STUDY ON THE THERMAL PERFORMANCE AND AIR DISTRIBUTION OF A DISPLACEMENT VENTILATION SYSTEM FOR LARGE SPACE APPLICATION K Sakai 1*, E Yamaguchi 2, O Ishihara 3 and M Manabe 1 1 Dept. of Architectural Engineering, Oita University, Oita, JAPAN 2 Graduate School of Science and Technology, Kumamoto University, Kumamoto, JAPAN 3 Dept. of Architecture and Civil Engineering, Kumamoto University, Kumamoto, JAPAN ABSTRACT The purpose of this study is to clarify the usefulness of a displacement ventilation air-conditioning system introduced into a multipurpose hall after CFD simulation and measurement. In the multipurpose hall of Kurume City, a displacement ventilation air-conditioning system equipped with a floor outlet had been adopted. A CFD simulation for the purpose of selecting an air condition system indicated the floor outlet system would be more effective for the design plan of the hall than a ceiling outlet system. Measurements for the purpose of determining the effectiveness and thermal performance of a displacement ventilation system were conducted after construction of the hall, and the obtained results for thermal performance and airflow distribution in the hall were consistent with the CFD simulation. INDEX TERMS Large space, Displacement ventilation, CFD, Measurement, Thermal comfort INTRODUCTION The adoption of the displacement air-conditioning system, one of many air-conditioning systems, was for the purpose of controlling indoor wind velocity and improvement in IAQ or increasing energy-saving performance (ASHRAE, 1997). Air conditioning in large spaces like gymnasiums must consider not only temperature control, but also games affected by wind velocity, such as table tennis and badminton. Although displacement ventilation systems appear to be useful as a cooling system for gymnasiums, and controllability and reduction of wind velocity is possible, there are few application examples in Japan. A displacement ventilation air-conditioning system with an equipped floor outlet has been adopted for the multipurpose hall (completion in 2001) in Kurume City. A CFD simulation had been conducted for selecting an air-conditioning system during the design plan, and after the selection, measurements were taken to determine the effectiveness and thermal performance of the displacement ventilation system. In this paper, the results, based on numerical analysis and measurement, of the estimation of usefulness of applied displacement ventilation systems for large spaces is shown. General features of the hall under study The multipurpose hall in this study has a floor space of 600 m 2, a ceiling height of 10m, and mobile spectator seats collapsed against the wall surface can be extended to accommodate 0 persons for lectures and entertainment. * Contact author email: sakaik@cc.oita-u.ac.jp 771
N 2m N c Air Outlet e a W O E (a) Inside view of the hall Lounge f b (b) Section(W-E) :Air temp. :Wind velo. :Surface temp, : + (c) Plan : +Globe temp.+humidity Figure 1. Diagram of multipurpose hall and measuring points d S Table 1 Specifications of the facility Application Gymnasium, Assembly, Conference Air Conditioning Unit Floor space 522m 2 (29m x 18m) Heat Source Absorption cooling/heating (LiBr) Ceiling height Minimum 8 m, maximum 11m Cooling ability 352kW Outlet area m 2 (0.4m x 70m) Heating ability 2kW Suction area 29 m 2 (1m x 29m) Fan power 880 m 3 /h Audience seating 0 seats O.A. supply 6000 m 3 /h Table 2 Simulation cases CASE Inlet type Supply size Return Location Inlet velocity Inlet Temp. Remarks Case1 Ceiling nozzle @0.3m x 0.3m x 20 Side wall 4.0 m/s 17 C Case2 Floor grille 0.m x 80m Ceiling 0.36 m/s 18 C Case3 Floor grille 0.m x 80m Side wall 0.36 m/s 18 C Case4 Floor grille 0.m x 80m Ceiling 0.36 m/s 18 C with Audience seating Generally, the gymnasium is used for badminton, table tennis, basketball, and other sports. Since the daytime summer temperature may reach 35 C with around 60% relative humidity, introduction of a cooling system is necessary for the Kyushu region in which the hall is located. On the other hand, consideration was required in the selection of an air-conditioning system for the sport of badminton, since the shuttle is affected if the indoor wind velocity exceeds 1.0m/s. Based on research during the design stage, a floor system was adopted because control of indoor wind velocity was possible. The building diagram and air-conditioning system are shown in Figure 1. By using a fan from the machine room, the cold air is blown out through the floor outlet from cold air chambers under the floor around the circumference of the multipurpose hall. The central ceiling is equipped with a suction opening and, using the attic as an exhaust chamber, circulates the air back to the machine room. The facility outline is shown in Table 1. 772
(a) Ceiling nozzle type (velocity vector( :1m/s ), temperature) (b) Floor outlet type(velocity vector( :1m/s ), temperature) Figure 2. Temperature and wind distribution (Simulation results, section:n-s) Table 3 Measurement schedule (July, 2001) 10 11 12 13 14 15 16 17 18 19 13 Air-Conditioning, Setup Temp. C 14 Air-Conditioning, Setup Temp. C 15 Air-Conditioning, Setup Temp. 22 C, with Audience sheet 16 AC, S.T. C Natural Ventilation AC, S.T. C 17 AC, S.T. C AC, S.T.22 C S.T.20 C S.T.22 C AC, S.T. C S.T. C DESIGN STAGE The steady state thermal performance and air distribution was obtained in the design plan of the hall. Numerical analysis of a ceiling nozzle outlet system and for a floor outlet system was obtained using a CFD simulation. A comparison was then conducted (Nagano, 1992). The m 18m 11m space was divided into 73x48x33 mesh using the standard k-e model with SIMPLEC (Doormaal et al., 1984, Patanker, 1980) in the examination. The wall surface temperature was calculated from outside air conditions and thermal transmittance (wall: 1W/m 2 K, glass: 5W/m 2 K), and the effect of the radiation was not considered. The examination is shown in Table 2. In addition, there appeared to be a problem in applying the k-e model in such a flow field, so reexamination with another turbulence model in future is necessary. Part of the calculation result is shown in Figure 2. In the ceiling nozzle outlet system, the blowing jet reached near the floor surface, and wind velocity in the playing areas reached nearly 1.0m/s when the spectator seats were utilized. The temperature of the interior hall was evenly distributed; however, the ceiling nozzle outlet system was not suited for games affected by wind velocity. In the floor outlet system, the room air velocity was kept at 0.3m/s or less. For temperature distribution, cold air accumulated near the floor surface raising concerns about comfort. From these results, the following conclusions were obtained. In displacement air conditioning the air volume cooled is less than in the ceiling system, and thus it becomes energy saving. In the case of the ceiling system, the blowing jet reached near the floor surface adversely affecting badminton and table tennis games. In displacement air conditioning, the wind velocity in the playing area can be kept at 0.3m/s or less. Since it was advantageous to have the better air quality conditions in the playing areas, the floor outlet system was adopted. In the floor outlet system, there were concerns over comfort level if the blowing air temperature was set low. We decided to set the temperature slightly high as a solution. 773
40 35 roof inside Tem p. 20 O utdoor 1000 Solar Rad. 15 500 10 0 0 2 4 6 8 10 12 14 16 18 20 22 Figure 3. Weather condition 00 Solar Radiation[W /m 2] 00 2000 1500 Vapor Tension[kPa] 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 O utdoor R eturn Supply 0.0 Figure 4. Humidity fluctuation 1.4 1.2 22 Supply 20 Return 18 Wind V elocity[m /s] 1.0 0.8 0.6 0.4 0.2 a b c d e f 0.0 Figure 5. Supply, Return air temp. fluctuation Figure 6. Wind velocity of floor outlet MEASUREMENT The measurement was important for understanding the thermal environment in the hall and understanding the airflow distribution in the playing area. Summary and measurements are shown in Figure 1. The measurement was conducted using hot wire anemometer for measuring wind velocity, and a T-type thermocouple for measuring surface temperature and air temperature in intervals of 1 minute. The measurement schedule is shown at Table 3. In addition, winter measurements will be taken in February 2002. MEASUREMENT RESULTS The measurement was taken on July 13-17, 2001. Since the weather was not stable during the measurement period, there was a thermal load in comparison with the equipment ability. As a representative result, the discussion uses July 14th. The fluctuation of outdoor temperature and solar radiation is shown in Figure 3. Air Conditioning System Taking air temperature and blowing vapor tension with suction opening as in Figure 4,5, the wind velocity of each outlet is shown in Figure 6. At the time of air-conditioning, supply temperature was about 23 C, and return temperature was about 29 C. Blowing humidity and suction humidity were almost equivalent. Since measurements were taken under conditions in which there was seldom a thermal load indoors, the system retained reserve cooling ability. The blowing airflow differed greatly depending on the place it blew out from the chamber under the floor. Airflow was a maximum of about 1.2m/s in the east outlet where the chamber airflow was straight, and a minimum of about 0.4m/s in the west outlet. It seems the shape of the chamber controls the velocity of the blowing airflow. Thermal Performance The change in temperature and wind velocity in the central hall is shown in Figure 7, 8. Figure 9 is the temperature change of the wall surface. The temperature 1m above the floor 774
31 29 27 h=10m h=7m h=4m h=1m Velocity[m /s] 0. 0. 0.20 0.15 0.10 0.05 0.00 h=0.5m h=1.5m h=2.5m h=3.5m Figure 7. Indoor air temp. fluctuation(point-o) Figure 8. Wind velocity fluctuation(point-o) 31 29 27 ceiling north south east west floor Figure 9. Wall surface temp. fluctuation SET*[deg.C] 31 h=3.5m h=2.5m 29 h=1.5m 27 Figure10. Calculation result of SET*(point-O) level was stable at about C and near the ceiling was about C at the time of air-conditioning. Although when using the spectator seats, temperature control to about 4m was a problem, the temperature of the space as a whole was kept almost constant, and thus was considered satisfactory. Room temperature reached the lowest minutes after air-conditioning start and was stabilized about 1 hour afterwards. The time for room temperature to fall below the setting temperature was about 10 minutes, and operation according to hall use was possible. The wind velocity near the floor surface was kept at 0.3m/s or less; velocity near the floor surface was the maximum. It was confirmed that this system was useful for games, which are influenced by wind velocity. For the purpose of evaluating comfort in the hall, SET* (Gagge et al, 1986), which was one of the comfort indices, was calculated using measured values. Figure 10 shows the changes in SET*. SET* becomes about during air-conditioning and the playing area (0-4m height) was comfortable. Figure 11 shows indoor temperature distribution from start time to stable temperature. From immediately after air-conditioning start, temperature decreases from near the floor surface were checked. It was inferred that the indoor temperature had formed temperature stratification and that the blowing air was reaching the playing area. The cooler temperature reached the height of the spectator seats minutes after air conditioning start. It was proven that the room temperature control kept the temperature almost equivalent throughout the whole space. CONCLUSION In this study, the CFD simulation was done in the design stage, and it was possible to obtain effective information to make a decision regarding the air condition system. Based on the measurement results, it was confirmed that this system was useful for games, which are influenced by wind velocity, and achieved the planned purpose of thermal performance and airflow distribution. Though it was exactly impossible, since there was a difference in the conditions, the correspondence of measured values and CFD simulation results confirmed the validity of the case study. In future work, the measurement results will provide feedback for the calculations in order to improve calculation accuracy. 775
10:00 10: 10:05 11:00 10:15 12:00 Figure 11. Temperature distribution of the hall (Measurement results, section:s-o-e) ACKNOWLEDGEMENTS The authors extend their sincere gratitude to the members of Ishihara Laboratory of Kumamoto University, Mr. Shimizu and Mr. Baba in Kurume City for their kind cooperation in the completion of the present study. REFERENCES ASHRAE HANDBOOK Fundamentals 1997. Chapter 31, SPACE AIR DIFFUSION: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Doormaal J P, Raithby G D. 1984. Enhancements of the SIMPLE Method for Predicting Incompressible Fluid Flows. Numerical Heat Transfer, vol.7, pp 147-163. Gagge A P, Fobelets A P, Berglund L G. 1986. A Standard Predictive Index of Human Response to the Thermal Environment, ASHRAE Transaction, vol.92, Part 2B, pp 709-727 Nagano S, Mima T. 1992. Ventilation Efficiency in a Two-Dimensional Enclosure with a Supply Outlet in the Ceiling or in the Floor. Proceedings of International Symposium on Room Air Convection and Ventilation Effectiveness, pp 553-559. Tokyo:ASHRAE Sakai K, Ishihara O, Nagano S. 1999. A Measurement of the Thermal Performance and Air Distribution of Indoor Sports Ground Using Swiring Flow Type Natural Ventilation System. Proceedings of the Eighth International Conference on Indoor Air Quality and Climate, vol. 4, pp 358-363. Edinburgh:Indoor Air 99. Patanker S V. 1980. Numerical heat transfer and fluid flows. New York:McGraw-Hill. 776