevailing in the hall, which favor the ascending of the warm air and its entrapment at higher levels, thus forming warm air pockets at the ceiling.

Fig. 11 Air temperature field (°C) between rows of air-inlet fans for the event case

Examining the dispersion of gaseous pollutants in the hall during the event, as well as the effectiveness of mechanical ventilation, the spatial distribution of metabolic CO2 emitted by the spectators is illustrated in Fig. 12. As can be seen, CO2 concentration in the hall exceeds 3,200 mg/m3, while according to ASHRAE standards, indoor levels must not exceed the outdoor ones by more than 1,260 mg/m3 (or must not exceed the value of 1,800 mg/m3). Given that CO2 concentration in the outdoor environment was 1,122 mg/m3 during the event (Table 3), the indoor concentrations well exceed the threshold limit. This indicates ineffective performance of the HVAC system and, thus, unsatisfactory indoor conditions. Figure 12 distinguishes three areas; the “low conc.” one above the arena and the first seat level (between 7- and 15-m height levels), as well as at the jet areas; the “moderate conc.” one with values up to 3,460 mg/m3 (between 4- and 19-m height levels), which also covers the second-level seats; and the “hot spot” area close to the ceiling, the playing area, the spectators, and especially the third-level seats. It


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Fig. 12 CO 2 concentration (×4,023 mg/m3) below air-inlet fans for the event case

seems that CO2 is accumulated at the peripheral zone of the indoor space (in a layer of 2–3 m width), while pollution stratification resembles the temperature stratification. Above the arena, however, CO2 decreases with height up to a height level of 10 m and then increases until the ceiling. The warm air pockets are characterized by high pollutant concentrations, also. The third-level seats suffer from inadequate air renewal, with CO2 levels ranging at 4,000 mg/m3, while relatively better conditions prevail above the firstlevel seats (2,897 mg/m3) at the height level of 18 m. Finally, it is interesting to note that CO2 concentrations at the playing area remain below 3,138 mg/m3, while values lower than that occur only very close to the ceiling fans from where “clean” air is admitted, verifying the ineffectiveness of mechanical ventilation. Regarding the comparison between simulated CO2 concentrations and measured ones during the event, pollution stratification is shown in both cases (Table 3). However, the model overestimates the concentrations of CO2 at the arena level and it underestimates them at the higher levels. In reality, there are leakages of indoor air through uncontrolled openings, such as the building envelope or incidental open doors, which cannot be taken into account in the model, and they offer air renewal that decreases the CO2 levels. For example, the doors opening during the event are possibly responsible for the lower concentrations measured experimentally at arena level.

Table 3 Measured and simulated CO2 concentrations during the event Average CO2 concentration (mg/m3)

Experimental value

Model value

Outdoor Arena level 1st seat level 2nd seat level

1,122 2,219 3,883 4,303

– 3,174 3,363 3,436

Better agreement is observed at the first seat level, while average CO2 concentration is underestimated at the second one. This may be attributed to the fact that the experimental value of 4,023 mg/m3 corresponds to the mean value of several spot measurements very close to the spectators.

4 Conclusions CFD codes are useful tools for assessing the environmental conditions prevailing in large enclosures because it is quite difficult to capture the characteristics of the airflow and temperature fields experimentally. They can offer important information to building and HVAC designers to improve the indoor air quality and comfort conditions. The CFD code PHOENICS was employed in this study to investigate the environmental conditions prevailing in a large indoor athletic hall under different ventilation and occupation conditions. The examined hall is mechanically ventilated using an HVAC system. The internal building layout was simulated in the PHOENICS environment and the model was validated against experimental measurements collected during a 10-day campaign in the hall. The computational results presented satisfactory agreement with the experimental data, taking into account that the flow field in large indoor spaces is in general characterized by low velocities. The airflow and temperature fields prevailing in the hall depicted temperature stratification, areas of low air velocities (at the arena) and of higher ones (at the spectators’ seats), and local strong air movements (drafts) and warm air pockets at the ceiling and the third-level seats. Pollution stratification and hot spot areas were also evident. Except for the basic case, the operation of the HVAC system was not able to offer acceptable indoor environmental conditions. As a result, the spectators of the upper seats suffered from high temperatures and CO2 concentrations leading to

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discomfort conditions, especially under heating conditions and during an athletic event. The above mentioned effects may be attributed to the large volume-to-floor surface ratio in addition to the periodically high occupancy density. If the HVAC system is properly designed, it is possible to actually condition the spectator and playing areas to achieve satisfactory environmental conditions. Hot air can be trapped near the roof, by properly moving the conditioned air near the spectator seats and the arena level, and then be removed by roof fans or handled by efiltrating the hot air by natural ventilation. Fresh air supply must be admitted at low levels so it does not mix with the upper air. Some air may also be extracted from the ceiling over the seating area to cause better mixing and prevent the formation of warm air pockets. Good air distribution also protects the athletes and spectators from drafts. Other design considerations include under-floor heating to obtain equal distribution of the indoor temperature (though it is rather difficult to regulate and adapt to different needs) and displacement ventilation, where cool fresh air is supplied at low level and existing air is extracted at top level, taking advantage of the natural trend of warm air to rise. This implies lower frictions and turbulence losses as air is assisted in its natural ascending flow and also fewer air flow rate requirements for cooling. However, these techniques are not problem-free nor always appropriate. It is also important to mention that smoking introduces a major burden on indoor air quality and mandates excessive air exchanges because it doubles the necessary ventilation rates, and thus, it should be forbidden or spectators should strictly comply with the regulations. In any case, decisions on HVAC systems in a building should be made based upon an integrated study because strong interactions among different conditioning patterns have a paramount influence on the final performance of the system. Acknowledgments The project is cofinanced within Op. Education by the European Social Fund and National Resources (IRAKLEITOS).


References 1. ASHRAE. (2003). ASHRAE Standard 62-2001 (rev.): Ventilation for acceptable air quality. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 2. Cheong, K. W. D., Djunaedy, E., Poh, T. K., Tham, K. W., Sekhar, S. C., Wong, N. H., et al. (2003). Measurements and computations of contaminants—Distribution in an office environment. Building and Environment, 38, 135–145. 3. Duci, A., Papakonstantinou, K., Chaloulakou, A., & Markatos, N. (2004). Numerical approach of carbon monoxide concentration dispersion in an enclosed garage. Building and Environment, 39, 1043–1048. 4. Guo, H., Lee, S. C., & Chan, L. Y. (2004). Indoor air quality investigation at air-conditioned and non air-conditioned markets in Hong Kong. Science of the Total Environment, 323, 87–98. 5. Junker, M., Koller, T., & Monn, C. (2000). An assessment of indoor air contaminants in buildings with recreational activity. Science of the Total Environment, 246, 139–152. 6. Lee, S. C., Li, W., & Ao, C. (2002). Investigation of indoor air quality at residential homes in Hong Kong. Atmospheric Environment, 36, 225–237. 7. Lee, S. C., Guo, H., Li, W. M., & Chan, L. Y. (2002). Intercomparison of air pollutant concentrations in different indoor environments in Hong Kong. Atmospheric Environment, 36, 1929–1940. 8. Li, W., Lee, S. C., & Chan, L. Y. (2001). Indoor air quality at nine shopping malls in Hong Kong. Science of the Total Environment, 273, 27–40. 9. Longhurst, J. W. S., & Brebbia C. A. (Eds.) (2006). Air pollution XIV. New Forest: WIT press. 10. Santamouris, M., & Asimakopoulos, D. (Eds.) (1995). Energy conservation in buildings: A manual for conscious design and operation of A/C systems. Athens: CIENE 11. Santamouris, M., & Asimakopoulos, D. (Eds.) (1996). Energy conservation in buildings: Energy concervation strategies for sports centers—Vol 1: Energy efficiency and indoor quality guidelines. Athens: CIENE 12. Spalding, D. B. (1981). A general purpose computer program for multi-dimensional one- and two-phase flow. Mathematics and Computers in Simulation, 23, 267–276. 13. Stathopoulou, O. I., & Assimakopoulos, V. D. (2005). Application of PHOENICS to athletic halls with HVAC ventilation. Paper presented at the 26th International Conference on Ventilation in Relation to the Energy Performance of Buildings, Brussels 14. Xing, H., Hatton, A., & Awbi, H. B. (2001). A study of the air quality in the breathing zone in a room with displacement ventilation. Building and Environment, 36, 809–820.