Development of a Personalised Microclimate Device for Localised Air Purification and Cooling

©Teaching and Learning Case Studies Teo AKH and Fadeyi MO (2026). Development of a personalised microclimate device for low-cost air purification and cooling for localised comfort. Teaching and Learning Case Studies #09. ISSUU Digital Publishing.

Development of a personalised microclimate device for lowcost air purification and cooling for localised comfort Andree Teo Kai Hui

Capstone project student and Lead researcher

Moshood Olawale Fadeyi Capstone project supervisor

Engineering Cluster, Singapore Institute of Technology, 1 Punggol Coast Road, Singapore 828608 Corresponding Email: fadeyi.moshood@singaporetech.edu.sg

CASE STUDY CONTEXT The Capstone Project undertaken by an undergraduate student and reported in this paper serves as a practical case study demonstrating the value of the supervisor's research in developing human cognitive governance for value-oriented problem diagnosis and solving. It also demonstrates how this transferable way of thinking can enable undergraduate students to produce scholarship of an academic standard suitable for publication in the Indoor Air Cartoon Journal. By internalising the transferable way of thinking embodied in the supervisor's research, the student developed appropriate mental models for understanding indoor air quality problems, formulated meaningful research questions, critically interpreted scientific evidence, integrated objective and subjective findings, exercised sound judgement, and translated these into informed engineering design decisions. This cognitive development enabled the student to progress beyond simply constructing a prototype to systematically diagnose a real-world indoor air problem and develop a personalised breathing-zone solution that balanced technical performance, usability, maintainability, and user value. Rather than merely transferring technical knowledge, the supervisor's research enabled the student to develop cognitive governance as an upstream capability for value-oriented problem diagnosis and solving. Consequently, this Capstone Project illustrates how the supervisor's research strengthens cognitive competency and its practical execution, providing upstream readiness for applied research, professional practice, and future scholarly contributions. ……………… COMPETENCY BASED EDUCATION CASE STUDY ……………

EXECUTIVE SUMMARY This Capstone Project investigated the development and evaluation of a personalised microclimate device designed to improve localised thermal comfort and air quality within the occupant's breathing zone through targeted airflow and low-cost filtration. The study was motivated by the

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limitations of conventional air-conditioning and mechanical ventilation (ACMV) and heating, ventilation, and air conditioning (HVAC) systems, which regulate overall indoor environmental conditions but do not always address the immediate microenvironment experienced by seated occupants. This limitation is particularly relevant in Singapore's hot and humid climate, where occupants may continue to experience warmth, stuffiness, or exposure to pollutants despite mechanically conditioned indoor environments. The study therefore examined whether a deskscale intervention could improve both objective environmental conditions and occupants' perceived experience within the breathing zone.

A functional prototype was developed by integrating targeted face and neck airflow, low-cost filtration, modular filter cartridges, particulate sensing with a red-green-blue (RGB) air-quality indicator, and simple manual speed control. An exploratory mobile application wireframe was also developed to investigate how a companion digital interface could support user interaction and environmental awareness. The design requirements were informed by a literature review and user survey, which identified the need for targeted airflow, cleaner local air, intuitive operation, and low operational burden.

The methodology combined controlled objective testing with subjective user evaluation. Objective testing was conducted under both occupied and unoccupied conditions using four operating states: No Prototype, Device Speed 1, Device Speed 2, and Device Speed 3. The principal performance indicator was the size-integrated particulate concentration across the 0.300–10.000 μm particle size range, while total volatile organic compounds (TVOCs) were used to evaluate the performance of the activated carbon filter. Carbon dioxide and relative humidity were recorded as supporting environmental parameters. User evaluation was subsequently conducted to assess perceived usefulness, thermal comfort, breathing-zone air acceptability, usability, operational burden, and overall user acceptance.

The results demonstrated that the breathing zone represents a distinct microenvironment, with pollutant concentrations differing from those measured elsewhere within the room. Under both occupied and unoccupied conditions, the prototype reduced particulate concentrations relative to the corresponding baseline condition without the prototype. TVOC concentrations were also reduced, indicating that the activated carbon filter contributed to reducing volatile and odorous pollutants. Although the magnitude of improvement varied according to airflow speed, occupancy, and initial pollutant conditions, all operating speeds generally improved breathing-zone environmental quality compared with the baseline condition. The user evaluation complemented these findings, with participants reporting that the prototype was easy to understand and operate, while the airflow was perceived as comfortable and beneficial. Participants also rated the prototype positively in terms of operational noise, perceived air freshness, and willingness to use the device during work or study. The RGB indicator and companion application wireframe further enhanced users' understanding of the device and its intended function.

The study also identified several opportunities for further refinement. Experimental variability associated with different occupants and changing background environmental conditions limited direct comparison between individual test runs, while the user evaluation involved a relatively small sample and short free-use sessions. Participants also identified several prototype

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implementation issues, including inconsistent touch-control responsiveness, weak magnetic filter retention, excessive RGB brightness, short USB cable length, and the overall size of the prototype.

Overall, this study demonstrates the feasibility of improving breathing-zone environmental quality through a low-cost personalised microclimate device that integrates targeted airflow, localised filtration, and user-centred design. The project contributes a functional proof-of-concept prototype, objective evidence supporting breathing-zone intervention, practical design knowledge for future personalised microclimate technologies, and preliminary insight into the potential role of companion digital interfaces in enhancing user interaction and environmental awareness.

Collectively, the findings establish a foundation for the continued development of personalised breathing-zone technologies that improve both indoor environmental quality and occupant experience.

Keywords: Personalised Microclimate; Breathing Zone; Indoor Air Quality; Localised Airflow; Low-Cost Filtration 1. INTRODUCTION 1.1 Background Indoor environmental quality is experienced by occupants not only at the room scale, but also in the immediate microenvironment surrounding individuals. For seated occupants, the area around the face and upper body is particularly important, as it is where inhalation occurs, and sensory cues such as stuffiness, lack of air movement, and thermal comfort are most strongly perceived.

However, many indoor environmental systems and integrated cooling-and-cleaning strategies are designed to be implemented for the entire room. Therefore, this creates a mismatch between how environmental performance is commonly measured and how it is experienced by occupants in shared indoor spaces. Therefore, occupants may remain exposed to pollutant plumes and discomfort locally, even when the room satisfies nominal thermal and indoor air quality (IAQ) benchmarks.

Hence, this gap becomes increasingly more important in Singapore, due to the hot-humid weather experienced by occupants, where the rising temperatures intensify the demand for cooling where occupants rely largely on air conditioning to cool down. In practice, occupants often seek thermal comfort through the usage of desk fans or handheld fans, even when the surrounding environment is mechanically cooled. These behaviours indicate that control for the entire room does not necessarily satisfy the environmental needs of an individual. In other words, the need is not only for spaces to be cooler, but for more effective and personalised control of the personal microclimate within the immediate breathing zone.

Concurrently, clean air remains as a major public health concern, as air pollution is one of the most critical environmental health risks globally. Particularly, PM2.5 is a significant pollutant due to its hazardous ability to penetrate deeply into the respiratory system and contribute to adverse health outcomes. Research has shown that air pollution as a major environmental risk factor to human health, and it was found that PM2.5 exposure is associated with respiratory, cardiovascular,

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neurological, inflammatory, oxidative, and immunotoxin effects. This makes PM2.5 the primary indicator of poor indoor air quality (Li et. al., 2017).

However, the most common desk-scale personal comfort device adopted by occupants is the table fan. Its widespread adoption shows that airflow targeted at the breathing zone is desirable and useful for thermal comfort within the microenvironment. However, the table fan does not remove particulate pollution, does not ensure cleaner inhaled air, and in some cases even carry pollutants towards the breathing zone depending on airflow direction and the position of the source. Hence, while the table fan provides local thermal comfort for the occupants, it does not address the need for providing clean, cooled air toward the personal space of the occupants. Therefore, it is necessary for a desk device that is capable of delivering targeted face/neck airflow, able to integrate low-cost filtration, convenient and simple for everyday use. This is the key motivator for this Capstone project where it seeks to develop a personalised microclimate device that can support both thermal comfort and improved indoor air quality at the breathing zone.

1.2 Problem Statement In Singapore, modern buildings typically rely on centralised Air-Conditioning and Mechanical Ventilation (ACMV) systems to maintain acceptable indoor environments for entire rooms or zones. These systems are designed to control the entire room, providing well-mixed air to meet the average setpoints of temperature, humidity, and contaminant levels in the occupied zone While effective at meeting benchmarking standards such as LEED or Green Mark, such an approach overlooks that, human comfort and exposure to invisible pollutants such as PM2.5 occur at the microenvironment.

This personal bubble is often termed the breathing zone, which is the immediate vicinity of each person’s nose, mouth, skin, and space where they are performing their tasks. The breathing zone is the region immediately surrounding the nose and mouth where inhaled air quality and local thermal conditions have the most direct physiological impact on occupants. Consequently, discomfort or pollutant exposure within the breathing zone may occur even when overall roomscale indoor environmental conditions appear acceptable (Frontczak and Wargocki, 2011; Melikov, 2004). Therefore, it is crucial that breathing zone is targeted. Conventional ACMV distributes air from diffusers typically located far from occupants, such as on ceilings, and mixes that air with existing room air before it reaches the occupant. This can lead to individuals breathing air less clean than the fresh air from the diffusers.

Additionally, some pollutant sources, such as dust can be resuspended at a desk, or exhalations from a nearby person can create contaminant concentrations around a person. Likewise, lack of airflow at a workstation can cause a sensation of stuffiness or overheating that is not reflected in the thermostat reading. In short, whole-room metrics are often misaligned with an occupant’s actual experienced environment. Occupants may remain subjected to local pollutant plumes and stagnant air pockets despite the existing ventilation systems. The problem is further exacerbated

by Singapore's hot and humid tropical climate, where the year-round demand for cooling places considerable emphasis on energy-efficient HVAC operation while maintaining acceptable indoor environmental quality (Shakya et al., 2021). Despite achieving acceptable room-scale environmental conditions, occupants may still experience thermal discomfort or a sensation of

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stuffiness because conventional HVAC systems do not always provide sufficient localised air movement within the breathing zone (Schiavon et al., 2017; Sekhar et al., 2005).

1.3 Research Gaps Conventional air-conditioning and mechanical ventilation (ACMV) and heating, ventilation, and air conditioning (HVAC) systems primarily regulate indoor environmental conditions at the room scale. This project was inspired by the Corsi–Rosenthal Box, which demonstrates that clean air can be delivered effectively using a simple, low-cost filtration concept. However, although the Corsi–Rosenthal Box provides highly effective room-scale particulate filtration, it is relatively bulky and is designed to clean the air within an entire room rather than deliver filtered airflow directly to an occupant's breathing zone (Dal Porto et al., 2022).

1.4 Research Questions Based on the problem framing and research purpose, the project posed several key research questions: RQ1(i) Can personalised microclimate control, incorporating targeted face and neck airflow with localised low-cost filtration, improve occupant experience in terms of perceived thermal comfort and breathing zone indoor air quality?

RQ1(ii) Which design parameters, including airflow directionality, controllability, acoustic performance, and user interface design, are required to achieve these outcomes in a desk-scale functional prototype?

RQ2 Under controlled unoccupied conditions, how effectively does the prototype improve breathing zone indoor air quality relative to the baseline condition, and how does its performance vary with fan speed?

RQ3(i) Under controlled occupied conditions with a fixed number of occupants performing standardised seated activities, how effectively does the prototype improve breathing zone indoor air quality relative to the baseline condition, and how does its performance vary with fan speed?

RQ3(ii) Based on a standardised and unbiased usability evaluation survey, how successful is the prototype at achieving occupant satisfaction, defined as —perceived usefulness; the improved face/neck thermal comfort and perceived breathing zone air acceptability, perceived burden; effort to operate, noise, and draft disturbance, and which fan speed setting maximises satisfaction?

2. LITERATURE REVIEW 2.1 Health Effect of Indoor Air Problem The need for clean air extends beyond occupant comfort to the protection of human health. Air pollution is recognised as one of the most significant global environmental health risks, contributing to a wide range of adverse health outcomes, including respiratory, cardiovascular, neurological, and developmental disorders. It remains one of the leading contributors to premature

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mortality worldwide (Fuller et al., 2022; Manisalidis et al., 2020). Among the various air pollutants, fine particulate matter (PM₂.₅) is recognised as one of the leading global risk factors for premature mortality, ranking fifth among all risk factors worldwide (Fuller et al., 2022). Owing to its small aerodynamic diameter (≤ 2.5 μm), PM₂.₅ can penetrate deeply into the respiratory tract and reach the alveolar region of the lungs, where it contributes to adverse respiratory, cardiovascular, and systemic health effects (Manisalidis et al., 2020). Even at non-lethal exposure levels, PM₂.₅ has been associated with an increased risk of allergic responses, respiratory infections, and other adverse health outcomes.

In addition to particulate matter, volatile organic compounds (VOCs) and odorous pollutants influence occupants' perception of indoor air quality, even when particulate concentrations are relatively low (Wolkoff and Nielsen, 2017; Marć et al., 2018). Consequently, improving the air surrounding an individual's breathing zone requires not only reducing particulate matter but also minimising VOCs and odorous pollutants. Clean air is therefore fundamental to human health and wellbeing, just as access to clean drinking water is essential for sustaining life. Given its critical importance to human health, preserving clean air has been advocated as a fundamental human right (Lelieveld, 2017). Collectively, these findings demonstrate that polluted air poses a direct threat to human health and wellbeing.

2.2 Breathing Zone and Personal Exposure The air surrounding a seated occupant is not always representative of the conditions measured by stationary room-level monitoring systems. This phenomenon is explained by the concept of the human personal cloud (HPC), whereby body heat, respiration, movement, clothing, and nearby pollutant sources create a distinct microenvironment around the occupant that may differ from the surrounding room air (Licina et al., 2015a and b; Rim and Novoselac, 2009). Consequently, roomscale measurements may not accurately represent the air actually inhaled by the occupant.

This distinction is particularly important when evaluating thermal comfort and breathing-zone air quality because local environmental conditions can vary with posture, activity, airflow patterns, and the presence of nearby occupants, even when the room-scale ACMV system maintains relatively stable environmental conditions (Lan et al., 2011). Furthermore, pollutant exposure within the breathing zone is governed by the interaction between the convective boundary layer surrounding the human body, the airflow generated by breathing, and the local airflow directed towards the face (Bivolarova et al., 2017).

Research has shown that personalised airflow does not necessarily reduce breathing-zone pollutant exposure unless it is appropriately designed to interact effectively with the human convective boundary layer and breathing flow. Airflow that is insufficient to penetrate the local boundary layer may provide limited improvement, whereas appropriately directed and sufficiently strong airflow can more effectively dilute pollutants within the breathing zone (Bivolarova et al., 2017).

These findings highlight the importance of designing localised airflow to modify the occupant's immediate microenvironment rather than relying solely on room-scale ventilation.

Similarly, existing thermal comfort models, including the Predicted Mean Vote (PMV) and adaptive comfort models, have been criticised for their limited ability to predict the comfort of

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individual occupants under real building conditions because they are primarily derived from population-based relationships rather than individual physiological and contextual variability (Warthmann et al., 2019). Together, these findings demonstrate that current approaches do not adequately account for the unique conditions experienced within an occupant's breathing zone.

Consequently, greater emphasis should be placed on understanding and controlling the breathing zone, as it represents the region where occupants directly inhale air and experience the immediate thermal and air quality conditions that influence both comfort and health.

2.3 Personalised Ventilation and Comfort Personalised environmental control has been widely investigated as a strategy for addressing the non-uniform thermal and air quality conditions experienced by individual occupants while providing greater individual control over the immediate microenvironment (Warthmann et al., 2019). In practice, occupants frequently use everyday devices such as desk fans and handheld fans to improve local thermal comfort, even in mechanically ventilated spaces. Experimental evidence demonstrates that airflow directed towards the face produces measurable physiological and perceptual benefits, with higher airflow rates resulting in greater facial cooling and faster recovery from breathlessness in healthy adults (Brew et al., 2024).

These findings demonstrate that localised facial airflow has a meaningful physiological effect and can significantly enhance perceived thermal comfort. However, airflow alone does not address the quality of the air being inhaled. While personalised ventilation systems have been developed to improve both thermal comfort and inhaled air quality, commonly used consumer devices such as desk fans are intended primarily to increase air movement rather than deliver filtered clean air to the breathing zone. This presents an opportunity to integrate targeted airflow with localised air filtration, thereby delivering clean air directly to the occupant's breathing zone while simultaneously improving thermal comfort.

2.4 Filter Selection Selecting an appropriate filtration strategy is essential because indoor air contains both particulate and gaseous pollutants, which require different filtration mechanisms for effective removal.

Consequently, filter selection should be guided by the types of pollutants most relevant to the occupant's breathing zone rather than adopting a single filtration approach for all pollutants. Highefficiency particulate air (HEPA) filters are widely recognised as the most effective technology for removing fine particulate matter, whereas gaseous pollutants such as volatile organic compounds (VOCs) and odorous compounds generally require sorption-based media, such as activated carbon (Azimi and Stephens 2013; Wolkoff and Nielsen, 2001; Zhang et. al., 2011).

The effectiveness of particulate filtration has been demonstrated under real residential conditions.

In a household study conducted in Taiwan, the introduction of a portable HEPA air cleaner reduced indoor PM₂.₅ concentrations from 33.5 ± 10.3 µg/m³ to 17.2 ± 10.7 µg/m³ (Chen et al., 2022). The study further showed that filtration performance was influenced by operational conditions, including airflow rate and window-opening behaviour. These findings demonstrate that effective breathing-zone air quality depends not only on filter efficiency but also on the ability of the airflow to deliver the filtered air to the occupant.

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In addition to particulate matter, indoor air may contain volatile organic compounds (VOCs) and odorous gaseous pollutants that adversely affect occupants' perception of indoor air quality.

Consequently, a secondary filtration stage is required to complement particulate filtration.

Activated carbon is widely used for the removal of gaseous pollutants because its highly porous structure enables contaminants to be removed primarily through adsorption (Marsh and RodríguezReinoso, 2006). Activated carbon has been shown to be effective in reducing VOCs, odours, and a wide range of gaseous contaminants, thereby improving perceived indoor air quality (Ma et al., 2019).

These findings suggest that a modular filtration system incorporating both a high-efficiency particulate filter and an activated carbon filter would enable the device to address both particulate and gaseous pollutants within the breathing zone. Such a modular configuration would improve breathing-zone air quality by reducing harmful pollutants and unpleasant odours while allowing the targeted airflow to enhance local thermal comfort.

2.5 Conclusion The literature demonstrates that clean air is fundamental to protecting human health, with PM₂.₅ serving as an important indicator for evaluating improvements in breathing-zone air quality. As the breathing zone represents the air directly inhaled by occupants, it should be prioritised in the design and evaluation of personalised microclimate systems. Although personalised airflow has been shown to improve perceived thermal comfort, existing solutions generally provide air movement without simultaneously delivering filtered clean air to the breathing zone.

The review further highlights the importance of adopting a modular filtration strategy capable of addressing both particulate and gaseous pollutants through appropriate filter selection. Such a configuration should accommodate high-efficiency particulate filtration together with activated carbon or other specialised filters that can be interchanged according to the predominant indoor pollutants. Collectively, these findings indicate that an effective personalised microclimate device should integrate targeted airflow with a flexible, pollutant-specific filtration system capable of delivering clean air directly to the occupant's breathing zone while enhancing thermal comfort.

These insights provide a clear evidence-based foundation for translating the identified requirements into engineering design specifications for the proposed prototype..

3. DESIGN SPECIFICATIONS 3.1 Design Basis Having established the need for an intervention focused on the breathing zone, the design direction is defined by how cleaner and cooler air can be delivered directly to the occupant, particularly to the face and upper body. Accordingly, the development of the prototype is guided by Research Question 1, which establishes both the intended outcomes of personalised microclimate control and the design parameters required to realise those outcomes in a functional desk-scale prototype, including airflow delivery, filtration, controllability, user interface, and usability.

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3.2 Data Collection for User Design Input To inform the design specifications of the proposed device, a questionnaire titled "How We Feel Indoor Air" was developed using Google Forms to obtain user-centred insights into occupants' perceptions of indoor environmental conditions. The survey explored experiences relating to thermal comfort, breathing-zone conditions, and the challenges associated with perceived thermal discomfort and indoor air quality during prolonged indoor activities. The findings were intended to identify user needs and establish evidence-based design requirements for the proposed personalised microclimate device.

3.2.1

Participants and Sampling Technique

A total of 37 participants completed the survey. Participants were recruited using a non-probability convenience sampling approach, with the questionnaire distributed through accessible communication networks. This sampling strategy was considered appropriate because the objective was not to estimate population characteristics but to obtain design-relevant insights from potential users of a desk-scale personalised microclimate device. The respondents represented individuals who spent prolonged periods in common indoor environments, including homes, offices, libraries, and study spaces.

3.2.2

Survey Instrument and Materials

The data collection instrument was a structured online questionnaire developed using Google Forms. It comprised a combination of multiple-choice questions, multiple-response questions, 10point Likert-type rating scales, and optional open-ended questions. The rating scales were used to measure perceptions such as the extent to which respondents experienced discomfort despite generally acceptable room conditions. Multiple-response questions explored common discomfort conditions, existing coping strategies, adaptive behaviours, and preferred environmental improvements. Open-ended questions enabled respondents to describe, in their own words, the characteristics of a comfortable indoor environment and the effects of insufficient airflow on their comfort, concentration, productivity, and overall experience.

The combination of quantitative and qualitative question formats supported both the identification of common response patterns and a deeper understanding of occupants' experiences. Closed-ended questions enabled descriptive analysis of user preferences and perceived needs, whereas openended responses provided contextual insights into why particular design features may be important.

3.3 Data Collection The survey link was distributed electronically through accessible communication channels.

Participation was voluntary, and respondents completed the questionnaire remotely. Responses were collected automatically through Google Forms for subsequent analysis. Figures 1–4 present the survey findings that informed the design requirements of the proposed device.

Figure 1: Responses regarding respondents’ opinions on microenvironment

Figure 2: Responses regarding respondents’ usual thermal experience and how much it affects them

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Figure 3: Responses regarding respondents’ opinions on microenvironment

Figure 4: Responses regarding respondents’ usual airflow direction and what they typically experience thermally

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3.4 User Personas To support the development of the proposed prototype, two user personas were developed based on the survey findings. The personas served as a human-centred design tool for translating occupants' recurring needs, behaviours, and environmental challenges into practical design requirements. Rather than representing specific individuals, the personas synthesise common user characteristics identified from the survey and provide a design direction for delivering localised thermal relief, personalised microclimate control, improved breathing-zone air quality, and an intuitive user interface.

3.4.1

Persona 1: The office resident

The first persona, The Office Resident, represents occupants who spend prolonged periods in centrally air-conditioned shared offices. This persona reflects the recurring need for personalised airflow despite the presence of room-scale air-conditioning, highlighting that centrally controlled ACMV systems do not always satisfy individual comfort requirements. The Office Resident requires targeted and adjustable airflow directed towards the face and upper body to improve thermal comfort and reduce afternoon fatigue while avoiding disturbance to nearby colleagues. As shared office environments may also contain unpleasant odours, the persona requires localised air filtration to improve breathing-zone air quality. The device should also provide simple, low-effort operation because it is intended for use during cognitively demanding work where complex controls or frequent maintenance would reduce usability.

3.4.2

Persona 2: The health-conscious student

The second persona, The Health-Conscious Student, represents occupants who spend extended periods studying in semi-enclosed indoor environments where stagnant air and odours may accumulate. This persona reflects survey responses indicating concerns about stale air, indoor pollutants, and the need for greater personal control over the immediate environment. The HealthConscious Student therefore requires a personalised microclimate that combines targeted airflow with effective air filtration to improve both breathing-zone air quality and perceived thermal comfort. To support everyday use, the device should incorporate replaceable modular filters and a simple visual indicator that communicates the current air quality in an intuitive manner.

3.4.3

Design implications

Collectively, the two personas indicate that the proposed device should integrate targeted airflow with modular air filtration while providing intuitive controls and straightforward maintenance.

These user-centred requirements directly informed the engineering design specifications developed for the prototype.

3.5 Functional Specifications Based on the identified user needs and personas, the proposed prototype was designed to satisfy five principal functional requirements.

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The first functional requirement is targeted airflow delivery. The device shall deliver airflow directly towards the occupant's face and upper body to provide localised thermal relief within the breathing zone. To achieve this, an axial fan is positioned within the base of the device, and the airflow is channelled through a flexible trunking into a ring-shaped outlet. This configuration enables the airflow to be directed efficiently towards the user while allowing the outlet to be repositioned according to individual preferences. The adjustable outlet also enables users to personalise the direction of the airflow without repositioning the entire device.

The second functional requirement is localised air filtration. The air supplied to the occupant shall pass through a filtration system integrated within the base of the device before being delivered to the breathing zone. The prototype incorporates a modular cartridge-based filtration system, with filter cartridges positioned on the four sides of the base to allow air to be drawn through the filters under negative pressure before reaching the fan. This configuration integrates air purification directly into the personalised airflow pathway while supporting a modular and maintainable design. The cartridge system also enables users to replace filters easily or substitute alternative filter media according to the target indoor pollutants.

The third functional requirement is user control. The prototype shall enable users to adjust its operation through a simple and intuitive interface. The current design incorporates two capacitive touch sensors: one for power control and another for fan-speed adjustment. This arrangement allows users to modify the airflow intensity according to their thermal comfort preferences while maintaining a straightforward user interaction.

The fourth functional requirement is environmental feedback. The prototype incorporates a PMS5003 particulate matter sensor to monitor local PM₂.₅ concentration and communicates the measured air quality through an RGB indicator. The visual feedback provides users with a simple indication of local air quality and supports filter maintenance by signalling when filter replacement may be required. The final functional requirement is portability. The device shall be sufficiently compact for desktop use while maintaining adequate stability during normal operation. The design is intended to support prolonged sedentary activities, including office work, studying, and computer-based tasks, without occupying excessive desk space or compromising usability.

3.6 Specifications for Performance and Evaluation Based on the identified user personas, the prototype was designed to provide clean air, targeted airflow, and improved perceived air quality within the occupants' immediate surroundings.

Accordingly, the primary performance objective of the prototype was to improve air quality within the occupant's breathing zone. Device performance was evaluated using the size-integrated optical particle concentration across the 0.3 μm –10 μm particle size range, measured by the TSI Optical Particle Sizer (OPS 3330), to determine the effectiveness of the prototype in reducing breathingzone particulate exposure. The prototype was configured with three distinct airflow settings to evaluate the relationship between airflow rate and particulate concentration within the breathing zone while providing users with adjustable airflow according to their preferences.

The airflow delivery system was designed to generate localised airflow that was sufficient to provide perceptible thermal relief and influence the breathing zone without producing excessive

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draft that could cause discomfort or irritation. This design decision was informed by the user personas, which indicated a preference for personalised airflow provided that it remained comfortable and not excessively intense. Finally, the prototype was designed to minimise user burden during prolonged desk-based use. The user interface was designed to support simple and intuitive operation, while the overall design sought to minimise operational noise, simplify routine maintenance, and facilitate straightforward filter replacement.

3.7 Design Development 3.7.1

Design modelling

The design of the prototype was informed by the findings from the literature review, the user personas, and the functional design specifications established in the preceding stages of the study.

Based on these requirements, a three-dimensional digital model of the prototype was developed using Rhinoceros 7 (Rhino 7). The digital model included the external housing, fan enclosure, ring-shaped airflow outlet, modular filter cartridges, cartridge mounting system, and other internal structural components required for assembly. Following completion of the digital model, the prototype components were fabricated using three-dimensional (3D) printing. The printed components included the external housing, internal cartridge frame, cartridge mounts, ring-shaped airflow outlet, and other structural parts necessary for prototype assembly and subsequent performance evaluation.

3.7.2

Ring air outlet design

The prototype incorporated a ring-shaped air outlet to direct airflow towards the occupant's face and upper body within the breathing zone. A bladeless configuration was adopted because it enclosed the fan within the base of the device, thereby eliminating exposed rotating blades and improving operational safety and user acceptability. The geometric concept of the ring outlet was developed after learning the basic construction principle of a bladeless fan from an online tutorial.

The concept employed an inner cylindrical body positioned concentrically within an outer housing, creating a continuous annular gap through which fan-driven air was discharged as a ring-shaped airflow. The geometry was subsequently adapted and refined to satisfy the functional requirements of the proposed prototype.

The ring outlet was modelled using Rhinoceros 7 (Rhino 7). The inner cylindrical body was designed with a height of 110 mm, while the outer housing had a height of 120 mm. A uniform annular gap of 5 mm was incorporated between the inner and outer surfaces to form the airflow outlet. This gap was a critical design feature because it provided the discharge pathway for the airflow generated by the fan. The internal cylindrical outlet region was designed with a diameter of 53 mm and a height of 50 mm, enabling airflow from the fan housing to be channelled into the annular outlet before being directed towards the occupant.

3.7.3

Modular filter cartridges

The filter cartridges were designed with a modular configuration to support both filter replaceability and flexibility in filter selection. Rather than permanently integrating the filters into

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the device housing, the prototype incorporated removable filter cartridges that housed the filter media and could be inserted into or removed from the main body of the device. This configuration enabled users to replace filters when required and to substitute alternative filter media according to the target indoor pollutants. Each cartridge measured 180 mm × 200 mm. This size was selected because it provided a practical rectangular geometry that enabled four cartridges to be arranged on the four side faces of the device housing.

The configuration maximised the available filtration area while allowing air to be drawn uniformly through the filters and into the centrally located fan. Each cartridge consisted of a two-part frame, comprising a front frame and a rear frame, which enclosed and secured the filter media within the cartridge body. Circular recesses were incorporated into the frame to accommodate magnets, enabling the cartridge halves to be opened and closed easily during filter installation and replacement. Figure 5 presents the cartridge components modelled using Rhinoceros 7 (Rhino 7) and fabricated using three-dimensional (3D) printing for integration into the prototype. a

b

c

Figure 5: (a) Primary Filter Cartridge (open) with HEPA filter sheet; (b) Secondary Filter Cartridge (open) with activated carbon (AC) filter sheet; (c) Example of a filter cartridge slotting mechanism and how the AC filter is placed behind the HEPA filter.

3.7.4

Filters

Commercially available filter media were selected and integrated into the modular filter cartridges.

The filter media were procured from an online retail marketplace, consistent with the project's lowcost design objective, which sought to evaluate whether readily accessible consumer components could be adapted for use in a personalised breathing-zone air-cleaning device. The primary filtration stage consisted of a High-Efficiency Particulate Air (HEPA) filter, which was cut to size and fitted into the modular cartridges. The HEPA filter served as the principal particulate removal layer and was intended to reduce airborne particulate concentrations within the occupant's breathing zone, thereby improving local indoor air quality (Chen et al., 2022).

The secondary filtration stage consisted of an activated carbon filter, which was cut to size and installed within the modular cartridge system. Activated carbon was selected because of its wellestablished adsorption capability for volatile organic compounds (VOCs), odorous compounds, and other gaseous pollutants commonly found in indoor environments, thereby improving the perceived freshness and acceptability of the air delivered to the user (Wolkoff and Nielsen, 2017).

3.7.5

Electronic components

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The electronic control system was developed around an Arduino Nano, which served as the central controller for the prototype. The Arduino coordinated the operation of the airflow delivery system, user controls, and environmental feedback by integrating a PMS5003 particulate matter sensor, two capacitive touch sensors, an RGB (red-green-blue) light-emitting diode (LED), and a pulsewidth modulation (PWM)-controlled axial fan. In operation, the Arduino continuously acquired PM₂.₅ measurements from the PMS5003 sensor, processed user inputs from the capacitive touch sensors, and adjusted both the fan speed and RGB LED output according to the programmed control logic. Figure 6a shows the electronic components integrated into the prototype.

The PMS5003 sensor provided real-time PM₂.₅ measurements, enabling the surrounding air quality to be monitored continuously. Sensor readings were updated approximately once per minute and were communicated through a simplified RGB LED indicator to minimise the need for users to interpret numerical measurements. A green LED indicated PM₂.₅ concentrations of ≤15 μg/m³, an amber LED indicated concentrations between 15 and 37.5 μg/m³, and a red LED indicated concentrations of >37.5 μg/m³. This simplified visual interface enabled users to recognise changes in local breathing-zone air quality quickly and also prompted users to inspect the surrounding environment or replace the filter media when elevated particulate concentrations persisted.

To minimise user interaction burden, manual operation of the prototype was implemented using two capacitive touch sensors. One sensor controlled the power function, while the second controlled the fan speed. When the prototype was powered on (see Figure 6b), successive touches of the speed-control sensor cycled the axial fan through three preset PWM speed levels, providing adjustable airflow while maintaining a simple and intuitive user interface. This control strategy was consistent with the low-burden design objective established during the user-centred design process, enabling prolonged use with minimal operational effort. b

a

Figure 6: (a) Details of fan components; (b) Final Prototype

3.7.6

App wireframe

Figure 7 shows a companion mobile application, ElevAir, developed and explored to support user interaction with the proposed device. At this stage, the application was developed solely as a wireframe rather than as a functional software system. The wireframe included several key interface screens, including a landing page, a breathing-zone status page, and a fan-speed control page. These interfaces were designed to demonstrate how breathing-zone air quality information

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and device controls could be presented digitally to improve user understanding and interaction with the prototype. The wireframe was intended to evaluate the clarity of the proposed layout, functionality, navigation, and overall user interface logic rather than the performance of the application itself.

Figure 7: App wireframe for ElevAir

4.

METHODOLOGY

4.1 Methodological Overview The methodology was designed to address RQ2 and RQ3 through a combination of controlled experimental testing and user-centred evaluation of the developed prototype. RQ2 investigated the technical performance of the prototype under controlled unoccupied conditions, whereas RQ3(i) evaluated its performance under occupied conditions representative of normal use. RQ3(ii) assessed user perceptions of the prototype through structured usability evaluation. This sequence enabled the technical performance of the device to be established before its perceived usefulness, usability, and acceptability were evaluated.

The methodology generated two complementary forms of evidence. The objective evaluation examined the effectiveness of the prototype in improving breathing-zone air quality through measurements of particulate matter, total volatile organic compounds (TVOCs), carbon dioxide, and relative humidity. The subjective evaluation examined users' perceptions of thermal comfort, breathing-zone air quality, usability, operational burden, and overall acceptance of the prototype.

4.2 No Occupant Conditions RQ2 was investigated under controlled unoccupied conditions to evaluate the performance of the prototype without interference from body heat plumes, respiration, movement, or other occupantrelated influences. Four prototype conditions were evaluated: No Prototype (baseline), Device

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Speed 1, Device Speed 2, and Device Speed 3. Each condition was tested over a 60-minute experimental period under controlled indoor environmental conditions.

The primary performance indicator was the size-integrated particulate concentration across the 0.300–10.000 μm particle size range, measured using the TSI OPS 3330. TVOC concentration was measured to evaluate the behaviour of gaseous pollutants and the contribution of the activated carbon filter, while carbon dioxide concentration and relative humidity were recorded as supporting environmental parameters. As the experiments were conducted at different times, direct comparison of raw measurements could be influenced by temporal variation in the indoor environment. To improve comparability, both absolute change and percentage change were calculated using measurements recorded at the 5th minute and 65th minute of each experimental run.

4.3 Occupied Conditions RQ3(i) was investigated under controlled occupied conditions to evaluate the performance of the prototype under representative operating conditions. The inclusion of an occupant introduced physiological and behavioural factors, including body heat plumes, respiration, and minor movement, that may influence breathing-zone airflow and pollutant transport.

Each prototype condition (No Prototype, Device Speed 1, Device Speed 2, and Device Speed 3) was evaluated during three independent occupant trials, with one participant completing each trial.

During each 60-minute experiment, participants remained seated, performed quiet desk-based activities, refrained from speaking, and remained within the room throughout the measurement period.

The same environmental parameters measured under unoccupied conditions were recorded during the occupied experiments. Because three independent trials were conducted for each prototype condition, the measured particulate concentration, TVOC concentration, carbon dioxide concentration, and relative humidity were aligned to a common 70-minute timeline and averaged to generate a representative dataset for each prototype condition.

4.4 Experimental Matrix The experimental matrix was developed to evaluate the performance of the prototype under different airflow settings and occupancy conditions. Four prototype conditions were investigated: (1) No Prototype (baseline), (2) Device Speed 1, (3) Device Speed 2, and (4) Device Speed 3. Each prototype condition was evaluated under four experimental scenarios comprising one unoccupied condition and three occupied conditions, where Occupant 1, Occupant 2, and Occupant 3 each completed an independent experimental run. This resulted in a total of 16 experimental runs (4 prototype conditions × 4 experimental scenarios), as shown in Table 1. The experimental design enabled comparisons between the baseline and intervention conditions while also evaluating the influence of airflow speed under both unoccupied and occupied environments.

Table 1: Experimental matrix showing prototype operating status and occupancy condition across the 16 test scenarios.

Page 19 Status of the developed solution

Occupancy Status

(1) Device Speed 1

No occupant present Occupant 1 Occupant 2 Occupant 3 No occupant present Occupant 1 Occupant 2 Occupant 3 No occupant present Occupant 1 Occupant 2 Occupant 3 No occupant present Occupant 1 Occupant 2 Occupant 3

(2) Device Speed 1

(3) Device Speed 2

(4) Device Speed 3

4.5 Prototype Preparation Prior to experimental testing, the prototype was sealed using adhesive tape at critical joints and openings to minimise unintended air leakage. The sealed locations included the base of the prototype, the upper opening of the filter housing used for filter installation and removal, and the interface between the filter housing and the capacitive touch sensor enclosure. Sealing these locations ensured that the majority of the airflow generated by the fan passed through the intended filtration pathway before being discharged through the ring outlet. This reduced uncontrolled airflow leakage that could otherwise influence breathing-zone measurements and compromise the consistency of the experimental conditions. The prototype remained sealed throughout all experimental runs.

4.6 Data Set-up Objective environmental measurements were conducted in a discussion room at the Singapore Institute of Technology (SIT) under controlled indoor conditions. The measurement system consisted of one TSI Optical Particle Sizer (OPS 3330) and two GrayWolf AdvancedSense Pro instruments. The OPS 3330 was co-located with one GrayWolf instrument at the primary sampling location representing the occupant's breathing zone. The second GrayWolf instrument was positioned approximately 1.5 m away within the same room to provide background environmental measurements.

The primary sampling location was maintained at a height of approximately 1.0 m above the floor, corresponding to the breathing zone of a seated occupant. This measurement height remained constant throughout all experiments. During intervention tests, the prototype was positioned approximately 0.8 m from the primary sampling location and oriented towards the measurement instruments to simulate the delivery of localised airflow to the breathing zone. The positions of the

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prototype and all measurement instruments were maintained throughout the study to ensure consistency across all experimental runs.

4.7 Experimental Procedure Each experimental session lasted approximately 8 hours, during which a 60-minute measurement period was designated as the principal analysis window. Under the unoccupied condition, the room remained unoccupied except for the researcher, who remained in a designated corner of the room throughout the experiment to minimise disturbance to the measurement environment.

Under the occupied condition, a single participant entered the room following a predetermined route, proceeded to the designated seating position, and performed quiet desk-based activities for 60 minutes. Participants were instructed to remain seated, refrain from speaking, and not leave the room throughout the measurement period. To ensure consistency across all experimental conditions, participant entry and exit times were standardised, seating positions were fixed, and the measurement instruments and prototype remained in the same locations throughout all experimental runs (Figure 8). During intervention tests, the prototype was switched on and oriented towards the primary breathing-zone sampling location.

prototype

Figure 8: Experimental layout of the occupied test condition, showing the room arrangement, researcher position, background measurement point, occupant microenvironment seat, and prototype placement under without-prototype and with-prototype scenarios.

Figure 9: Measurements with OPS3330 (denoted as green) and AdvancedSense GrayWolf (denoted as red) Without Prototype

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Figure 9: Measurements with OPS3330 and AdvancedSense GrayWolf With Prototype

4.8 User Testing RQ3(ii) was investigated through a user-centred evaluation of the developed prototype to assess its perceived usefulness, usability, user burden, and overall acceptance. This stage complemented the objective performance evaluation by examining whether the technical improvements achieved by the prototype were perceptible and meaningful to users during normal operation.

4.8.1

Participants and sampling

Participants were recruited using convenience sampling from accessible peer networks, consistent with the intended user group of the proposed device, namely individuals who spend prolonged periods undertaking desk-based work or study in indoor environments. A total of 10 participants completed the user evaluation.

4.8.2

Data collection instruments

A structured user evaluation questionnaire was developed specifically for this study. The questionnaire comprised six sections covering participant and session information, pre-test environmental conditions, post-test environmental experience, usability and perceived burden, filter cartridge evaluation, and overall user feedback. It was designed to evaluate perceived changes in thermal comfort, breathing-zone air quality, airflow acceptability, ease of operation, operational noise, airflow disturbance, perceived usefulness, and overall satisfaction with the prototype.

Particular emphasis was placed on evaluating the modular filter cartridge system, including the ease of understanding its operation, replacing the filter media, handling the cartridges, and the effectiveness of the magnetic fastening mechanism. The questionnaire incorporated Likert-scale items, multiple-choice questions, multiple-response questions, and open-ended responses to obtain both quantitative and qualitative feedback. Unless otherwise stated, perception-based questionnaire items employed a five-point Likert scale. For statements assessing agreement, the scale ranged from 1 = Strongly disagree to 5 = Strongly agree. For environmental perception items, the scale was adapted to the wording of each question, with 1 consistently representing the least favourable condition (e.g., very uncomfortable or not fresh at all) and 5 representing the most favourable condition (e.g., very comfortable or very fresh). This approach enabled consistent interpretation of participants' perceived environmental conditions and usability responses.

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4.8.3

User testing procedure

At the beginning of each session, participants completed the pre-test section of the questionnaire to record their initial perception of the indoor environment. They were then provided with the prototype for a 30-minute free-use session, during which they could adjust the fan speed, replace the filter cartridges, and observe the RGB air-quality indicator. Immediately after the session, participants completed the remaining sections of the questionnaire to evaluate their perceived thermal comfort, breathing-zone air quality, usability, operational burden, filter cartridge system, and overall impressions of the prototype.

Figure 10: An example of a participant's free-use session with the prototype.

Throughout each session, the researcher remained in the room in a non-participatory role, seated in a corner away from each participant to minimise interference with natural interaction. Where appropriate, observational notes were recorded, particularly when participants experienced difficulties related to filter replacement, cartridge closure, magnetic retention, or the size and portability of the prototype.

4.9 Methodological Limitations Several methodological limitations should be considered when interpreting the findings of this study. First, the occupied experiments were conducted using different participants rather than repeated trials with the same individual. Although all experimental runs were standardised with respect to seating position, activity, entry pathway, and test duration, some degree of interindividual variability could not be eliminated.

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Second, the experiments were conducted in discussion rooms that relied on passive ventilation.

Consequently, the indoor environmental conditions were not expected to remain identical across all experimental sessions because passive ventilation performance is influenced by dynamic outdoor conditions, including wind speed, outdoor temperature, relative humidity, infiltration, and airflow behaviour (ASHRAE, 2021; Allard & Ghiaus, 2012).

Third, the user evaluation involved a relatively small sample of 10 participants, and each participant interacted with the prototype for 30 minutes. Consequently, the subjective findings primarily reflect short-term user perceptions and may not fully represent long-term usability, user acceptance, or sustained operational performance. Despite these limitations, the experimental methodology incorporated standardised testing procedures, consistent measurement locations, controlled prototype positioning, and identical evaluation protocols across all experimental conditions. These measures were implemented to minimise uncontrolled variation and improve the comparability of the experimental data.

5. RESULTS AND DISCUSSION 5.1 Result Interpretation This chapter presents the findings from the objective performance evaluation and user-centred evaluation of the developed prototype. The findings are organised according to the research questions. RQ2 presents the performance of the prototype under unoccupied conditions, RQ3(i) presents the performance under occupied conditions, and RQ3(ii) presents the user evaluation findings.

5.2 Breathing Zone Microenvironment Figure 11 and Tables 2 to 3 show the comparison of microenvironment vs background under no prototype and at speed 3 scenarios. Comparison between the breathing-zone and background measurement locations showed that TVOC concentrations remained consistently higher within the breathing zone than at the room background location throughout the experiments. Under the No Prototype condition, breathing-zone TVOC concentrations ranged from a peak of 618 ppb to a minimum of 487.33 ppb, whereas the corresponding background concentrations remained substantially lower, ranging from 124.33 ppb to 112.33 ppb. Similarly, under Device Speed 3, despite the prototype operating at its highest airflow setting, breathing-zone TVOC concentrations remained higher than the background, decreasing from 1651 ppb to 844.67 ppb, while the background concentrations ranged from 293.33 ppb to 172.67 ppb.

Across both baseline and intervention conditions, the breathing-zone measurements consistently exceeded those recorded at the background location, demonstrating a persistent spatial difference in local air quality. These findings indicate that the air immediately surrounding the occupant behaved differently from the overall room environment and that background room measurements alone would not adequately represent an occupant's actual exposure to gaseous pollutants at the point of inhalation. The results therefore reinforce the importance of evaluating indoor air quality

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at the breathing zone, where pollutant exposure is most directly experienced, rather than relying solely on room-level measurements.

Figure 11: Comparison of microenvironment vs background under no prototype and at speed 3 scenarios.

Table 2: TVOC concentration range under Device (No prototype) Parameters Peak value Lowest Value

Breathing Zone (ppb) 618.00 487.33

Background (ppb) 124.33 112.33

Table 3: TVOC concentration range under Device (Speed 3) Parameters Peak value Lowest Value

Breathing Zone (ppb) 1651.00 844.67

Background (ppb) 293.33 172.67

This observation is consistent with the design rationale of the present study, which prioritises the breathing zone as the primary point of intervention rather than relying solely on room-level indoor environmental conditions. The results suggest that the breathing zone constitutes a dynamic local microenvironment, where pollutant concentrations are continuously influenced by the occupant and the immediate surrounding environment.

Consequently, measurements obtained at the room background location may underestimate the gaseous pollutant exposure experienced directly by the occupant. These findings reinforce the importance of delivering targeted, filtered airflow directly to the breathing zone as a means of improving local air quality. They also provide further support for the design requirements established under RQ1, which identified localised airflow and integrated air filtration as essential features of the proposed personalised microclimate device.

5.3 Total Volatile Organic Compounds (TVOC) This section examines Total Volatile Organic Compounds (TVOC) levels obtained by the AdvancedSense Graywolf in the breathing zone across all prototype statuses under both unoccupied and occupied scenarios. Each plot covers a 70-minute window, comprising 5 minutes

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before the prototype is switched on, 60 minutes of active operation, and 5 minutes after switching off. These results helped clarify whether the prototype influenced the volatile compounds and whether the influence varied with the fan speed settings.

5.3.1

TVOC levels under unoccupied conditions

Figure 12 shows the TVOC Graph Comparison across all speeds (Without Occupant), while Table 4 shows the TVOC reduction under unoccupied conditions. Under the unoccupied condition, the No Prototype scenario exhibited only a modest decline in TVOC concentration, decreasing from 789 ppb at the beginning of the measurement period to 666 ppb at the end, corresponding to a 15.59% reduction.

All three prototype operating speeds produced greater reductions than the baseline condition.

Device Speed 1 achieved a 45.54% reduction, while Device Speed 2 decreased from 199 ppb to 166 ppb, corresponding to a 16.58% reduction. Device Speed 3 produced the largest percentage reduction, achieving a 51.29% decrease over the measurement period. Although Device Speed 3 achieved the greatest percentage reduction, Device Speed 2 maintained the lowest absolute TVOC concentration throughout the experiment.

Figure 12: TVOC Graph Comparison across all speeds (Without Occupant)

These findings indicate that the reduction in TVOC concentration depended not only on the selected airflow speed but also on the initial pollutant concentration. The consistently low TVOC concentrations observed under Device Speed 2 suggest that lower initial pollutant levels contributed to the lower absolute concentrations recorded throughout the experiment. In contrast, the larger percentage reduction observed under Device Speed 3 suggests that higher airflow enhanced the delivery of contaminated air through the activated carbon filter. As activated carbon removes gaseous pollutants through adsorption, its effectiveness depends on the contact between the contaminated air and the filter medium (Ma et al., 2020). The results therefore suggest that

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airflow conditions influenced the adsorption process and consequently the observed reduction in breathing-zone TVOC concentration.

Table 4: TVOC reduction under unoccupied conditions Prototype Value at 5th minute Value at 65th minute Status (ppb) (ppb)

Reduction (%)

No Prototype Speed 1 Speed 2 Speed 3

15.60 45.54 16.58 51.29

5.3.2

789 426 199 425

666 232 166 207

TVOC levels under occupied conditions

Figure 13 shows the TVOC Graph Comparison across all speeds (With Occupant), while Table 5 shows the TVOC reduction under occupied conditions. Under the occupied condition, the No Prototype scenario again demonstrated only a modest reduction in TVOC concentration, decreasing from 578 ppb to 491.67 ppb, corresponding to a 14.59% reduction. All prototype operating speeds produced greater reductions than the baseline condition. Device Speed 1 achieved a 23.16% reduction, Device Speed 2 achieved a 15.24% reduction, and Device Speed 3 produced the greatest reduction at 39.22%, corresponding to a decrease of 558.33 ppb.

Figure 13: TVOC Graph Comparison across all speeds (With Occupant)

Although the TVOC concentrations recorded under Device Speed 3 remained higher than those observed under the other operating speeds throughout much of the experiment, this reflected the substantially higher initial concentration rather than poorer device performance. The experiment commenced with a TVOC concentration of 1435.67 ppb, considerably higher than the other prototype conditions. Despite this more challenging starting condition, Device Speed 3 achieved the largest percentage reduction over the measurement period.

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Table 5: TVOC reduction under occupied conditions Prototype Value at 5th minute Value at 65th minute Status (ppb) (ppb)

Reduction (%)

No Prototype Speed 1 Speed 2 Speed 3

14.59 23.16 15.24 39.32

578.00 678.33 486.33 1435.67

491.67 521.00 411.67 861.67

This finding suggests that the prototype remained effective in reducing breathing-zone TVOC concentrations even under conditions of elevated pollutant loading. Under occupied conditions, where the breathing-zone microenvironment is continuously influenced by the occupant and the surrounding environment, the ability of the prototype to achieve substantial reductions under high initial TVOC concentrations demonstrates the potential effectiveness of combining localised airflow with activated carbon filtration.

5.3.3

Occupancy effect

Figure 14 shows the comparison of Reduction at Speed 3 With and Without Occupant. Comparison between the unoccupied and occupied experiments showed that the presence of an occupant influenced the observed TVOC response. Under the unoccupied condition, Device Speed 1 and Device Speed 3 achieved greater percentage reductions than under the corresponding occupied condition. As shown in Figure 5.5, Device Speed 3 reduced the breathing-zone TVOC concentration by 51.29% under the unoccupied condition compared with 39.22% under the occupied condition. This smaller reduction under occupied conditions suggests that the prototype operated within a more challenging breathing-zone environment, where volatile organic compounds (VOCs) were continuously introduced into the local microenvironment.

Figure 14: Comparison of Reduction at Speed 3 With and Without Occupant

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This interpretation is consistent with previous research demonstrating that occupants are a continuous source of indoor VOCs through exhaled breath and emissions from the skin, thereby contributing to the replenishment of VOCs within the breathing zone (Wang et al., 2022). Despite this additional pollutant source, the prototype continued to produce substantial reductions in breathing-zone TVOC concentration, indicating that the localised airflow and activated carbon filtration remained effective under representative occupied conditions.

5.3.4

Discussion for TVOC

Overall, the TVOC results indicate that the developed prototype was effective in reducing volatile organic compound concentrations within the breathing zone under both unoccupied and occupied conditions. In contrast, the No Prototype condition exhibited only modest reductions in TVOC concentration, suggesting that passive room conditions alone were insufficient to substantially improve the gaseous pollutant levels experienced within the local breathing zone. The introduction of targeted airflow combined with activated carbon filtration consistently produced greater reductions in TVOC concentration, demonstrating the benefit of directing filtered air towards the occupant's immediate microenvironment.

Among the three operating speeds, Device Speed 3 achieved the greatest percentage reduction under both unoccupied and occupied conditions. Although this operating condition began with the highest initial TVOC concentrations, it still produced the largest proportional reduction over the experimental period. This finding suggests that the prototype remained effective even when the breathing-zone microenvironment was subjected to elevated pollutant levels. The larger reduction observed at the highest airflow setting is also consistent with the adsorption mechanism of activated carbon, where pollutant removal depends on the transport of contaminated air through the filter medium (Ma et al., 2020).

The occupied experiments further demonstrated that the presence of an occupant influenced the observed TVOC response. Percentage reductions were generally lower than those obtained under unoccupied conditions, suggesting that the breathing-zone microenvironment was continuously influenced by additional volatile organic compound emissions associated with occupant presence.

This interpretation is consistent with previous studies showing that occupants contribute volatile organic compounds through exhaled breath and skin emissions, thereby continuously replenishing VOC concentrations within the immediate breathing zone (Wang et al., 2022). Despite this additional pollutant source, the prototype continued to achieve substantial reductions in TVOC concentration, indicating that the combination of localised airflow and activated carbon filtration remained effective under representative occupied conditions.

These findings reinforce the importance of evaluating and improving breathing-zone air quality rather than relying solely on room-level environmental conditions. The limited reduction observed under the No Prototype condition suggests that occupants may remain exposed to elevated VOC concentrations despite the absence of obvious changes in the wider room environment. Exposure to elevated concentrations of volatile organic compounds has been associated with adverse effects on perceived air quality, occupant comfort, and symptoms commonly associated with Sick Building Syndrome, including eye, nose, and throat irritation (Wolkoff and Nielsen, 2017; Wolkoff, 2013). Consequently, the reductions achieved by the prototype suggest that delivering

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filtered air directly to the breathing zone has the potential to improve local air quality and enhance the immediate environmental conditions experienced by occupants.

5.4 Total Particulate Concentration Results The total particulate concentration measured using the TSI Optical Particle Sizer (OPS 3330) is presented in this section. Particle concentration was represented by the size-integrated concentration across the 0.300–10.000 μm particle size range under the four prototype conditions (No Prototype, Device Speed 1, Device Speed 2, and Device Speed 3). Comparisons were made between the unoccupied and occupied experiments to evaluate the influence of airflow speed and occupant presence on breathing-zone particulate concentration.

5.4.1

Total particulate concentration levels under unoccupied conditions

Figure 15 shows the total particulate concentration comparison across all speeds (Without Occupant). Under the unoccupied condition, the No Prototype scenario showed a reduction of 3717 particles/cm³, corresponding to a 16.81% reduction over the 60-minute operational period.

Although particulate concentration declined naturally over time, relatively high particle concentrations remained throughout the experiment. All three intervention conditions produced greater reductions than the baseline condition. Device Speed 1 reduced the particulate concentration by 1463 particles/cm³, corresponding to a 17.68% reduction. This improvement was only marginally greater than that observed under the No Prototype condition, suggesting that the lowest airflow setting provided limited enhancement of breathing-zone particulate removal.

Figure 15: Total Particulate Concentration Comparison across all speeds (Without Occupant)

A substantially greater reduction was achieved at Device Speed 2, where particulate concentration decreased by 1048 particles/cm³, corresponding to a 40.68% reduction. The greatest reduction was observed at Device Speed 3, where particulate concentration decreased by 8820 particles/cm³, corresponding to a 76.34% reduction. A pronounced decline in particulate concentration was observed approximately 15 minutes after prototype activation, indicating that the higher airflow

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enhanced the transport of particulate-laden air through the filtration pathway, thereby improving particulate removal within the breathing zone. Overall, the results demonstrate that increasing airflow speed substantially improved particulate removal under unoccupied conditions, with Device Speed 3 providing the greatest reduction in breathing-zone particulate concentration.

Table 6: Total particulate concentration reduction under unoccupied conditions Value at 5th minute Value at 65th minute Reduction (%) Prototype (#/cm3) (#/cm3) Status No Prototype Speed 1 Speed 2 Speed 3

5.4.2

22114 8264 2123 10682

18397 6696 1500 2771

16.81 17.68 40.68 76.34

Total particulate concentration levels under occupied conditions

Figure 16 shows the total particulate concentration comparison across all speeds (With Occupant).

Under the occupied condition, the No Prototype scenario showed a reduction of 1255.33 particles/cm³, corresponding to a 10.00% reduction over the experimental period. Although particulate concentration decreased slightly over time, relatively high concentrations remained throughout the experiment. The prototype produced different levels of improvement across the three operating speeds. Device Speed 1 achieved a reduction of only 372.67 particles/cm³, corresponding to a 5.87% reduction. The relatively small reduction suggests that the lowest airflow setting was insufficient to substantially improve breathing-zone particulate concentration when an occupant was present

Figure 16: Total Particulate Concentration Comparison across all speeds (With Occupant)

Greater improvements were observed at the higher airflow settings. Device Speed 2 reduced particulate concentration by 521.67 particles/cm³, corresponding to a 21.69% reduction. The greatest reduction was achieved by Device Speed 3, where particulate concentration decreased by

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607.33 particles/cm³, corresponding to a 26.90% reduction. Although the percentage reductions obtained under occupied conditions were generally smaller than those observed under unoccupied conditions, Device Speed 3 consistently produced the greatest reduction in breathing-zone particulate concentration. These findings suggest that higher airflow remained effective despite the additional particulate load associated with occupant presence.

5.4.3

Occupancy effect

Figure 17 shows the comparison of the reduction at Speed 1 with and without occupant.

Comparison between the unoccupied and occupied experiments demonstrated that occupant presence influenced the observed particulate reduction under all prototype conditions. Under the No Prototype condition, particulate concentration decreased by 3717 particles/cm³ (16.81%) under the unoccupied condition but only by 1255.33 particles/cm³ (10.00%) when an occupant was present.

This finding suggests that the breathing-zone microenvironment became more challenging once an occupant was introduced. A similar pattern was observed under all three prototype operating speeds. At Device Speed 1, particulate concentration decreased by 1463 particles/cm³ (17.68%) under the unoccupied condition compared with 372.67 particles/cm³ (5.87%) under the occupied condition. At Device Speed 2, the percentage reduction decreased from 40.68% under the unoccupied condition to 21.69% under the occupied condition. Likewise, Device Speed 3 achieved a 76.34% reduction without an occupant but a 26.90% reduction when an occupant was present.

Figure 17: Comparison of Reduction at Speed 1 With and Without Occupant

The consistently smaller reductions observed under occupied conditions suggest that occupant presence introduced additional particulate matter into the breathing-zone microenvironment, thereby reducing the overall effectiveness of the prototype. This interpretation is consistent with previous studies showing that occupants continuously generate aerosol particles through normal

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physiological activities, including breathing, speaking, and coughing (Johnson and Morawska 2009). Consequently, the occupied experiments represented a more demanding operating environment than the corresponding unoccupied experiments.

5.4.4

Discussion for total particulate concentration

Overall, the particulate concentration results demonstrate that the developed prototype consistently reduced breathing-zone particulate concentrations under both unoccupied and occupied conditions. The magnitude of improvement increased with airflow speed, with Device Speed 3 producing the greatest reduction, followed by Device Speed 2, while Device Speed 1 produced comparatively modest improvements. These findings indicate that airflow rate plays an important role in determining the effectiveness of the prototype in reducing particulate concentrations within the breathing zone.

The occupied experiments further demonstrated that occupant presence reduced the magnitude of particulate removal observed under identical prototype settings. This finding is consistent with previous research demonstrating that occupants continuously generate aerosol particles through normal respiratory activities, thereby increasing particle concentrations within the breathing-zone microenvironment (Johnson and Morawska 2009). Despite this additional particle source, the prototype continued to reduce particulate concentrations under all intervention conditions, demonstrating its effectiveness under representative occupied environments.

The results also reinforce the importance of evaluating air quality at the breathing zone rather than relying solely on room-level measurements. The relatively small reduction observed under the No Prototype condition suggests that passive room conditions alone were insufficient to substantially reduce breathing-zone particulate exposure. In contrast, directing filtered airflow towards the occupant consistently produced greater reductions in particulate concentration, demonstrating the value of combining localised airflow with particulate filtration.

Exposure to fine particulate matter has been associated with adverse respiratory and cardiovascular health outcomes (Pope III and Dockery 2006). Consequently, improving particulate removal within the breathing zone remains an important objective for personalised indoor air quality interventions. The present findings suggest that further optimisation of the combined airflow delivery and filtration system may enhance particulate removal under occupied conditions, where the breathing-zone microenvironment is continuously influenced by occupant-generated particles.

5.5 User Testing The user evaluation was completed by 10 participants following a 30-minute free-use session with the prototype. The findings presented in this section summarise participants' perceptions of the prototype's usefulness, usability, controllability, operational burden, and overall acceptance under representative desk-based conditions.

5.5.1

Condition before using prototype

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Figure 18 show the thermal comfort condition and general information of subjects before usage of prototype. The pre- prototype usage responses indicated that participants generally perceived their immediate desk environment to be warm, stuffy, and uncomfortable prior to using the prototype.

Many participants also reported experiencing perspiration and insufficient airflow, suggesting that their immediate microenvironment did not adequately support thermal comfort during desk-based activities.

Figure 18: Thermal comfort condition and general information of subjects before usage of prototype (Note: 5 is the best scenario while 1 is the worst scenario).

Most participants indicated that they had previously used personal desk fans or similar cooling devices, demonstrating familiarity with personalised airflow solutions. Despite this prior experience, participants expressed a desire for improved airflow and better air quality around their immediate workspace before commencing the evaluation. These findings indicate that participants entered the evaluation with an existing need for improved local thermal comfort and breathingzone air quality. Consequently, the prototype was evaluated by users who already perceived deficiencies in their immediate indoor environment, providing an appropriate basis for assessing its perceived usefulness and user acceptance.

5.5.2

Usability and intuitiveness

The prototype received consistently positive evaluations for its overall usability and intuitiveness.

Most participants agreed that the device was easy to understand and straightforward to operate.

The fan speed controls were also rated highly, with the majority of responses indicating that participants could distinguish and adjust the different speed settings without difficulty. These findings suggest that the overall interaction logic of the prototype was intuitive and that participants were generally able to understand its basic operation with minimal guidance.

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Although the usability ratings were consistently high, the responses indicated a small degree of variation in the perceived ease of adjusting the fan speed. While most participants found the speed controls easy to operate, a small number provided lower ratings. This suggests that, although the control concept was readily understood, the interaction was not perceived to be equally effortless by all users.

Participants also reported only limited reliance on the instruction sheet during the evaluation. Most indicated that they referred to the instructions only briefly, while a smaller number reported that they did not require them at all. Furthermore, almost all participants agreed that they would have been able to operate the prototype without the instruction sheet. These findings suggest that the prototype was largely self-explanatory, with the instruction sheet serving primarily as a source of reassurance during first-time use rather than an essential operating guide.

The open-ended responses, however, identified several practical issues associated with the physical interface. The most frequently reported concern related to the capacitive touch controls.

Several participants commented that the power and speed controls were insufficiently responsive and occasionally required multiple touches or firmer contact before the intended action was registered. These findings indicate that, although the operating logic of the prototype was intuitive, the responsiveness of the hardware interface did not consistently match users' expectations.

Consequently, refinement of the touch-control implementation represents an important opportunity for improving the overall user experience in future prototype iterations.

5.5.3

Perceived comfort and usefulness

Participants responded positively to the prototype's ability to improve their immediate microenvironment. Most agreed that the airflow delivered by the device was comfortable and did not cause noticeable discomfort or disturbance during use. This finding is important because the effectiveness of a personalised airflow device depends not only on its ability to deliver air but also on whether the airflow remains acceptable to users during prolonged exposure. The responses therefore suggest that the airflow generated by the prototype achieved an appropriate balance between providing perceptible cooling and maintaining user comfort.

Participants also reported improvements in the perceived quality of their immediate environment.

Most agreed that the area around their face felt more comfortable and that the surrounding air felt fresher and more pleasant while using the prototype. These perceptions are consistent with the intended purpose of the device, which was to improve thermal comfort and perceived breathingzone air quality through the delivery of filtered localised airflow. The subjective responses therefore complement the objective findings by indicating that the measured environmental improvements were also perceptible to users.

The prototype was also evaluated positively in terms of its operational noise. All participants considered the noise level acceptable and indicated that it would not interfere with studying or working. This finding is particularly important for a desktop device intended for prolonged use in offices, libraries, and study spaces, where excessive operational noise could reduce user acceptance despite satisfactory environmental performance.

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Participants also expressed a strong willingness to use the prototype during desk-based activities.

All participants indicated that they would consider using the device while studying or working, suggesting that the prototype was perceived not only as functional but also as having practical value within its intended application. This finding indicates a high level of user acceptance and suggests that the proposed concept has potential for integration into everyday desk-based environments.

Although the overall evaluation was favourable, responses regarding the suitability of the prototype for desk use exhibited greater variation than the other usability measures. While most participants considered the prototype suitable for desktop use, several assigned only moderate ratings. This pattern was consistent with the qualitative feedback, where participants repeatedly commented that the prototype was relatively bulky and occupied a noticeable amount of desk space. These findings suggest that, although the functional concept and user interaction were well received, further refinement of the physical dimensions and overall form factor would improve its suitability for use in space-constrained work and study environments.

5.5.4

Maintainability of filter system

Participants evaluated the maintainability of the filter system positively overall. Most agreed that the purpose of the filters was easy to understand and that the operation of the modular filter cartridges was straightforward. Participants also reported that the cartridges were easy to recognise and identify, and all considered the modular cartridge arrangement practical for regular use. These findings suggest that the maintenance concept of the filtration system was readily understood and that participants recognised the intended approach to routine filter replacement.

Participants also demonstrated a high level of understanding regarding when the filters should be replaced and how the replacement process should be performed. Although most responses were at the highest rating level, a small number of participants provided slightly lower ratings, indicating some variation in the perceived ease of maintenance. Similarly, participants generally expressed confidence in replacing the filters independently, although moderate ratings were also observed.

A comparable pattern was evident in the evaluation of the cartridge opening and closing mechanism. While most participants regarded the mechanism as straightforward to operate, responses were more varied than those relating to the conceptual understanding of the cartridge system. In contrast, reinserting the filter cartridges into their designated slots consistently received positive evaluations, suggesting that the alignment and installation process was generally intuitive.

The qualitative feedback provided additional insight into these findings. Participants appreciated the modular cartridge concept and commented favourably on the inclusion of the pull tab, which facilitated cartridge removal. However, several practical limitations were also identified. The most frequently reported concerns related to the strength of the magnetic fastening mechanism, the flexibility of the activated carbon filter sheet, occasional misalignment of the filter media within the cartridge, and the perception that the cartridge halves were not securely held together during handling. Several participants also commented that the filter replacement procedure required greater effort during the first attempt before becoming familiar with the mechanism.

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Taken together, the quantitative and qualitative findings indicate that the maintainability concept of the modular filter system was well accepted by participants. The principal limitations were associated with the physical implementation of the prototype rather than with the maintenance concept itself. These findings suggest that future iterations should focus on improving the robustness of the cartridge assembly, strengthening the magnetic fastening mechanism, improving filter retention within the cartridge, and simplifying the filter replacement process while retaining the modular design philosophy.

5.5.5

RGB indicator

Participants evaluated the RGB air-quality indicator positively overall. All participants agreed that the indicator was easy to notice, while most agreed that it clearly communicated the condition of the surrounding air. Most participants also regarded the indicator as helpful rather than distracting.

These findings suggest that the RGB indicator functioned effectively as a simple visual feedback mechanism, enabling users to interpret the air-quality status of their immediate microenvironment with minimal effort.

The qualitative feedback further supported these findings. Several participants commented that the RGB indicator enhanced their understanding of the immediate air conditions and provided useful real-time feedback during operation. This suggests that the indicator contributed to users' awareness of their breathing-zone environment and enhanced the perceived functionality of the prototype beyond that of a conventional desk fan.

Despite these positive evaluations, the qualitative responses also identified opportunities for improvement. Several participants reported that the brightness of the RGB indicator was excessive for prolonged desk-based use and could become visually distracting, particularly when positioned close to the user. These findings suggest that, although the visual feedback concept was well accepted, the display characteristics require further refinement. Participants recommended incorporating adjustable brightness levels or a night mode to improve visual comfort while maintaining the informational value of the indicator.

5.5.6

Application wireframe feedback

The ElevAir application wireframe was evaluated positively by participants. Most agreed that the proposed interface was easy to understand, that the layout was logical, and that the functions were relevant to the prototype. Participants also considered the information presented by the application to be useful and indicated that it would serve as a helpful companion to the device. The breathingzone status screen and the fan speed control screen were particularly well received, suggesting that the proposed interface aligned well with the functions that participants considered most important.

These findings indicate that the conceptual design of the application was intuitive and visually coherent.

The qualitative feedback provided additional insight into participants' perceptions. Several described the interface as clear, modern, and easy to navigate. Participants particularly valued the ability to monitor breathing-zone air quality and adjust fan speed through a digital interface. Some also suggested extending the application to include filter replacement reminders, maintenance

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guidance, and educational information on indoor air quality, indicating that they viewed the application as having the potential to support both device operation and user awareness.

It should be noted that the application was evaluated solely as a wireframe rather than as a fully functional mobile application. Consequently, the findings reflect participants' perceptions of the proposed interface design rather than the usability or performance of an operational system.

Although the conceptual evaluation suggests that a companion application could complement the prototype, further development and user testing of a functional application would be required to determine its long-term usability and practical value. In addition, the potential benefits of a companion application should be balanced against the project's objective of maintaining a simple, low-burden user experience. Therefore, the application should be regarded as an optional enhancement rather than an essential component of the current prototype.

5.5.7

Overall design and preferred speed

Overall, participants evaluated the prototype positively in terms of its overall design and usability.

Most agreed that the prototype was user-friendly and that its overall design was appropriate for its intended purpose. However, responses regarding its suitability for desk use were more varied.

Although the overall ratings remained positive, many participants selected moderate rather than the highest ratings. This pattern was consistent with the qualitative feedback, in which participants repeatedly commented that the prototype was relatively bulky and occupied a noticeable amount of desk space. These findings suggest that, although the functional concept and overall user experience were well received, further refinement of the physical dimensions and form factor would improve its suitability for everyday desktop use.

Participants also expressed differing preferences regarding the three airflow settings. Device Speed 3 received the highest proportion of preferred responses, followed by "All Speeds", Device Speed 2, and finally Device Speed 1. The distribution of responses indicates that participants did not converge on a single universally preferred operating speed. Instead, user preference appeared to vary according to individual expectations and comfort requirements. This finding complements the objective performance evaluation, which demonstrated that higher airflow speeds generally produced greater reductions in particulate and TVOC concentrations. While Device Speed 3 offered the greatest environmental improvement, some participants appeared to prefer lower airflow settings or the flexibility to adjust the airflow according to their immediate comfort needs.

These findings suggest that providing multiple user-selectable airflow settings is preferable to adopting a single fixed operating speed, allowing the prototype to accommodate individual differences in thermal comfort and personal preference.

5.5.8

Qualitative feedback

The open-ended feedback identified a clear set of recurring strengths and weaknesses. These are summarised in Table 7. These are encouraging results as the weaknesses identified were not directed at the core purpose of the device, but rather at physical aspects that can be physically addressable in future iterations. Subjects generally understood the intention of the device and found that it improved their perceived experience within their microenvironment. Therefore, the

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next stage of development should prioritise the compactness, and improve the physical interaction of the device. Figure 19 shows users’ feedback on the prototype and the ElevAir App. Table 7: Summary of Qualitative Feedback Theme Strengths Identified by Participants Airflow Targeted airflow to the face and neck performance proved effective, offering noticeable relief. The airflow was described as smooth, comfortable, and beneficial in reducing stuffiness.

Acoustic The device was consistently described performance as quiet and suitable for work or study use.

Weaknesses Identified by Participants Some users preferred stronger or more adjustable control over airflow direction and range.

No major acoustic weaknesses were identified, although long-term testing may still be needed.

Comfort and air perception

Several participants reported that the air These benefits were subjective and may felt fresher and that unpleasant odours or depend on room conditions and user stuffiness appeared to be reduced during expectations. use.

Physical adjustability

The flexible trunking was viewed positively because it allowed the airflow to be redirected without moving the entire device.

Some users suggested that a greater range of movement or easier adjustment could further improve usability.

Filter concept

The filter cartridge concept was viewed as accessible and less intimidating than conventional fan or air purifier maintenance. The pull-tabs were particularly appreciated.

The physical implementation of the cartridge was less convincing, with repeated comments about weak magnets, thin activated carbon sheets, and imperfect filter fit.

Controls

Users generally understood the device controls, operating logic, and speed settings.

Desk integration

Several participants found the touch controls insufficiently responsive. Some also felt that separate power and speed controls were unnecessary.

The prototype was regarded as useful for The device was repeatedly described as desk work and study. somewhat bulky for smaller desks, and the USB cable was considered too short for flexible placement.

RGB indicator

The RGB indicator was perceived as meaningful, easy to notice, and useful for understanding indoor air conditions.

Some participants felt that the RGB light was too bright and could become distracting during prolonged desk use.

App wireframe

The app wireframe was perceived as clear, relevant, modern, and potentially helpful for regular use. It made the prototype feel more complete.

As the app was only presented as a wireframe, some users noted that its practical usefulness could not yet be fully evaluated.

Overall impression

The prototype was widely regarded as thoughtful, useful, and promising, with strong potential for further development.

Most weaknesses were related to implementation details rather than rejection of the overall concept.

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Figure 19: Users’ feedback on the prototype and the ElevAir App

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5.6 Discussion of Results 5.6.1

RQ1(i): Breathing zone improvement

RQ1(i) Can the provision of personalised microclimate control with targeted face/neck airflow and localised low-cost filtration improve occupant experience as indicated by perceived thermal comfort and breathing zone indoor air quality with particulate and TVOC concentration reduction as the primary metric?

The findings provide a positive answer to RQ1(i). The developed prototype improved both the objective environmental conditions and the subjective experience within the breathing zone, demonstrating that a personalised breathing-zone intervention can enhance occupant experience without modifying the entire room environment.

Objective measurements consistently showed reductions in both total particulate concentration and TVOC concentration when the prototype was operating compared with the corresponding No Prototype condition. Although the magnitude of improvement varied according to airflow speed and occupancy status, the prototype consistently reduced pollutant concentrations within the breathing zone. The occupied experiments further demonstrated that, although the reductions were smaller than those observed under unoccupied conditions, the prototype remained effective despite operating within a dynamic microenvironment continuously influenced by occupant-generated particles and volatile compounds.

The subjective evaluation complemented these findings. Participants consistently reported that the airflow was comfortable, that the area around the face felt more pleasant, and that the surrounding air felt fresher during operation. These perceptions indicate that the measured improvements in breathing-zone air quality translated into meaningful improvements in user experience.

Taken together, the objective and subjective findings demonstrate that targeted airflow combined with localised filtration can improve breathing-zone environmental quality while enhancing occupants' perceived thermal comfort and air acceptability. The results therefore demonstrate the value of designing interventions specifically for the occupant's immediate breathing zone rather than relying solely on room-scale environmental control.

5.6.2

RQ1(ii): Design parameters

RQ1(ii) Which design parameters (i.e., airflow directionality, controllability, noise, and interface clarity) are required to deliver these outcomes in a desk-scale functional prototype?

The findings indicate that successful implementation of a personalised breathing-zone device depends on more than filtration performance alone. Instead, effective performance requires the integration of several complementary design parameters that collectively influence both environmental performance and user experience.

The objective evaluation demonstrated that airflow directionality and airflow speed played important roles in determining particulate and TVOC reduction within the breathing zone. Higher

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airflow settings generally produced greater pollutant reduction, highlighting the importance of delivering filtered air directly towards the occupant rather than simply increasing room air movement.

The user evaluation further identified several design characteristics that influenced overall acceptance of the prototype. Participants consistently rated the prototype positively in terms of usability, operational noise, airflow comfort, interface clarity, and the modular filter concept.

However, several opportunities for refinement were also identified. The responsiveness of the capacitive touch controls, the robustness of the magnetic filter cartridge assembly, the physical dimensions of the prototype, and the brightness of the RGB indicator were repeatedly identified as areas requiring further improvement.

These findings demonstrate that successful breathing-zone devices require an appropriate balance between environmental performance and user-centred design. Consequently, future iterations should optimise both the technical performance and the physical implementation of the prototype to improve usability, maintainability, and long-term user acceptance.

5.6.3

RQ2 and RQ3(i): Particulate effectiveness under unoccupied and occupied conditions

RQ2 Under controlled unoccupied conditions, how effective is the prototype in achieving breathing zone air quality improvement when compared to the baseline condition, and how does efficacy vary with fan speed?

RQ3(i) Under controlled occupied conditions with fixed headcount and standardised seated activity, how effective is the prototype in achieving breathing zone air quality improvement when compared to the baseline condition, and does efficacy vary with fan speed, consistent with RQ2?

The findings demonstrate that the prototype improved breathing-zone air quality under both unoccupied and occupied conditions, thereby providing positive responses to RQ2 and RQ3(i).

However, the magnitude of improvement was influenced by both airflow speed and occupant presence.

Under unoccupied conditions, the breathing-zone environment represented a relatively stable pollutant field, allowing the prototype to achieve larger reductions in particulate concentration and TVOC concentration. Under occupied conditions, the prototype operated within a dynamic breathing-zone microenvironment continuously influenced by occupant-generated particles, exhaled volatile compounds, thermal plumes, and normal respiratory activity. Consequently, pollutant concentrations were continually replenished, resulting in smaller percentage reductions than those observed under unoccupied conditions.

These smaller reductions should not be interpreted as reduced device effectiveness. Rather, they demonstrate that the prototype continued to improve breathing-zone air quality while operating under more representative and challenging conditions. Across both experimental scenarios, higher airflow settings generally produced greater pollutant reduction, although the relative performance of individual speed settings varied according to the initial pollutant concentration and the stability of the surrounding microenvironment.

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The findings therefore demonstrate that breathing-zone air quality is strongly influenced by occupant presence and that personalised airflow combined with localised filtration can effectively reduce pollutant exposure under both controlled and occupied conditions. These results further reinforce the importance of evaluating breathing-zone conditions directly rather than relying solely on room-level environmental measurements.

5.6.4

R3(ii): User satisfaction, usability, and acceptance

RQ3(ii) Based on a standardised and unbiased usability evaluation survey, how successful is the prototype at achieving occupant satisfaction, defined as —perceived usefulness; the improved face/neck thermal comfort and perceived breathing zone air acceptability, perceived burden; effort to operate, noise, and draft disturbance, and which fan speed setting maximises satisfaction?

The findings provide a positive response to RQ3(ii) by demonstrating that the prototype achieved a high level of perceived usefulness, usability, and early user acceptance while simultaneously identifying opportunities for further refinement.

Participants consistently reported improvements in airflow comfort, perceived freshness of the surrounding air, and overall breathing-zone comfort during use. These subjective findings complemented the objective measurements by demonstrating that the measured improvements in breathing-zone air quality were also perceptible to users. Participants also rated the prototype positively in terms of usability, operational noise, maintainability of the modular filter system, the RGB air-quality indicator, and the proposed companion application wireframe. Furthermore, all participants indicated that they would consider using the prototype during desk-based activities, suggesting that the device was perceived as having practical value beyond a proof-of-concept prototype.

The user evaluation also identified several engineering improvements for future iterations. The most frequently reported concerns related to the responsiveness of the capacitive touch controls, the robustness of the magnetic filter cartridge assembly, the length of the USB cable, the overall physical size of the prototype, and the brightness of the RGB indicator. These findings indicate that the principal limitations were associated with the physical implementation of the prototype rather than with its underlying design concepts.

Overall, the subjective evaluation demonstrates that the prototype successfully balanced perceived usefulness with operational burden. Although several aspects of the physical implementation require refinement, participants generally regarded the prototype as practical, understandable, and beneficial for improving their immediate microenvironment. The findings therefore support the proposition that personalised breathing-zone interventions can deliver measurable environmental improvements while also achieving meaningful user acceptance under representative desk-based conditions.

6. CONCLUSION 6.1 Summary of the Findings

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This study investigated the feasibility of improving the breathing-zone microenvironment through a personalised microclimate device that combines targeted airflow with low-cost particulate and gaseous filtration. The study was motivated by the recognition that conventional room-scale environmental control does not necessarily reflect the conditions experienced directly by occupants at the breathing zone, where pollutant exposure and thermal perception occur.

Consequently, the project explored whether a localised intervention could provide measurable improvements in breathing-zone air quality while enhancing occupants' perceived comfort and user experience.

The findings demonstrated that the proposed prototype successfully improved the breathing-zone microenvironment. Objective measurements showed reductions in both particulate concentration and total volatile organic compounds (TVOCs) under both unoccupied and occupied conditions compared with the corresponding baseline scenarios without the prototype. Although the magnitude of improvement varied according to airflow speed, occupancy, and initial pollutant conditions, the prototype consistently improved breathing-zone air quality relative to the baseline.

The experiments also demonstrated that the breathing zone behaved differently from the surrounding room environment, reinforcing the importance of evaluating and designing interventions specifically for the occupant's immediate microenvironment.

The subjective evaluation complemented these objective findings. Participants generally perceived the airflow to be comfortable, reported improvements in the freshness of the surrounding air, and considered the prototype easy to understand and operate. The modular filter system, RGB airquality indicator, and proposed companion application were also positively received. Although several opportunities for refinement were identified, including improvements to the touch controls, cartridge assembly, and physical form factor, the prototype demonstrated that measurable improvements in breathing-zone air quality could also translate into meaningful improvements in user experience.

Overall, this study demonstrates that personalised breathing-zone interventions represent a practical approach for improving the immediate environmental conditions experienced by occupants. By integrating targeted airflow, localised filtration, and user-centred design within a desktop-scale prototype, the project establishes a foundation for the continued development of personalised indoor environmental control technologies.

6.2 Contributions of Study This study makes several contributions to the development of personalised breathing-zone environmental control systems. First, it demonstrates the feasibility of integrating targeted airflow, localised particulate and gaseous filtration, modular filter cartridges, environmental sensing, visual air-quality feedback, and manual user control within a single desktop-scale personalised microclimate device. The prototype provides a practical proof of concept that breathing-zone interventions can be implemented using readily accessible, low-cost components.

Second, the study contributes objective evidence that localised intervention at the breathing zone can improve particulate concentration and TVOC levels under both unoccupied and occupied conditions. These findings reinforce the importance of evaluating indoor air quality at the

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breathing zone rather than relying solely on room-level environmental measurements. Third, the study demonstrates the importance of incorporating user-centred evaluation into the development of personalised indoor environmental technologies. The user evaluation showed that objective improvements in breathing-zone environmental quality were accompanied by corresponding improvements in perceived comfort, air freshness, usability, and overall user acceptance. These findings highlight the importance of integrating engineering performance with user experience during the design process.

Fourth, the study contributes practical design knowledge for future development of personalised microclimate devices. The findings identify key design parameters, including airflow directionality, controllability, operational noise, maintainability, interface clarity, and physical compactness, that influence both environmental performance and user acceptance. The study also identifies specific prototype limitations that provide clear directions for future engineering refinement. Finally, the study provides an initial exploration of integrating a companion digital interface with a personalised microclimate device. Although evaluated only as a conceptual wireframe, participants responded positively to the proposed application, suggesting that digital support may enhance user awareness, control, and interaction while complementing the physical prototype.

6.3 Limitations Several limitations should be considered when interpreting the findings of this study. First, the experimental conditions did not begin with identical initial particulate and TVOC concentrations.

Consequently, differences in pollutant reduction reflected not only prototype performance but also variations in the initial environmental conditions. For this reason, performance was interpreted using both absolute and percentage changes rather than relying solely on final concentration values. Second, the experiments were conducted in discussion rooms employing passive ventilation. As a result, background indoor environmental conditions were influenced by changing outdoor environmental conditions, making it difficult to maintain completely identical testing conditions throughout all experimental sessions.

Third, the user evaluation involved a relatively small sample and short evaluation period.

Consequently, the subjective findings primarily represent early perceptions of usability and user acceptance rather than long-term adoption or sustained user experience. Finally, the prototype remained an early-stage engineering implementation. Several issues identified during user testing, including the responsiveness of the touch controls, magnetic cartridge retention, physical dimensions, and RGB brightness, reflect implementation limitations rather than limitations of the underlying design concept.

6.4 Recommendations for Future Work Future work should focus on further refinement of both the engineering implementation and the evaluation methodology of the proposed prototype. From an engineering perspective, future iterations should improve the responsiveness of the capacitive touch controls, strengthen the magnetic fastening mechanism of the modular filter cartridges, improve filter retention within the

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cartridge assembly, reduce the overall size of the prototype, extend the USB power cable, and incorporate adjustable RGB brightness to improve long-term user comfort.

Future experimental work should employ repeated trials under more closely matched initial environmental conditions to isolate the influence of airflow speed more effectively. Longerduration experiments would also provide valuable insight into the long-term stability and persistence of breathing-zone air quality improvement during extended operation. The user evaluation should be expanded to include a larger and more diverse participant population together with longer evaluation periods. Such studies would provide stronger evidence regarding usability, comfort, long-term acceptance, and the influence of user characteristics on prototype performance.

Finally, the proposed ElevAir companion application should be developed beyond the wireframe stage and evaluated as a functional mobile application. Future work should investigate how digital support can enhance environmental awareness, filter maintenance, and user interaction while preserving the low-burden design philosophy established by the present study. Overall, the findings demonstrate that the proposed design concept is technically feasible and positively received by users. Future development should therefore focus on transforming the current proofof-concept prototype into a more robust, compact, and practical personalised microclimate device suitable for everyday desk-based environments.

ACKNOWLEDGEMENTS The support of the Singapore Institute of Technology in providing a conducive environment for real-life, problem-solving, and competency-based education is sincerely appreciated. The case study presented in this paper is based on the Capstone Project designed, conducted, written, and submitted by the undergraduate student in partial fulfilment of the requirements for the Bachelor of Engineering (Honours) in Sustainable Built Environment. The Capstone Project was undertaken under the guidance and supervision of the supervisor.

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THE STUDENT RESEARCHER’S REFLECTION “My Capstone journey has been the most purposeful and intellectually transformative experience throughout my 16 years of education. At the beginning of this project, I was intrigued by indoor air quality mainly from a conventional building performance perspective. In Year 2, my understanding of IAQ from the Indoor Environment Quality module was still relatively shallow. I tended to think of air quality at the room scale, such as whether a space met general ventilation benchmarking or whether the room felt acceptable overall. I understood IAQ as something that belonged to the whole room. Through Capstone, however, my thinking matured significantly. I now view indoor environmental experience as something that is not just the space itself, but also at the microenvironment. The personal zone around the face, neck, and upper body, where inhalation actually occurs and where thermal and air quality sensations are felt most directly, differs from average room conditions. This shift in my understanding changed the way I viewed IAQ, and also the way I approach problem solving in sustainable building engineering.

When I first received the problem statement from Prof. Moshood, I was curious. What exactly does microclimate mean? As we had more discussions and confirmation on the title, I thought to myself, “This is it, this is going to be something meaningful!”. And well, it truly was. It paved the way for me to move beyond broad assumptions and engage with actual conditions experienced by humans. I started by wondering about more precise questions. What does the occupant actually breathe? What do they feel? How can the device I develop actually improve the condition? This shaped the concept and the direction I wanted to head toward. I then gained a much stronger understanding to this project, understanding the crucial need for solutions for the microenvironment.

At the same time, this project showed me that working on microenvironment research is not straightforward. One difficulty I faced was that although ideas such as pollutant exposure, microenvironmental differences, and human emissions are clearly important and also recognised, not all of these are studied in recent literature in the depth that I initially expected. A number of studies that discuss microenvironment and human related emissions are older. Thus, making it difficult to confirm my findings and to understand the measurement data obtained. I had to think more critically about how to interpret my results, how to connect my work to earlier literature, and how to justify why these concepts still matter. In that sense, I learned that some of the most important parts of IAQ are not always studied in detail, despite the microenvironment being highly relevant to human health and exposure.

This is where the Indoor Air Cartoon Journal and the way of thinking became especially valuable to me. What helped me the most during my project was the content, and especially the mindset behind them. The writing was clear, direct, and purposeful. It did not rely on overly decorative academic language and showed that strong research do indeed come from strong thinking. Through reading these materials, I began to understand that the quality of a research project depends heavily on whether the researcher has correctly diagnosed the problem before attempting to solve it. This had a profound impact on me, teaching me that engineering is not only about creating a project or applying a technology. It is also about identifying the right problem, defining the gap between current and desired performance, understanding the causal chain, and proposing an intervention that genuinely addresses that gap.

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Before this Capstone, I did not consciously think about how mental models shape engineering decisions. Through the Indoor Air Cartoon perspective, I came to value and appreciate that problem solving requires structured thinking, reasoning, awareness and the ability to align decisions with human wellbeing. In my own project, this meant moving away from a superficial idea that I am just making a fan with a filter. It goes deeper and more meaningful than that. “Central building systems operate at room scale, occupants experience discomfort and exposure at microenvironment scale, common desk fans provide airflow and not clean air, therefore, there is a meaningful gap for developing a localised device that can improve perceived comfort and breathing zone air quality while occupants can control their own microenvironment.” This was what stuck by me and what I abided by throughout this project, giving me more coherence.

Through the Indoor Air Cartoon Journal, I was able to understand more about how the direct air we breathe in affects us directly as well. This helped me shape many of my decisions for the prototype, such as the modular filter cartridges. The IAQ cartoon journal taught me that user satisfaction should consider perceived burden as well. Therefore, a device that has low perceived burden can be translated into a valuable and useful device that is convenient to others. Only with that, then users would be satisfied and adopt the device in their daily lives, thus, they will be able to experience the benefits that come with it. I learnt a lot about conducting objective and clear experiments, analysing particulate and TVOC trends, with the guidance of Prof. Moshood. Linking these findings to occupant experience taught me to become more critical and more disciplined in the manner I interpret data.

Another aspect that makes this journey especially meaningful to me is that this was my first solo project carried from start to finish. This experience was both challenging and rewarding. I feel happy and honoured to have worked on this project, which has allowed me to make decisions independently, persist through uncertainty, and take on more responsibility.

I am grateful for the opportunity to have worked with Prof. Moshood. I appreciate his way of thinking, his technical guidance, and the intellectual direction that the Indoor Air Quality Cartoon Journal and Prof Moshood brought to this project. These were tools to help me move beyond technical performance but also to human function, cognitive and meaningful problem diagnosis.

This has left a strong impression on me, and has shaped the way I now think about research and engineering.

To reflect, my Capstone journey has enhanced my technical knowledge, strengthened my research, and reshaped my thinking and approach to engineering problems. The IAQ Cartoon Journal played a crucial role in this development by showing me the value of clear reasoning and cognitive maturity. For that reason, this project has not only contributed to my academic growth, but also the kind of engineer and researcher I hope to become.”