Numerical Simulation of Indoor Thermal Environment Effected by Air Supply Temperature and Grille Angle on Stratum Ventilation in a Typical Office Procedia Engineering 121 ( 2015 ) 779 – 784 Available online at www.sciencedirect.com 1877-7058 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ISHVAC-COBEE 2015 doi: 10.1016/j.proeng.2015.09.030 ScienceDirect 9th International Symposium on Heating, Ventilation and Air Conditioning (ISHVAC) and the 3rd International Conference on Building Energy and Environment (COBEE) Numerical Simulation of Indoor Thermal Environment Effected by Air Supply Temperature and Grille Angle on Stratum Ventilation in a Typical Office Hangyu Zhaoa, Zeqin Liua,b,c, *, Zhenjun Zuoa aKey Laboratory of Tianjin Refrigeration Technology, Tianjin University of Commerce, Tianjin, 300134, China bEngineering Research Center of the Ministry of Education of Refrigeration Technology cEngineering Center of Tianjin Refrigeration Technology Abstract Based on for indoor thermal environment and human thermal comfort, the air distribution in a typical air-conditioned office in the mode of stratum ventilation was simulated with the Fluent Airpak simulation software in this paper. The variation regularity of indoor thermal environment effected on air supply temperature and grille angle was explored and human thermal comfort and energy efficiency was analyzed. The following conclusions could be obtained. Under this condition with air supply angle and other parameters unchanging, air conditioning room temperature appeared overall upward trend with the air temperature increased; The average indoor wind speed appeared overall upward trend; the average indoor predicted percentage of dissatisfaction PPD decreased firstly and then increased. When the air temperature was 20 , PPD achieved the minimum value. When the air supply temperature and other parameters were unchanging, the average value of PPD was increased firstly and then decreased with the air supply angle changing. When the air supply angle was 90 degrees, PPD achieved the maximum value. © 2015 The Authors.Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of ISHVACCOBEE 2015. Keywords: Stratum Ventilation; Numerical Simulation; Air Supply Angle; Thermal Comfort * Corresponding author. Tel.: +86-22-60170565; fax: +86-22-26675724. E-mail address: liuzq@tjcu.edu.cn © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ISHVAC-COBEE 2015 http://crossmark.crossref.org/dialog/?doi=10.1016/j.proeng.2015.09.030&domain=pdf http://crossmark.crossref.org/dialog/?doi=10.1016/j.proeng.2015.09.030&domain=pdf 780 Hangyu Zhao et al. / Procedia Engineering 121 ( 2015 ) 779 – 784 1. Introduction The main nomenclatures of this article were as follows: Nomenclature density, kg/m3 u velocity, m/s laminar dynamic viscosity, kg/(m·s) t turbulent dynamic viscosity, kg/(m·s) t time dissipation rate k turbulent kinetic energy x coordinate ,i j free index PPD predicted percentage of dissatisfaction PMV predicted mean vote With the growth of environmental pollution and world energy crisis, Asian countries have put forward that the summer indoor air temperature should be appropriately raised to response the energy crisis and mitigate the greenhouse effect. The mainland of China raised the summer guidance temperature of public buildings to 26 , and with the increase of indoor design temperature, the ANSI/ASHRAE Standard 55-2010 also recommended that the thermal uncomfortable feeling be eliminated by increasing the summer wind speed [1]. For indoor persons, the air quality in human breathing zone was directly related to the human body health and work efficiency[2]. With the consideration of these factors, a concept of stratum ventilation that applied to the small room was proposed by the City University of Hong Kong, Zhang Lin [3]. Stratum ventilation was a way of sending fresh air directly to the breathing zone by the wind-gap situated on the side wall and a little above the working area. So far, the amount of the foreign research reports in this field was rather little. T.Tchow, C.Ftsang, K.FFong, L.S.Chan by experimental and numerical studies showed that the design temperature of air-conditioned room could be improved by the stratum ventilation without compromising thermal comfortable feeling [4]. Tian Lin’s study proved that good thermal comfortable feeling could be achieved by stratum ventilation [5]. Xi'an Jiaotong University, Wang Fenghao et al. have explored the airflow characteristics of the office stratum ventilation and displacement ventilation. They also have analysed the work zone under the two ventilation ways and temperature field, velocity field, CO2 concentration field et al. near human bodies. Professor Zhang Lin reported a high temperature air conditioning study under stratum ventilation [3]. 2. Theoretical model Based on the content of this study, the mathematical model for numerical simulation would be simplified. It was that there were no other heat source and solid roadblock in addition to indoor multi-point heat sources, in the same time making the following assumptions: 1) Indoor fluid was steady and incompressible; 2) The air after being treated by air-conditioning was delivered into air conditioning room via inlet and mixed thoroughly with indoor air. The variation regular pattern of indoor temperature field could be obtained by Fluent Airpak simulation software. RNG k- ɛ turbulence model was set as flow model, which was similar to the standard k-ɛ model but more accurate. The impact of low Reynolds number was also considered in this model [6]. The transport equations for k and ε were as follows [7]: ( ) ti k i j k j k k ku p t x x x (1) 781 Hangyu Zhao et al. / Procedia Engineering 121 ( 2015 ) 779 – 784 2 * 1 2( ) t i k i j j u C p C t x x x k k (2) Where, 3 0* 2 2 3 1 1 C C C , Sk , 1 22 ij ijS S S and 1 2 ji ij j i uu S x x . kp was the production of turbulent kinetic energy. ijS was the mean rate of strain tensor. The values of the constants were derived as follows: 0.0845C , 0.7194k , 0.7194 , 1 1.42C , 2 1.68C , 0 4.38 , 0.012 . For the calculation of predicted percentage of dissatisfaction PPD, programs should be firstly compiled by MATLAB mathematics calculated software. Then calculated the predicted mean vote PMV that was put forward by Professor Fanger in 1970, and in the end the PPD value would be predicted through the following formula [8]: 4 20.03353 0.2179 100 95 PMV PMV PPD e (3) 3. Numerical simulation model In order to analyse the numerical simulation results of indoor air conditioning with the experimental data, the physical model of numerical simulation was established in accordance with the geometry dimension of experimental air-conditioned room, namely 6.0 m (length, x) × 4.0 m (width, y) × 3.5 m (height, z). The room set 10 point heat sources and 4 analog people that had fixed heat. The article supposed that the building envelopes’ heat transfer be simply added to the heat of chamber point sources to explore this issue’s study subjects. Fig. 1. was the model chart of air conditioning air supply. Fig. 1. the model of air conditioning air supply 4. Discussion Fig. 2. to Fig. 6. were distribution charts of air temperature in y-z plane with the air supply temperature was constant 20 , and respectively, the air supply angles were 30 degrees, 60 degrees, 90 degrees, 120 degrees, 150 degrees. Their temperature tangent planes lied in three section positions (x=1.5, 3.0, 4.5) where measurement points were arranged in experiment. As could be seen from the figures, at different air supply angles, the temperature within the space of human activity conformed the requirements of the design temperature basically. Only when the air supply angles were 30 degrees and 150 degrees, the indoor temperature was high, and the temperature stratification at vertical direction was very obvious under all conditions, and the return air’s temperature was the highest. When the air supply angle was 90 degrees, all temperature of an air-conditioned room was the most evenly distributed, but the energy utilization 782 Hangyu Zhao et al. / Procedia Engineering 121 ( 2015 ) 779 – 784 factor was lower, and was not conducive for energy saving. As the air supply angles of 60 degrees and 120 degrees, the temperature difference of head and foot was smaller, and the thermal comfort was better. Fig. 2. the air supply angle was 30 degrees Fig. 3. the air supply angle was 60 degrees Fig. 4. the air supply angle was 90 degrees Fig. 5. the air supply angle was 120 degrees Fig. 6. the air supply angle was 150 degrees Fig. 7. the PPD in the air-conditioned room 783 Hangyu Zhao et al. / Procedia Engineering 121 ( 2015 ) 779 – 784 Fig. 7. showed that under the condition of the air supply temperature unchanging, indoor predicted percentage of dissatisfaction PPD appeared an overall trend of changing from increase to decrease with the increase of air supply angles. When the grille angle was 90 degree, the PPD reached a maximum value, which larger than 10%, but did not meet the requirements of human thermal comfort. When the air supply angles were 30 degrees, 45 degrees, 135 degrees, 150 degrees, under the condition of different air supply temperature, the indoor predicted percentage of dissatisfaction PPD was lower than 10%, meeting human thermal comfort requirements. Fig. 8. to Fig. 11. were distribution charts of air temperature in y-z plane with the air supply angle was constant 90 degrees, and respectively, the air supply temperature was 19 , 20 , 21 , 22 . Under the air supply way of stratum air conditioning, when air supply angles and other parameters unchanging, indoor temperature and average wind speed in air-conditioned room appeared overall upward trend with the air supply temperature increased. 5. Conclusion In the air-conditioned design, the analysis to the indoor thermal environment and thermal comfort could provide a reference for the designers selecting the appropriate stratum air supply temperature and air supply angle in design, which could improve the thermal comfort of the stratum air supply room. By exploring the impact of the stratum air supply temperature and air supply angle to indoor air temperature and the value of PPD, this paper could get the following conclusions: Under the air supply way of stratum air conditioning, when the air supply angles and other parameters unchanging, air conditioning room temperature appeared overall upward trend with the air temperature increased; The average indoor wind speed appeared overall upward trend; the average indoor predicted percentage of dissatisfaction PPD decreased firstly and then increased. When the air temperature was 20 , PPD achieved the minimum value. When the air supply temperature and other parameters were unchanging, the average value of PPD was increased firstly and then decreased with the air supply angle changing. When the air supply angle was 90 degrees, PPD achieved the maximum value. Fig. 8. the air supply temperature was 19 Fig. 9. the air supply temperature was 20 Fig. 10. the air supply temperature was 21 Fig. 11. the air supply temperature was 22 784 Hangyu Zhao et al. / Procedia Engineering 121 ( 2015 ) 779 – 784 Acknowledgement This study was supported by the fund Program of the Development of Science and Technology of Tianjin Municipal Education Commission under the contract No.20120910. References [1] ASHRAE, ANSI/ASHRAE Standard 55-2010, Thermal Environmental Conditions for Human Occupancy. American Society of Heating, Refrigerating, and Air-conditioning Engineers Inc. Atlanta, 2010. [2] Z.Q. Liu, G. Li, C.X. Zheng, The simulation and calculation of indoor thermal environment and the PPD evaluation index affected by three typical air-conditioning supply modes, HVAC&R Research. 20 (2014) 343-350. [3] Z. Lin, T.T. Chow, Stratum ventilation-A solution of high temperature air condition, Journal of Chemical Industry and Engineering. 59 (2005) 235-239. [4] Z. 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