“…1 a, and the internal flow pattern is relatively complicated. With multiple heat sources, such as equipment on the ground or sunshine, the air flow stratification phenomenon sometimes occurs in these spaces (Lau and Niu 2003 ; Cheng et al 2015 ). Fig.…”
The natural smoke exhaust system for tall spaces is more advantageous than the mechanical type of exhaust. In Taiwan, the effectiveness of natural smoke exhaust systems is inspected only by checking the vent area size. However, the air flow field in a tall space is very complicated, both at ordinary times or during fires. This study used Schlieren Photography technique, on the principle that light rays are refracted when penetrating materials of different densities, to test and simulate the dynamic measurement of hot air in tall space model. A single-mirror Schlieren system, including an 838 mm (H) × 736 mm (W) square concave mirror, as well as the focal length of 3100 mm was adopted. The experimental process of six smokeless candles were used for 1/12.5 model experiment to record the dynamic distribution and accumulation of air flow in the abovementioned space. FDS software was used to simulate various fire scenarios. The different locations of openings in some cases were studied with the maximum temperature scales of 40 and 45 °C, separately. The simulation results and experimental images showed highly similar hot air flow patterns. Schlieren Photography was proved capable of recording and visualizing the dynamic flow of hot air immediately, directly and accurately.
“…1 a, and the internal flow pattern is relatively complicated. With multiple heat sources, such as equipment on the ground or sunshine, the air flow stratification phenomenon sometimes occurs in these spaces (Lau and Niu 2003 ; Cheng et al 2015 ). Fig.…”
The natural smoke exhaust system for tall spaces is more advantageous than the mechanical type of exhaust. In Taiwan, the effectiveness of natural smoke exhaust systems is inspected only by checking the vent area size. However, the air flow field in a tall space is very complicated, both at ordinary times or during fires. This study used Schlieren Photography technique, on the principle that light rays are refracted when penetrating materials of different densities, to test and simulate the dynamic measurement of hot air in tall space model. A single-mirror Schlieren system, including an 838 mm (H) × 736 mm (W) square concave mirror, as well as the focal length of 3100 mm was adopted. The experimental process of six smokeless candles were used for 1/12.5 model experiment to record the dynamic distribution and accumulation of air flow in the abovementioned space. FDS software was used to simulate various fire scenarios. The different locations of openings in some cases were studied with the maximum temperature scales of 40 and 45 °C, separately. The simulation results and experimental images showed highly similar hot air flow patterns. Schlieren Photography was proved capable of recording and visualizing the dynamic flow of hot air immediately, directly and accurately.
“…results revealed that the location of the exhaust diffuser had a significant impact on the level of the layers of thermal stratification that influenced the cooling coil load as a result. Cheng et al [6] reported that 20.8% of energy savings were achieved when the supply inlet was located at the floor level and the return outlet was located at the occupied level. They also found that the distribution of the supply diffuser improved energy saving and indoor thermal comfort in the occupied zone.…”
The Heating, Ventilating and Air Conditioning (HVAC) system's most critical goal is to develop a comfortable and healthy environment and reduce indoor pollutant concentration. An effective design of HVAC system involves the appropriate installation of the exhaust and supply outlet with regard to a room's geometry configuration, distribution of indoor thermal conditions and indoor heat sources. The ventilation efficiency and energy saving in most air distribution systems are greatly affected by the supply, return and exhaust diffuser location arrangements [1]. If the ventilation process is incomplete or incorrect in the occupied zone, there is a possibility that people in these places may lose their working efficiency and even deteriorate their health. The first condition to be considered in order to prevent this unwanted possibility is the cleanliness of the air. Air temperature, air distribution and velocity in the area are other important elements. Thermal comfort is the definition of the comfort of the people in the occupied zone while continuing their physical or mental activities under physical factors such as temperature, humidity and air circulation. Thermal comfort is felt after a certain period of time in the occupied zone [2]. The main factors affecting thermal comfort conditions are given below [3].
Personal FactorsClothing: The resistance given by clothing to reasonable heat gain transfer.Metabolic heat: It is the heat person produce by physical activity. The stationary person will tends to feel colder than the exercise person. [4].
Environmental FactorsAir velocity: The velocity of the air that the person touches. The faster the air moves, the higher the heat exchange between the air and the person.Air Temperature: The temperature of the air around the body (dry-bulb).Radiant Temperature: Expressed as the temperature of an environment (including heat generating equipment, surfaces, sky and sun). This is commonly defined as the mean radiant temperature (MRT) and any strong unidirectional radiation such as radiation from the sun. Air humidity: It is defined as the ratio of water vapor to a given volume of air. Awad et al. [5] used various exhaust diffuser locations to investigate velocity distribution and air flow patterns. The
“…Cheng et al [11] reported that a 14 20.8% of energy saving was achieved when the supply inlet located at the floor level and the 15 return outlet located at occupied level. They also found that, the energy saving and indoor 16 thermal comfort were improved by distributing the supply diffuser in the occupied zone.…”
mentioning
confidence: 99%
“…influenced by changing the positions of the room's heat sources, and they also found that by 9 increasing the height of heat source location the convective heat becomes less significant. 10 Cheng et al [18] performed the experimental and numerical study in a room chamber to 11 investigate the influences of changing return opening on both thermal comfort and energy 12 saving. In their experiments, the combination between the lamps and some exhaust opening walls, ceiling and floor were supposed to be adiabatic.…”
mentioning
confidence: 99%
“…The term c p × ṁe × (T e − T set ) refers to the amount of cooling coil load reduction which is 11 widely used to evaluate the energy saving in the STRAD system [11,18,52,53] . This term 12 was used in the present work to calculate the amount of energy saving for each case.…”
7In an office room, many factors affect the pattern of airflow, thermal comfort, indoor air quality and 8 energy saving. In this study, the effects of the location of exhaust diffusers where the warm and 9 contaminant air is extracted and their relation to room heat sources on thermal comfort and energy 10 saving were investigated numerically for an office served by a displacement ventilation system. The 11 indoor air quality in the breathing level and the inhaled zone were also evaluated. The contaminants 12 were released from window and door frames in order to simulate the contaminants coming from 13 outside. The amount of energy consumption and the indoor thermal environment for various exhaust 14 locations were investigated numerically using the computational fluid dynamics techniques. The 15 results showed that the thermal indoor environment, thermal comfort, quality of indoor air and energy 16 saving were greatly improved by combining the exhaust outlets with some of the room's heat sources 17 such as ceiling lamps and external walls. In particular, a 25.0 % of energy saving was achieved by 18 combining the exhaust diffuser with room's ceiling lamps. In addition, locating the exhaust diffuser 19 near the heat sources also reduced the cooling coil load by 13.8 %. The risk of a large difference in 20 temperature between the head and foot levels, increased particle concentration in the occupied zone, 21 as well as increased energy consumption was also clearly demonstrated when the exhaust and 22 recirculated air outlet (return opening) were combined in one unit in the occupied boundary area that 23 2 is located at 2m away from the occupants. Thus, for the optimum energy saving and better indoor 1 environment, the combination of the indoor heat sources with the exhaust outlet is necessary. 2
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