Local Air Conditioning Research Articles

Investigation on temperature range for thermal comfort in nonuniform environment

This study uses the previously adopted local ventilation air-conditioning mode to study the effect of temperature on thermal comfort for subjects. Three room temperatures (26, 28, 30°C (78.8, 82.4, 86°F)) and three local ventilation temperatures (20, 26, 28°C (68, 78.8, 82.4°F)) were used for the study. The air velocity was purposely set low for the local ventilation tests, in order to focus on the temperature combinations between the ambient and local air temperature from the local ventilation device. Eighteen subjects participated in the experiment, using the within-subjects design method. During exposure in the room, the subjects reported thermal sensation and thermal comfort accompanied by the skin temperature measurement of the subjects. The room temperature of 28°C (82.4°F) combined with the local ventilation temperature of 26°C (78.8°F) (28°Crt and 26°Clv (82.4°Frt and 78.8°Flv)) was assessed to be the most comfortable environment. Through the experiments, the neutral room temperature of 26°C (78.8°F) combined with the local ventilation temperature of 20°C (68°F) as well as the warm room temperature of 30°C (86°F) combined with 26°C (78.8°F) was found to be within the comfortable range. The results imply that compared with the traditional air conditioning mode, which creates a uniform comfortable environment by setting the air temperature to be 26°C (78.8°F), the adoption of local ventilation could improve the thermal comfort while consuming less energy.

0316 局所冷房による自動車乗員の快適性に関する研究(GS01-4 熱工学・流体工学,オーガナイズドセッション 13:「噴霧及び燃焼現象の解明とその利用技術」)

0316 局所冷房による自動車乗員の快適性に関する研究(GS01-4 熱工学・流体工学,オーガナイズドセッション 13:「噴霧及び燃焼現象の解明とその利用技術」)

435 データセンター用C02熱輸送システムにおける熱交換器の性能評価(エネルギー有効利用(3))

In normal datacenter, a large amount of heat is generated by ICT facilities. Especially the occurrence of heat spot is linked to a decrease in air conditioning efficiency and a risk of overheat for blade server. To solve the problem, we focused attention on CO_2 heat transport system. This system adopts CO_2 as working fluid. And it is supposed to use of local air conditioning system. In this study, we looked at the property of cross-fin tube heat exchanger as local cooling equipment in this system. In this paper, we investigated the effect of air volume flow rate in natural cycle and forced cycle on this heat exchanger. In the result, pressure drop of working fluid has an increasing tendency as increase of air volume flow rate in forced cycle.

Experimental Study of Non-Isothermal Diverging Swirling and Non-Swirling Annular Jets with Central Aspiration

An experimental study of annular jets with central aspiration is presented. Two flow regimes were studied for creating either local air conditioning or local ventilation systems. The local air-conditioning system was developed by maintaining the same flow rates of the non-swirling annular jet and central aspiration. A new concept of a ‘local ventilation system’ was created by combining the swirling annular air jet impinging on the plate and central aspiration. Due to the rather small consumption of energy, the tested air-conditioning and ventilation systems are very functional and capable of maintaining local and confined micro-climate or ventilated zones in large volumes.In order to study dynamic and thermal conditions in the air conditioning system an experimental rig was built and tested. The results of the experimental research, using visualization and thermocouple measurements as well as 2D velocity fields obtained by a LDV system are presented and discussed. The visualizations show the existence of a stable calm low velocity zone in the core of the annular air jet. The thermocouple measurements, as well as LDV measurements, prove the dynamic and thermal stability of the region. A dynamically and thermally defined stable local zone is a protected volume where comfort conditions can be maintained. Velocity measurements also show the size of the vortex located between the annular jet exhaust and the central air return.Another experimental rig was built in order to study the conditions created by the proposed ventilation system. The presence of an aspirating ascending jet in the form of swirling flow – tornado, was registered between the proposed device and the impingement plate. This flow regime is very efficient in ventilating the local zone.

Analysis of Reduction Strategies for Air Pollutants Discharged from Emission Sources and their Impact on the Seoul Metropolitan Area

The Korean government enacted the "Special Law for Improving Air Quality of Metropolitan Area" in 2003. According to this plan, Korean government plan to lower the concentrations of <TEX>$PM_{10}$</TEX> and <TEX>$NO_x$</TEX> to <TEX>$40{\mu}g/m^3$</TEX> and 22 ppb, respectively, by 2014. In this study, we analyze emission reduction strategies to lower their concentration. Emission reduction for the supply of mass energy and regenerative energy are compared with several scenarios. According to the results, 713 t/y of <TEX>$NO_x$</TEX> and 165 t/y of <TEX>$PM_{10}$</TEX> will be reduced by enhancing the number of households supplied by local heating and air conditioning. And also 5 t/y of <TEX>$PM_{10}$</TEX> and 312 t/y of <TEX>$NO_x$</TEX> will be reduced by replacing conventional energy with solar energy by 2014.

トレーサーガスを用いた局所排気フードの捕集能力評価

A local exhaust hood is one of the most commonly used controls for harmful contaminants in the working environment. In Japan, the performance of a hood is evaluated by hood velocity measurements, and administrative performance requirements for hoods are provided as control velocities by the Japanese Industrial Safety and Health Law. However, it is doubtful whether the control velocity would be the most suitable velocity for any industrial hood since the control velocity is not substantiated by actual measurements of the containment ability of each hood. In order to examine the suitability of the control velocity as a performance requirement, a hood performance test by the tracer gas method, using carbon dioxide (CO(2)), was conducted with an exterior type hood in a laboratory. In this study, as an index of the hood performance, capture efficiency defined as the ratio of contaminant quantity captured by the hood to the total generated contaminant quantity, was determined by measuring the CO(2) concentrations. When the assumptive capture point of the contaminant was located at a point 30 cm from the hood opening, a capture efficiency of >90% could be achieved with a suction velocity of less than the current control velocity. Without cross draft, a capture efficiency of >90% could be achieved with a suction velocity of 0.2 m/s (corresponding to 40% of the control velocity) at the capture point. Reduction of the suction velocity to 0.2 m/s caused an 80% decrease in exhaust flow rate. The effect of cross draft, set at 0.3 m/s, on the capture efficiency differed according to its direction. When the direction of the cross draft was normal to the hood centerline, the effect was not recognized and a capture efficiency of >90% could be achieved with a suction velocity of 0.2 m/s. A cross draft from a worker's back (at an angle of 45 degrees to the hood centerline) did not affect the capture efficiency, either. When the cross draft blew at an angle of 135 degrees to the hood centerline, a capture efficiency of >90% could be achieved with a suction velocity of 0.4 m/s. The reduction of suction velocity would beneficially reduce running costs of local exhaust hoods and air conditioning. Effective and economical exhaustion would be achieved if the minimum velocity obtained by the tracer gas method were to be substituted for the excessive control velocity.

Wind-tunnel measurements of flow field characteristics around a heated model building

The heat transfer from directly or indirectly heated buildings to the ambient air induces buoyancy effects. The superposition of atmospheric approach flow and buoyancy changes the flow field when compared with the non-heated case. This can affect, e.g., the spreading of pollutants which are either transported by the oncoming flow or released from the building. When problems of local air pollution, pollutant transport, air ventilation and air condition around buildings are of interest, the superposition of approach flow and buoyancy-driven flow has not often been considered in detail so far. Within this paper, flow field analyses around non-heated and heated model buildings are given which were carried out in an atmospheric boundary layer wind tunnel. To measure the flow field around the buildings, a 2-d-LDA-system was used. The aim of the investigations was to show the phenomenological changes in the flow field of heated buildings when compared with the non-heated case.