This study aims to suggest an improved experimental method to reveal the ability of indoor plants to reduce CO2 concentrations, as well as to display the individual CO2 reduction characteristics of various indoor plants in accordance with this improved method. In previous studies, experiments were conducted under the condition in which the CO2 concentration in the experimental chamber is set only once to a high initial level of 1,000 ppm. However, in real conditions, CO2 concentration gradually increases in a room after the occupants enter. Hence, the existing experimental method can be improved in view of "light saturation and CO2 compensation". Accordingly, in this study, the CO2 reduction characteristics of indoor plants under 2 conditions used in the existing method of measurement (Case 1) and the condition in the new method, which considers that CO2 concentration gradually increases through the respiration of experimental animals (Case 2)-were measured and compared against each other. For all plant samples, the level of CO2 reduction was higher in Case 2 than in Case 1, and the rate of CO2 reduction increases with time. The inflection point of CO2 concentration appeared at leaf areas of 9,000 cm 2 in peace lily and areca palm, and 6,000 cm 2 in weeping fig.Additional key words: CO2 reduction quantity, compensation point, indoor air quality, respiration of experimental animals Hort. Environ. Biotechnol. 52(3):321-329. 2011.

This research has investigated physical variables affecting indoor thermal comfort and subjective responses of thermal comfort of students in a university in Korea in which the weather is oceanic temperate climate, and has been performed to contribute to the research fields of Sustainable Thermal Standard and Adaptive Thermal Comfort (ATC). This research is based on the ISO 7730-2005 standard and the ATC theories and 4 main variables of PMV such as dry bulb temperature (Ta), relative humidity (RH), black bulb temperature (Tg), and air velocity (Va) are measured once a week during two regular semesters. A clothing insulation, a thermal sensation vote (TSV), an acceptability of thermal environment, and a preference for cooling and heating are investigated at the same time using a questionnaire. This study was carried out for 26 weeks during the spring season, from March to June 2009, and the autumn season, from September to December 2009. The main achievements of this study are as follows. Monthly Mean Outdoor Temperature (MMOT) and Operative Temperature (OT) in the classroom during research periods are 7.4~23.3°C and 17.5~29.0°C, respectively. The acceptability ratio of thermal environment shows over 80% when the range of OT in the classroom is 17~25°C, and the range can be applicable to operative index of heating and cooling of classroom. The mean TSV of respondents is almost "neutral (0)" when the PMV in the classroom moves to "neutral (0)" and "slightly cool (-1)", and the TSV is almost "+1.5" when the PMV moves to "slightly warm (+1)". The acceptability ratio of thermal environment is slightly different from ASHRAE Standard 55-2004. So it is necessary to more investigate standard range of acceptability of thermal environment in oceanic temperate climate region using much more databases.

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High density polyethylene (HDPE) tube has been successfully utilized in surface water source heat pump (SWSHP) system as a surface water heat exchanger. Since the heat transfer coefficient (U value) of the HDPE tube directly affects performance and energy efficiency of SWSHP, this research aims to increase U value of HDPE tube by grooving external surface of conventional 32A HDPE tube to reduce cross-sectional volume. The final shape of grooved HDPE tube is similar to that of fin. In order to verify the performance of grooved HDPE tube, the U values of grooved and smooth tube were compared experimentally. According to the results, U value of grooved tube showed approximately 21.5% increase with natural convection and 23.5% with forced convection system than U values obtained from smooth tube. The reason for such increase in U value was found to be the reduction in cross-sectional volume of the HDPE tube.

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