PACを用いた膜天井放射空調の冷房性能に関する実験的研究

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  • COOLING PERFORMANCE OF CEILING RADIANT TEXTILE AIR CONDITIONING SYSTEM WITH PAC BY FULL-SCALE EXPERIMENT
  • PAC オ モチイタ マク テンジョウ ホウシャ クウチョウ ノ レイボウ セイノウ ニ カンスル ジッケンテキ ケンキュウ

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 Radiant air conditioning systems have attracted many people's interest due to the high capabilities of energy saving and maintaining a comfortable indoor environment at the same time. There are two types of radiant air conditioning systems, water type or air type. It is usual to use water as refrigerant, but it is difficult to install this system and maintain system performance, so the number of introduction example using air-type has been increasing lately. There is also a problem about the drought from diffuser of air conditioning system, so some researchers use textile and provide low velocity supply to prevent drought.<br> In this study, the authors suggest a new radiant air conditioning system, ceiling radiant textile air conditioning system with package air conditioner (Package Air Conditioner). In a room with PAC installed, we introduced the textile layer covering the ceiling below the PAC. By using existing PAC, the complexity of installation will become lower compared to the typical air conditioning system. The aim of this study is to investigate the thermal environment when operating the new radiant system and to develop an optimal method of using this system. This system controls the indoor environment utilizing the radiant effect of textile and the airflow through textile.<br> In order to clarify the actual phenomenon, we conducted several experiments under 6 conditions, changing the supply airflow angle, pre-set temperature of PAC, airflow rate from PAC or heat generation rate. We also set up a "guide" below the inlet of PAC which prevents supply air from being drawn into the inlet of PAC and is made of non-flammable corrugated carton. Moreover, in order to increase the airflow rate through textile, we cut the part of textile under the guide and made an opening. Experiments in a total of 18 cases were carried out and compared under three conditions, "no guide", "guide on textile" and "guide with opening", combined with previous 6 conditions, thus we conducted the experiment in 18 cases. In this study, the temperature, concentration of carbon dioxide as a tracer gas, and heat transfer rate by radiation were measured. Airflow rate through textile is calculated by tracer gas method.<br> In all cases, the temperature difference between FL+100mm and FL+1700mm is less than 3°C, which meets the recommendation in ASHRAE 55, and the temperature in Indoor space is close to pre-set temperature of PAC, so the cooling effect is biggest in the cases of “guide with opening” condition. In “guide with opening” condition, temperature distributions were almost same without in Case4, pre-set temperature of PAC was different, so PAC can be operated according to heat load in Indoor space. As for radiant effect, the average temperature differences between the textile surface and room air were compared, and the radiant effect is larger in the cases of “no guide” and “guide on textile” conditions.<br> Estimated exchange airflow rate are doubled when using guide, and increased by five times when the opening was provided below the inlet. The effect of opening at the bottom of the guides was larger than that of only using guide because the pressure loss across the textile was significant and its supply airflow rate decreases due to the resistance of textile. In “no guide” condition, the correlation coefficient between airflow rate and temperature difference between attic and indoor space was 0.91 (Q1) and 0.88 (Q2), which shows that the correlation between exchange airflow rate and temperature difference is stronger for “no guide” condition, compared to the other conditions with that resulted in smaller correlation coefficient.

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