CMU Intellectual Repository: Analysis of thermal comfort and particulate matter dispersion in a classroom under natural ventilation = การวิเคราะห์ค่าความสบายเชิงความร้อนและการกระจายตัวของอนุภาคมลสารในห้องเรียนภายใต้การระบายอากาศแบบธรรมชาติ / Chanawat Nitatwichit

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Thesis Title Analysis of Thermal Comfort and Particulate Matter Dispersion in a Classroom under Natural Ventilation

Author Mr. Chanawat Nitatwichit

Degree Doctor of Philosophy (Mechanical Engineering)

Thesis Advisory Committee Asst. Prof. Dr. Yottana Khunatorn Chairperson Assoc. Prof. Dr. Chutchawan Tantakitti Member Asst. Prof. Dr. Nakorn Tippayawong Member

ABSTRACT

The main objective of this work is to experimentally and numerically investigate the effect of natural ventilation on thermal comfort and dispersion behavior of particulate matter inside a classroom. In this study, simulation of the flow inside a model room is conducted using CFD technique. Examination of relationship between indoor airflow patterns and thermal comfort and a relationship between indoor airflow patterns with dispersion behavior of particles are performed. Optimal conditions of indoor airflow patterns associated with thermal comfort and indoor air quality due to dispersion of particles are evaluated and recommended. The model room is in accord to a standard-sized classroom specified by Department of General Education (8 m u 8 m). CFDRC^TM software is used as a tool with a weather data as a base reference of boundary condition including air velocity, air temperature, relative humidity, and wind direction. Weather data of Chiang Mai during school period is employed as a boundary condition in the modeling. Thermal comfort index, i.e. PMV refers to thermal comfort zone in accordance with the reference method of ASHRAE standard 55 and Thailand comfort chart. Indoor air quality (respirable particle) refers to an Occupational Safety and Health (OSH) standard of working environment of Thailand.

The numerical results of the building model were qualitatively validated with experimental set-up using flow visualization with hydrogen bubble technique. The numerical results of classroom model were verified using measuring data within real classroom. The numerical results were found to agree well with experimental results.

The flow simulation of building domain was performed with prevailing wind to identify a proper strategy of flows around building. Four-storey school building domain had three classrooms in each of 2^nd - 4^th floor except the ground floor is open space with no wall. Wind speed and directions close to openings were averaged and used to represent the inlet boundary conditions of the classroom domain. Simulated results revealed that the cross orientation of building to wind direction might not always be necessary to obtain thermally comfortable environment in the classroom. Cross ventilating flows through the openings were investigated. The opening discharge coefficients of six different type windows and a door were determined. Wind, stack and combined effects through the openings were characterized and compared for a range of different wind speeds and surface wall temperatures. Results showed that sliding windows gave the highest Cdvalue among openings considered by stack effect. Casement and side hung (90^O) windows appeared to provide high air exchange rates.

Their discharge coefficients ranged between 0.63 and 0.83. As far as combined effects are

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concerned, buoyancy was found to be significant at low wind speed (0.25 m/s). Acceptable indoor airflow patterns and thermal distributions can be expected in the occupied zone. The findings from this investigation are useful to develop a plan for a natural ventilation strategy of classrooms to enhance thermal comfort levels. A classroom model with a capacity of 32 students is of standard dimensions (8.0 m long u 8.0 m wide u 3.5 m high). The room was equipped with standard school desks and manikins were included in the classroom domain.

The simulation was carried out, focusing on a comfortable indoor thermal environment of the occupants. Main inlet flow from openings was not found to affect students directly. However, a comfortable feeling can occur within the occupied zone in winter where ambient temperature was low. At incoming wind speed of 4.0 m/s, mean PMV values were found to range from -0.75 to -0.26. Particle trajectory was determined while entered the openings and flew within the classroom. It was found that low incoming wind speed (0.5 m/s) and stack effects influenced its trajectory. The trajectory that entered through the windows was suppressed and curved down to occupants. Diagonal wind thru the opening brought the particulate matter to occupant, which occupied downstream.

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