Erin L. Hult

Formaldehyde and acetaldehyde exposure mitigation in US residences: in-home measurements of ventilation control and source control.

Measurements were taken in new US residences to assess the extent to which ventilation and source control can mitigate formaldehyde exposure. Increasing ventilation consistently lowered indoor formaldehyde concentrations. However, at a reference air exchange rate of 0.35 h(-1), increasing ventilation was up to 60% less effective than would be predicted if the emission rate were constant. This is consistent with formaldehyde emission rates decreasing as air concentrations increase, as observed in chamber studies. In contrast, measurements suggest acetaldehyde emission was independent of ventilation rate. To evaluate the effectiveness of source control, formaldehyde concentrations were measured in Leadership in Energy and Environmental Design (LEED)-certified/Indoor airPLUS homes constructed with materials certified to have low emission rates of volatile organic compounds (VOC). At a reference air exchange rate of 0.35 h(-1), and adjusting for home age, temperature and relative humidity, formaldehyde concentrations in homes built with low-VOC materials were 42% lower on average than in reference new homes with conventional building materials. Without adjustment, concentrations were 27% lower in the low-VOC homes. The mean and standard deviation of formaldehyde concentration was 33 μg/m(3) and 22 μg/m(3) for low-VOC homes and 45 μg/m(3) and 30 μg/m(3) for conventional.

The breaking of interfacial waves at a submerged bathymetric ridge

The breaking of periodic progressive two-layer interfacial waves at a Gaussian ridge is investigated through laboratory experiments. Length scales of the incident wave and topography are used to parameterize when and how breaking occurs. Qualitative observations suggest both shear and convection play a role in the instability of waves breaking at the ridge. Simultaneous particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) measurements are used to calculate high resolution, two-dimensional velocity and density fields from which the local gradient Richardson number Ri g is calculated. The transition to breaking occurred when 0.2 ≤ Ri g ≤ 0.4. In these wave-ridge breaking events, the destabilizing effects of waves steepening in shallow layers may be responsible for breaking at higher Ri g than for similar waves breaking through shear instability in deep water (Troy & Koseff, J. Fluid Mech. , vol. 543, 2005 b , p. 107). Due to the effects of unsteadiness, nonlinear shoaling and flow separation, the canonical Ri g > 0.25 is not sufficient to predict the stability of interfacial waves. A simple model is developed to estimate Ri g in waves between finite depth layers using scales of the incident wave scale and topography. The observed breaking transition corresponds with a constant estimated value of Ri g from the model, suggesting that interfacial shear plays an important role in initial wave instability. For wave amplitudes above the initial breaking transition, convective breaking events are also observed.

Ventilation Control of Volatile Organic Compounds in New U.S. Homes: Results of a Controlled Field Study in Nine Residential Units

In order to optimize strategies to remove airborne contaminants in residences, it is necessary to determine how contaminant concentrations respond to changes in the air exchange rate. The impact of air exchange rate on the indoor concentrations of 39 target volatile organic compounds (VOCs) was assessed by measuring air exchange rates and VOC concentrations at three ventilation settings in nine residences. Active sampling methods were used for VOC concentration measurements, and passive perfluorocarbon tracer gas emitters with active sampling were used to determine the overall air exchange rate corresponding to the VOC measurements at each ventilation setting. The concentration levels and emission rates of the target VOCs varied by as much as two orders of magnitude across sites. Aldehyde and terpene compounds were typically the chemical classes with highest concentrations, followed by alkanes, aromatics, and siloxanes. For each home, VOC concentrations tended to decrease as the air exchange rate was increased, however, measurement uncertainty was significant. The indoor concentration was inversely proportional to air exchange rate for most compounds. For a subset of compounds including formaldehyde, however, the indoor concentration exhibited a non-linear dependence on the timescale for air exchange

Estimates of uncertainty in multi-zone air leakage measurements

Abstract Although standards for single-zone air leakage tests are widely used, there are no existing standards for several multi-zone cases including: 1) testing air leakage between adjacent zones or 2) testing leakage to the outside from a single unit in a multi-zone building. While a range of test procedures have been used to determine inter-zone leakage using fan-pressurization, the accuracy of the methods can vary significantly. Using field measurements and simulations, we compared the uncertainty in the leakage between two adjacent zones for different measurement and calculation methods. The most accurate method for determining leakage between two adjacent zones using a single blower door has 25% uncertainty and the most accurate two-door test has 16%. In multi-family housing buildings, air leakage from a single zone to the outside is often measured by pressurizing adjacent units to the same test pressure, i.e., a guarded test approach. We investigated how two common sources of uncertainty affect zone-to-outside leakage test results using the guarded zone test method: 1) pressure fluctuations in the different units, and 2) interconnected zones that are not pressurized during the test. While the uncertainty in leakage to outside due to pressure fluctuations and calibration error in guarded test results is relatively small (4–14%), leakage to interstitial zones may have a much more substantial impact (on the order of 30–100% of the leakage directly to the outdoors).

Measurement Methods to Determine Air Leakage Between Adjacent Zones

Measurement Methods to Determine Air Leakage Between Adjacent Zones Erin L. Hult, Darryl J. Dickerhoff, Phillip N. Price Environmental Energy Technologies Division September 2012