Rasmus Lund Jensen

Distribution of exhaled contaminants and personal exposure in a room using three different air distribution strategies

UNLABELLED The level of exposure to human exhaled contaminants in a room depends not only on the air distribution system but also on peoples different positions, the distance between them, peoples activity level and height, direction of exhalation, and the surrounding temperature and temperature gradient. Human exhalation is studied in detail for different distribution systems: displacement and mixing ventilation as well as a system without mechanical ventilation. Two thermal manikins breathing through the mouth are used to simulate the exposure to human exhaled contaminants. The position and distance between the manikins are changed to study the influence on the level of exposure. The results show that the air exhaled by a manikin flows a longer distance with a higher concentration in case of displacement ventilation than in the other two cases, indicating a significant exposure to the contaminants for one person positioned in front of another. However, in all three cases, the exhalation flow of the source penetrates the thermal plume, causing an increase in the concentration of contaminants in front of the target person. The results are significantly dependent on the distance and position between the two manikins in all three cases. PRACTICAL IMPLICATIONS Indoor environments are susceptible to contaminant exposure, as contaminants can easily spread in the air. Human breathing is one of the most important biological contaminant sources, as the exhaled air can contain different pathogens such as viruses and bacteria. This paper addresses the human exhalation flow and its behavior in connection with different ventilation strategies, as well as the interaction between two people in a room. This is a key factor for studying the airborne infection risk when the room is occupied by several persons. The paper only takes into account the airborne part of the infection risk.

Singlet-Oxygen-Mediated Cell Death Using Spatially-Localized Two-Photon Excitation of an Extracellular Sensitizer

Controlling and quantifying the photosensitized production of singlet oxygen are key aspects in mechanistic studies of oxygen-dependent photoinitiated cell death. In this regard, the commonly accepted practice of using intracellular photosensitizers is, unfortunately, plagued by problems that include the inability to accurately (1) quantify the sensitizer concentration in the irradiated domain and (2) control the local environment that influences light delivery and sensitizer photophysics. However, capitalizing on the fact that singlet oxygen produced outside a cell is also cytotoxic, many of these problems can be avoided with the use of an extracellular sensitizer. For the present study, a hydrophilic dendrimer-encased membrane-impermeable sensitizer was used to generate an extracellular population of singlet oxygen upon spatially localized two-photon irradiation. Through the use of this sensitizer and this approach, it is now possible to better control the singlet oxygen dose in microscope-based time- and space-resolved single cell experiments. Thus, we provide a solution to a limiting problem in mechanistic studies of singlet-oxygen-mediated cell death.

The risk of airborne cross‐infection in a room with vertical low‐velocity ventilation

UNLABELLED Downward flow ventilation systems are one of the most recommended ventilation strategies when contaminants in rooms must be removed and people must be protected from the risk of airborne cross-infection. This study is based on experimental tests carried out in a room with downward flow ventilation. Two breathing thermal manikins are placed in a room face to face. One manikins breathing is considered to be the contaminated source to simulate a risky situation with airborne cross-infection. The position of the manikins in relation to the diffuser and the location of diffuser in the room as well as the distance between the manikins are being changed to observe the influence of these factors on the personal exposure of the target manikin. The results show that the DWF in different situations often is unable to penetrate the microenvironment generated by the manikins. The downward ventilation system can give an unexpected high level of contaminant exposure of the target manikin, when the distance between the manikins is reduced. PRACTICAL IMPLICATIONS Several guidelines recommend the downward ventilation system to reduce the risk of cross-infection between people in hospital rooms. This study shows that this recommendation should be taken into careful consideration. It is important to be aware of people position, position to other thermal loads in the room, and especially be aware of the distance between people if the exposure to the exhaled contaminants wants to be reduced.

Influence of air stability and metabolic rate on exhaled flow

The characteristics of contaminant transport and dispersion of exhaled flow from a manikin are thoroughly studied in this article with respect to the influence of two important factors: air stability conditions and metabolic rates. Four cases with the combinations of stable and neutral conditions as well as lower (1.2 met) and higher (2 met) metabolic rates for a breathing thermal manikin are employed. The exhaled contaminant is simulated by smoke and N2 O to visualize and measure the contaminant distribution both around and in front of the manikin. The results show that the microenvironment around the manikin body can be affected by different air distribution patterns and metabolic heating. Under stable conditions, the exhaled contaminant from mouth or nose is locked and stratified at certain heights, causing potentially high contaminant exposure to others. In addition, velocity profiles of the pulsating exhaled flow, which are normalized by mean peak velocities, present similar shapes to a steady jet. The outlet velocity close to the mouth shows decrement with both exhalation temperature and body plume. The velocity decay and concentration decay also show significant dependence on air stability and metabolic level.

Measuring the exhaled breath of a manikin and human subjects

Due to scarcity of accurate information and available data of actual human breathing, this investigation focuses on characterizing the breathing dynamic process based on the measurement of healthy human subjects. The similarities and differences between one breathing thermal manikin and the human subjects, including geometry and breathing functions, were thoroughly studied. As expected, actual human breathing is more complicated than that of the manikin in terms of airflow fluctuations, individual differences, and exhaled flow directions. The simplification of manikin mouth structure could result in overestimated exhaled velocity and contaminant concentration. Furthermore, actual human breathing appears to be relatively stable and reproducible for an individual person in several conditions and is also accompanied by some uncertainties simultaneously. The averaged values are used to analyze the overall characteristics of actual human breathing. There are different characteristics of the exhaled breath between male and female subjects with or without wearing a nose clip. The experimental results obtained from the measurement of human subjects may be helpful for manikin specification or validation and accuracy assessment of CFD simulations.

Airborne cross-infection risk between two people standing in surroundings with a vertical temperature gradient

The transmission of exhaled small particles from one person to another in an indoor environment can take place both directly (in the microenvironment around the persons) and via the room air distribution. The impact of these transmission routes for two persons is investigated in detail by evaluating the exposure to gaseous substances (simulating particles <5 μm) in a room with a vertical temperature gradient obtained by displacement ventilation. Experiments are conducted with two breathing thermal manikins—one the source and the other the target. In the experiments, the distance between the two manikins varies from 1.1 to 0.35 m (43 to 14 in.). A tracer gas N2O is used to represent the gaseous substances exhaled by the source manikin. The concentration of N2O is measured to study the impact on the exposure of the distance between manikins and manikin positions (face to face, face to the side of the target manikin, face to the back of the target manikin, and a seated source manikin). The exposure increases with decreasing distance between the manikins, and the highest values are obtained in the face-to-face position. Face to the side also creates some exposure of the target manikin, while face toward the target manikins back does not give any direct exposure through the microenvironment. The thermal stratification in the room supports a significant exposure of the target manikin when the source manikin is seated and breathing toward the chest of a standing manikin.

Human exhalation characterization with the aid of schlieren imaging technique

Abstract The purpose of this paper is to determine the dispersion and distribution characteristics of exhaled airflow for accurate prediction of disease transmission. The development of airflow dynamics of human exhalation was characterized using nonhazardous schlieren photography technique, providing a visualization and quantification of turbulent exhaled airflow from 18 healthy human subjects whilst standing and lying. The flow shape of each breathing pattern was characterized by two angles and averaged values of 18 subjects. Two exhaled air velocities, u m and u p , were measured and compared. The mean peak centerline velocity, u m was found to decay correspondingly with increasing horizontal distance x in a form of power function. The mean propagation velocity, u p was found to correlate with physiological parameters of human subjects. This was always lower than u m at the mouth/nose opening, due to a vortex like airflow in front of a single exhalation cycle. When examining the talking and breathing process between two persons, the potential infectious risk was found to depend on their breathing patterns and spatial distribution of their exhaled air. Our study when combined with information on generation and distributions of pathogens could provide a prediction method and control strategy to minimize infection risk between persons in indoor environments.

Experimental investigation of the influence of the air jet trajectory on convective heat transfer in buildings equipped with air-based and radiant cooling systems

The complexity and diversity of airflow in buildings make the accurate definition of convective heat transfer coefficients (CHTCs) difficult. In a full-scale test facility, the convective heat transfer of two cooling systems (active chilled beam and radiant wall) has been investigated under steady-state and dynamic conditions. With the air-based cooling system, a dependency of the convective heat transfer on the air jet trajectory has been observed. New correlations have been developed, introducing a modified Archimedes number to account for the air flow pattern. The accuracy of the new correlations has been evaluated to±15%. Besides the study with an air-based cooling system, the convective heat transfer with a radiant cooling system has also been investigated. The convective flow at the activated surface is mainly driven by natural convection. For other surfaces, the complexity of the flow and the large uncertainty on the CHTCs make the validation of existing correlations difficult.

Financial Investments for Zero Energy Houses: The Case of Near-Zero Energy Buildings

Abstract This chapter describes the concept of near-zero energy buildings and the importance of financial investments to renovate residential buildings. A case study estimates the investments and makes a financial evaluation of renovation intended to turn a detached house into a near-zero energy house in Denmark and how this can apply to other Baltic nations. It shows the investment efficiency and the values of such indicators as simple payback time, return of investments, net present value, and internal rate of return expected when the house in question turns into a near-zero energy building. In addition, investments into active sustainable energy systems used in the house models reviewed here have been assessed separately. The chapter also presents an opinion survey of real estate and construction professionals, academic circles, and politicians about the perspectives of near-zero energy buildings in Lithuania and abroad.

Interactive Building Design Space Exploration Using Regionalized Sensitivity Analysis

Monte Carlo simulations combined with regionalized sensitivity analysis provide the means to explore a vast, multivariate design space in building design. Typically, sensitivity analysis shows how the variability of model output relates to the uncertainties in models inputs. This reveals which simulation inputs are most important and which have negligible influence on the model output. Popular sensitivity methods include the Morris method, variance-based methods (e.g. Sobol’s), and regression methods (e.g. SRC). However, such methods only address one output at a time, which makes it difficult to prioritize and fixate inputs when considering multiple outputs. In this work, the primary outcome is a novel sensitivity method denoted TOM, which relies on Kolmogorov-Smirnov two-sample (KS2) statistics to rank inputs due to their influence on multiple outputs. A secondary method, denoted TOR, provides a real-time sensitivity measure when exploring data with the interactive parallel coordinate plot (PCP). The latter is an effective tool to explore stochastic simulations and to find high-performing building designs. The proposed methods help decision makers to focus their attention to the most important design parameters. As case study, we consider building performance simulations of a 15.000 m2 educational centre with respect to energy demand, thermal comfort, and daylight.