Arsen Krikor Melikov

Air Turbulence and sensation of draught

The impact of turbulence intensity (Tu) on sensation of draught has been investigated. Fifty subjects, dressed to obtain a neutral thermal sensation, were in three experiments exposed to air flow with low (Tu 55%) turbulence intensity. In each experiment the sedentary subjects were exposed to six mean air velocities ranging from 0.05 m/s to 0.40 m/s. The air temperature was kept constant at 23°C. They were asked whether and where they could feel air movement and whether or not it felt uncomfortable. The turbulence intensity had a significant impact on the occurence of draught sensation. A model is presented which predicts the percentage of people dissatisfied because of draught as a function of air temperature, mean velocity and turbulence intensity. The model can be a useful tool for quantifying the draught risk in spaces and for developing air distribution systems with a low draught risk.

Personalized ventilation: evaluation of different air terminal devices

Personalized ventilation (PV) aims to provide clean air to the breathing zone of occupants. Its performance depends to a large extent on the supply air terminal device (ATD). Five different ATDs were developed, tested and compared. A typical office workplace consisting of a desk with mounted ATDs was simulated in a climate chamber. A breathing thermal manikin was used to simulate a human being. Experiments at room air temperatures of 26 and 20 °C and personalized air temperatures of 20 °C supplied from the ATDs were performed. The flow rate of personalized air was changed from less than 5 up to 23 l/s. Tracer gas was used to identify the amount of personalized air inhaled by the manikin as well as the amount of exhaled air re-inhaled. The heat loss from the body segments of the thermal manikin was measured and used to calculate the equivalent temperature for the whole body as well as segments of the body. An index, personal exposure effectiveness, was used to assess the performance of ATDs in regard to quality of the air inhaled by the manikin. The personal exposure effectiveness increased with the increase of the airflow rate from the ATD to a constant maximum value. A further increase of the airflow rate had no impact on the personal exposure effectiveness. Under both isothermal and non-isothermal conditions the highest personal exposure effectiveness of 0.6 was achieved by a vertical desk grill followed by an ATD designed as a movable panel. The ATDs tested performed differently in regard to the inhaled air temperature used as another air quality indicator, as well as in regard to the equivalent temperature. The results suggest that PV may decrease significantly the number of occupants dissatisfied with the air quality. However, an ATD that will ensure more efficient distribution and less mixing of the personalized air with the polluted room air needs to be developed.

Integrating CFD and building simulation

Abstract To provide practitioners with the means to tackle problems related to poor indoor environments, building simulation and computational fluid dynamics can usefully be integrated within a single computational framework. This paper describes the outcomes from a research project sponsored by the European Commission, which furthered the CFD modelling aspects of the ESP-r system. The paper summarises the form of the CFD model, describes the method used to integrate the thermal and flow domains and reports the outcome from an empirical validation exercise.

Performance of personalized ventilation in conjunction with mixing and displacement ventilation

Two types of air terminal devices for a personalized ventilation system in conjunction with either a mixing or a displacement total-volume ventilation system were installed in a mock-up of an office. Two occupants were simulated by means of breathing thermal manikins. A constant amount of clean air was distributed between the systems at different combinations of airflow rates. The performance of the systems was evaluated based on the contaminant concentration in and temperature of the inhaled air, as well as temperature, velocity, and contaminant distribution in the occupied zone. The results showed that personalized ventilation will always be able to improve the inhaled air quality in rooms with mixing ventilation. In rooms with displacement ventilation, personalized ventilation will improve the inhaled air quality with regard to pollution emitted from the floor covering. The inhaled air quality with regard to human-produced contaminants, such as virulent agents associated with exhaled air or bioeffluents, may be improved as well. The improvement will depend on the efficiency of the personalized ventilation system and its ability to promote mixing. The experimental data document that the design of air terminal devices for personal ventilation and their use have a large impact on the inhaled air quality and thermal comfort of occupants.

Methods for air cleaning and protection of building occupants from airborne pathogens

Abstract This article aims to draw the attention of the scientific community towards the elevated risks of airborne transmission of diseases and the associated risks of epidemics or pandemics. The complexity of the problem and the need for multidisciplinary research is highlighted. The airborne route of transmission, i.e. the generation of pathogen laden droplets originating in the respiratory tract of an infected individual, the survivability of the pathogens, their dispersal indoors and their transfer to a healthy person are reviewed. The advantages and the drawbacks of air dilution, filtration, ultraviolet germicidal irradiation (UVGI), photocatalytic oxidation (PCO), plasmacluster ions and other technologies for air disinfection and purification from pathogens are analyzed with respect to currently used air distribution principles. The importance of indoor air characteristics, such as temperature, relative humidity and velocity for the efficiency of each method is analyzed, taking into consideration the nature of the pathogens themselves. The applicability of the cleaning methods to the different types of total volume air distribution used at present indoors, i.e. mixing, displacement and underfloor ventilation, as well as advanced air distribution techniques (such as personalized ventilation) is discussed.

The Acceptable Air Velocity Range for Local Air Movement in The Tropics

The perception of locally applied airflow was studied with tropical subjects who had become passively acclimatized to hot conditions in the course of their day-to-day life. During the experiments, 24 subjects (male and female) performed normal office work in a room equipped with six workstations. They were exposed to local airflow from the front and toward the face at six air velocities (0.15, 0.3, 0.45, 0.6, 0.75, and 0.9 m/s) at ambient temperatures of 26°C, and 23.5°C and local air temperatures of 26°C, 23.5°C, and 21°C. Each combination was maintained for 15 minutes, during which the subjects responded to computer-administered questionnaires on their thermal and draft sensations using visual-analogue scales. The results showed that the subjects preferred air movement within a certain range, i.e., a higher percentage was dissatisfied at both low and high velocity values. Most dissatisfaction with air movement is caused by thermal sensation, with air movement perception accounting for a smaller proportion. The subjects preferred air movement to be between “just right” and “slightly breezy” and preferred their thermal sensation to be between “neutral” and “slightly cool.” The study also identified an acceptable air velocity range from 0.3 up to 0.9 m/s under the experimental conditions. This velocity range is relevant for the design of personalized ventilation in practice. This preferred velocity range is higher than the maximum velocity permissible under ASHRAE Standard 55 (ASHRAE 2004) in situations where subjects have no control over local air movement.

Protection of Occupants from Exhaled Infectious Agents and Floor Material Emissions in Rooms with Personalized and Underfloor Ventilation

The performance of two personalized ventilation systems supplying air at the breathing zone was tested in conjunction with underfloor ventilation generating two different airflow patterns in a full-scale test room. Two breathing thermal manikins were used to simulate occupants. The distribution of pollutants associated with exhaled air and floor material emissions was evaluated at various combinations of personalized and underfloor airflow rates. Compared to underfloor ventilation alone, personalized and underfloor ventilation provided excellent protection of seated occupants from any pollution, while the concentration of exhaled air pollution increased in the room. The two types of personalized ventilation performed differently. Subsequent analyses of airborne infection transmission risk indicated that personalized ventilation could become a supplement to traditional methods of infection control.

Human Response to Five Designs of Personalized Ventilation

Human response to five different air terminal devices (ATDs) for a personalized ventilation system (PVS) was studied in an experimental office under well-defined conditions. A group of 30 human subjects assessed air quality and rated their thermal comfort and perception of draft. Two temperature levels, 23°C and 26°C, and two background levels of air quality in the office, high and low, were studied during the experiments. Under all conditions the personalized ventilation system provided outdoor air at a temperature of 20°C. All PVSs allowed for individual control of the airflow rate as well as for adjustments of the supply air direction. Results showed that all ATDs studied significantly improved perceived air quality at the workstation. The greatest improvement was obtained when the pollution level and the temperature in the office were high. The thermal environment created with all systems was assessed as acceptable. Subjects were able to improve thermal comfort with all ATDs studied. The subjects identified which of the tested ATDs they preferred.

Experimental Study of Dispersion and Deposition of Expiratory Aerosols in Aircraft Cabins and Impact on Infectious Disease Transmission

The dispersion and deposition characteristics of polydispersed expiratory aerosols were investigated in an aircraft cabin mockup to study the transmission of infectious diseases. The airflow was characterized by particle image velocimetry (PIV) measurements. Aerosol dispersion was measured by the Interferometric Mie Imaging (IMI) method combined with an aerosol spectrometer. Deposition was investigated using the fluorescent dye technique. Downward air currents were observed near the seats next to the side walls while upward airflows were observed near other seats. The downward airflow showed some effects on suppressing the dispersion of aerosols expelled by the passenger sitting in the window seat. Results show that the cough jet could bring significant amount of aerosols forward to the row of seats ahead of the cougher and the aerosols were then dispersed by the bulk air movements in the lateral direction. The aerosols expelled from a cough took 20–30 s to reach the breathing zones of the passengers seated within two rows from the cougher. Increasing the ventilation rate improved the dilution and reduced the aerosol exposure to passengers seated close to the source, but the aerosol dispersion increased, which heightened the exposure to passengers seated further away. 60–70% of expiratory aerosols in mass were deposited, with significant portions on surfaces close to the source, suggesting that disease transmission risk via indirect contact in addition to airborne risk is possible. The physical transport processes of expiratory aerosols could be used to shed insights on some epidemiological observations on in-flight transmission of certain infectious diseases.

Modeling the Fate of Expiratory Aerosols and the Associated Infection Risk in an Aircraft Cabin Environment

The transport and deposition of polydispersed expiratory aerosols in an aircraft cabin were simulated using a Lagrangian-based model validated by experiments conducted in an aircraft cabin mockup. Infection risk by inhalation was estimated using the aerosol dispersion data and a model was developed to estimate the risk of infection by contact. The environmental control system (ECS) in a cabin creates air circulation mainly in the lateral direction, making lateral dispersions of aerosols much faster than longitudinal dispersions. Aerosols with initial sizes under 28 μm in diameter can stay airborne for comparatively long periods and are favorable for airborne transport. Using influenza data as an example, the estimated risk of infection by inhalation are at least two orders of magnitude higher than the risk of infection by contact. An increase in the supply airflow rate enhances ventilation removal and the dispersion of these aerosols. It reduces the risk of infection by inhalation for passengers seated within one row and one column from the index patient but it increases the risk for passengers seated further away. The deposition fraction increases with aerosol size. The ECS supply airflow rate has insignificant impact on the deposition behavior of these large aerosols, making the impact on the risk of infection by contact insignificant. Comparatively, the contact behavior of passengers is highly influential to the contact infection risk. Passengers seated within one row from the index patient are subject to contact risks that are one to two orders of magnitude higher than are passengers seated further away.