Zhecho Dimitrov Bolashikov

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.

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.

Exposure of health care workers and occupants to coughed airborne pathogens in a double-bed hospital patient room with overhead mixing ventilation

The exposure of a doctor and a second patient was studied in a simulated two-bed hospital isolation room. The room was ventilated at three air change rates (3 h−1, 6 h−1, and 12 h−1) by mixing air distribution keeping at 22°C (71.6°F). The effect of the distance between the doctor and the coughing person, the posture of the coughing patient (lying sideways facing the doctor or on back), and the position of the doctor (facing the coughing patient or standing sideways) was examined with respect to exposure to coughed air. A thermal manikin with realistic body shape and surface temperature distribution was used to resemble the doctor. A coughing patient (equipped with cough generator) lying in one bed and another patient in the second bed were simulated by two heated dummies with simplified geometry. The cough consisted of 100% CO2. The peak cough time was 4 s, when the doctor was closest to the sick patients bed, and more than doubled for the exposed patient. The level of exposure (peak concentration level) depended strongly on the positioning and distance of the doctor from the infected patient and posture of the coughing patient. Peak concentration level varied widely from 194 to 10,228 ppm. Ventilation rates of 12 h−1 (recommended by present hospital standards) resulted in background velocities exceeding 0.5 m/s (98.43 fpm), suggesting elevated risk from draught discomfort.

Control of the Free Convective Flow around the Human Body for Enhanced Inhaled Air Quality: Application to a Seat-Incorporated Personalized Ventilation Unit

This paper reports on methods for control of the free convective flow around the human body, with the aim of improving inhaled air quality. The methods were studied with sea-incorporated personalized ventilation (PV)—two PV nozzles placed sideways at the head level of a seated occupant supplied the clean air. Another pair of control nozzles below the PV nozzles, the height of the shoulders, either provided an additional amount of clean PV air or exhausted part of the air from the free convective flow. The effectiveness of the methods for enhancing the quality of the inhaled air was studied in full-scale room experiments. A thermal manikin with a realistic free convective flow was used to resemble an occupant in a state of thermal neutrality at a sedentary activity level. Numerous experiments comprising different combinations of nozzle sizes, supply and exhaust flow rates, and direction of the supplied PV flows and of the control flows, etc., were performed under isothermal conditions at 20°C (68°F) and 26°C (78.8°F). The methods of control proved to be efficient and made it possible to increase the amount of clean air into inhalation at reduced personalized flow rate and to reduce the risk of draft.

Experimental investigation on reduced exposure to pollutants indoors by applying wearable personalized ventilation

A wearable personalized ventilation unit able to improve inhaled air quality and reduce risk from airborne disease contamination is reported. The performance of the personalized ventilation device relies on control over the flow interaction near the face of a person by inserting a reduced amount of clean air into the breathing zone. Experiments at 23°C (73.4°F) were performed in a full-scale test room with a breathing thermal manikin resembling a seated occupant in a state of thermal comfort, with a realistic free convection flow around the body and breathing cycle. The room air was mixed with tracer gas. The personalized ventilation supplied isothermally clean air from circular or elliptical nozzles of different diameters (equivalent diameter: 0.025–0.035 m [0.08–0.12 ft]) positioned near the mouth of the manikin. The enhancement of inhaled air quality was studied by varying the initial velocity (0.2–0.6 m/s [0.66– 1.97 fps]), the distance between the nozzles and the mouth (0.02–0.06 m [0.07–0.2 ft]), or the direction of the jet (front, side, or below). The personalized ventilation made it possible to increase up to 94% the portion of clean air into the air inhaled. A wearable personalized ventilation unit can significantly reduce (more than six times) the number of secondarily infected occupants compared to mixing ventilation.

Improved inhaled air quality at reduced ventilation rate by control of airflow interaction at the breathing zone with lobed jets

Inhaled air quality at a reduced supply of clean air was studied by controlling the airflow interaction at the breathing zone of a person using lobed jets as part of personalized ventilation (PV). Experiments were performed in a full-scale test room at 23°C (73.4°F) with a breathing thermal manikin seated at a workstation, with realistic free-convection flow around the body and a normal breathing cycle. The air in the room was mixed with tracer gas R134a. Clean air was supplied isothermally from three nozzles with circular, four-leafed clover, and six-edged star openings of 0.025 m (0.08 ft) equivalent diameter. The nozzles were positioned frontally at the face within the boundary layer and centered to the mouth. The enhancement of inhaled air quality by changing the initial velocity (0.2–0.6 m/s, 0.66–1.97 fps) and the distance from the mouth (0.02–0.06 m, 0.07–0.20 ft) was studied. The control over the interaction between the inserted jets and the free convection flow was efficient. Over 80% clean PV air was measured in inhalation. The worst performing nozzle was the four-leafed clover: its best performance yielded 23% clean air inhalation, at the shortest distance and the highest velocity. The other lobed nozzle, the six-edged star, performed similarly to the circular nozzle.

Effect of the Environmental Stimuli upon the Human Body in Winter Outdoor Thermal Environment

In order to manage the outdoor thermal environment with regard to human health and the environmental impact of waste heat, quantitative evaluations are indispensable. It is necessary to use a thermal environment evaluation index. The purpose of this paper is to clarify the relationship between the psychological thermal responses of the human body and winter outdoor thermal environment variables. Subjective experiments were conducted in the winter outdoor environment. Environmental factors and human psychological responses were measured. The relationship between the psychological thermal responses of the human body and the outdoor thermal environment index ETFe (enhanced conduction-corrected modified effective temperature) in winter was shown. The variables which influence the thermal sensation vote of the human body are air temperature, long-wave thermal radiation and short-wave solar radiation. The variables that influence the thermal comfort vote of the human body are air temperature, humidity, short-wave solar radiation, long-wave thermal radiation, and heat conduction. Short-wave solar radiation, and heat conduction are among the winter outdoor thermal environment variables that affect psychological responses to heat. The use of thermal environment evaluation indices that comprise short-wave solar radiation and heat conduction in winter outdoor spaces is a valid approach.

Behavioral Thermoregulation Model for Evaluation of Outdoor Thermal Environment

In the outdoor environment, the effect of the physical environmental factors that compose the sensational and physiological temperature is remarkably large in comparison to the indoor environment. The purpose of this paper is to propose and develop a behavioral thermoregulation model in the outdoor environment, in order to predict the mean skin temperature for the evaluation of outdoor environment. This model is based on a Two-Node Model, and has three components: direct solar radiation, indirect solar radiation, and heat conduction. Each body part consists of core and skin layers. The model formula, by ratio of body weight of skin layer of heat conductance between skin and core layer, was included in this model. To verify this model, experiments were conducted. It was shown from the relation between ETFe (Enhanced conduction-corrected modified effective temperature) and mean skin temperature that it is possible to quantity explicitly the effects owing to outdoor environmental factors, short-wave solar radiation, heat conduction etc. It was made clear that the current model is valid for simulated mean skin temperature in the outdoor environment.

Wearable personal exhaust ventilation: Improved indoor air quality and reduced exposure to air exhaled from a sick doctor

Exposure reduction to exhaled air from a sick doctor wearing a personal exhaust unit incorporated in a headset-microphone was studied. Experiments were performed in a full-scale test room furnished as a double-bed hospital room with overhead ventilation at 3, 6, and 12 air changes per hour. Room air temperature was 22°C. A breathing thermal manikin with a body size and shape similar to the body of an average Scandinavian woman was used to mimic a “sick” doctor. The manikin was equipped with artificial lungs with a realistic breathing cycle (2.5-sec inhalation, 2.5-sec exhalation, and 1-sec pause) and a tidal flow rate of 6 L/min. A second thermal manikin and heated dummy were used to resemble lying patients. Exhaled air by the doctor was mixed with tracer gas to mimic pathogens. The wearable personal exhaust unit was positioned frontally by the mouth of the doctor at three distances: 0.02, 0.04, and 0.06 m. It was operated at 0.25 or 0.50 L/s under mixing background ventilation at three air changes per hour. The effect of the wearable exhaust unit geometry by modifying the exhaust surface, as well as the posture of the doctor, standing or seated, was also studied. The use of the wearable personal exhaust resulted in cleaner air in the room compared to mixing alone at 12 air changes per hour, reducing the exposure of the two patients. The nozzle geometry and posture of the doctor affected the indoor exposure to exhaled air. The high potential to capture exhaled air makes the device efficient against airborne pathogens in densely occupied spaces.