Tracer Gas Tests Research Articles

A Comprehensive Validation of Two Airflow Models - COMIS and CONTAM

Abstract Several airflow and contaminant dispersion models have been developed to study air distribution in buildings. This paper reports the results of a comprehensive validation of two models: COMIS and CONTAM. The validation process was carried out at three different levels; inter-program comparison; validation with experimental data which was collected in a controlled environment; and finally, validation with field measurement data. At the inter-program level, the airflow rates and pressure values predicted by COMIS and CONTAM for a four-zone paper building were compared with the airflow rates and pressures predicted by CBSAIR, AIRNET and BUS. The results show good agreement between these software programs. The second level of validation compares the models’ predictions with measured data collected in a controlled environment. Fan pressurisation, smoke and tracer gas tests were conducted to estimate the permeability of building envelope components, to locate cracks, and to determine the interzonal airflow rates between rooms. The results confirm that there is good agreement between predictions made by COMIS and CONTAM; there are, however, some differences between these models’ predictions and the measured data. The predictions made by these models were also compared with the results of a tracer gas measurement carried out in a residential building. The predicted and measured values were in good agreement.

Domestic ducted forced-air heating: Duct system leakage and heating energy use

A residential ducted forced-air heating system was investigated to assess the impact of duct system leakage. Ductwork pressurisation and tracer gas techniques were used to quantify leakage in the heating duct system, and added infiltration to the house caused by duct leaks. Determination of leakage fraction by pressurisation tests showed a distribution loss of 23% in supply ductwork and 3% for the return duct during normal operation of the air heater's circulation fan. Tracer gas tests showed that the house infiltration is affected by the duct system leakage: infiltration increased from 0.1 ac h-1 for no ducting, to 0.21 and 0.5 ac h-1 with heating ductwork when the circulation fan is off and on respectively. A direct calculation shows the heat loss due to duct leakage to be about 45% of the house peak winter load. Hourly simulation of the space heating requirements indicates an annual increase of 35% in heating load due to heating duct leakage and transmission losses.

A procedure for measurement of ventilation effectiveness in residential buildings

Ventilation effectiveness is expressed by two newly defined terms: relative contaminant removal effectiveness and removal efficiency. The relative removal effectiveness is defined as the relative ratio between the rate of contaminant removal and rate of room air replacement. The removal efficiency is the percentage of the total generated contaminant removed by purpose-provided openings. A series of tracer gas tests was performed to simulate the contaminant migration and the removal of the contaminant generated by a point source in a residential building. The values of relative removal effectiveness are calculated from test results. The removal efficiency is then obtained from the values of relative removal effectiveness for two concerned tests. The new terms can be used to assess the air quality related building problems and help in the design stage in decisions among alternative schemes.

Thermal performance monitoring results from the residential standards demonstration program

The Model Conservation Standards (MCS) were developed by the Northwest Power Planning Council in 1983. These standards were designed to save large amounts of space heating energy in new U.S. residential construction in the Pacific Northwest. Creation of the MCS resulted in a desire to demonstrate the actual savings of such energy efficiency standards. The Bonneville Power Administration sponsored the Residential Standards Demonstration Program (RSDP) in 1984 which resulted in the construction of 410 energy-efficient single-family homes in the four-state region. Typically these buildings incorporated design features such as high levels of insulation for attic, walls and floors, triple-glazed windows and airtight construction with heat-recovery ventilation. These MCS dwellings have been compared against another group of 410 new, but conventional homes in the Northwest to determine the actual savings of such efficiency standards for space heat. Each house was monitored for at least one year using a triple metering system that recorded energy use for space heat, domestic hot water and appliances. Average interior and exterior temperatures were also collected during the monitoring period. Extensive data was assembled from audit and survey information on the construction of the homes, their heating systems and other occupancy-related characteristics. This paper both summarizes results of the RSDP project and scrutinizes certain aspects associated with the buildings' monitored thermal performance. Monitored space heat savings for the energy-efficient MCS houses compared to the control buildings averaged 27.5 kWh/m 2 of floor area for the overall sample of 524 houses. Data analysis showed that differing levels of insulation in the buildings is the most powerful explanation for these differences. The program also illustrated how collection of simple end-use metering data can provide insight into the energy-use characteristics of residential buildings. Among other findings, we discovered that the type of heating system plays a large role in determining the relative efficiency of electrically heated houses. Residences with electric forced-air heating systems used an average of 15.9 kWh/m 2 more space heating energy than those without them. Houses with heat pumps or those using wood as their primary heat source used much less space heat electricity. We also discovered that houses with fireplaces tended to use more space heat energy. The study also examined infiltration and ventilation-related measures on the houses using fan pressurization and perfluorocarbon tracer gas (PFT) tests. We found that the RSDP control homes, intended to be representative of of current building practice in the Pacific Northwest, have relatively low rates of natural air infiltration — an average of about 0.4 air changes per hour (ACH). The natural air infiltration rate of the MCS houses tended to be tighter, on the order of 0.25 ACH. Air-to-air heat exchangers in the MCS houses were used an average of 9 h per day, and increased the overall ventilation rate in these homes to about 0.35 ACH.

A tracer pulse method for the assessment of airflow patterns in a particleboard mill.

A tracer pulse method was used to investigate the spread of airborne formaldehyde from its source into the surrounding air and the distribution of the air supply in a particleboard mill. The contaminant flow was labeled with sulfur hexafluoride, and the supply of outdoor air with nitrous oxide. The pulse responses of the injected tracer gases were interpreted in terms of the age concept. The result of improvements in the ventilation system was studied through measurements of the formaldehyde concentration and with tracer gas tests. It was found that the approach used in this paper is applicable to charting airflow patterns in a complex industrial environment.