Direct capture efficiency of a local exhaust system is defined by introducing an imaginary control box surrounding the contaminant source and the exhaust opening. The imaginary box makes it possible to distinguish between contaminants directly captured and those that escape. Two methods for estimation of direct capture efficiency are given: (I) a numerical method based on the time-averaged Navier-Stokes equations for turbulent flows; and (2) a field method based on a representative background concentration.

Unique air flow windows and dual air-conditioning systems provide occupant comfort and energy conservation.

There are many unanswered questions about the typical effects of duct system operation on the infiltration rates and energy usage of single-family residences with HVAC systems in their basements. In this paper, results from preliminary field studies and computer simulations are used to examine the potential for improvements in efficiency of air distribution systems in such houses. The field studies comprise thermal and flow measurements on four houses in Maryland. The houses were found to have significant envelope leakage, duct leakage, and duct conduction losses.

This paper describes a framework for a figure of merit by which the energy performance of thermal energy distribution systems (e.g., duct systems) in residences could be characterized. The proposed figure of merit is designed to be incorporated into design guides, state energy codes and/or utility DSM programs.

ASTM has recently standardized a methodology for measuring the leakage of residential air distribution systems to unconditioned zones. The standard includes two alternative leakage measurement techniques, one of which requires only a blower door, whereas the second technique requires a flowcapture 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 objectives of this project were to develop and test a simplified duct-leakage measurement technique that could be used as part of both new-construction and retrofit DSM programs for residential duct systems.

Maintaining proper differential pressure in lab spaces is one of the most challenging tasks facing the environmental control engineer.

This handbook describes the use of tracer-gas techniques for measurement of airflow in ducts. Initial measurements were carried out in the laboratory to examine the accuracy of these techniques. The mixing of tracer gases (eg, sulphur hexafluoride, SF6) in ducts of various shapes and sizes was examined using different types of tracer injector. Airflow estimated using tracer-gas techniques (eg, constant-injection, pulse-injection) was compared with measurements made with traditional instrumentation such as pitot-tubes and hot-wire anemometers.