Abstract—In the tropics, indoor thermal environment is usually provided by a cooling mode to maintain comfort all year. Indoor thermal environment performance is sometimes different from the standard or from the first design process because of operation, maintenance, and utilization. The field study of thermal environment in the green building is still limited in this region, while the green building continues to increase. This study aims to clarify thermal performance and subjective perception in the green building by testing the temperature set-points. A Thai green office was investigated twice in October 2018 and in May 2019. Indoor environment variables (temperature, relative humidity, and wind velocity) were collected continuously. The temperature set-point was normally set as 23 °C, and it was changed into 24 °C and 25 °C. The study found that this gap of temperature set-point produced average room temperature from 22.7 to 24.6 °C and average relative humidity from 55% to 62%. Thermal environments slight shifted out of the ASHRAE comfort zone when the set-point was increased. Based on the thermal sensation vote, the feeling-colder vote decreased by 30% and 18% when changing +1 °C and +2 °C, respectively. Predicted mean vote (PMV) shows that most of the calculated median values were negative. The values went close to the optimal neutral value (0) when the set-point was set at 25 °C. The neutral temperature was slightly decreased when changing warmer temperature set-points. Building-related symptom reports were found in this study that the number of votes reduced continuously when the temperature was warmer. The symptoms that occurred by a cooler condition had the number of votes more than ones that occurred by a warmer condition. In sum, for this green office, there is a possibility to adjust a higher temperature set-point to +1 °C (24 °C) in terms of reducing cold sensitivity, discomfort, and symptoms. All results could support the policy of changing a warmer temperature of this office to become “a better green building”. Keywords—Thermal environment, green office, temperature set- point, comfort. I. INTRODUCTION ECENTLY, green building continues to be developed rapidly in the tropics [1]. Indoor environment is one of the main criteria because it is important to people who live inside in the building. Indoor air quality (IAQ) and its effects on health and comfort have been studied in several parts for decades [2]. The green building is potential to reduce energy use and improve satisfaction [3]. The gap between the design performance was sometimes different from the actual Tanadej Sikram is with the Department of Architecture and Building Engineering, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji-shi, Tokyo 192-0379 Japan (phone: +81 42-677-2694, e-mail: tanadej.si@ gmail.com). performance when the use of energy consumption was exceeding [4]. The actual thermal environment in the tropics was often controlled as low as those in the temperate climate zone [5]. The comfort temperature of some countries in Southeast Asia (Indonesia, Malaysia, and Singapore) was between 25.6 and 26.4 °C which was lower than that of other regions [6]. To achieve the ideal indoor thermal environment quality, the office needs to deal with energy saving and satisfaction by adjusting several factors. For example, the study of [7] in the UK tried to adjust temperature set-points in the shared-space office from 22 to 24 °C in summer. This study declares that changing higher temperature in this range did not affect discomfort levels, but thermal environments were better fit to the summer comfort zone. It was also beneficial to energy consumption in the long term [8]. However, occupants in the green office may expect higher levels of IAQ [9]. The acceptable vote in the conventional cellular office can be changed rapidly when the set-point was colder than 23 °C and warmer than 26 °C [10]. It is questionable that how much the set-point can be adjusted in the green large-scale building. In order to support more evidence, this paper present one part of the ongoing study in the tropics which mainly focuses on a case study in Bangkok, Thailand. It aims to identify a current situation of indoor thermal environment and try to enhance satisfaction by following the previous study of changing temperature set- point. It would be advantage to the office to apply to air- conditioning management to support a better green building performance in the tropics. II. METHODOLOGY A. Indoor Environment Measurement The surveyed office is located in a center of Bangkok, Thailand. The office has obtained LEED Gold certification with a well-operated building management. The air conditioning system of the office is central water chiller system. The building uses the fresh-air system for the ventilation. During the survey, outdoor temperature was most stable but sometimes it was cloudy. The average of outdoor temperature during the day was between 32 and 35 °C. The average humidity was ranging at 78%–84%. In fact, the owner was aiming to apply the concept of saving energy and wellbeing encouragement in the office. So, we had an opportunity to do the actual test which was on the 11 th floor. Table I describes the information of the office. T. Sikram, M. Ichinose, R. Sasaki Field Study on Thermal Performance of a Green Office in Bangkok, Thailand: A Possibility of Increasing Temperature Set-Points R World Academy of Science, Engineering and Technology International Journal of Civil and Environmental Engineering Vol:14, No:3, 2020 78 International Scholarly and Scientific Research & Innovation 14(3) 2020 ISNI:0000000091950263 Open Science Index, Civil and Environmental Engineering Vol:14, No:3, 2020 publications.waset.org/10011089/pdf