C Howard-Reed’s research while affiliated with National Institute of Standards and Technology and other places

Unlabelled: A polymethylpentene film loaded with toluene is being developed as a reference material to support the reliable measurement of volatile organic compound emissions from building materials using environmental chambers. Earlier studies included the measurement of the material-phase diffusion coefficient (D) and material/air partition coefficient (K) at 23°C. A fundamental mass-transfer model can then be used to predict toluene emissions from the reference material at 23°C, serving as a reference for validating chamber-measured emission profiles. In this study, the effect of temperature and humidity on performance of the reference material was investigated. Reference material emissions were measured at 10, 23, and 30°C and at different relative humidity (RH) levels. D and K at different temperatures and RH were determined using an independent method. Results showed that RH does not significantly affect D and K and had no effect on emissions. However, emissions increased substantially at elevated temperatures due to the relationship between D and temperature. A statistical analysis shows good agreement between model-predicted and measured gas-phase concentrations, indicating that the model can accurately predict emission profiles as a function of temperature. The reference material can therefore be applied to a wide range of emission chamber testing conditions. Practical implications: A reference material with a dynamic emissions profile was previously developed as a validation tool for emission testing in chambers. This follow-up study investigated the effect of temperature and humidity on the performance of the reference material. The results show that the reference material can be used to calibrate and validate chamber testing procedures over a broad range of environmental conditions.

This study measured ventilation rates using SF6 decay tests in fourteen big-box retail buildings. The sampling method used the standard tracer gas decay procedure defined in ASTM E741 by separating the sampling locations into three to six zones depending on the size of the retail floor area. In each zone, the SF6 samples from different locations were checked to confirm uniformity of concentration. The air exchange rates in retail stores ranged widely from 0.20 h-1 to 1.50 h-1, with an average air exchange rate of 0.62 h-1. Out of thirty experiments in fourteen retail buildings, only 30% of the measured ventilation rates satisfied the total ventilation rate requirement of ASHRAE Std. 62 that includes both floor and occupancy ventilation components. Interestingly, 63% of the measured ventilation rates satisfied the total ventilation requirement, if the actual occupancy rates were used instead of the default occupancy rates defined in ASHRAE Std. 62.

This study investigated the possibility of identifying chemical pollutant profiles and concentration levels that result in a high level of acceptance indoors. In addition, a multizone simulation tool, CONTAM, developed by the National Institute of Standards and Technology (NIST) (US), was used to estimate optimal source strengths for the pollutants of interest in a typical Finnish single family house. VTT indoor air and material emission databases were used to identify and differentiate chemical pollutant profiles and concentration levels that are measured in complaint vs. noncomplaint residential buildings. The results indicate that certain volatile organic compound (VOC) profiles result in a high level of acceptance indoors. The simulation performed for a typical Finnish single family house showed that to achieve optimal total volatile organic compound (TVOC), formaldehyde, and single VOC concentration levels of less than 300 μg/m3, 30 μg/m3, and 10 μg/m 3, respectively, the specific emission rate (SER) should be less than 92 μg/m2h, 10 μg/m2h, and 4 μg/m2h respectively.

Unlabelled: Because of concerns about indoor air quality, there is growing awareness of the need to reduce the rate at which indoor materials and products emit volatile organic compounds (VOCs). To meet consumer demand for low emitting products, manufacturers are increasingly submitting materials to independent laboratories for emissions testing. However, the same product tested by different laboratories can result in very different emissions profiles because of a general lack of test validation procedures. There is a need for a reference material that can be used as a known emissions source and that will have the same emission rate when tested by different laboratories under the same conditions. A reference material was created by loading toluene into a polymethyl pentene film. A fundamental emissions model was used to predict the toluene emissions profile. Measured VOC emissions profiles using small-chamber emissions tests compared reasonably well to the emissions profile predicted using the emissions model, demonstrating the feasibility of the proposed approach to create a diffusion-controlled reference material. Practical implications: To calibrate emissions test chambers and improve the reproducibility of VOC emission measurements among different laboratories, a reference material has been created using a polymer film loaded with a representative VOC. Initial results show that the film's VOC emission profile measured in a conventional test chamber compares well to predictions based on independently determined material/chemical properties and a fundamental emissions model. The use of such reference materials has the potential to build consensus and confidence in emissions testing as well as 'level the playing field' for product testing laboratories and manufacturers.

As part of an ongoing effort to better understand the performance of indoor air cleaners in real buildings, the National Institute of Standards and Technology (NIST) has completed a series of air cleaner field tests and model simulations. This paper focuses on experiments to measure the removal of decane with two different gaseous air cleaners in a test house. Due to the lack of gaseous air cleaner field testing protocols, a field test method was developed using semi-real-time measurements and mass balance analysis. To date, 24 experiments have been completed with single-pass removal efficiencies ranging from 30 % to 44 %. A full factorial analysis revealed that factors such as air cleaner location, status of the heating and air conditioning system, relative humidity and temperature significantly affect air cleaner performance. These results have been used to develop a regression model to predict air cleaner removal rates based on these factors, as well as to evaluate the predictive capability of the indoor air quality model CONTAM.

To provide additional validation data for the multizone airflow and contaminant model, CONTAMW, experiments were performed in an occupied three-storey townhouse in Reston, VA. A tracer gas, sulfur hexafluoride (SF6), was manually injected within one room of the house and the concentration of SF6 was then measured in nine rooms. This same process was then recreated in CONTAMW and the resulting predictions were statistically compared to the measured values. A total of 10 experiments were conducted and simulated between May 2000 and June 2001. In four cases, the heating and air-conditioning system fan was operating. SF6 was injected in the recreation room (basement level), the kitchen= dining room (main level) and the master bedroom (upstairs level). A statistical comparison of measurements and predictions was performed per ASTM D5157 (ASTM 1997) for all cases. Comparisons were made for overall zone average concentrations and individual zone transient concentrations. The results for zone average concentrations were very good with many cases meeting most or all of the D5157 criteria. Several cases showed a poor to fair correlation between average measurements and predictions due to discrepancies with a single zonemdashthe main floor bathroommdashbut excluding that zone resulted in these cases meeting or nearly meeting the D5157 criteria. Comparisons of individual zone transient concentrations were mixed with many good to excellent cases but also numerous fair to poor. Zones other than the bathroom had occasional poor comparisons between predictions and measurements but no consistent discrepancies. The predicted SF6 concentration averaged over all zones and cases was within 10% of the average measured concentration.

The National Institute of Standards and Technology (NIST) is conducting a study on the indoor air quality (IAQ) impacts and engineering solutions related to the transport of pollutants from attached garages to residential living spaces. Natural or fan-induced pressure differences across air leakage paths in house-garage (HG) interfaces can result in the transport of the contaminants generated in garages into adjacent living spaces. This paper summarises a literature review on the transport of pollutants from garages to residential living spaces and describes a field study to estimate the range of airtightness of attached garages and of HG interfaces in the United States. Although the body of literature on pollutant transport from attached garages to residential buildings is limited, the studies reviewed provide substantial evidence that transport of contaminants from garages has the potential to negatively impact residential IAQ in either an acute (e.g., carbon monoxide from automobiles) or chronic manner (e.g., storage of chemical products). However, the literature contains few answers on issues such as the airtightness and geometry of the HG interface, the impact of heating and cooling equipment in the garage, and the effectiveness of potential engineering solutions. To address one gap in understanding these issues, the airtightness of garages and HG interfaces was measured in five residences using fan pressurisation. While the small sample of houses limits generalisation of the results, a range of house ages, styles, and sizes was included. For all homes tested, the garage was found to be at least twice as leaky as the house, based on air change per hour at 50 Pa. The leakiness of the garage envelope, based on surface area normalised effective leakage area at 4 Pa (ELA4/SA), ranges from a high of nearly eleven times to a low of two and a half times that of the house exterior envelope leakage. On average, the HG interface was almost two and a half times as leaky as the rest of the house envelope, when based on ELA4/SA. However, this average is somewhat skewed due to one HG interface measured in this study that is almost eleven times as leaky as the rest of the house envelope. Conversely, a larger Canadian study found HG interfaces to be comparable to house envelopes but found the average garage to be about ten times as leaky as houses – possibly because Canadian houses are consistently tighter than U.S. houses (Fugler et al. 2002). The knowledge gained from this review and the field study will be used in a simulation study of the potential occupant exposure to pollutants from attached garages and to explore potential engineering solutions to this IAQ problem.

A year-long investigation of air change rates in an occupied house was undertaken to establish the effects of temperature, wind velocity, use of exhaust fans, and window-opening behavior. Air change rates were calculated by periodically injecting a tracer gas (SF(6)) into the return air duct and measuring the concentration in 10 indoor locations sequentially every minute by a gas chromatograph equipped with an electron capture detector. Temperatures were also measured outdoors and in the 10 indoor locations. Relative humidity (RH) was measured outdoors and in five indoor locations every 5 min. Wind speed and direction in the horizontal plane were measured using a portable meteorological station mounted on the rooftop. Use of the thermostat-controlled attic fan was recorded automatically. Indoor temperatures increased from 21 degrees C in winter to 27 degrees C in summer. Indoor RH increased from 20% to 70% in the same time period. Windows were open only a few percent of the time in winter but more than half the time in summer. About 4600 hour-long average air change rates were calculated from the measured tracer gas decay rates. The mean (SD) rate was 0.65 (0.56) h(-1). Tracer gas decay rates in different rooms were very similar, ranging only from 0.62 to 0.67 h(-1), suggesting that conditions were well mixed throughout the year. The strongest influence on air change rates was opening windows, which could increase the rate to as much as 2 h(-1) for extended periods, and up to 3 h(-1) for short periods of a few hours. The use of the attic fan also increased air change rates by amounts up to 1 h(-1). Use of the furnace fan had no effect on air change rates. Although a clear effect of indoor-outdoor temperature difference could be discerned, its magnitude was relatively small, with a very large temperature difference of 30 degrees C (54 degrees F) accounting for an increase in the air change rate of about 0.6 h(-1). Wind speed and direction were found to have very little influence on air change rates at this house.