Detailed Experimental data of Indoor Air and Thermal Environment in the Working Spaces using Under-floor Air Distribution (UFAD) System

Transcription

1 Detailed Experimental data of Indoor Air and Thermal Environment in the Working Spaces using Under-floor Air Distribution (UFAD) System PC Chou a, *, CM Chiang b, NT Chen b, CW Liao a, PR Chung a a Department of Interior Design, Shu-Te University, Taiwan b Department of Architecture, National Cheng-Kung University, Taiwan * address: paul@mail.stu.edu.tw Abstract The state-of-the-art development shows the under-floor air distribution (UFAD) system is beneficial for energy saving and thermal comfort, because of supplying air directly to the occupants zone. However, most of these researches were conducted from the developed countries located in the temperate/frigid zone. In order to identify the performance of the UFAD system, which was adopted in Taiwan (Subtropical hot-and-humid climate), this paper presents a set of detailed experimental data of thermal stratifications in working spaces. These data were obtained from a new two-room full-scale chamber and test facilities at Shu-Te University (STU). The thermal stratifications of the UFAD system were measured under the summertime. The results are showed the different phenomenon between the daytime and nighttime, and these data are especially essential for the validating CFD simulation for numerical prediction. 1. Introduction Arthur Rosenfeld, Ph.D., founder of the Center of Building Science at Lawrence Berkeley Laboratory, cited a study showing that the huge link between IAQ and productivity in an office building and the serious initiative to improve indoor air quality will have a tremendous return (Turner, 1998). The indoor environment is important to occupants health and mental sensation because up to % of a typical person s time is spent indoors, i.e. most of employees with sedentary lifestyles take more than 2 hours per day in their offices (Platts-Mills, 1998). And the Thermal Comfort and Indoor Air Quality as the key issues of indoor environment have been presented (Fanger, 1996). The above performances can be improved by utilizing ventilation system. Modern buildings were obviously found to lean increasingly on the HVAC system, which was used for controlling the indoor climate via driving the heat exchanger. After the year of 1973, the energy crisis led the investor to reduce the air-exchange rate to build the energy-saving building (Fanger, 1988). However, recent research was shown that the occupants in high airtight buildings broke out the SBS (sick building syndrome), besides, the components of HVAC system would emit indoor air pollutants (Godish and Spengler, 1996). In order to solve the above problems, two approaches (the experiments and numerical simulations) have been adopted to describe the characteristics of stack effect of displacement ventilation (Chiang and Chou, et al., 1998). A recent literature review, the interviews with engineers have shown that the use of UFAD system results in measurable improvements in thermal comfort, indoor air quality, and user satisfaction, comparing their performance to traditional ceiling-based systems (Brahme and Loftness, et al., 22). This paper presents experiment data obtained under the subtropical climate. The thermal stratification was monitored by data-logger with 12-channel thermo-couples, and PMV-PPD values were also measured.

2 2. Experimental Facility 2.1. The chambers and HVAC systems The purpose of the test facility built at STU is proposed for research and teaching thermal comfort, indoor air quality, energy efficiency, ventilation mechanism, and HVAC systems. The two-room type chamber with modular components is designed for changing the different setting to observe the physical parameters of indoor environment. The test chamber, as shown in Figure 1(1), consists of one buffer-room and two test-rooms. The enclosure is combined from partition panels with thermal resistance of 3.7 m 2 k/w. The geometry of these two test-rooms is extremely similar. Each test room is installed a separate HVAC system and distributes make-up air from UFAD system in Room A and traditional ceiling-based system in Room B respectively. All the diffusers and exhausts can be moved and operated simultaneously or individually in both chambers. Table 1 shows the dimensions of the chambers and also shows the capacity of HVAC systems. Figure 1(2) illustrates the HVAC system configuration and control interface. The interface allows an interactive control of the systems. An operator can set an overall temperature and humidity or change any parameters, such as the percentage of the cooling load, heating load, and humidifying rate, by clicking the icon and typing the number into the pop-up window. Outdoor Room A Room B (1) Two-room chamber (2) The control interface of HVAC system Figure 1. Sketch of the test facility Table 1. Dimension and HVAC system capacity of the test facility Items Test Room Room A Room B Dimension Length 2.21 m 3.38 m 3.38 m Width 3. m 3. m 3. m 2.7 m 2.4 m 2.4 m Modular system. m. m. m Window size none 2.89 m(w) 1.7 m(h) none Capacity of HVAC system Chiller 15, kcal/hr for all chambers system FCU (fan coil unit) AHU (air handling unit) AHU Supply fan 51 m 3 /hr 24 m 3 /hr 24 m 3 /hr Heater none 4 kw 4 kw Humidifier none 8 kg/hr 8 kg/hr Fresh air 12 m 3 /hr for all chambers

3 2.2. Equipment The major measuring equipment includes: A thermo-couple system for measuring outdoor/indoor air temperatures, A thermal comfort system for evaluating the thermal comfort of indoor climate and heat stress, and A multi-purpose meter for air velocity, air volume flow, temperature, and relative humidity measurements. We use a 12-channel data logger with thermo-couples to measure air temperature. First two channels are for monitoring the temperatures of the outdoors and buffer room, and the rest ten channels are to measure the indoor temperature profiles. The error of temperature measurements by the entire system is about.3 C. The INNOVA 1221 data logger with comfort module UA1276 is adopted to measure the physical parameters used in evaluating thermal comfort such as (in accordance with ISO 77) PMV and PPD. The probe position is set at middle of the room and FL +1.1m height, where represents the occupants breathing zone in seat. The air movement is generally slow in a room. There is factually no one perfect instrument to provide reliable results when the air velocity is lower than.1 m/s at many locations in a room. Therefore, we use a thermo-anemometer in measuring the inlet velocity from the UFAD system. The accuracy is ±.3 m/s or ±.5% of the readings Test procedure In order to observe the characteristics of the UFAD system performed in Taiwan, we conducted several measurements in summertime with different vent systems, time periods, and measured positions. The indoor climate of both test rooms was controlled at the temperature of 26 C and relative humidity of 5% by DDC system, and the remote sensors were installed at the sided wall of test rooms at the height of breathing zone. The heat sources indoors were one real PC system generated 25W and four sets of overhead lighting used the sixteen 2W fluorescent lamps totally. The occupants in the test room were arranged by two researchers, and operated the test instruments. A total of ten thermo-couples were used to measure the vertical temperature profile, which were supported on a movable pole from the floor to ceiling in equidistance. Measurements were conducted under steady-state conditions by stabilizing the room thermal and fluid parameters for more than two hours before recording the data. Figure 2 shows the pre-test results of the test facility. Good stability of this 12 thermo-couples monitored in a same point, because the standard error was.3 C. The benchmarks of the capacity of the HVAC system in Room A were measured at the positive change rate of C/hr and the negative change rate of 6.35 C/hr in temperature Temperature ( ) : :2 :4 P1 P2 P3 P4 P5 P6 P7 P8 P9 P1 P11 P12 :6 :8 :1 :12 :14 Time (min) :16 :18 :2 :22 :24 Temperature ( ) : :6 P1 P2 P3 P4 P5 P6 P7 P8 P9 P1 P11 P12 :12 :18 :24 : :36 Time (min) (1) Stability test for the thermo-couple system (2) Capacity curve of the HVAC system Figure 2. Pre-test results of the test facility :42 :48 :54 1:

4 3. Results 3.1. Comparison of thermal stratifications between UFAD and Ceiling diffuser system Table 2 shows the measured results of the thermal stratifications. The temperature magnitude of three sections of both test room were measured. The stratification was plotted as the contour of shading value by visualization software. Seven tones of the gray were represented as the temperature scale from 21 to 27 C. These post-process plots are practical for designers to identify the thermal profiles from the different air supply system. Table 2. Comparison of thermal stratifications between the UFAD and CD systems Room A: UFAD System Room B: Ceiling Diffuser System A1 S3 section in Room A B1 S3 section in Room B A2 S4 section in Room A B2 S4 section in Room B A3 S5 section in Room A B3 S5 section in Room B

5 3.2. Thermal profiles in the room with UFAD system Figure 3 shows three scene of the comparisons on the temperature profiles. Compared to the traditional ceiling diffuser system, the shading value of the plots in the UFAD case performs the blend grays, which represents a moderate temperature of 23.3 C at the height of 1.2 m. Because of maintaining the same temperature in the breathing zone, it can be measured the lower inlet air velocity from the multi-apertured elevated floor. In Room B (the traditional ceiling diffuser case), cold air was jetted out from the ceiling side to the breathing zone directly with higher air velocity, which caused the Cold Draft, and accumulated in the upper zone of the room space. In Room A (the UFAD case), cold air spread from the floor diffuser and exhausted through the vent on the ceiling Outdoors Outdoors Rm.A P Rm.A P2 Nighttime Room A Rm.A P3 Daytime Room B (1) Different positions in Room A (2) Differences between daytime and nighttime (3) Central positions of both rooms Figure 3. Temperature Profiles in rooms 3.3. Comparisons on thermal profiles measured in the daytime and nighttime Figure 4 shows the measured results of temperature profiles of Room A. The curves with circle mark represent the measurement in daytime, and the curves with square mark stand for the measurement in nighttime. Although the difference of outdoor daytime temperature and nighttime temperature is significant, the profiles of most indoor positions are similar. 4. Conclusions This paper presents the detailed thermal data of a room with UFAD system. The data are beneficial for validating a CFD program. This phenomenon of displacement ventilation, which induced by the UFAD system, is not only reasonable to mix the heats fluxed from the equipment and occupants, but also favorable to relieve the cold draft. It is also useful for indoor environment design. Acknowledgements Support from the National Science Council of ROC through grant No. NSC Z in this study is gratefully acknowledged. Also, we are especially grateful to ARCHILIFE Research Foundation for their financial support.

6 References Brahme, R. and Loftness, V.; et al. (22). IAQ, energy, and cost implications of under- floor air distribution systems. Proceedings of Indoor Air 22, 4, Chiang, C.M. and Chou, P.C.; et al. (1999). The influence of HVAC systems on indoor air quality in the office buildings in commercial districts in Taiwan. Proceedings of 1999 Asia-Pacific Conference on the Built Environment, F5, 1-6. Chiang, C.M. and Chou, P.C.; et al. (21). A methodology to assess the indoor environment in care centers for senior citizens, Building and Environment, 36(4), OA A5 A4 A OA B5 B4 B3 B2 B OA C5 C4 C3 C2 C OA D5 D4 D3 D2 D OA Temperature Figure 4. Key Map E5 E4 E3 E2 E Temperature profiles in the room with UFAD system Chou, P.C. and Chiang, C.M.; et al. (1998). Effects of window positions on the air flow distribution in a cross-ventilated residential bedroom. Indoor+Built Environment, 7(5-6), -7. Fanger, P.O. (1996). The Philosophy behind Ventilation: Past, Present and Future. Proceedings of Indoor Air 96, 4, Kim, J.J.; Chang, J.D. and Park, J.C. (22). Computer modeling of underfloor air supply system. Proceedings of Indoor Air 22, 4, Turner, F. (1998). Achieving IAQ and Efficiency. ASHRAE Journal, 4(12), Webster, T.L. and Bauman, F.S.; et al. (22). Thermal stratification performance of underfloor air distribution (UFAD) systems. Proceedings of Indoor Air 22, 4, Holland, D. and Livchak, A. (22). Improving indoor air quality in schools by utilizing displacement ventilation system. Proceedings of Indoor Air 22, Vol. 4,