A tool for determining sheltering efficiency of mechanically ventilated buildings against outdoor hazardous agents (original) (raw)
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Indoor Aerosol Modeling: Basic Principles and Practical Applications
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The type and amount of indoor air pollutants affects the comfort and quality of indoor environments. Therefore, indoor air quality is an important issue with different social, economic, and health aspects because people in developing countries spend most of their time indoors being exposed to different kinds of indoor pollutants. The indoor air quality can be assessed empirically by measuring the pollutant concentrations or can be predicted by means of mathematical models. An indoor aerosol model describes the dynamic behavior of indoor air pollutants. The basic concept of indoor air models is the mass-balance-conservation where several factors that govern the indoor particle concentrations can be described. These factors may include direct emissions from indoor sources, outdoor aerosol particles penetrating indoors as a result of the ventilation and filtration processes, deposition onto indoor surfaces, and removal from indoor air by means of ventilation. Here we present principles of indoor aerosol models and we also give examples of different kind of models.
Relationships Between Indoor and Outdoor Contaminants in Mechanically Ventilated Buildings
Indoor Air, 1996
It is shown that comparing measured indoor and outdoor contaminant concentrations can be misleading if the concentrations vary with time and if the averaging periods are too short. In this article an alternative methodology aimed at estimating the internal source and sink effects in mechanically ventilated buildings is described. The methodology is based on both the results from continuous measurements, and calculations under transient conditions. The relative importance of indoor sources and outdoor sources is established by a comparison of the measured indoor concentration and a calculated indoor concentration of a compound. Furthermore, dynamic calculations are used to investigate how the indoor concentrations of contaminants originating outdoors and contaminants emitted from indoor sources are influenced by temporal reductions of the airflow rate. Reducing the outdoor airflow rate during periods with high outdoor concentrations can significantly reduce the indoor levels of pollutants for situations in which the outdoor sources are more important than the indoor sources. Ekberg filtration and the possible need for additional mechanical cooling are not evaluated.
Atmospheric Environment, 2004
Indoor and outdoor particle size distributions, indoor-outdoor pressure difference, indoor air-exchange rate, and meteorological conditions were measured at an uninhabited apartment located in a busy street in Copenhagen during 1month long fall, winter and spring campaigns. Particle penetration was estimated from concentration rebound measurements following HEPA filtering of the indoor air by fitting a simple deterministic model. The model included measured air exchange rates and published surface deposition loss rates. This model was then used to predict indoor particle concentration. The model predicted well the indoor concentration of coarse (1.2-4 mm) particles of outdoor origin for the fall and spring campaign. The model performed less well for the fine (0.5-1.2 mm) particle concentration and the winter campaign. The association between the ratio measured/predicted indoor concentration and factors not included in the deterministic model was analysed statistically and the result was used to determine a correction factor to the model prediction. The correction factor was found to depend on wind velocity, outdoor relative humidity, and air exchange rate. Including the correction factor reduced the ratio of the 95 percentile to the 5 percentile by an average of 26% for the fine particles and 12% for the coarse particles. The ratio measured/predicted concentration using the correction factor was found to be the highest during periods where it was most likely that occupants were present in other apartments. The results suggest that factors such as particle chemical composition, within building transport patterns, and occupant behaviour in other apartments should be identified and quantified in future studies, and that these factors need to be included in predictive models. r
A balance-point outdoor concentration was proposed to represent the value of outdoor concentration at which the air exchange between indoor and outdoor does not affect the indoor and outdoor pollutant concentration ratio (I/O). When the outdoor particle concentration is higher than the balance-point outdoor concentration, an increase in the indoor and outdoor air exchange results in a higher indoor particle concentration level and vice versa. Indoor particulate matter concentration and its relationship with outdoor particle concentration for a hypothetical naturally ventilated building are studied using a simple steady-state model. The effects of various factors such as air infiltration exchange rate, ambient particle concentration, indoor source intensity, and human activity on I/O, and the correlation between indoor and outdoor concentration were investigated, and the results compare reasonably well with the results reported in the literature. r
Transport process of outdoor particulate matter into naturally ventilated buildings
Building and Environment, 2022
Natural ventilation of buildings can bring in fresh air, remove indoor air contaminants, and improve indoor thermal comfort. However, ventilation may also bring outdoor pollutants and/or aerosol into the buildings to affect the indoor air quality. This study uses a computational fluid dynamics model and a Lagrangian particle tracking model to investigate the transport process of outdoor particulate matter (PM) into a naturally ventilated building. The simulation results indicate that the entrance rate of outdoor PM contaminants is in the range of 7%-25%, depending on the particle size and the distance between the pollutant source and the building. The indoor concentration of PM 2.5 decreases as the external wind speed and ventilation rate increase. In other words, sufficient natural ventilation can remove indoor particulate contaminants. In addition, the deposition rates in long buildings are larger than that in short buildings, owing to the sluggish airflow inside the long buildings. This study also estimates the time scales of particle deposition and ventilation-induced advection. The results reveal that the ventilation-induced airflow dominates the removal of fine particles PM 1 and PM 2.5 , whereas the ventilation and deposition are equally important for coarse particle PM 10 .
Modelling of indoor air pollutants dispersion: new tools
IOP Conference Series: Earth and Environmental Science, 2018
Ventilation systems are used for create a thermally comfortable environment and good indoor air quality. It is therefore essential to have adequate tools for predicting the performance of these systems. Among the various approachs, the computational fluid dynamics could be a useful tool for the design of the ventilation system. When dealing with pollutants dispersion problems, a steady state averaged simulation can be misleading because it is not able to properly predict and model peak concentrations, which can be relevant even if temporary. An interesting approach is the use of LES (Large Eddy Simulations) simulations to obtain a better description of concentrations oscillations. In this framework, the aim of this work is the validation of simulation carried out using the FDS (Fire Dynamic Simulator) software with an actual case study, already studied with a mock-up. Secondly, two new configurations of the ventilation system are proposed, in order to stress the capacity of the soft...
Building removal of particulate pollutant plume during outdoor resuspension event
Building and Environment, 2014
The capacity of buildings to reduce the outdoor pollutant level during particle transport has not been thoroughly investigated. This study demonstrates that CFD modeling combined with multizone modeling can provide a complete picture on the fate and transport of PM pollutant plume passing a building. A plume intersecting a 6 m  6 m  6.3 m building with concentrations of 56, 93, 93, and 74 mg/ m 3 for 0.85 mm, 2.63 mm, 3.94 mm, and 8.77 mm particles, respectively, is simulated. The building removal rates are 79 AE 4 mg/h, 182 AE 10 mg/h, 209 AE 12 mg/h, 280 AE 26 mg/h, which are 0.1%, 0.13%, 0.15%, and 0.25% of the plume source emission rates, respectively. The building removal is mainly contributed by the deposition to the building envelope and deposition in the building cracks. The building removal rate varies with particle size, and is more affected by wind direction than the air intake location for the building air handling system. The resulting indoor PM concentration, estimated via multizone modeling, varies with particle size and zone, and is affected by the alignment of building crack openings and wind direction. The demonstrated simulation method can be used to investigate the reduction of a pollutant plume by high-density building clusters in the urban environment as well as the human exposure to the plume indoors. As compared to well-mixed models, the CFD generated spatially-resolved pollutant concentration around the building improves the accuracy of the prediction of indoor exposure to outdoor PM plumes.
Ultrafine and Fine Particulate Matter Inside and Outside of Mechanically Ventilated Buildings
The objectives of this study were to measure levels of particulate matter (PM) in mechanically ventilated buildings and to improve understanding of filtration requirements to reduce exposure. With the use of an Ultra High Sensitivity Aerosol Spectrometer and an Aerodyne Mass Spectrometer, ultrafine (0.055–0.1 µm) and fine (0.1–0.7 µm) indoor and outdoor PM was measured as a function of time in an office, a university building, and two elementary schools. Indoor particle levels were highly correlated with outdoor levels. Indoor and outdoor number concentrations in Denver were higher than those in Boulder, with the highest number concentrations occurring during summer and fall. The ratio of indoor-to-outdoor (I/O) PM was weakly but positively correlated with the amount of ventilation provided to the indoor environment, did not vary much with particle size (ranged between 0.48 and 0.63 for the entire size range), and was similar for each period of the week (weekend vs. weekday, night vs. day). Regression analyses showed that ultrafine indoor PM baseline concentrations were higher at night from nighttime infiltration. A lag time was observed between outdoor and indoor measurements. Weekday days had the shortest lag time of 11 min, and weekend nighttime lags when the HVAC was not in use were 50 to 148 min. Indoor-outdoor PM concentration plots showed ultrafine PM was more correlated compared to fine, and especially when the HVAC system was on. Finally, AMS data showed that most of the PM was organic, with occasional nitrate events occurring outdoors. During nitrate events, there were less indoor particles detected, indicating a loss of particulate phase nitrate. The results from this study show that improved filtration is warranted in mechanically ventilated buildings, particularly for ultrafine particles, and that nighttime infiltration is significant depending on the building design.
Modeling Indoor Dispersion of Aerosols or Vapors and Subsequent Vented Fire or Explosion
2000
PresentationConsiderable developmental work has gone into modeling dispersion of accidental outdoor releases; less has been applied to indoor releases. Indoor dispersion is characterized by the influence of a ventilation system and confining surfaces that facilitate aerosol rainout. Stratification can occur so that only part of a room contains flammable vapors, giving rise to so-called partial volume deflagrations. Indoor explosions are more complex to treat because there are two important regimes: before and after explosion vents, windows, or other panels open. We describe here a model, WELMIX, to calculate time-varying concentration changes within a room from time-varying inputs such as occur with pool evaporation. The model allows for gas sensors in the room connected to automatic controls of the fresh air/recycle ratio and ventilation rate. We illustrate here the influence of ventilation rate and fresh air/recycle ratio on concentrations. A mixing efficiency is applied that is u...