Manuela J. R. Lúcio

Air quality inside a school building: air exchange monitoring, evolution of carbon dioxide and assessment of ventilation strategies

Abstract This paper presents an assessment of indoor air quality and various ventilation strategies inside a school building located in the south of Portugal. In the first phase, ventilation rate was experimentally evaluated using the tracer gas method. In the second part, different airflow typologies were investigated and, after calculating the air exchange and flow rates for each of them, the evolution of metabolic carbon dioxide inside the spaces was numerically estimated. Ventilation measurements were made in classrooms, auditorium, offices, staff and computer rooms. The assessment of ventilation was based on evaluating the carbon dioxide produced by the occupants for three ventilation approaches; these were: one based on cross-flow natural ventilation (in current use) and two based on forced ventilation systems. In the case of the forced systems, one was based on providing a constant flow to meet the required Portuguese ventilation standard in the main occupied rooms while the other was an adjusted constant rate based on a simple calculation procedure that took into consideration the air quality needs of all the spaces including corridors and atria. This approach was developed to produce an efficient yet inexpensive ventilation approach that did not incorporate expensive sensors and control systems. Carbon dioxide evolution predictions were made using software that evaluated the thermal response and the air quality of a building with complex topology. The numerical model used to evaluate air quality, was based on mass conservation integral equations in which the final equations system was solved through the Runge-Kutta-Fehlberg method with error control. A statistical study of the occupation cycle in the school building during the day was developed.

Evaluation of Thermal Comfort in Slightly Warm Ventilated Spaces in Nonuniform Environments

The present work analyzes and evaluates the global thermal comfort and local thermal discomfort levels of an occupant subjected to a symmetric nonuniform airflow, originated in common use ventilators. Several incident airflow directions are studied and their effects are described. The global thermal comfort level is evaluated through a multi-nodal numerical model that simulates human and clothing thermal responses, while the local thermal discomfort level is analyzed using an empirical model that predicts draft risks. The computational model of the human body and clothing thermal systems is based on the energy balance integral equations for human body tissue, blood, and clothing, as well as mass balance integral equations for the blood and transpired water in skin surface and the clothing. The human body is divided into 35 elements, each one in several layers of tissue, which could be protected through some clothing layers. A thermoregulatory system model was adapted to control the human body tissue temperature. The experimental tests were carried out in a test chamber in controlled environmental conditions; a thermal manikin was used to simulate the human posture, an indoor climate analyzer was used to measure the environmental variables around the occupant, and two ventilators were used to produce an airflow field around the occupant. The frontal and ascendant airflows from the ventilators placed in front of the occupant are characterized and their velocities around the occupant are measured for several incident angles. The global thermal comfort conditions of the occupant are evaluated both with and without ventilation, and the local thermal discomfort level is evaluated with ventilation for slightly warm, moderate environments.

Evaluation of indoor air quality in classrooms equipped with cross-flow ventilation

Abstract In this work the evaluation of indoor air quality in a classroom equipped with cross-flow ventilation is presented. A numerical methodology, based on comparison with experimental data, used in the evaluation of the air exchange rate, airflow rate and the age of the air, was applied in the first phase of this work. The evolution of carbon dioxide inside spaces, with different airflow typologies, was then predicted in the second part. The study was based on a school located in the South of Portugal. In the experimental methodology the tracer gas decay method was applied. In order to reduce the experimental time, the first minutes of the test were measured, while the remaining decay was obtained using a numerical exponential regression. Natural and forced cross-flow ventilation topologies were analyzed. In the case of forced ventilation, fresh air from the external environment was driven into the classroom through an air inlet using a supply fan. An extract strategy was also used in which stale air was mechanically extracted from the classroom. Natural ventilation consisted of opening perimeter and above-door windows. The forecast of carbon dioxide evolution was made using software that evaluates the thermal response of and air quality in a building with complex topology. The numerical model used to evaluate internal air quality was based on energy and mass conservation integral equations. These were solved using the Runge-Kutta-Fehlberg method with error control.

Study of Airflow around Occupants Seated in Desks Equipped with Upper and Lower Air Terminal Devices for Slightly Warm Environments

This paper will discuss the study of turbulent and mean airflow exiting air terminal devices and surrounding occupants seated in classroom desks for slightly warm environments equipped with personalized ventilation systems with upper and lower air terminal devices. In the turbulent airflow analysis the air root mean square, the air turbulence intensity, and the air velocity fluctuations frequencies are calculated, while in the mean airflow analysis the mean air velocity and temperature, the human body skin temperature, and the thermal comfort indexes are evaluated using a multi-node thermal regulation model for two different airflow rates. In the experimental tests made in a wood chamber a manikin, a ventilated desk, and two interior climate analyzers are used. The fluctuations of air velocity and temperature are measured in the air terminal devices and in 15 human body sections around the manikin, while the mean value of air relative humidity and mean radiant temperature are evaluated inside the experimental chamber. The mean air temperature in the air terminal devices is around 28°C (82.4°F), while the mean radiant temperature in the occupation area, the mean air temperature far from the occupation area, and the internal mean air relative humidity in the occupation area are around 28°C (82.4°F), 28°C (82.4°F), and 50%, respectively. The airflow rate in tests I and II are 25.75 m3/h (15.16 ft3/min) and 48.04 m3/h (28.27 ft3/min), respectively. The mean air velocity, root mean square, and turbulence intensity for test I are 0.59 m/s (1.94 ft/s), 0.13 m/s (0.43 ft/s), and 22.4%, in the upper air terminal device, and 0.9 m/s (2.96 ft/s), 0.15 m/s (0.49 ft/s), and 16.7%, in the lower air terminal device; while, for test II they are 1.72 m/s (5.64 ft/s), 0.16 m/s (0.52 ft/s), and 9.4%, in the upper air terminal device, and 1.06 m/s (3.48 ft/s), 0.16 m/s (0.52 ft/s), and 14.9%, in the lower air terminal device. In test I the mean air velocity and the airflow rate are higher in the lower exit air terminal device than in the upper exit air terminal device; while in test II, the opposite is true. It is also true that the skin temperature is slightly lower in test II than in test I, mainly in human body sections near the air terminal devices, such as the chest, arms, and legs. The occupant in test I conditions is thermally uncomfortable; however, in test II conditions, the obtained results are near the comfort recommendations.

Evaluation of Local Thermal Discomfort in a Classroom Equipped with Cross Flow Ventilation

Abstract This paper presents an evaluation of the local thermal discomfort level in a classroom equipped with cross ventilation, for a typical moderate summer day in Portugal. Three different ventilation configurations based on window and door opening were considered. In each, the thermal comfort, air quality and acoustical comfort conditions were also evaluated. This experimental study was made in the South of Portugal, exposed to a Mediterranean climate. Thermal comfort was based on the PMV index, the air quality was based on the air renovation rate and acoustical comfort levels were based on the reverberation time, voice clarity, definition and early reflection ratio. The detailed local thermal discomfort analysis was based on draught risk and uncomfortable air velocity fluctuations. Other measurements included relative humidity, the radiative mean temperature, carbon dioxide concentration (tracer gas decay), and noise level decay of impulsive response. Results showed that for the warmest of weather open windows and classroom door gave the best air quality and comfort conditions.

Numerical Study of the Influence of Opaque External Trees with Pyramidal Shape on the Thermal Behaviour of a School Building in Summer Conditions

This paper describes a numerical study of the influence of opaque external trees with pyramidal shape on the thermal behaviour of a school building in Summer conditions. The software used simulates the thermal response of buildings with complex topology under transient conditions. This software has previously been validated by real studies both in Summer and Winter conditions. The school building considered is localised in the South of Portugal. It has three levels divided into 97 rooms or spaces, 1277 main structures and 211 windows with plain transparent glass. In the model, the building is shaded by 49 ‘‘opaque’’ trees of pyramidal shape growing in front of the windows on one side of each building considered. The simulation considered a typical Summer school day with clear sky and with 800 occupants in the building. Two situations with the same configuration were analysed. In the first one, the trees (located in front of the windows) were placed to the West and South-West of the buildings, while in the second one, after a 180° building rotation, they were to the East and North-East. Both situations were studied with and without the presence of trees. Temperatures in the building and the occupant’s thermal comfort conditions were calculated.