Addressing Thermal Comfort Indoors and Outdoors: Novel Ventilation Systems for Safety and Comfort in Indoor Spaces and Mitigating Outdoor Thermal Discomfort in the Arab Region

Abstract

Students spend most of their academic life indoors, inside classrooms. These spaces should be carefully designed to maintain acceptable indoor environmental quality (IEQ) and boost the students’ cognitive performance and academic outcomes. Achieving acceptable IEQ levels faces many challenges which should be addressed. In fact, classrooms present a high occupancy density which creates a high thermal load and poor indoor air quality affecting thus the thermal comfort and health of the students. In addition, such spaces are characterized by close seating arrangement which accentuates the risk of cross-infection by pathogens released from an infected student. Therefore, considerable efforts should be made to come up with adequate techniques to provide acceptable thermal comfort and air quality levels and confine the spread of contagious pathogens inside classrooms. This should be achieved without compromising energy efficiency. The remainder of the student time is allocated to engaging in outdoor activities. In this matter, understanding outdoor thermal discomfort is crucial for pedestrians, as well as for shaping environmental health, urban planning, and climate adaptation strategies. As global temperatures are increasing due to climate change, cities worldwide are experiencing more frequent and intense heat waves that threaten public health. Identifying the factors contributing to outdoor thermal discomfort is necessary for urban planners, architects, and policymakers to create sustainable, resilient cities that provide comfortable outdoor environments. This work addresses human thermal comfort both indoors and outdoors, hence it is divided into two parts. In the first part, this work proposes novel hybrid ventilation strategies with minimal energy consumption to enhance the IEQ inside classroom spaces. The first proposed ventilation strategy is the pulsating jet ventilation (PJV) system that imitates the transient behavior of natural wind by supplying the air in an ON-OFF manner inside the classroom. This ventilation system enhances the convective heat transfer between the human body and its surroundings and creates elevated thermal comfort level at elevated room temperature. In addition, with a careful selection of the system parameters such as the supply airflow rate and intermittency period, the PJV is able to maintain the CO2 at acceptable levels. However, the intermittent aspect of the PJV creates high turbulence levels inside the classroom which aggravates the spread of infectious pathogens released by infected students and elevates the cross-infection risks. The second proposed ventilation system is the downward piston ventilation (DPV) which is highly recommended in hospital rooms to contain the spread of contaminants and ensure acceptable air quality levels. This system is based on the “push-pull” principle and supplies a high flowrate of clean air in a downward parallel manner from the ceiling level. However, this system requires an elevated energy bill to be able to supply high airflow rates at cool temperatures into the classroom. It was noticed that each of the suggested ventilation systems has its advantages, but it also presents several drawbacks, necessitating the use of "add-on" devices to achieve comprehensive functionality. The most practical and energy-efficient “add-on” devices are the portable air cleaners (PACs), the upper-room ultraviolet germicidal irradiation (UR-UVGI) lamps, and the localized exhaust (LE) devices. These devices are proposed to assist the ventilation systems (PJV and DPV), and their effectiveness is tested using computational fluid dynamic simulations by developing 3D models of the classroom and its different components in ANSYS software. The developed models were validated experimentally, and used to simulate the velocity fields, temperature fields, contaminants spread, and potential cross-infection risks inside the classroom. In the second part, this work examines outdoor thermal comfort in the Eastern Mediterranean and Middle East region spanning from 10 °N to 50 °N in latitude and from 20 °E to 60 °E in longitude for an overall period of 43 years ranging from 1980 to 2023 using ERA5 reanalysis data. It explores spatiotemporal variations in weather parameters (i.e., dry bulb temperature, relative humidity, and wind speed) to identify the year during which a climatic shift occurs and analyze its severity in each city of the studied domain. Then, the comfort levels are plotted across the region using five different thermal comfort indices: the effective temperature (ET), the heat index (HI), the humidex (HD), the wet bulb globe temperature (WBGT), and the temperature humidity index (THI). The number of discomfort hours per summer day and their trend of variations are calculated for major cities across the region and for each year of the studied period. In addition, the relation between discomfort days and El Niño southern oscillation events is investigated throughout the 43 years.