Moon, Hyeun Jun
15 July 2005
Microbial growth is a major cause of Indoor Air Quality (IAQ) problems. The implications of mold growth range from unacceptable musty smells and defacement of interior finishes, to structural damage and adverse health effects, not to mention lengthy litigation processes. Mold is likely to occur when a favorable combination of humidity, temperature, and substrate nutrient are maintained long enough. As many modern buildings use products that increase the likelihood of molds (e.g., paper and wood based products), reported cases have increased in recent years. Despite decades of intensive research efforts to prevent mold, modern buildings continue to suffer from mold infestation. The main reason is that current prescriptive regulations focus on the control of relative humidity only. However, recent research has shown that mold occurrences are influenced by a multitude of parameters with complex physical interactions. The set of relevant building parameters includes physical properties of building components, aspects of building usage, certain materials, occupant behavior, cleaning regime, HVAC system components and their operation, and other. Mold occurs mostly as the unexpected result of an unforeseen combination of the uncertain building parameters. Current deterministic mold assessment studies fail to give conclusive results. These simulations are based on idealizations of the building and its use, and therefore unable to capture the effect of the random, situational, and sometimes idiosyncratic nature of building use and operation. The presented research takes a radically different approach, based on the assessment of the uncertainties of all parameters and their propagation through a mixed set of simulations using a Monte Carlo technique. This approach generates a mold risk distribution that reveals the probability of mold occurrence in selected trouble spots in a building. The approach has been tested on three building cases located in Miami and Atlanta. In all cases the new approach was able to show the circumstances under which the mold risk could increase substantially, leading to a set of clear specifications for remediation and, in for new designs, to A/E procurement methods that will significantly reduce any mold risk.
Lester Ting Chung Lee (11495881)
22 November 2021
<p>Swimming is the second most common form of recreational activity in the U.S. Swimming pool water and air quality should be maintained to allow swimmers, pool employees, and spectators to use the pool facility safely. One of the major concerns regarding the health of swimmers and other pool users is the formation of disinfection by-products (DBPs) in swimming pools. Previous research has shown that volatile DBPs can adversely affect the human respiratory system. DBPs are formed by reactions between chlorine and other compounds that are present in water, most of which are introduced by swimmers, including many that contain reduced nitrogen. Some of the DBPs formed in pools are volatile, and their transfer to the gas phase in pool facilities is promoted by mixing near the air/water interface, caused by swimming and pool features.</p> <p><a>Swimming pool water treatment processes can play significant roles in governing water and air quality.</a> Thus, it is reasonable to hypothesize that water and air quality in a swimming pool facility can be improved by renewing or enhancing one or more components of water treatment.</p> <p>The first phase of the study was designed to identify and quantify changes in water and air quality that are associated with changes in water treatment at a chlorinated indoor pool facility. Reductions of aqueous NCl<sub>3 </sub>concentration were observed following the use of secondary oxidizer with its activator. This inclusion also resulted in significant decreases in the concentrations of cyanogen chloride (CNCl) and dichloroacetonitrile (CNCHCl<sub>2</sub>) in pool water. The concentration of urea, a compound that is common in swimming pools and that functions as an important precursor to NCl<sub>3</sub> formation, as well as a marker compound for introduction of contaminants by swimmers, was also reduced after the addition of activator.</p> <p>The second phase of this study involved field measurements to characterize and quantify the dynamic behavior of indoor air quality (IAQ) in indoor swimming pool facilities, particularly as related to volatile compounds that are transferred from swimming pool water to air. Measurements of water and air quality were conducted before, during, and after periods of heavy use at several indoor pool facilities. The results of a series of measurements at different swimming pool facilities allowed for examination of the effects of swimmers on liquid-phase DBPs and gas-phase NCl<sub>3</sub>. Liquid-phase NCl<sub>3</sub> concentrations were observed to gradually increase during periods of high swimmer numbers (<i>e.g.</i>, swimming meets), while liquid-phase CHCl<sub>3</sub> concentration was nearly constant in the same period. Concentrations of urea displayed a steady increase each day during these periods of intensive use. In general, the highest urea concentrations were measured near the end of each swimming meet. </p> <p>Measurements of IAQ dynamics during phase 2 of the study demonstrated the effects of swimmers on the concentrations of gas-phase NCl<sub>3 </sub>and CO<sub>2</sub>, especially during swimming meets. The measured gas-phase NCl<sub>3</sub> concentration often exceeded the suggested upper limits of 300 µg/m<sup>3</sup> or 500 µg/m<sup>3 </sup>during swimming meets, especially during and immediately after warm-up periods, when the largest numbers of swimmers were in the pool. Peak gas-phase NCl<sub>3</sub> concentrations were observed when large numbers of swimmers were present in the pools; measured gas-phase concentrations were as high as 1400 µg/m<sup>3</sup>.<sup> </sup>Concentrations of gas-phase NCl<sub>3</sub> rarely reached above 300 µg/m<sup>3</sup> during regular hours of operation. Furthermore, the types of swimmers were shown to affect the transfer of volatile compounds, such as NCl<sub>3</sub>, from water to air<sub> </sub>in pool facilities. In general, adult competition swimmers promoted more rapid transfer of these compounds than youth competition swimmers or adult recreational swimmers. The measured gas-phase CO<sub>2</sub> concentration often exceeded 1000 ppm<sub>v</sub> during swimming meets, whereas the gas-phase CO<sub>2</sub> concentration during periods of non-use of the pool tended to be close to the background (ambient) CO<sub>2</sub> concentration or slightly more than 400 ppm<sub>v</sub>. This phenomenon was largely attributed to the activity of swimmers (mixing of water and respiratory activity) and the normal respiratory activity of spectators. </p> <p>IAQ models for gas-phase NCl<sub>3</sub> and CO<sub>2</sub> were developed to relate the characteristics of the indoor pool environment to measurements of IAQ dynamics. Several assumptions were made to develop these models. Specifically, pool water and indoor air were assumed to be well-mixed. The reactions that were responsible for the formation and decay of the target compounds were neglected. Two-film theory was used to simulate the net mass-transfer rate of volatile compounds from the liquid phase to the gas phase. Advective transport into and out of the air space of the pool were accounted for. The IAQ model was able to simulate the dynamic behavior of gas-phase NCl<sub>3</sub> during regular operating hours. Predictions of gas-phase NCl<sub>3</sub> dynamics were generally less accurate during periods of intensive pool use; however, the model did yield predictions of behavior that were qualitatively correct. Strengths of the model include that it accounts for the factors that are believed to have the greatest influence on IAQ dynamics and is simple to use. Model weaknesses include that the model did not account liquid-phase reactions that are responsible for formation and decay of the target compounds. The IAQ model for NCl<sub>3</sub> dynamics could still be a useful tool to form the basis for recommendations regarding the design and operation of indoor pool facilities so as to optimize IAQ.</p><p>Measurements of CO<sub>2</sub> dynamics indicated qualitatively similar dynamic behavior as NCl<sub>3</sub>. Because of this, it was hypothesized that CO<sub>2</sub> may represent a surrogate for NCl<sub>3</sub> for monitoring and control of IAQ dynamics. To examine this issue in more detail, a conceptually similar model of CO<sub>2 </sub>dynamics was developed and applied. The model was developed to allow for an assessment of the relative contributions of liquid®gas transfer and respiration by swimmers and spectators to CO<sub>2</sub> dynamics. The results of this modeling effort indicated that the similarity of CO<sub>2</sub> transfer behavior to NCl<sub>3</sub> may allow use of CO<sub>2</sub> as a surrogate during periods with few to no spectators in the pool; however, when large numbers of spectators are present, the behavior of CO<sub>2</sub> dynamics may not be representative of NCl<sub>3</sub> dynamics because of spectator respiration.</p><p></p> <br>
Monitoring air quality indicators and energy consumption in Dalarnas Villa during operation of a demand-controlled exhaust ventilation systemGarman, Ian, Haj Ahmad, Ahmad January 2020 (has links)
A real-world study was undertaken of the indoor air quality in a recently-built single family home in central Sweden, to establish whether demand controlled ventilation provided superior interior conditions, when compared with other air supply strategies, including the standard used by the Swedish buildings regulator. The property was highly airtight, with ventilation achieved using a forced exhaust system. Extraction was possible from all rooms of the house, and using a Renson Healthbox air handling unit, the rates of air flow from each room could be adjusted either according to a time schedule, or under demand control according to the unit’s sensing of the air quality in individual rooms. Five ventilation modes were evaluated, each for a period of 24 hours. Occupancy of the house was standardised, with test participants. Two separate air quality monitors were deployed to verify whether measurements made at the air handling unit were representative of the conditions that occupants experienced. Key measurements were the stable level of carbon dioxide overnight in an occupied double bedroom and the time taken for that room to refresh to background CO2 level the following day. The time taken for a kitchen/living room to similarly refresh was also examined. The study found that demand controlled ventilation achieved indoor air quality – assessed on carbon dioxide concentration – comparable with rates of fixed ventilation far greater than the regulated standard. In doing so, the air volume exchanged over a representative day was 33 % less than that standard, providing for significant energy savings. The parallel monitoring of air quality inside the room and via the air exhaust duct showed noticeable variation, but indicated the air handling unit under demand control would never ventilate insufficiently, based on its internal CO2 sensors.
Neeraja Balasubrahmaniam (8802989)
07 May 2020
<p>Infant exposure to the microbial and allergenic content of indoor floor dust has been shown to play a significant role in both the development of, and protection against, allergies and asthma later in life. Resuspension of floor dust during infant locomotion induces a vertical transport of particles to the breathing zone, leading to inhalation exposure to a concentrated cloud of coarse (> 1μm) and fine (≤ 1μm) particles. Resuspension, and subsequent exposure, during periods of active infant locomotion is likely influenced by gait parameters. This dependence has been little explored to date and may play a significant role in floor dust resuspension and exposure associated with forms of locomotion specific to infants. This study explores associations between infant locomotion dynamics and floor dust resuspension and exposure in the indoor environment. Infant gait parameters for walking and physiological characteristics expected to influence dust resuspension and exposure were identified, including: contact frequency (steps min<sup>-1</sup>), contact area per step (m<sup>2</sup>), locomotion speed (m s<sup>-1</sup>), breathing zone height (cm), and time-resolved locomotion profiles. Gait parameter datasets for standard gait experiments were collected for infants in three age groups: 12, 15, and 19 months-old (m/o). The gait parameters were integrated with an indoor dust resuspension model through a Monte Carlo framework to predict how age-dependent variations in locomotion affect the resuspension mass emission rate (mg h<sup>-1</sup>) for five particle size fractions from 0.3 to 10 μm. Eddy diffusivity coefficients (m<sup>2</sup> s<sup>-1</sup>) were estimated for each age group and used in a particle transport model to determine the vertical particle concentration profile above the floor.</p><p>Probability density functions of contact frequency, contact area, locomotion speed, breathing zone height, and size-resolved resuspension mass emission rates were determined for infants in each group. Infant standard gait contact frequencies were generally in the range of 100 to 300 steps min<sup>-1 </sup>and increased with age, with median values of 186 steps min<sup>-1 </sup>for 12 m/o, 207 steps min<sup>-1</sup> for 15 m/o, and 246.2 steps min<sup>-1</sup> for 19 m/o infants. Similarly, locomotion speed increased with age, from 67.3 cm s<sup>-1 </sup>at 12 m/o to 118.83 cm s<sup>-1</sup> at 19 m/o, as did the breathing zone height, which varied between 60 and 85 cm. Resuspension mass emission rates increased with both infant age and particle size. A 19 m/o infant will resuspend comparably more particles from the same indoor settled dust deposit compared to a 15 m/o or 12 m/o infant. Age-dependent variations in the resuspension mass emission rate and eddy diffusivity coefficient drove changes in the vertical particle concentration profile within the resuspended particle cloud. For all particle size fractions, there is an average of a 6% increase in the resuspended particle concentration at a height of 1 m from the floor for a 19 m/o compared to a 12 m/o infant. Time-resolved locomotion profiles were obtained for infants in natural gait during free play establish the transient nature of walking-induced particle resuspension and associated exposures for infants, with variable periods of active locomotion, no motion, and impulsive falls. This study demonstrates that floor dust resuspension and exposure can be influenced by the nature of infant locomotion patterns, which vary with age and are distinctly different from those for adults.</p>
Tebbe, Hope M.
18 October 2017
No description available.
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