Mark P. Modera

Indoor Air Quality Impacts of Ventilation Ducts: Ozone Removal and Emissions of Volatile Organic Compounds

The concentrations of contaminants in the supply air of mechanically ventilated buildings may be altered by pollutant emissions from and interactions with duct materials. We measured the emission rate of volatile organic compounds (VOCs) and aldehydes from materials typically found in ventilation ducts. The emission rate of VOCs per exposed surface area of materials was found to be low for some duct liners, but high for duct sealing caulk and a neo-prene gasket. For a typical duct, the contribution to VOC concentrations is predicted to be only a few percent of common indoor levels. We exposed selected materials to ~100-ppb ozone and measured VOC emissions. Exposure to ozone increased the emission rates of aldehydes from a duct liner, duct sealing caulk, and neoprene gasket. The emission of aldehydes from these materials could increase indoor air concentrations by amounts that are as much as 20% of odor thresholds. We also measured the rate of ozone uptake on duct liners and galvanized sheet metal to predict how much ozone might be removed by a typical duct in ventilation systems. For exposure to a constant ozone mol fraction of 37 ppb, a lined duct would initially remove ~9% of the ozone, but over a period of 10 days the ozone removal efficiency would diminish to less than 4%. In an unlined duct, in which only galvanized sheet metal is exposed to the air-stream, the removal efficiency would be much lower, ~0.02%. Therefore, ducts in ventilation systems are unlikely to be a major sink for ozone.

Comparison of measured and predicted infiltration using the LBL infiltration model

The LBL infiltration model was developed in 1980; since that time many simultaneous measurements of infiltration and weather have been made allowing comparison of predictions with measured infiltration. This report presents the LBL model as it currently exists and summarizes infiltration measurements and corresponding predictions. These measurements include both long-term and short-term data taken in houses with climates ranging from the mild San Fransisco bay area to the more extreme mid-west. This data also provides a database for comparison with other infiltration models and provides a starting point for the determination of the accuracy and precision of air infiltration models. In this report we have presented the LBL infiltration model and have used field data to validate it. For short-term measurements the model predicts to within 20% for well defined environments (e.g. the MITU trailer) and slightly higher for other situations. The long-term (one week) average infiltration is accurate to 7%; in the Owens-Corning houses the long-term average error increases to up to 15%. A detailed examination of the LBL model using data from Mobile Infiltration Test Unit was used to probe the model and suggest areas for future research. 13 refs., 12 figs., 14 tabs.

Particle Deposition in a Two-Dimensional Slot from a Transverse Stream

ABSTRACT This paper addresses the problem of coarse mode particle deposition in a two-dimensional slot from a transverse flow. A dimensional analysis enables us to identify five independent dimensionless groups: the leak Reynolds number, Re, the dimensionless velocity gradient of the approaching flow, α, the Stokes number, Stk, the slot aspect-ratio, e/h, and the interception parameter, dp/h.. A sticky aerosol (MMD ≊3–7 μm; GSD ≊ 2–3) was injected into a 15 cm diameter duct and blown out through a rectangular opening (3 × 40 mm; e = 0.6 mm) drilled in a direction perpendicular to the flow. A video camera was set up to continuously monitor the leak behavior in time. The image then was digitized, enabling us to assess the slot-width as a function of time. It appeared that the slot could be sealed in less than 20 minutes. These results were compared with a simplified model based on a scale analysis of the deposition velocity on the slot thickness. Agreement between predicted and measured leak-widths is very ...

Signal attenuation due to cavity leakage

The propagation of sound waves in fluids requires information about three properties of the system: capacitance (compressibility), resistance (friction), and inductance (inertia). Acoustical design techniques to date have tended to ignore the frictional effects associated with airflow across the envelope of the acoustic cavity (e.g., resistive vents). Since such leakage through the cavity envelope is best expressed with a power law dependence on the pressure, standard Fourier techniques that rely on linearity cannot be used. In this article, the theory relevant to nonlinear leakage is developed and equations presented. Potential applications of the theory to techniques for quantifying the leakage of buildings are presented. Experimental results from pressure decays in a full‐scale test structure are presented and the leakage so measured is compared with independent measurements to demonstrate the technique.

Sealing ducts in large commercial buildings with aerosolized sealant particles

LBNL-42414 Sealing Ducts in Large Commercial Buildings with Aerosolized Sealant Particles M. P. Modera, O. Brzozowski ** , F. R. Carrie * , D. J. Dickerhoff, W. W. Delp, W. J. Fisk, R. Levinson, D. Wang Abstract Electricity energy savings potential by eliminating air leakage from ducts in large commercial buildings is on the order of 10 kWh/m 2 per year (1 kWh/ft 2 ). We have tested, in two large commercial buildings, a new technology that simultaneously seals duct leaks and measures effective leakage area of ducts. The technology is based upon injecting a fog of aerosolized sealant particles into a pressurized duct system. In brief, this process involves blocking all of the intentional openings in a duct system (e.g., diffusers). Therefore, when the system is pressurized, the only place for the air carrying the aerosol particles to exit the system is through the leaks. The key to the technology is to keep the particles suspended within the airstream until they reach the leaks, and then to have them leave the airstream and deposit on the leak sites. The principal finding from this field study was that the aerosol technology is capable of sealing the leaks in a large commercial building duct system within a reasonable time frame. In the first building, 66% of the leakage area was sealed within 2.5 hours of injection, and in the second building 86% of the leakage area was sealed within 5 hours. We also found that the aerosol could be blown through the VAV boxes in the second building without impacting their calibrations or performance. Some remaining questions are (1) how to achieve sealing rates comparable to those experienced in smaller residential systems; and (2) what tightness level these ducts systems can be brought to by means of aerosol sealing. Ecole Nationale Superieure d’arts et Metiers (ENSAM), Paris, France On leave from Ecole Nationale des Travaux Publics de l’Etat, Laboratoire des Sciences de l’Habitat, DGCB – URA CNRS 1652, 2 rue Maurice Audin, 69518 Vaulx-en-Velin Cedex, France

Experimental investigation of aerosol deposition on slot- and joint-type leaks

Abstract This paper deals with the quantification of the sealing effectiveness of slot- and joint-type leaks by aerosol deposits. A sticky aerosol (MMAD ≈4.9 μm ; GSD ≈2.7) was injected into a duct and blown out through machined slot- and joint-type leaks located on the duct wall. For both leak-types, the crack exit was a rectangular opening of 1.7×50 mm . The pressure difference across the leaks was kept constant during the plugging process, while the airflow rate through the openings was continuously monitored. The deposition patterns were recorded and the average deposition efficiencies were obtained through the measurement of the particle mass collected in the crack. Instantaneous sealing rates were obtained from the leakage airflow time series. The normalized sealing rate (NSR) introduced in this paper allows one to compare the instantaneous sealing efficiencies as the leaks are subjected to various boundary conditions. For our specific leak geometries and boundary conditions, the three key results of these experiments are: (a) inertial impaction near the entry point is the major cause of the decline of the leakage flow rate for either type of leak; (b) the pressure variations in the 100– 400 Pa range do not have a significant effect on the average deposition efficiency; (c) the average deposition efficiency of the slot- and joint-type leaks used are in the range of 25% and 85%, respectively. We also observed that there exists a critical joint-leak size below which the NSR decreases significantly.

Exterior Exposed Ductwork: Delivery Effectiveness and Efficiency

Most of California`s light commercial buildings use air transport through ductwork for thermal distribution. The same air distribution systems are often used to provide both thermal comfort and ventilation. Some air distribution ductwork is installed on rooftops, exposed directly to the outside environment. As such, there exist potential energy penalties related to externally installed ductwork. In order to evaluate the magnitude of these penalties, a case study was conducted of a one-story community college building, located in California`s Sacramento Valley. The majority of the building`s air distribution ductwork was located on the roof. Energy-related issues studied in this case included duct-related thermal losses (duct leakage and conduction), delivery effectiveness and efficiency, thermal comfort issues and the effect of a roof retrofit (additional insulation and a reflective coating). The building in this study underwent a retrofit project involving additional insulation and a highly reflective coating applied to the roof and ducts. As part of this project, methods were developed to analyze the air distribution system effectiveness independent of the introduction of outside air through an outside air damper. A simplified model was developed to predict the effectiveness and efficiency of the distribution system. The time frame of the retrofit allowed two separate three week monitoring periods. Despite the fact that the ducts started off with a conduction efficiency of 97%, the delivery efficiency was on average only 73% (with a supply side effectiveness of 78% and return effectiveness of 92%). This is due to the losses from the ducts being located on the roof. The retrofit increased the delivery efficiency to an average of 89% (with a supply side effectiveness of 90% and return effectiveness of 99%), reducing the average energy use for conditioning by 22%. The model predicted, on average, the results within 10%, or better, of measured results.

Effects of air infiltration on the effective thermal conductivity of internal fiberglass insulation and on the delivery of thermal capacity via ducts

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Effects of Duct Improvement and ENERGYSTAR Equipment on Comfort and Energy Efficiency

LBNL 43723 Effects of Duct Improvement and E NERGY S TAR Equipment on Comfort and Energy Efficiency I. Walker, M. Sherman, J. Siegel, and M. Modera Environmental Energy Technologies Division Energy Performance of Buildings Group Lawrence Berkeley National Laboratory Berkeley, CA 94720 July 1999 This study was sponsored by the U.S. Environmental Protection Agency, through the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. Publication of research results does not imply EPA endorsement of or agreement with these findings.

Field comparison of alternative techniques for measuring air distribution system leakage

ASTM has recently standardized a methodology for measuring the leakage of residential air distribution systems to unconditioned zones [ASTM Test Method for Determining the External Air Leakage of Air Distribution Systems by Fan Pressurization (E 1554-93)]. The standard includes two alternative leakage measurement techniques. One technique requires only a blower door, whereas the second technique requires a flow-capture hood as well as a blower door. This paper reports on the results of field measurements in 30 houses using both measurement techniques, and analyzes the relative strengths and weaknesses of the two techniques. The repeatability of each of the techniques, as well as the comparability of the results from the two techniques, is examined. A key issue addressed is the importance of duct pressure measurements in each of the two techniques. Analyses show that the leakage measured with the blower-door-only technique would have been negatively biased by 30% to 50% if the duct pressure had not been incorporated into the measurements and analyses as specified in the standard. Similarly, it is shown that supply leakage measurements with the flow-capture-hood technique would have been negatively biased by 33% if the envelope pressure differential had been used instead of the duct pressure differential.