Kenneth L. Revzan

A Concentration Rebound Method for Measuring Particle Penetration and Deposition in the Indoor Environment

Continuous, size resolved particle measurements were performed in two houses in order to determine size-dependent particle penetration into and deposition in the indoor environment. The experiments consisted of three parts: (1) measurement of the particle loss rate following artificial elevation of indoor particle concentrations, (2) rapid reduction in particle concentration through induced ventilation by pressurization of the houses with HEPA-filtered air, and (3) measurement of the particle concentration rebound after house pressurization stopped. During the particle concentration decay period, when indoor concentrations are very high, losses due to deposition are large compared to gains due to particle infiltration. During the concentration rebound period, the opposite is true. The large variation in indoor concentration allows the effects of penetration and deposition losses to be separated by the transient, two-parameter model we employed to analyze the data. For the two houses studied, we found that as particles increased in diameter from 0.1 to 10 w m, penetration factors ranged from ∼1 to 0.3 and deposition loss rates ranged from 0.1 and 5 h m 1 . The decline in penetration factor with increasing particle size was less pronounced in the house with the larger normalized leakage area.

A method for simulating the performance of photosensor-based lighting controls

Abstract The unreliability of photosensor-based lighting controls continues to be a significant market barrier that prevents widespread acceptance of daylight dimming controls in commercial buildings. Energy savings from the use of daylighting in commercial buildings is best realized through the installation of reliable photoelectric lighting controls that dim electric lights when sufficient daylight is available to provide adequate background and/or task illumination. In prior work, the authors discussed the limitations of current simulation approaches and presented a robust method to simulate the performance of photosensor-based controls using an enhanced version of the radiance lighting simulation package. The method is based on the concept of multiplying two fisheye images: one generated from the angular sensitivity of the photosensor and the other from a 180 or 360° fisheye image of the space as “seen” by the photosensor. This paper includes a description of the method, its validation and possible applications for designing, placing, calibrating and commissioning photosensor-based lighting controls.

Detailed kinetic modeling of soot formation in ethylene/air mixtures reacting in a perfectly stirred reactor

A series of perfectly stirred reactor (PSR) calculations has been performed that allow the comparison of numerical predictions for sooting trends in PSRs with those observed in experiments. A detailed chemical kinetics model for soot production is employed that has been extensively tested for laminar flames. The chemical kinetics model is used without any adjustments. The PSR code Aurora that is a CHEMKIN III application has been modified considerably to incorporate the method of moments. Gas-phase and surface reactions are rigorously coupled in the model. Predicted sooting characteristics are consistent with behavior observed experimentally for premixed laminar flames and well-stirred reactors. Specifically, soot volume fraction exhibited the same qualitative behavior with equivalence ratio, temperature, and pressure as observed for flames. Concentration profile shapes were consistent with profile shapes measured for flames as well. The model also predicts soot threshold values and the relationship of soot volume fraction with temperature and equivalence ratio that has been observed experimentally for well-stirred reactors. Under the conditions of the present investigation, soot formation dynamics was dominated by nucleation. The temperature dependence of surface reaction rates revealed the importance of the HACA mechanism (H-abstraction-C 2 H 2 addition reaction sequence) in surface growth. Under PSR conditions, coupling the gasphase and surface chemistry is significant with the degree of coupling increasing with pressure.

Characteristics of fine particle growth events observed above a forested ecosystem in the sierra nevada mountains of california

Atmospheric aerosols from natural and anthropogenic processes have both primary and secondary origins, and can influence human health, visibility, and climate. One key process affecting atmospheric concentrations of aerosols is the formation of new particles and their subsequent growth to larger particle sizes. A field study was conducted at the Blodgett Forest Research Station in the Sierra Nevada Mountains of California from May through September of 2002 to examine the effect of biogenic volatile organic compounds on aerosol formation and processing. The study included in-situ measurements of concentration and biosphere-atmosphere flux of VOCs, ozone, aerosol size distribution, aerosol physical and optical properties, and meteorological variables. Fine particle growth events were observed on approximately 30 percent of the 107 days with complete size distribution data. Average particle growth rates measured during these events were 3.8 ± 1.9 nm hr−1. Correlations between aerosol properties, trace gas concentrations, and meteorological measurements were analyzed to determine conditions conducive to fine particle growth events. Growth events were typically observed on days with a lesser degree of anthropogenic influence, as indicated by lower concentrations of black carbon, carbon monoxide, and total aerosol volume. Days with growth events also had lower temperatures, increased wind speeds, and larger momentum flux. Measurements of ozone concentrations and ozone flux indicate that gas phase oxidation of biogenic volatile organic compounds occur in the canopy, strongly suggesting that a significant portion of the material responsible for the observed particle growth are oxidation products of naturally emitted very reactive organic compounds.

Indoor Radon and Its Decay Products: Concentrations, Causes, and Control Strategies

This report is an introduction to the behavior of radon 222 and its decay products in indoor air. This includes review of basic characteristics of radon and its decay products and of features of the indoor environment itself, all of which factors affect behavior in indoor air. The experimental and theoretical evidence on behavior of radon and its decay products is examined, providing a basis for understanding the influence of geological, structural, and meteorological factors on indoor concentrations, as well as the effectiveness of control techniques. We go on to examine three important issues concerning indoor radon. We thus include (1) an appraisal of the concentration distribution in homes, (2) an examination of the utility and limitations of popular monitoring techniques and protocols, and (3) an assessment of the key elements of strategies for controlling radon levels in homes.

Modeling radon entry into Florida slab-on-grade houses.

Radon entry into a Florida house whose concrete slab is supported by a permeable concrete-block stem wall and a concrete footer is modeled. The slab rests on backfill material; the same material is used to fill the footer trench. A region of undisturbed soil is assumed to extend 10 m beyond and below the footer. The soil is assumed homogeneous and isotropic except for certain simulations in which soil layers of high permeability or radium content are introduced. Depressurization of the house induces a pressure field in the soil and backfill. The Laplace equation, resulting from Darcys law and the continuity equation, is solved using a steady-state finite-difference model to determine this field. The mass-transport equation is then solved to obtain the diffusive and advective radon entry rates through the slab; the permeable stem wall; gaps at the intersections of the slab, stem wall, and footer; and gaps in the slab. These rates are determined for variable soil, backfill, and stem-wall permeability and radium content, slab-opening width and position, slab and stem-wall diffusivity, and water table depth. The variations in soil permeability and radium content include cases of horizontally stratified soil. We also consider the effect of a gap between the edge of the slab and the stem wall that restricts the passage of soil gas from the stem wall into the house. Calculations indicate that the total radon entry rate is relatively low unless the soil or backfill permeability or radium content is high. Variations in most of the factors, other than the soil permeability and radium content, have only a small effect on the total radon entry rate. However, for a fixed soil permeability, the total radon entry rate may be reduced by a factor of 2 or more by decreasing the backfill permeability, by making the stem wall impermeable and gap-free, (possibly by constructing a one-piece slab/stem-wall/footer), or by increasing the pressure in the interior of the stem wall (by ensuring that there is a large pressure drop across the slab/stem-wall gap), thereby reducing radon entry into the wall from the soil. Use of an impermeable stem wall and a low-permeability fill in combination is predicted to reduce the radon entry rate by 71%.

Parametric modelling of temporal variations in radon concentrations in homes

The /sup 222/Rn (radon) concentrations in the living area, the basement, and the underlying soil of a New Jersey home have been measured at half-hour intervals over the course of a year, as have indoor and outdoor temperatures, wind speed and direction, indoor-outdoor and basement-subslab pressures; in addition, periods of furnace operation have been logged. A preliminary version of a mathematical model is developed that demonstrates the dependence of the radon concentrations on the environmental variables and the extent of furnace use, with the purposes of improving the ability to predict occurrences of elevated concentrations in general, increasing the usefulness of short-term measurements in particular, and assisting in the devising of remedial measures. The possibility of determining the model parameters from knowledge or measurement of geological and structural characteristics is discussed. >