Improving Indoor Air Quality to Reduce COVID-19 Infections in School - Selected Works

Department of Architecture Faculty of Architecture and Planning King Abdulaziz University

Design Guidelines for Improving Indoor Air Quality and Reduce COVID-19 Infection Possibilities in Schools Postgraduate Research Projects By: Eng. Siraj Mahmoud Eng. Omar Al-heishi Eng. Feras Balkhi Eng. Yousef Khoja Supervisor: Dr-Ing. Mohannad Bayoumi

Academic Year 2019-2020

CONTENTS

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Improving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method

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By: Omar Al-heishi

Reconsidering School Design, Assessment Ventilation Efficiency influences on COVID19 at generic classrooms spaces in different climates of Saudi Arabia By: Feras Balkhi

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Improving the Efficiency of Mechanical Ventilation of the Classrooms to Reduce the Risk of Infection of COVID-19

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By: Yousef Khoja

By: Omar Al-heishi

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Redesigning Classroom Windows to Control Daylight to Reduce the risk of Infection with COVID-19 By: Siraj Mahmoud

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Indoor Air Quality (IAQ),Mitigating CO2 concentration in classrooms using adjacent corridors and atriums By: Feras Balkhi

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

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Methods to prevent the spread of COVID19 in classrooms using mechanical and hybrid ventilation systems By: Yousef Khoja

1. Proving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method By: Omar Al-hebshi

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1. RESEARCH PROBLEM

To examine thermal sensation of the university students, Google form based questionnaire was published in variety of social media, 75 students participated in the questionnaire The questionnaire contains only one question asking the students to evaluate their thermal sensation inside the classroom by choosing one of the PMV scale's values : cold, cool, slightly cool, neutral, slightly warm, warm and hot, questionnaire results are shown in the Fig 1. Results of the questioner indicate that 17.13 %, 33.30 % and 18.60% of the students have cold, cool and slightly cool sensations respectively while only 22.60% of the students voted that they have a neutral sensation. Results of the questionnaire illustrated that temperature sensation inside classrooms is tend to be cold and lower than the comfort zone of the students.

Fig. 1: Results of the implemented questionnaire to evaluate students' thermal sensation of the students

Proving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method

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2. RESEARCH OBJECTIVE Improving thermal sensation inside classrooms by testing other ventilation types and controlling air temperature / air velocity without making major changes in the existing buildings and with minimum technical complexity.

3. RESEARCH QUESTION What is the best configuration of mechanical air supply diffusers in classrooms to improve thermal sensation and help avoid draft under certain conditions?

4. LITERATURE REVIEW In a study carried out by Kumar et al. [1] The researchers investigated the progress in thermal comfort studies about classrooms over the last 50 years in different parts of the world to gives detailed insight of the thermal comfort studies done in classrooms across the world.

Table 1 summarize recommended values of air velocity and air temperature extracted from the studies investigated by Kumar and his team about university classrooms within subtropical and hot-humid climatic zones as these are the climatic conditions of Jeddah where our targeted classrooms located.

In order to comply with ASHRAE 55, the recommended thermal limit on the 7-point scale of PMV is between -0.5 and 0.5. ISO 7730 expands on this limit, giving different indoor environments ranges. ISO defines the hard limit as ranging between -2 and +2, for existing buildings between -0.7 and +0.7, and new buildings ranging between -0.5 and +0.5 [2].

Table 2 gives recommended levels of acceptance for operative temperature and air velocity for three classes of environment according to ASHRAE 55 and ISO 7730 as explained above.

Proving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method

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4. LITERATURE REVIEW Table 1: Summary and averages of air temperature and velocity extracted from the study of Kumar and his team

Table 2: Recommended levels of acceptance for operative temperature and air velocity according to ASHRAE 55 and ISO 7730

In another study carried out by Fong et al. [3] in Hong Kong to investigate the acceptability of thermal conditions under three different ventilation strategies: Mixing ventilation (MV), Displacement ventilation (DV) and stratum ventilation (SV), the first strategy

(MV) is the most conventional air distribution method as the supply air is pumped into the occupied zone using fans and mix completely with the existing air before making any contact with the occupants, It is common in this strategy to use the vertical supply from the ceiling to avoid any obstacles such as partitioning walls. The second ventilation strategy is the displacement ventilation (DV) in which supply air is driven at a low level and reach the occupants before becoming warmer and thus lighter and extracted from the ceiling.

Proving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method

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4. LITERATURE REVIEW Jackman [4] recommend using lower air velocities - less than 0.25 m/s - in case of displacement ventilation to avoid disrupting comfort of occupants. The third ventilation mode is the stratum ventilation (SV) where air supply horizontally using diffusers mounted at head or chest level on the walls of a room. Fong and his colleagues concluded the stratum ventilation strategy (SV) can provide mor satisfactory thermal conditions for the occupants even at elevated temperature up to 27.1-27.9 °C. According to Toftum [5] who demonstrated that in metabolic rates between 1.1-1.4 met (sedentary metabolic rate) and temperatures from 22.5-23.5 °C, with air velocities less than 0.25 m/s at 1.1 m above the floor, only few occupants complained of air draft and preferred lower air velocities, while most of occupants preferred no change at the same temperature range and air velocity range of 0 to 0.2 m/s.

5. METHODOLOGY measurement results in addition to evaluating the current conditions according to the relevant standards 4. Detecting the problems 5. Simulate the current situation in both classrooms to optimize the validation of the simulation 6.

Simulate the proposed scenarios for each classroom separately to enhance the current situation 7. Evaluating the proposed scenarios based on the results of the simulation to determine the best one 8. Selecting the best scenario for both classrooms. Methodology steps are illustrated in Fig. 2.

Proving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method

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5. METHODOLOGY

surfaces area and orientation in order to have a significant sample that represents the whole building.

The characteristics regarding architecture typologies, air conditioning system, electrical lighting, number of sittings, windows, classroom area, number of sittings and finishing materials are reported in Table 3 for each of the investigated classrooms.

Table 3: Characteristics of the investigated classrooms

Fig. 2: Results of the implemented questionnaire to evaluate students' thermal sensation of the students

6. CASE STUDY ROOMS Two classrooms in building 535 of the preparatory year faculty were selected, the selection of the classrooms based on several factors such as the availability of the students and teachers during the day, classroom area, number of students, window Proving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method

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7. DATA COLLECTION Air temperature and air velocity has been recorded for each seat location inside classrooms, 60 and 45 readings have been taken from classrooms A and b respectively based on how many seatings each classroom contains. 10 readings have been taken for each point each of which lasted for 10 minutes at 1.1 meters from the floor of the classroom.

Fig. 3: Pictures from classroom A

Measurement process Took a place between 1 and 4 PM when classrooms in the faculty of the preparatory year are usually occupied by students in October 9th 2019. Figs. 3 , 4 show some pictures of classrooms A and B respectively while Fig. 5 shows detailed plans of the selected classrooms.

Fig. 4: Pictures from classroom B

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7. DATA COLLECTION

Fig. 5: Detailed plans of the selected classrooms

Fig.6 show the distribution of air temperature and air velocity readings in classroom A according to ASHRAE 55 and average values from table 1. in term of air velocities, most values lay down 0.30 m/s which is very acceptable range according to Toftumm [5].

Air temperature readings - as shown in Fig.6 in a red points - indicate clearly that most of the values are not included within ASHRAE 55 comfort zone, although these readings are not compatible with ASHRAE 55, almost all of them are located

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7. DATA COLLECTION within 1 degree down the limit ( between 22 and 23 °C ) what might not be a significant issue .

Fig. 7 show the distribution of air temperature and air velocity readings in classroom B according to ASHRAE 55 and average values from table 1.

Unlike classroom A, classroom B showed less air velocities an all readings are lower than 0.18 m/s which is also fine according to Toftumm [5] as previously mentioned.

Air temperature readings in classroom B are much farther from ASHRAE 55 comfort zone as air temperature in many locations / seating places lays between 22 and 21 °C unlike classroom A which mean cooler sensation and less thermal comfortability.

Fig. 6: Temperature and velocity readings in classroom A

Fig. 7: Temperature and velocity readings in classroom B

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8. SIMULATING CURRENT CONDITIONS Fig. 8 shows the inlets, outlets and air flow in classroom A while Fig. 9 shows inlets, outlets and air flow in classroom B. Figs. 10 and 11 show the simulation results of classrooms A and B in their current conditions respectively in horizontal and vertical sections. The black arrows in the figures represent areas with a value (air temperature or air velocity) that comply with the comfort requirements mentioned before while the red arrows indicate to locations where temperature or velocity values don't fit in the comfort zones limits.

Fig. 8: Inlets, outlets and air flow in classroom A

Fig. 9: Inlets, outlets and air flow in classroom B

Proving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method

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8. SIMULATING CURRENT CONDITIONS

Fig. 10: Distribution of air temperature and air velocity in classroom A

Proving thermal sensation in classrooms with respect to draft avoidance by optimizing the mechanical air supply method

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8. SIMULATING CURRENT CONDITIONS

Fig. 11: Distribution of air temperature and air velocity in classroom B

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9. CFD SIMULATION OF PROPOSED SCENARIOS In this part, four different ventilation strategies or scenarios are going to be tested and compared with the current conditions in the classrooms to optimize thermal sensation.

In all four scenarios the supply air temperature and velocity will be fixed to 24 °C and 2 m/s respectively, these scenarios ordered as following :

Fig. 12: Air flow simulation using Mixing Ventilation in classrooms A and B respectively

1. Mixing ventilation scenario (MV) in two different cases 2. Displacement ventilation (DV) 3. Stratum ventilation (SV), Figures 12,13 and 14 show the simulation of air flow with these scenarios respectively in the two classrooms.

Fig. 15 illustrates the four proposed scenarios while table 4 show the framework settings applied to run the CFD simulation for these scenarios using Ansys Fluent after validating the CFD program using the experimental measurements.

Fig. 13: Air flow simulation using Displacement Ventilation in classrooms A and B respectively

Fig. 14: Air flow simulation using Stratum Ventilation in classrooms A and B respectively

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9. CFD SIMULATION OF PROPOSED SCENARIOS Some scenarios showed high compatibility with ASHRAE 55 standard in term of PMV value especially in cases of displacement and stratum ventilation methods as shown in Fig. 16 which represent the tested scenarios in addition to the current conditions with ASHRAE 55 recommended PMV zone highlighted in light green.

Table 4: CFD simulation framework for the scenarios

Fig. 15: Proposed scenarios for alternative ventilation strategies

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9. CFD SIMULATION OF PROPOSED SCENARIOS

Fig. 16: Evaluating scenarios based on PMV value

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10. CONCLUSION This study was conducted to enhance thermal sensation in the classrooms by testing and comparing several mechanical ventilation strategies using CFD simulation, the main conclusion of the present work can be summarized in the following points: 1. The distribution of air temperature and air velocity varies in different places within the classrooms, while the best places include the middle section and the front one adjacent to the window, the worst sections generally are the ones at the back of the classroom opposite to the windows, where air temperature and air velocity are much further from the comfort limits .

3. Testing different ventilation methods with reducing supply air temperature to 22 °C and retaining supply air velocity at 2 m/s showed that the currently installed displacement ventilation method don’t give the recommended PMV value by ASHRAE 55, although the PMV value of this method can be enhanced by using linear ceiling diffusers as tested in scenario 1.1 .

4. The two best ventilation strategies in the two classrooms are the stratum and displacement ventilation in order, as both resulted in more consistence distribution of air temperature and air velocity in addition to PMV values which are closer to neutral conditions.

2. The current conditions of the classrooms don’t fit within ASHRAE 55’s comfort zone, whereas air temperature is lower than 23 °C in most cases (it should be between 23-26 °C to match ASHRAE 55), air velocities tend to be lower than 0.25 m/s usually is ok.

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11. REFFERENCES 1.1 Secondary Title Here

1.

Kumar, M., Ooka, R., Rijal, H. B., Kumar, S., & Kumar, A. (2019). Energy & Buildings Progress in thermal comfort studies in classrooms over last 50 years and way forward. Energy & Buildings, 188–189, 149–174.

2.

Guenther, Sebastian. "What Is PMV? What Is PPD? The Basics of Thermal Comfort." www.simscale.com.

Last modified September 18, 2019. https://www.simscale.com/blog/2019/09/wh at-is-pmv-ppd/.

3.

Fong, M. L., Vic Hanby, Rick Greenough, Z. Lin, and Y. Cheng. 2015. “Acceptance of Thermal Conditions and Energy Use of Three Ventilation Strategies with Six Exhaust Configurations for the Classroom.” Building and Environment

4.

P.J. Jackman, Displacement Ventilation, BSRIA, 1990. Technical Memorandum 2/90.

5.

Toftum, Jorn. (2004). Air movement - Good or bad?. Indoor air. 14 Suppl 7. 40-5. 10.1111/j.16000668.2004.00271.x.

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2. Improving the Efficiency of Mechanical Ventilation of the Classrooms to Reduce the Risk of Infection of COVID-19 By: Omar Al-hebshi

Improving the Efficiency of Mechanical Ventilation of the Classrooms to Reduce the Risk of Infection of COVID-19

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1. INTRODUCTION Throughout the human history, the humanity has faced a lot of disasters, wars and countless different challenges, but COVID-19 is totally different invisible enemy. Countries around the world have developed their own procedures to deal with this pandemic such as quarantine, but everyone agrees that total lockdown is not a solution [1]. Closure due to COVID-19 lockdown involved most of the facilities around the world specially the most crowded ones including schools, UNESCO reported that around 60% of the students around the globe had their education effected because of the pandemic lockdown [2]. Recent research outlined the probability of spreading COVID-19 through a long-range aerosols in badly ventilated restaurants in Guangzhou, China [3].

Majority of viruses including COVID-19 are smaller than 100 nm in size, the droplets carrying the virus contain water and some organic materials, increasing the concentration of these droplets in the air can increase the risk of infection specially when the air is stagnant, this could be worsen in the crowded space such as schools particularly with insufficient ventilation system[1].

ASHRAE stated that making changes in building's ventilation system can reduce the exposure to the infected droplets and thus the risk of infection[4].

In addition, Adequate distribution of the inlets and outlets of the ventilation system guarantee balanced delivery of ventilation air within the space what keeps the air moving and prevent air stagnation [5]. Previous research showed that healthy individuals sitting around table more than 1 meter from an infected person have got the infection, the author interpreted that by the transmission of the droplets containing the virus via the air stream generated by the air conditioning system [6]. Correct orientation of airflow and balanced pressure generated by welldesigned and maintained ventilation system can mitigate the risk of infection [7].

According to the World Health Organization (WHO), COVID-19 could infect people in hot humid environments as well as the cold dry environments.

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1. INTRODUCTION In cold environments, drying the mucus in the mouth can reduce its defensive abilities. So, it is mandatory to ensure supplying enough ventilated air (30 m3 /h per person) in addition to air temperature between 17-28 °C and air humidity between 40-70% [8].Respiratory droplets are generated during the respiration activities such as sneezing, coughing and speaking. once they release to the air, they start moving based on the fluid dynamics of the particles and the conditions of the surrounding environment [9].Several factors control the transmission of the infectious droplets in the air including: density, velocity and size of the droplets when they release during the respiratory process in addition to the indoor air velocity and flow direction [10]. Small droplets can remain in the air for a considerable amount of time, any particles below 5μm are considered airborne [9].

Researches conducted by Oregon university outlined how air conditioning or hybrid ventilation can stimulate the spread the pathogens for more than 6 feet even if the source was located far from the system inlets, it is not just the amount of fresh air that needs to be discussed, but also the dynamics of the flow and its distribution in the zones.

Previous research has conducted a comparative study on three different ventilation strategies in a double patient ward. The three ventilation strategies have the same air change rate of 12.3 h1. Flow patterns of the respiratory aerosols were analyzed and compared in the three strategies.

Strategy 1 has the inlets and outlets on the same wall side. Strategy 2 has the inlets and outlets on opposite sides of walls. Strategy 3 has one inlet in the ceiling while two outlets are mounted in far sidewall. Results showed that flow patterns of the different droplets and particles depend on their diameters, and that ventilation strategy 1 has the highest ability to remove the smaller particles [11].

A closer look to the literature on the efficiency of ventilation systems in reducing viruses' infection in schools and classrooms, however, reveals a number of gaps and shortcomings. The majority of previous studies were limited to assess ventilation performance in preventing and spreading diseases in healthcare facilities and restaurants.

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1. INTRODUCTION

2. METHODOLOGY 2.1 Case Study Rooms

Furthermore, how ventilation systems can influence the spread of infection inside the classrooms? and how can they be employed to provide healthier indoor environment and reduce infection possibilities? These are arguably important questions to be addressed in this study to bridge the mentioned research gap.

American Institute of Architecture (AIA) [12] indicated two different classroom sizes that are the most common in schools and determined the occupancy of each one before and during the pandemic considering the safety measure as demonstrated below:

This paper addresses the efficiency of different ventilation strategies on the age of air, indoor air quality and thermal comfort of students, so far lacking in the scientific literature.

2.1.1 Single Classroom: the size of this classroom is 148.6 m², this classroom used to hold 24 students before the pandemic or 3 m²/student as shown in Figure 1 . After the pandemic, the capacity of this classroom was reduced to only 21 students or 6.1 m²/student as shown in Figure 2 .

2.1.2 Double Classroom: the size of this classroom is 74.3 m², this classroom used to hold 48 students before the pandemic or 3 m²/student as shown in Figure 3. After the pandemic, the capacity of this classroom was reduced to only 24 students or 6.1 m²/student as shown in Figure 4.

These two sizes of the classrooms were chosen to be the samples to simulate during this study

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2. METHODOLOGY

2. METHODOLOGY

2.1 Case Study Rooms

2.1 Case Study Rooms

Fig. 1: Single classroom before the pandemic

Fig. 3: Double classroom before the pandemic

Fig. 2: Single classroom during the pandemic

Fig. 4: Double classroom during the pandemic

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2. METHODOLOGY

2. METHODOLOGY

2.2 Ventilation Methods

2.2 Ventilation Methods

This study is going to investigate the previously mentioned classrooms under the following ventilation strategies: The first ventilation strategy is Mixing Ventilation (MV) which is the most conventional air distribution method as the supply air is pumped into the occupied zone using fans and mix completely with the existing air before making any contact with the occupants, it is common in this strategy to use the vertical supply from the ceiling to avoid any obstacles such as partitioning walls. The second ventilation strategy is the Displacement Ventilation (DV) in which supplied air is driven at a low level and reach the occupants before becoming warmer and lighter and extracted from the ceiling. It is recommended to use lower air velocities - less than 0.25 m/s - in case of displacement ventilation to avoid disrupting comfort of occupants. The third ventilation mode is the Stratum Ventilation (SV) where air is supplied horizontally using diffusers mounted at head or chest level on the walls of a room. The three ventilation strategies are illustrated in Figure 5.

Fig. 5: Ventilation strategies used in the study

2.3 Procedures Based on the assumption of how the air movement in the zone can affect the transmission of infection, this study has been divided into two parts: studying the conditions of the sample classrooms before and during the pandemic to analyze each case individually and stablish a comparison between the two cases at the end.

Each part consists of the following steps: 1. Simulating the three ventilation system (MV, DV and SV) in the single classroom.

2. Simulating the same three ventilation systems in the double classroom.

3. Evaluate the results of the simulation based on a specific criterion described in Evaluation Criteria section.

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2. METHODOLOGY

2. METHODOLOGY

2.3 Procedures

2.4 Evaluation Criteria

4. Comparing the simulation results based on the evaluation criteria for the two classrooms before and during the pandemic.

Simulation results are going to be evaluated based on sets of criteria illustrated in Figure 7 as following:

5. Determining the best ventilation strategy for each part of the study and for each one of the two classrooms based on the evaluation criteria.

1. Essential criteria: include air quality indices of age of air, humidity and CO2 levels.

The flow chart in Figure 6 demonstrate the methodology of this study and Table 1 show the different cases to be tested in the simulation process of the study.

2. Supplementary criteria: include thermal comfort indices of predicted mean vote (PMV), predicted percentage of dissatisfied (PPD) and thermal ventilation effectiveness (TVE).

3. Air movement analysis using the CFD technology.

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2. METHODOLOGY 2.4 Evaluation Criteria

Fig. 6: Methodology procedures of the study

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2. METHODOLOGY

2. METHODOLOGY

2.4 Evaluation Criteria

2.4 Evaluation Criteria PPD is an index used to estimate the percentage of people who feel uncomfortable under certain thermal conditions.

PMV is a seven-point index to predict thermal sensation of occupants ranging from hot (+3) to cold (-3). The acceptable thermal environment with PPD < 10, must have PMV value between - 0.5 and + 0.5.

Fig. 7: Evaluation criteria of the study Table 1: Framework of the study

Thermal Ventilation Effectiveness can calculated from the following equation: TVE = (Tⅇ-Ts)/(T-Ts) Where

be

Equation 1 [13]

Te

= Air temperature at exhaust

Ts

= Air temperature at supply

T

= Mean room temperature

ASHRAE 62-2004 suggested VE value = 1 for cool air ceiling supply systems, and VE value = 1.2 for DV [14].

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2. METHODOLOGY

2. METHODOLOGY

2.5 Simulation’s Boundary Conditions

2.6 Grid Independence Analysis

Table 2 demonstrate the boundary conditions of the simulation regarding classroom properties, occupants, controller setpoints and operating Schedules.

Table 2 Boundary conditions of the simulation 1. Classroom properties Classroom Location Length Width Height Ventilation system type Supply air temperature Ventilation Methods 2. Occupants Number of occupants Clothing level

Metabolic rate 3.Controller Setpoints Targeted temperature Targeted relative humidity Simulated period 4. Operating Schedules Classes Time Windows opening schedule Door opening schedule

Jeddah, Saudi Arabia Vary from Case to Case Vary 3m VAV, temperature control 18 °C MV, DV, SV Vary 0.57 clo (Trousers, short-sleeve shirt, socks, shoes and underwear)

Ansys Fluent was used to generate the airflow model for the previous cases. Meshing of the geometry was completed using ANSYS meshing tool. Tetrahedrons meshing method was used and sizing of the mesh was set to increase mesh resolution in and around air inlets and outlets.

Grid independent test was conducted using different mesh qualities as shown in Figure 8, Table 3 shows the total number of nodes and elements of the single classroom geometry.

Table 3 Boundary conditions of the simulation Mesh Qualities`

Mesh Nodes

Mesh Elements

1 met (sitting quietly condition)

Coarse

66,343

343,639

21 - 25 °C 40 – 60 % 31 of January (Coldest day of the year in Jeddah) (21).

Medium

91,730

480,698

Fine

116,137

611,834

Finest

145,207

770,197

(7-10 am), (10-11 am break time), (11 am – 1 pm).

Never Open break time (10-11 am)

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2. METHODOLOGY

2. METHODOLOGY

2.6 Grid Independence Analysis

2.6 Grid Independence Analysis The grid independent test results indicated that the values of mean air velocity in the model don't change after the fine mesh in a significant rate as Figure 9 shows, based on this result, the fine mesh quality will be selected to complete the rest of the simulation process.

Hybrid initialization method was used to initialize the solution and number of iterations was set to 500. k- ε model was used to conduct the simulation in this study using RNG settings of this model as shown in the Table 4 below.

Table 4 Used CFD model's properties Constant

Value

Cmu

0.0845

C1-Epsilon

1.42

C2-Epsilon

1.68

Wall Prandtl Number

0.85

Figure 8 Grid independent test's tested mesh qualities

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2. METHODOLOGY

3. Results and Discussion

2.6 Grid Independence Analysis

3.1 Pre-Pandemic Results

Figure 9 Grid independent test results

Table 5 shows the age of air for the single classroom before the pandemic under the three ventilation systems as following: The yellow color with mixing ventilation indicates mean age of air of 0.64 h. Although this value is a bit high, small green spots right below the inlets show less age of air than their surroundings. The dark green with orange with displacement ventilation indicate mean age of air of 0.49 h, the orange color appears basically at the inner side opposite to the door where two air inlets were fixed in the nearby wall.

Lowest air age value of 0.25 h was generated using stratum ventilation, air with lowest age is concentrated at the center of the classroom as indicated by cyan color, age of air is increasing gradually from the center to the edges of the classroom as the colors is changing to the green then yellow near the walls as indicated in Table 5.

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3. Results and Discussion 3.1 Pre-Pandemic Results Table 5: Simulation results of the single classroom before the pandemic

3.1.1 Single Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

1. Mixing Ventilation (MV)

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3. Results and Discussion 3.1 Pre-Pandemic Results Table 5: Simulation results of the single classroom before the pandemic

3.1.1 Single Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

2. Displacement Ventilation (DV)

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3. Results and Discussion 3.1 Pre-Pandemic Results Table 5: Simulation results of the single classroom before the pandemic

3.1.1 Single Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

3. Stratum Ventilation (SV)

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3. Results and Discussion 3.1 Pre-Pandemic Results Table 6 Shows the age of air for the double classroom before the pandemic under the three ventilation systems as following: Mixing ventilation resulted in the highest age of air with 0.69 h as we can see a circle of red and yellow colors around the center of the classroom which means high age of air surrounding a light green spot that represents lower age of air.

Displacement ventilation generated mean age of air of 0.41 ha in the classroom, the graph contains a mixture of yellow and green colors and some orange spots at the middle and nearby walls indicate high age of air.

Stratum ventilation resulted in the lowest age of air of only 0.36 h, the graph is showing light green starting from the walls to the middle of the classroom and striped with quit darker green lines that outlining the paths of the supply air and representing lower age of air.

In addition to the age of air, Table 7 shows the remaining values of the indoor air quality and thermal comfort factors including: mean relative humidity, mean CO2 level, PMV, PPD and TVE. Table 7 demonstrates that in both single and double classrooms, the ventilation system with the lowest age of air usually has some of the best values in term of the other factors mentioned in the table.

From Table 7. In the single classroom, Stratum Ventilation results in mean age of air of 0.25 h, relative humidity of 51.37 %, PPD of 9 % and PMV of -0.36. In the other hand, Mixing Ventilation resulted in mean age of air of 0.64, relative humidity of 63.48 %, PPD of 12 %, PMV of -0.40 and TVE of 0.86. These numbers indicate the advantage of the Stratum Ventilation over the other systems specially the Mixing Ventilation.

In the double classroom, Stratum Ventilation resulted in age of air of 0.36 h, relative humidity of 56.75 %, PMV of -0.31, PPD of 9% and TVE of 1.1. In the other hand, Mixing Ventilation resulted in mean age of air of 0.69 h, relative humidity of 60.13 %, PPD of 14 %, PMV of -0.45 and TVE of 1. These numbers indicate the advantage of Stratum Ventilation over the other systems especially the Mixing Ventilation.

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3. Results and Discussion 3.1 Pre-Pandemic Results Table 6: Simulation results of the double classroom before the pandemic

3.1.2 Single Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

1. Mixing Ventilation (MV)

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3. Results and Discussion 3.1 Pre-Pandemic Results Table 6: Simulation results of the double classroom before the pandemic

3.1.2 Single Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

2. Displacement Ventilation (DV)

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3. Results and Discussion 3.1 Pre-Pandemic Results Table 6: Simulation results of the double classroom before the pandemic

3.1.2 Single Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

3. Stratum Ventilation (SV)

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3. Results and Discussion 3.1 Pre-Pandemic Results

Table 7: Pre-pandemic simulation results Ventilation Method / Parameters

Single Classroom

Double Classroom

Indoor Air Quality

Thermal Comfort

Mean Age of Air (H)

Mean Relative Humidity (%)

Mean CO2 Level (PPM)

Mean PMV

Mean PPD

TVE

1. Mixing Ventilation (MV)

0.64

63.48

526.2

-0.40

12

0.86

2. Displacement Ventilation (DV)

0.49

55.62

530.5

-0.28

10.5

1.05

3. Stratum Ventilation (SV)

0.25

51.73

573.1

-0.36

9

0.98

1. Mixing Ventilation (MV)

0.69

60.13

540.9

-0.45

14

1

2. Displacement Ventilation (DV)

0.41

54.58

562.7

-0.36

11

0.87

3. Stratum Ventilation (SV)

0.36

56.75

504.8

-0.31

9

1.1

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3. Results and Discussion 3.2 Post-Pandemic Results Table 8 shows the age of air for the single classroom during the pandemic under the three ventilation systems as following: Mixing ventilation has the highest mean age of air among the three ventilation strategies with 0.61 h, mixture of yellow and green colors can be seen in the table with light green spots right below the air inlets representing lower age of air. The displacement ventilation has the lowest mean age of air of 0.37 h as indicated with the light green color in the table, the same grade of green color through the classroom means consistent distribution of air age in the zone.

Stratum ventilation comes in between regarding age of air, as it generates mean age of air of 0.39 h in the classroom. High values are concentrated around the edges of the classroom as illustrated in the table which indicates that air is stagnant at these points nearby the walls, the middle area shows better situation as it appears in green color what means lower age of air.

Table 9 illustrates the age of air for the double classroom during the pandemic under the three ventilation systems as following: In mixing ventilation, generated mean age of air reached 0.65 h which is the highest value compared to the other strategies, red and yellow colors at the edges of the classroom and near walls indicate a stagnant air unlike the middle part of the classroom that appears in green indicating less age of air than the edges. Consistent light green generated by displacement ventilation indicates low air age of 0.4 h, light yellow spots can be seen in the middle of the classroom in the area between the air outlets in which age of air is a bit higher than their surroundings.

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3. Results and Discussion 3.2 Post-Pandemic Results Table 8: Simulation results of the single classroom after the pandemic

3.2.1 Double Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

1. Mixing Ventilation (MV)

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3. Results and Discussion 3.2 Post-Pandemic Results Table 8: Simulation results of the single classroom after the pandemic

3.2.1 Double Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

2. Displacement Ventilation (DV)

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3. Results and Discussion 3.2 Post-Pandemic Results Table 8: Simulation results of the single classroom after the pandemic

3.2.1 Double Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

3. Stratum Ventilation (SV)

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3. Results and Discussion 3.2 Post-Pandemic Results The stratum ventilation appears in the table in a light yellow with mean age of air of 0.54 h. Green lines starting from walls to the center of the classroom outline the path of the supply airstream, light orange spots between the green lines indicate that air age is increasing slightly in the area between the inlets.

Table 10 demonstrates that in both single and double classrooms, the ventilation system with the lowest age of air usually has some of the best values in terms of the other factors as we see with displacement ventilation in the double classroom.

In the Double classroom, Displacement Ventilation results in mean age of air of 0.40 h, relative humidity of 45.04 %, PPD of 6.1 %, PMV of 0.21 and TVE of 1.15. In the other hand, Mixing Ventilation resulted in mean age of air of 0.65, relative humidity of 55.43 %, PPD of 8 %, PMV of 0.32 and TVE of 094. These numbers indicate the advantage of the Displacement Ventilation over the other systems specially the Mixing Ventilation.

From Table 10. In the single classroom, Displacement Ventilation results in mean age of air of 0.37 h, relative humidity of 40.26 %, PPD of 6 % and PMV of -0.21. In the other hand, Mixing Ventilation resulted in mean age of air of 0.61, relative humidity of 54.20 %, PPD of 7.2 %, PMV of -0.29 and TVE of 0.97. These numbers indicate the advantage of the Displacement Ventilation over the other systems specially the Mixing Ventilation.

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3. Results and Discussion 3.2 Post-Pandemic Results Table 9: Simulation results of the double classroom after the pandemic

3.2.2 Double Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

1. Mixing Ventilation (MV)

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3. Results and Discussion 3.2 Post-Pandemic Results Table 9: Simulation results of the double classroom after the pandemic

3.2.2 Double Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

2. Displacement Ventilation (DV)

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3. Results and Discussion 3.2 Post-Pandemic Results Table 9: Simulation results of the double classroom after the pandemic

3.2.2 Double Classroom Ventilation Method

3D Layout of Classroom with ventilation method

Horizontal Section at 1.2 m for Age of Air

Air Age (H)

3. Stratum Ventilation (SV)

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3. Results and Discussion 3.1 Pre-Pandemic Results

Table 10: Post-pandemic simulation results Ventilation Method / Parameters

Single Classroom

Double Classroom

Indoor Air Quality

Thermal Comfort

Mean Age of Air (H)

Mean Relative Humidity (%)

Mean CO2 Level (PPM)

Mean PMV

Mean PPD

TVE

1. Mixing Ventilation (MV)

0.61

54.20

497.62

-0.29

7.2

0.97

2. Displacement Ventilation (DV)

0.37

40.26

520.52

-0.21

6

1.15

3. Stratum Ventilation (SV)

0.39

42.31

506.40

-0.15

4.2

1.05

1. Mixing Ventilation (MV)

0.65

55.43

524.03

-0.32

8

0.94

2. Displacement Ventilation (DV)

0.40

45.04

492.0

-0.21

6.1

1.15

3. Stratum Ventilation (SV)

0.54

50.43

510.5

-0.29

7.4

1.17

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3. Results and Discussion 3.3 Comparing Airflow Pattern Air flow patterns indicate that using stratum and displacement ventilation result in less distraction of the flow in the zone and create flow line heading in one way directly from the inlet through the zone to the outlet unlike the mixing ventilation in which lines are mixed

And follow a complicated paths through the zone which may help transmitting any particles held in the air to the whole zone including viruses as shown in Table 11.

Table 11: Air flow pattern in single and double classrooms using the three ventilation strategies

1. Single Classroom Mixing Ventilation (MV)

Displacement Ventilation (DV)

Stratum Ventilation (SV)

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3. Results and Discussion 3.3 Comparing Airflow Pattern Table 11: Air flow pattern in single and double classrooms using the three ventilation strategies

2. Double Classroom Mixing Ventilation (MV)

Displacement Ventilation (DV)

Stratum Ventilation (SV)

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3. Results and Discussion 3.4 Improving Displacement Ventilation This section is an attempt to increase the efficiency of the displacement ventilation which showed the best signals in both classrooms during the pandemic as explained in the previous section. The development process in this section include two scenarios: 3.4.1 Scenario A:

and 3 show more regularity and sharpness of lines than step 1, in addition, in step 1 circular movement of air can be seen near the upper corners of the room what can increase the age of air at these areas, whereas this movement has almost disappeared in steps 2 and 3.

Involve the following steps as demonstrated in Figure 10: 1. Forming the outlets as a square frame centering the ceiling of the classroom.

2. Create partitions to sperate the class into three lines of desks and limit the movement of air between the students.

3. Extend the ceiling outlet to be as close as possible to the students.

Meshes were generated for each step according to the same settings used previously, Table 12 show mesh configurations and air flow patterns for each step of the scenario A, steps 2

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3. Results and Discussion 3.4 Improving Displacement Ventilation

Figure 10 Steps of Scenario A of developing the displacement ventilation

Step A1

Step A2

Step A3

Mesh

Flow Perspective

Table 12: Meshes and flow patterns of scenario A development steps

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3. Results and Discussion 3.4 Improving Displacement Ventilation Table 12: Meshes and flow patterns of scenario A development steps

Step A1

Step A2

Step A3

Horizontal Section

Vertical Section

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3. Results and Discussion

3. Results and Discussion

3.4 Improving Displacement Ventilation

3.4 Improving Displacement Ventilation

3.4.2 Scenario B:

3.4.3 Evaluating the Two Scenarios

Involve the following steps as demonstrated in Figure 11:

To evaluate the two scenarios, air velocities at the outlets were measured in each step for each scenario. Results showed that air velocity has increased in the second and third step of each scenario as illustrated in Figure 12.

1. Creating one square outlet in the ceiling for each student.

2. Create partitions to sperate the class into three lines of desks and limit the movement of air between the students.

3. Extend the ceiling outlet to be as close as possible to the students. Meshes were generated for each step according to the same settings used previously, Table 13 show mesh configurations and air flow patterns for each step of the scenario B, similar to scenario A, steps 2 and 3 show more regularity and sharpness of lines than in step 1, in addition, in step 1 circular movement of air can be seen near the upper corners of the room what can increase the age of air at these areas, these movements have almost disappeared in steps 2 and 3.

The higher air velocity at the outlets, the faster air is moving out of the classroom, thus lower age of air and less air stagnation in the zone. This can be interpreted that changing outlet configurations, installing partitions and extending the outlets toward the ground can help reducing the age of air in the classrooms.

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3. Results and Discussion 3.4 Improving Displacement Ventilation

Figure 11: Steps of Scenario B of developing the displacement ventilation

Step A1

Step A2

Step A3

Mesh

Flow Perspective

Table 13: Meshes and flow patterns of scenario B development steps

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3. Results and Discussion 3.4 Improving Displacement Ventilation Table 13: Meshes and flow patterns of scenario B development steps

Step A1

Step A2

Step A3

Horizontal Section

Vertical Section

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4. Conclusion This study has proved that the way ventilated air is supplied into the classroom can influence air quality and thus infection possibilities of Sars COV-2 and any other airporn viruses by reducing the air age and air humidity in which viruses are contained.

each step, results showed that air velocities have increased after adding partitions in the classroom and extending the outlets which indicated that air is moving faster and thus less air age in the zone.

Testing three different ventilation systems in two classrooms with different sizes demonstrated that Stratum Ventilation gives best results in terms of air quality and thermal comfort in the two classrooms before the pandemic while Displacement Ventilation had the lowest age of air and air humidity with lower density classrooms during the pandemic as demonstrated in Table 14.

To improve the efficiency of displacement ventilation, two scenarios (A and B) were developed in three steps for each one and tested using CFD. To evaluate the age of air in the classroom under the two scenarios, air velocities were measured at the outlets in.

Figure 12: Air velocities at outlets in Scenarios' A and B

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4. Conclusion Table 14: Comparing indoor air quality and thermal comfort before and during the pandemic for the two classrooms

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5. Recommendations The main objective of this study is to come up with a simple guideline to help protecting the students from getting infected inside the classrooms, this objective can be summarized in the following guidelines as demonstrated in Figure 13 :

The use of partitions and changing the configurations of the inlets and outlets might extend the explanations of the impact of these factors in age of air and viruses’ viability.

1.Using the Stratum Ventilation method has proved higher efficiency in terms of indoor air quality and thermal comfort in the classrooms when classrooms are full of students.

2. After applying social distancing majors, Displacement Ventilation can reduce air age and humidity more efficiently and thus help reducing the possibility of infection.

3. Utilizing the partitions and extending ceiling outlets can help improving the efficiency of displacement ventilation by speeding up the air movement and reduce age of air in the classrooms.

Due to the limitations of this study, Future research on

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5. Recommendations

Figure 13 Recommendations of the study

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6. References P. Kumar and L. Morawska, “Could fi ghting airborne transmission be the next line of defence against COVID19 spread ?,” City Environ. Interact., vol. 4, no. 2019, p.

100033, 2020.

[2] UNESCO, “School closures caused by Coronavirus (Covid-19),” https://en.unesco.org, 2020. [Online].

Available: https://en.unesco.org/covid19/educationresponse.

[Accessed: 15-Sep-2020].

[3] Y. Li et al., “Evidence for probable aerosol transmission of SARS-CoV-2 in a poorly ventilated restaurant,” medRxiv, p. 2020.04.16.20067728, Apr. 2020.

[4] AIA, “Reopening America : Strategies for Safer Schools,” https://www.aia.org/, 2020. [Online]. Available: https://www.aia.org/resources/6299247-reopeningamerica-strategies-for-saferbui?editing=true&tools=true&utm_medium=website&ut m_source=archdaily.com

[5] A. K. Melikov, “Advanced air distribution: improving health and comfort while reducing energy use,” Indoor Air, vol. 26, no. 1, pp. 112–124, Feb. 2016.

[6] J. Lu et al., “COVID-19 Outbreak Associated with Air Conditioning in Restaurant, Guangzhou, China, 2020,” Emerg. Infect. Dis., vol. 26, no. 7, pp. 1628– 1631, Jul. 2020.

[7] ASHRAE, “ASHRAE Issues Statements on Relationship Between COVID-19 and HVAC in Buildings,” https://www.ashrae.org/, 2020.

[Online].

Available: https://www.ashrae.org/about/news/2020/ashrae -issues-statements-on-relationship-betweencovid-19-and-hvac-in-buildings. [Accessed: 15Sep-2020].

[8] K. Iwata, A. Doi, and C. Miyakoshi, “International Journal of Infectious Diseases Was school closure effective in mitigating coronavirus disease 2019 ( COVID-19 )? Time series analysis using Bayesian inference,” Int. J. Infect. Dis., vol. 99, pp. 57–61, 2020.

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6. References [9] T. Lipinski, D. Ahmad, N. Serey, and H. Jouhara, “Review of ventilation strategies to reduce the risk of disease transmission in high occupancy buildings,” Int. J. Thermofluids, vol. 7–8, p. 100045, 2020.

[10] Z. Y. Han, W. G. Weng, and Q. Y. Huang, “Characterizations of particle size distribution of the droplets exhaled by sneeze,” J. R. Soc. Interface, vol. 10, no. 88, p. 20130560, Nov. 2013.

[13] H. B. Awbi, “Energy efficient room air distribution,” Renew. Energy, 1998.

[14] “Standard 62.1-2013 - American Society of Heating, Refrigerating and Air-Conditioning Engineers.”

[Online].

Available: https://ashrae.iwrapper.com/ASHRAE_PREVIEW_ ONLY_STANDARDS/STD_62.1_2013. [Accessed: 03Jan-2021].

[11] J. Ren, Y. Wang, Q. Liu, and Y. Liu, “Numerical Study of Three Ventilation Strategies in a prefabricated COVID-19 inpatient ward,” Build. Environ., no. July, p. 107467, 2020.

[12] “Reopening America: Strategies for safer buildings AIA.” [Online].

Available: https://www.aia.org/resources/6299247-reopeningamerica-strategies-for-saferbui?editing=true&tools=true&utm_medium=website&ut m_source=archdaily.com. [Accessed: 15-Sep-2020].

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Indoor Air Quality (IAQ), Mitigating CO2 concentration in classrooms using adjacent corridors and atriums By: Feras Balkhi

1

1. INTRODUCTION Problem statement Indoor air quality (IAQ) is an essential factor that decides occupants’ level of satisfaction and performance.

Classroom are more critical due to typically high occupancy density. The over-crowdedness of classroom is a serious and quite common issue.

The larger the classroom, the greater the dilution of levels of carbon dioxide (CO2) and pollutants, and the longer good air quality can be maintained. In an average size classroom with a volume of 181 cubic meters, 30 occupants and no ventilation, the air quality becomes poor in just 30 minutes [1].

Ventilation can be the most important factor affecting IAQ, as confined air in closed space without renewal can be contaminated by several pollutants, including: Radon, CO2, carbon dioxide, bacteria and other volatile chemical particles [3].

Occupants are the main indoor source of CO2. The CO2 is easy to measure as a surrogate for indoor pollutants.

Indoor CO2 levels are a good indicator of ventilation efficiency witch directly indicate to the quality of the indoor air [3].

Indoor Air Quality (IAQ), Mitigating CO2 concentration in classrooms using adjacent corridors and atriums

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2. RESEARCH QUESTION Improving thermal sensation inside classrooms by testing other ventilation types and controlling air temperature / air velocity without making major changes in the existing buildings and with minimum technical complexity.

3. OBJECTIVE This paper aims to test the viability of air exchanging between the classrooms and other adjacent indoor spaces, to enhance the overall levels of CO2 concentration, as a quick solution for an overcrowded classroom.

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4. LITERATURE REVIEW IAQ in classrooms Classrooms has a large occupancy density. Where classroom occupants, on daily bases spend most of there active day within it. This space creating an interactive and educational environment that must be reviewed and assessed by the IAQ conditions. In particular, the greater number of occupants with one unchanged space, which leads to the classroom spaces.

Thermal comfort affecting CO2 concentration in classrooms Several studies indicated CO2 as a factor of evaluation for air quality in space. Maintaining the temperature and relative humidity as effects of CO2 concentration.

The correlated with relevant environmental parameters is humidity, radiant temperature, air velocity. CO2 concentrations and temperatures are important factors within buildings, it's affecting the occupant performance and particularly cognitive performance regarding all mental activities such as thinking, reasoning, and remembering [4].

The evaluating of CO2 concentrations as indicator of air quality, maintaining temperature, and relative humidity are the common and related factors that affect the IAQ in the classrooms.

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4. LITERATURE REVIEW IAQ influences on occupants in classrooms IAQ in schools is often very low. and the indoor air pollutants have an impact on occupants' health, comfort, and productivity [5].

Cold, hot and warm sensations can negatively affect mental performance for memory and attention tasks while mild cooling sensation can improve mental alertness [4].

Low rates of ventilation in classrooms significantly reduce pupils’ attention and vigilance, and negatively affect memory and concentration and the physical environment. Therefore, affects teaching and learning [6].

Building-related symptoms were significantly and positively associated with the concentration of colony-forming units of molds in floor dust: eye irritation, throat irritation, headache, concentration problems, and dizziness [7].

Investigations have proven the effectiveness of evaluating and improving IAQ may enhance the educational space and the Comprehension of students.

Decreasing classrooms’ temperature from 25°C to 23°C, and also increasing temperature from 20°C to 23°C whilst decreasing CO2 levels from 1800 ppm and/or 1000 ppm to 600 ppm significantly improved the performance of adult students in a memory and attention tasks [4].

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4. LITERATURE REVIEW Importance of ventilation affecting CO2 Classrooms have a higher level above 1000 ppm. A. S. Hassan Abdallah found the reason of this problem was because teachers close the doors and depend on mechanical fans and single side ventilation from windows for ventilation without continuous airflow of fresh air. Also found CO2 level decreases during the school break in 30 minutes due to the opening door without student occupation [8].

In study showed that the energy demand in school buildings was reduced by 38% for a CO2-DCV compared with CAV system. [9].

In study, the DCV system was able to deliver and maintain a good IAQ, even at reduced air flow rates.

The VAV dampers or extract fans respond well to predefined set points of CO2 concentration and temperature. Even at low air flow rates, it was noticed that the ventilation efficiency was not affected. This shows that demand-controlled ventilation is effective in distributing the air even at reduced air flow rates. [10] Indoor Air Quality (IAQ), Mitigating CO2 concentration in classrooms using adjacent corridors and atriums

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5. METHODOLOGY This study investigates a prototype classroom building in Jeddah, as case study. The study involved maintaining the thermal comfort and evaluating CO2 concentration.

The case windows condition is not designed with natural ventilation systems (no opining windows).

In set of mechanically air-conditioned space using CAV system.

Study simulating a combined approach by exchanging the air-conditioned adjacent common spaces (i.e. corridors and atriums) with the classrooms. Also, should not ignore the over crowdedness issue of classrooms, by reconsidering the occupancy schedule and number of occupants, which causes a high level of CO2 concentration.

The reason of high CO2 concentrations was the low intensity of ventilation and a high number of occupants during the lecture time in one closed space [7].

Selecting and study one classroom as a case sample.

Using the field measurement devices will set up the device in the middle of the classroom with a height of 1.1m for the level of the occupants breathe, to evaluate the IAQ of the space.

The measuring device used to evaluate the relative humidity and temperature of the study sample to calculate the thermal comfort effect. Validate using the collected data. Field observations such as space dimensions and occupants’ number of the space to get the full current condition of the case sample.

Maintaining thermal comfort. Then, simulating CO2 as an indicator of air quality, occupancy density, and mechanical system type, using software (IDA ICE).

Reviewing the occupant's densities and typical scheduling of the classrooms. Studying and applying the occupancy scheduling of adjacent spaces to simulate the study case.

Discussing influences of any change may cause by one classroom to reach a quick solution of space efficiency with the lowest potential losses of change space.

Then comparing the scenarios and results. aiming to upgrade the IAQ of space in Saudi Arabia classrooms to confirm the findings and scale the problem size which may lead to new policy and refurbishment of schools.

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5. METHODOLOGY Installing CO2 sensors as a parameter of the IAQ condition in the classroom. Also, promoted conscious ventilation in each classroom by involving the teachers to manage the manual airing and suggests frequent and short periods of window openings [9].

Measurements devices were installed in one of the buildings of the current preparatory year in educational classroom to measure the IAQ using (HOBO onset data logger U10-003) Specific for measure CO2 concentration in air, temperature and relative humidity of these enclosed spaces as shown in the drawing. The designed occupation capacity of the classroom is 40 occupants (Figure 1).

Monitoring in more than one period depending on the space condition in terms of use. Install accurate measuring devices that detect and record measurements of temperature and relative humidity within the case sample (Figure 2,3,4).

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6. METHODOLOGY Study tools

HOBO onset data logger U10-003

IDA ICE

Specific for measure CO2 concentration in air,

Specific for measure CO2 concentration in air,

temperature and relative humidity

temperature and relative humidity

Measurements devices were installed in one of the buildings of the current preparatory year (No.535) in educational classroom to measure the quality determinants of these enclosed spaces as shown in the drawings.

IDA Indoor Climate and Energy (IDA ICE) is a Building performance simulation (BPS) software.

IDA ICE is a simulation application for the multizonal and dynamic study of indoor climate phenomena as well as energy use. The implemented models are state of the art, many studies show that simulation results and measured data compare well.

The variables were monitored in more than one period depending on the space condition in terms of use.

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6. METHODOLOGY

Indoor Air Quality (IAQ), Mitigating CO2 concentration in classrooms using adjacent corridors and atriums

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7. ANALYSIS The two most important variables affecting the thermal comfort in the classroom is temperature and relative humidity. The data average readings were shown on the Psychrometric chart to determine whether the results were within the range of thermal comfort zone or not. As shown in the diagram (Figure 5), data average is placed in the comfort zone.

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7. ANALYSIS Because of the hot climate of Jeddah, the exterior edge facade of the classroom is exposed to high temperatures that may affect the indoor thermal comfort (Figure 6,7) The study trying to find a quick solution without effecting the thermal comfort in classrooms.

Considering this condition rate maintained and not negatively affected, as it is related to CO2, which may affect the study solutions.

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7. ANALYSIS CO2 monitored in two different days, one on a day off and the other due workday where occupants are in the classroom. According to the typical scheduling of the classroom, it is divided into two periods. The first period has the general studying subjects, which contains a larger number of occupancy and almost getting to the full capacity of the classroom. And its starting from 8:00 a.m. until 12:00 p.m. The chart shows a high increase in CO2 concentrations in the lecture due to the classroom.

Consequently, CO2 emissions due to student’s congestion increase to a concentration level of 1270 ppm (Table 2), which is above the standard. Although the accumulation of CO2 in the last few hours, the second period comes after one hour of lunch break with no occupancy inside the classroom.

Therefore, the chart showing a drop in CO2 concentration. Continuously, Starting the second period at 13:00 p.m., until 16:00 p.m. This period has specialized subject courses, which contains less number of occupancy than the morning period. Clearly, the chart showing a good continuous result of the evening period.

Because of the low number occupancy which often being less than the space half design capacity (Figure 4).

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7. ANALYSIS CO2 concentration can be reduced by reducing the number of occupants in the classroom. The large number of occupants in one closed space such as the classroom, increases the rates of CO2 concentration.

This classroom contains a high number of occupants above the standard by 40 occupancies for 68.5m2 with furniture in rows and freely arranged. Each occupant needs a space of 1.8 - 2.0 m2 in the classroom [12]. (Figure 10) According to the standard, in the simulation the occupants number was reduced to 30 occupants in the classroom to fits the designed space. A good decrease in the CO2 concentration level by 12.5% can make a good help to reduce the CO2 concentration in classroom. (Figure 11)

pp pp pp pp pp pp pp pp

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7. ANALYSIS Classroom adjacent spaces (i.e. corridors and atriums) tend to have better CO2 levels due to its occupancy schedule/density. Taking advantage of the total fresh air entering the building from the CAV system. The adjacent common spaces have a large space of unused fresh air compared to the closed classroom spaces (Figure 20).

By exchanging the air between these spaces, it can make utilization of the adjacent common spaces as a reserve of fresh air, to mitigate the CO2 accumulate concentrations in the closed and fully occupied classrooms. This approach is not impacting the energy consumption by using a new fresh air.

Because it's using the fresh air that is already inside the building. Moreover, not impacting the thermal comfort of using outdoor ventilation in the hot climate. Aiming to reach the lowest potential losses of building physical change (Figure 19).

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8. RESULTS Entering the data collected of the field measurements into the simulation software for an entire floor of the building based on maximum capacity of the educational spaces, scheduling and duration of the break times is equal to 10 minutes between every two classes and one our break after 12:00 pm.

As evaluation of the current condition. The simulation results Shows the IAQ suffocation of the classrooms due to CO2 accumulatio (Figure 22). All the classrooms showing a high level of CO2 concentration above 1000 ppm. The classrooms 45 and 48 got the highest levels of CO2 concentration reaches above 2000 ppm, because of the high number of occupants, and with the smallest designed classroom spaces.

As shown the adjacent corridors and atriums have the lowest concentrations of CO2, because the occupation schedule of this spaces is usually low.

Examining the previous of exchanging the fresh air between these spaces and classrooms to mitigate the CO2 levels.

Indoor Air Quality (IAQ), Mitigating CO2 concentration in classrooms using adjacent corridors and atriums

16

8. RESULTS Applying the proposed solution by using the simulation software. All the spaces on one of the building floors, opened to each other to verify the effectiveness. By opening a rectangular aperture in each classroom to infiltration the classroom air to the adjacent space with the high unused fresh air to mitigate the CO2 accumulate concentrations (Figure 23).

Indoor Air Quality (IAQ), Mitigating CO2 concentration in classrooms using adjacent corridors and atriums

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8. RESULTS Due to the simulation, by opening a rectangular aperture in each classroom allowing to air infiltration to adjacent spaces finding a decrease in the highest value of the CO2 concentration in classroom number 48 by 29.6%, from 2008 ppm to 1414 ppm (Figure 25).

CO2 response Average values of CO2 concentration in classrooms generally decreased by 13.1%. In scenario 01, the total average CO2 in classrooms was 1513 ppm, decreased to 1314 ppm after applying the scenario 02. Seeking to drop the CO2 concentrations nearly to 1000 ppm. Noticing an increase in CO2 concentration levels at the corridors and atriums caused by the accumulate of CO2 in adjacent classrooms. In scenario 01, the average CO2 for corridors and atriums was 880 ppm. But, the scenario 02 increased that average CO2 concentrations to 1026 ppm. That is not making a problem like the ones in the classrooms, because it contains a high occupancy rate while in its counterpart (Figure 26).

Indoor Air Quality (IAQ), Mitigating CO2 concentration in classrooms using adjacent corridors and atriums

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8. RESULTS Scenario 02 (DCV with air exchange) Demand controlled ventilation (DCV) is a feedback control method to maintain indoor air quality that automatically adjusts the ventilation rate provided to space in response to changes in conditions such as occupant number or indoor pollutant concentration.

In this case, applying the DCV system could be more efficient because of the building condition of the high intensity of occupation and the low space's area of classrooms.

CAV system with CO2 sensor in extract air Installing the CO2 sensor in the extract duct. The concentration of CO2 is continuously measuring and represents the mean value in the building. Due to the feedback control, an increase of the CO2 concentration leads to an increased flow rate. (Figure, 24) The system checks the air quality in the extract duct every 30 min and increases the airflow according to the sensor signal. The systems start in idle mode with fans turned off. Every 30 min, the CO2 concentration is checked after the systems was operated on basic flow rate for 5 min. If the concentration is below 600 ppm, the system goes to idle again, if it is above 600 ppm, the basic flow rate is activated for 30 min. Then, the concentration is checked again. If the value is then still above 600 ppm, the systems goes to the nominal flow rate until concentrations are below 600 ppm again. If it has decreased and is now below 600 ppm again, the system goes to idle mode. [13]

Indoor Air Quality (IAQ), Mitigating CO2 concentration in classrooms using adjacent corridors and atriums

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8. RESULTS The decrease in the highest value of the CO2 concentration in classroom 48 from 2008 ppm to 880.8 ppm. Also, the average values of CO2 concentration generally decreased by 49.3%. The decreasing point for classrooms scenario 01 compared with scenario 03 decreased by 746 ppm.

Comparing scenario 03 with the current condition into adjacent spaces, the CO2 concentration is almost the same.

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8. RESULTS

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10. CONCLUSION In conclusion, Although the natural ventilation is important to the classroom design should consider the windows able to open. But maintaining thermal comfort in the space in a good condition, aiming to find a quick solution with fewer losses in the meantime can be able

by Allowing more fresh air in the classrooms.

Taking advantage of the total fresh air entering the building form the CAV system, using the adjacent spaces can be modified to exchange the unused fresh air with fully occupied classrooms to reduce the total pollution of CO2 concentration.

The results showing the effectiveness of opening a rectangular aperture in each classroom allowing to air infiltration between classrooms and adjacent spaces.

This approach is not impacting the energy consumption by using new fresh air. Because it's using the fresh air that is already stored inside the building.

Installing CO2 sensors in the spaces that expected more occupancies to control each space needed more fresh air such as the fully occupied classrooms comparing it to the rest of the adjacent spaces in the building. The openings can be manually controlled by the teacher classroom monitoring the CO2 sensors informing of the IAQ condition.

In the current condition is an accumulation of CO2 concentrations in classrooms with the CAV system in closed spaces.

As a quick solution, scenario 02 can be a proper proposal for this case. because it's keeping the same condition without much changing at the building.

Although, it's reducing the general average of CO2 levels in classrooms by 200 ppm as average. in corridors, it's going above 1000 ppm at a slight level which is fine for the common spaces.

Applying the VAV-DCV system is the optimum approach in case of a long term solution. The simulation shows a generally decreased CO2 levels by 49% comparing scenario 03 with the current condition.

CO2-sensors monitor CO2 level in the air in the indoor spaces.

An air-handling system that employs data from the sensors to regulate the amount of supply air. The VAV dampers or extract fans respond well to predefined set points of CO2 concentration.

Indoor Air Quality (IAQ), Mitigating CO2 concentration in classrooms using adjacent corridors and atriums

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11. REFFERENCES 1.

[1] Velux, Building Better Schoools: Six ways to help our children learn. .

2.

[2] “Introduction to Indoor Air Quality | Indoor Air Quality (IAQ) | US EPA,” 2019. [Online]. Available: https://www.epa.gov/indoor-air-quality-iaq/introductionindoor-air-quality. [Accessed: 26-Feb-2020].

3.

[3] 2014.

4.

[4] A. Riham Jaber, M. Dejan, and U. Marcella, “The Effect of Indoor Temperature and CO2 Levels on Cognitive Performance of Adult Females in a University Building in Saudi Arabia,” Energy Procedia, vol. 122, pp. 451–456, 2017.

5.

1.

[9] M. Mysen , S. Berntsen , P Nafstad , P.G Shild , Occupancy density and benefits of demand-controlled ventilation in Norwegian primary schools , Energy Build. 37 (2005) 1234–1240 .

2.

[10] B. Merema, M. Delwati, M. Sourbron, and H. Breesch, “Demand controlled ventilation (DCV) in school and office buildings: Lessons learnt from case studies,” Energy Build., vol. 172, pp. 349–360, 2018.

3.

[11] S. Bonino, “Carbon Dioxide Detection and Indoor Air Quality Control,” Occup. Health Saf., vol. 85, no. 4, pp.

46–48, 2016.

4.

[12]

5.

[13] A. Merzkirch, S. Maas, F. Scholzen, and D. Waldmann, “A semi-centralized, valveless and demand controlled ventilation system in comparison to other concepts in field tests,” Build. Environ., vol. 93, no. P2, pp.

21–26, 2015.

Sick Classrooms Caused by Rising CO2 Levels.

[5] S. V č ko á, P. Kapalo, Ľ. M č a o á, E. K. Burdová, and V. Imreczeová, “Investigation of Indoor Environment Quality in Classroom - Case Study,” Procedia Eng., vol. 190, pp. 496–503, 2017.

6.

[6] Z. Bakó-Biró, D. J. Clements-Croome, N. Kochhar, H. B. Awbi, and M. J. Williams, “Ventilation rates in schools and pupils’ performance,” Build. Environ., 2012.

7.

[7] H. W. Meyer, H. Würtz, P. Suadicani, O. Valbjørn, T. Sigsgaard, and F. Gyntelberg, “Molds in floor dust and building-related symptoms in adolescent school children,” Indoor Air, vol. 14, no. 1, pp. 65–72, Feb. 2004.

8.

[8] A. S. Hassan Abdallah, “Thermal Monitoring and Evaluation of Indoor CO2 Concentration in Classrooms of Two Primary Governmental Schools in New Assiut City, Egypt,” Procedia Eng., vol. 205, pp. 1093–1099, 2017.

E. Neufert, Neufert. 2012.

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Reconsidering School Design, Assessment Ventilation Efficiency influences on COVID19 at generic classrooms spaces in different climates of Saudi Arabia By: Feras Balkhi

Assessment Ventilation Efficiency influences on COVID19 at generic classrooms spaces in different climates of Saudi Arabia

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1. INTRODUCTION Social distancing refers to actions to reduce the number and duration of contacts and increase the physical distance between individuals to slow the spread of a communicable disease. Separate from hand hygiene and use of personal protective equipment such as facemasks, social distancing practices include actions that create more space between students in classrooms and hallways; canceling activities that bring students into close contact.

Schools also represent a challenging setting for social distancing, as multiple stakeholders with different needs (e.g., teachers, administrators, parents, students, public health departments, state and local governmental agencies) are involved. Guidance on social distancing in Saudia Arabia schools have focused on school closure.

OBJECTIVE Prolonged school closures can have a significant impact on the level of education, leading to a major failure in the educational process.

The study aims to conduct a study and evaluation of ventilation efficiency in the classroom, as ventilation is a large part of the transportation process for users within the educational space, improving the ventilation rate reduces the possibility of disease transmission greatly.

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2. LITERATURE REVIEW A. Circulating ventilation - Split air conditioning systems - Ceiling fans

ASHRAE standards dictate a minimum ventilation rate of 5 L/s per person or 0.9 L/s.m2 in educational facilities.

- Hybrid ventilation systems B. Mixing ventilation systems - Air handling units (AHU) - Mechanical ventilation with heat recovery (MVHR)

Reported CO2 measurements in several thousand classrooms has shown that all classroom averages exceeded 1000 ppm (0.1%) which is an indicator of a ventilation rate lower than 7 L/s/person at default occupancy.

- Positive input ventilation C. Displacement ventilation systems - Continuous extract ventilation - Natural ventilation measures (Predominantly windows)

- Natural ventilation systems

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2. LITERATURE REVIEW Recirculating ventilation The simulations showing the potential spread of coronavirus in a social space (dining hall) with an air recirculating unit.

Natural ventilation

The simulations showed how fresh air from an open window could carry the virus to a vent.

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2. LITERATURE REVIEW In many schools and other high occupancy buildings, the target ventilation rates are rarely met. The benefits of better health and attendance and resultant economic outcomes largely outweighed the capital investment of installing, renovating, or retrofitting appropriate ventilation solutions, even before the COVID-19 pandemic.

Research Question Are the current ventilation strategies outdated and inadequate for such contagious diseases?

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2. METHODOLOGY Study criteria

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2. METHODOLOGY Study conditions

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2. METHODOLOGY Study Method

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2. METHODOLOGY Study framework

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3. ANALYSIS Simulation and analyze

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3. ANALYSIS Simulation and analyze

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3. ANALYSIS Simulation and analyze

Assessment Ventilation Efficiency influences on COVID19 at generic classrooms spaces in different climates of Saudi Arabia

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Assessment Ventilation Efficiency influences on COVID19 at generic classrooms spaces in different climates of Saudi Arabia

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3. ANALYSIS Simulation and analyze

Assessment Ventilation Efficiency influences on COVID19 at generic classrooms spaces in different climates of Saudi Arabia

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3. ANALYSIS Simulation and analyze

Assessment Ventilation Efficiency influences on COVID19 at generic classrooms spaces in different climates of Saudi Arabia

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Assessment Ventilation Efficiency influences on COVID19 at generic classrooms spaces in different climates of Saudi Arabia

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3. ANALYSIS CFD Simulation summary

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4. RESULTS Study results evaluation conc nt aton

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4. RESULTS Study results evaluation

Assessment Ventilation Efficiency influences on COVID19 at generic classrooms spaces in different climates of Saudi Arabia

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4. RESULTS Study results evaluation

Assessment Ventilation Efficiency influences on COVID19 at generic classrooms spaces in different climates of Saudi Arabia

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4. RESULTS Reviewing study results

Assessment Ventilation Efficiency influences on COVID19 at generic classrooms spaces in different climates of Saudi Arabia

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4. RESULTS Comparing scenarios in different climates (scale bars)

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4. RESULTS Comparing scenarios in different climates

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4. RESULTS Comparing scenarios in different climates

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4. RESULTS Comparing scenarios in different climates

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4. RESULTS Comparing scenarios in different climates

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5. CONCLUSION JEDDAH

Dhahran

The results in Jeddah show that the (VAV), CO2 control system gives the best possible results despite the climate in Jeddah. in general, does not achieve the required target for relative humidity because it is a coastal city in most cases, on the contrary, in the age of the air where there is a significant improvement in it significantly when opening the windows for only one hour in the break times.

Although Dhahran is a coastal city, the relative humidity has achieved its target with average numbers. The (VAV), humidity control system gives the best results despite the closeness between it and the (CAV) system. However, opening the windows for one hour gives a better reduction in the age of air, which favors the (VAV), humidity control system.

Riyadh

Abha

The city of Riyadh is a desert city, as it usually does not face problems with relative humidity, but the problem lies in the age of air concentrated in the space for a long time. Opening the window for one hour in the middle of the day gives better results in the age of air, as it is reduced further, in addition to the (VAV), CO2 control system.

The climate inside the space in Abha is not a problem, because it is a mountain city, so the relative humidity is often very good. And the fact that the (CAV) system gives the best results in the age of air. It is preferred to be used as a system in this case.

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5. CONCLUSION The results show that opening the window for one hour in the middle of the day at the break time gives a significant and noticeable advantage in the results, which reduces the age of air and allows more fresh air to the purification of the space.

It is not necessary to use a unified system for all schools in the KSA due to the difference in the climate in each region, as it is preferable to use a separate system and a different technique for each region separately.

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6. REFERENCES [1] European Centre for Disease Prevention and Controls, “Heating, Ventilation and Air-Conditioning Systems In The Context of COVID-19,” no. June, pp. 1–5, 2020.

[2] C. Sun and Z. Zhai, “The efficacy of social distance and ventilation effectiveness in preventing COVID-19 transmission,” Sustain. Cities Soc., vol. 62, no. July, p.

102390, 2020.

[3] “Coronavirus disease (COVID-19): Ventilation and air conditioning.”

[Online].

Available: https://www.who.int/news-room/q-a-detail/coronavirusdisease-covid-19-ventilation-and-air-conditioning.

[Accessed: 23-Dec-2020].

[5] “Ho Airplane Ventilation Actually Works | CheapAir.” [Online].

Available: https://www.cheapair.com/blog/how-airplaneventilation-actually-works/. [Accessed: 24-Dec2020].

[6] J. N. Zitter, P. D. Mazonson, D. P. Miller, S. B. Hulley, and J. R. Balmes, “ c a t cabin air recirculation and symptoms of the common co ” J. Am. Med. Assoc., vol. 288, no. 4, pp. 483–486, 2002.

[4] “Middle East Respiratory ( MERS-CoV ) Infection,” no.

January, 2020.

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Methods to reduce CO2 concentration in classrooms using hybrid ventilation By: Yousef Khoja

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

1

1. Introduction 1.1 Introduction Achieving the highest levels of education and culture is a goal for all contemporary societies.

The competition between contemporary societies is based on this basis, therefore, the need to review and continuously develop the educational systems and educational establishments was a necessity. The difficulties faced by contemporary societies are the large number of population densities and the increase in the need to provide education to all components of society and all people equally and fairly, but this increase in numbers. It also resulted in the need to develop educational facilities to accommodate these numbers and suit the current conditions of such communities.

This increase is the lack of quality of the internal space in general and the lack of indoor air quality in particular. Educational performance and public health levels within these internal spaces, and many studies have shown that the rise of carbon dioxide in the classroom leads to health problems and affect the educational levels of the student

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

2. Introduction 2.1 points of departure

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

2. Literature review 2.1 Literature

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

2. Literature review 2.1 Literature

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

2. Literature review 2.1 Literature

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

2. Literature review 2.1 Literature

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

3. Research methodology 3.1 workflow

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

3. Research methodology 3.2 Research sample

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

3. Research methodology 3.2 Measurement

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

3. Research methodology 3.3 Analysis of measurement results

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

3. Research methodology 3.4 Building simulation Model

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.1 Simulation Results

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.1 Simulation Results

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.1 Simulation Results

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.1 Simulation Results

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.1 Simulation Results

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.1 Simulation Results

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.1 Simulation Results

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.1 Simulation Results

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.1 Simulation Results

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.1 Simulation Results

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.2 Result comparison

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.2 Result comparison

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.2 Result comparison

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.2 Result comparison

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.3

CFD Result comparison

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.4 Scenario

1 vs Scenario 2

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.4 Scenario

1 vs Scenario 2

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.4 Scenario

1 vs Scenario 2

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

4. Results 4.4 Scenario

1 vs Scenario 2

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

5. Conclusion & Recommendations 5.1 Conclusion

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

5. Conclusion & Recommendations 5.2 Recommendations

Methods to reduce CO2 concentration in classrooms using hybrid ventilation

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems By: Yousef Khoja

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

1

1. Points of departure 1.1 Introduction

The present study aimed to develop ventilation methods to prevent the spread of Coronavirus-2019 (COVID -19) in classrooms since the potential risk of COVID -19 transmission through aerosols exists. A generic model was developed and simulated using indoor climate and energy simulation software (IDA -ice).

Development of different ventilation methods in three Saudi cities by comparing simulation results from these methods to obtain the best solution. By simulating three mechanical systems and suggesting four window designs, an appropriate system of mechanical and hybrid ventilation was found for each city

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

2. Literature review 2.1 Literature Reference No.

Purpose

Information

It is transmitted mainly through humans to humans via air droplets(sneezing and coughing)as well as load speech By air: The presence of the virus in the air was monitored for a period of 3 hours, and it may exceed that, since the duration of its presence in the air is not completely clear.

By direct contact: Especially by shaking hands or touching the face with the hand

[1]

COVID -19 transmission

Several studies have shown that ventilation systems inside airplanes are among the most successful systems in reducing the spread of the COVID-19. These systems use( 50%) fresh air, and (50%) of the air is filtered by the HEMP filter system.

Moreover, as WHO recommended maintaining an effective ventilation system can reduce the spread of COVID-19 in the indoor spaces if the air exchange rate increases. Reducing recirculation of air in mechanical systems and increasing the fresh air is considered a better solution for reducing the spread of the COVID-19

[2]

Ventilation Recommendations

The duration of infectivity of the virus in the air and on surfaces depends on the rates of humidity and different temperatures as reported by the European Center for Disease Prevention and Control. In addition, extending the time people sit in the same space increases the rate of viral attack

[3]

Environmental effect on COVID-19 spread

Mixed ventilation increases the risk of transmission, while conventional ventilation reduces the risk of transmission. So far, no evidence that COVID-19 can travel through heating, ventilation, and air-conditioning (HVAC) vents has been reported. An HVAC system is considered low risk if it requires constant attention and maintenance; however, small droplets and droplet nuclei may be able to move through the vents. An air conditioner can help spread the virus to remote places within the closed space, especially if it relies on recycling air. Therefore, it is preferable to use (HVAC), especially if it depends on the constant presence of natural air. Reducing recycled air and bringing outdoor air into the system is the best option for reducing airborne spread. Increasing the rate of air exchange every hour reduces the spread of infection. This process can be achieved by relying on natural or mechanical ventilation, which is subject to availability

[4]

Review for different ventilation methods

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

2. Literature review 2.1 Literature Reference No.

Purpose

Information

In another study, aerosol removal and surface deposition in a realistic classroom environment by using computational fluid- particle dynamics (CFPD) was investigated to understand the effect of removing air particles while opening the windows while the air conditioner continues to operate and comparing the results with the window when it is closed. A normal window can open up to (50%), which is the total window width. The window opening was tested at (0%–50%-in 10% increments). The results of the study showed that the total number of particles that exited through the window and the air conditioner system increased by (38%). On average, (69%) of particles are removed when the window is open compared to (50%) when it is closed. One of the most important findings of the study was the effect of air conditioning layout on the transport of air particles. Opening windows in addition to having the air conditioner on caused an increase in the removal of air particles by (38%) and reduction in the spread of infection by (80%)

[5]

Case study

Case study

it was found that the number of students inside the closed space did not affect the risk of spreading the virus if the ventilation system was not changed. Thus, changing the rate at which fresh air enters space is extremely important. Also, increasing the size or height of the space may help to slightly reduce infection spread

[6]

[7]

Thermal comfort standards

the comfort zone according to ASHRAE 55-2017

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

2. Literature review 2.2 Psychrometric chart

“Interactive Psychrometric Chart - HVAC.” HVAC/R and Solar Energy Engineering, 21 June 2020, hvac-eng.com/interactive-psychrometric-chart/.

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.1 Scope

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.2 Research sample

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.2 Research sample

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.2 Research sample

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.2 Research sample

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.3 Simulation grid

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.4 Framework

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.5 Mechanical systems specifications

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.6 Proposals for window designs

B

The first window proposa

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.6 Proposals for window designs

C

The second window proposal

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.6 Proposals for window designs

D

The third window proposal

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

3. Research methodology 3.6 Proposals for window designs

E

The Fourth window proposal

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.1 Jeddah

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.1 Jeddah

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.1 Jeddah

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.1 Jeddah

A reduction in air age by (40.2%)

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.1 Jeddah

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.1 Jeddah

(45.6%) decrease in the average air age during the winter season and a decrease of (51.1%) in the summer

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.2 Riyadh

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.2 Riyadh

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.2 Riyadh

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.3 TABUK

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.3 TABUK

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

4. Results •4.3 TABUK

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

5. Conclusion •5.1 Jeddah

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

5. Conclusion •5.2 Riyadh

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

5. Conclusion •5.3 TABUK

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

5. Conclusion JEDDAH

The mechanical ventilation system (CAV) with the windows closed, after optimization can reduce the air age inside the classroom to (17.1 min and 17.2 min) for the summer and winter seasons, respectively, which can reduce the spread of infection in the classroom. The first proposal for windows (B) with a mechanical ventilation system (CAV) is considered a hybrid ventilation solution for the classroom as it reduces the air age to (16.1 min and 16.3 min) in winter and summer respectively, without affecting thermal comfort in the classroom

RIYADH

The CAV system with the second proposal for windows (C) and third proposal (D) maintained the thermal comfort zone in the summer only. The second proposal for windows with a mechanical system (CAV) was the lowest in air age with an average of (21.9 min) in the summer.

TABUK

The CAV system with the fourth proposals for windows and (E) maintained the thermal comfort zone in the summer only. The fourth proposal for windows with a mechanical system (CAV) was the lowest in air age with an average of (25.1 min) in the summer.

Conclusion

Hybrid ventilation system with CAV system found to be the best solution for the three cities for thermal comfort and ensuring a low air age.

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems

20. REFFERENCES 1.1 Secondary Title Here [1] AMBOSS. (2020). COVID-19 (coronavirus disease 2019). https://www.amboss.com/us/knowledge/COVID-19_(coronavirus_disease_2019)

[2] WHO. (2020). Coronavirus disease (COVID-19): Ventilation and air conditioning. World Health Organization. https://www.who.int/newsroom/q-a-detail/coronavirus-disease-covid-19-ventilation-and-air-conditioning

[3] European Centre for Disease Prevention and Controls. (2020). Heating, Ventilation and Air-Conditioning Systems In The Context of COVID19. June, 1–5. https://www.ecdc.europa.eu/sites/default/files/documents/Ventilation-in-the-context-of-COVID-19.pdf

[4] Jayaweera, M., Perera, H., Gunawardana, B., & Manatunge, J. (2020). Transmission of COVID-19 virus by droplets and aerosols: A critical review on the unresolved dichotomy. In Environmental Research (Vol. 188, p. 109819). Academic Press Inc. https://doi.org/10.1016/j.envres.2020.109819

[5] Abuhegazy, M., Talaat, K., Anderoglu, O., Poroseva, S. V., & Talaat, K. (2020). Numerical investigation of aerosol transport in a classroom with relevance to COVID-19. Physics of Fluids, 32(10). https://doi.org/10.1063/5.0029118

[6] Sun, C., & Zhai, Z. (2020). The efficacy of social distance and ventilation effectiveness in preventing COVID-19 transmission. Sustainable Cities and Society, 62(June), 102390. https://doi.org/10.1016/j.scs.2020.102390

[7] The American Society of Heating, R. and A.-C. E. (ASHRAE). (2017). Thermal environmental conditions for human occupancy.

ANSI/ASHRAE Standard - 55, 7, 6.

[8] “Interactive Psychrometric Chart - HVAC.” HVAC/R and Solar Energy Engineering, 21 June 2020, hvac-eng.com/interactive-psychrometricchart/.

Methods to prevent the spread of COVID-19 in classrooms using mechanical and hybrid ventilation systems