The primary purpose of a laboratory exhaust system is to remove and convey fumes from the fume hoods and laboratory spaces to an area for safe discharge. This requires discharge conditions that allow good dispersion and prevent re-entrainment. Since laboratories are usually designed for once through air ( 100% makeup air with no recirculation), a secondary purpose is energy recovery from the exhaust stream. Laboratory exhaust systems have typically one of two arrangements.

This paper describes the wind tunnel study conducted on behalf of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to evaluate and quantify the effect of architectural screens on rooftop concentration levels due to effluent from short stacks. An equivalent stack height (ESH) concept is introduced, which is used to develop a stack height reduction (SHR) factor that may be used in conjunction with existing stack design procedures found in the 1997 ASHRAE Handbook-Fundamentals to account for the presence of architectural screens.

Laboratory exhaust stacks should be designed with sufficient height and exit momentum to avoid re-entry of exhaust and possible air quality problems, and the design should be evaluated before construction. One evaluation method is presented in this paper that combines dilution prediction equations from the 1997 ASHRAE Handbook-Fundamentals (1997} and a dilution criteria of Halitsky (1988). This method is less conservative than a geometric method in the ASHRAE Handbook and is less costly than wind-tunnel modeling.

This paper presents a computational fluid dynamics ( CFD) study of the indoor environment provided by a cold air distribution system using three alternative types of diffusers, i.e., a square multi--cone type, a wall-mounted nou.le type, and a ceiling nozzle type. The surface condensation risk on the diffusers is also discussed using the CFD results and a simple condensation model. An innovative proposal to prevent surface condensation and cold air dumping when using multicone circular diffusers with cold air is presented.

Displacement ventilation may provide better indoor air quality than mixing ventilation. Proper design of displacement ventilation requires information concerning the air temperature difference between the head and foot level of a sedentary person and the ventilation effectiveness at the breathing level. This paper presents models to predict the air temperature difference and the ventilation effectiveness, based on a database of 56 cases with displacement ventilation. The database was generated by using a validated CFD program and covers four different types of U.S.

The use of raised access flooring systems for office environments has become much more frequent in recent years. Power and data cables housed in the floor cavity can easily be accessed and modified to accommodate changes in the occupancy and use of the space. This cavity can also be used as a supply air plenum, which allows introduction of conditioned air through the floor.

This paper presents a set of detailed experimental data of room airflow with displacement ventilation. These data were obtained from a new environmental test facility. The measurements were conducted for three typical room configurations: a small office, a large office with partitions, and a classroom. The distributions of air velocity, air velocity fluctuation, and air temperature were measured by omnidirectional hotsphere anemometers, and contaminant concentrations were measured by tracer gas at 54 points in the rooms. Smoke was used to observe airflow.

This paper describes a methodology for simulating the transport of smoke and hot gases in buildings. The approach is based on the use of efficient CFD techniques and high performance computers to solve a form of the Navier-Stokes equations specialized to the smoke movement problem. The fire is prescribed in a manner consistent with a mixture fraction based approach to combustion, but the combustion phenomena themselves are not simulated. The mixing and transport of smoke and hot gases are calculated directly from an approximate form of the Navier-Stokes equations.

NFPA Standard 92B presents computational methods for determining the position of a smoke layer in a large-volume space. Although NFPA 92B is a guide to smoke management design, the methods have been adopted, with certain modifications, by model building codes and are mandated for use in atriums and large-volume spaces. This paper makes use of a recently developed CFD fire model to assess the NFPA 92B calculation methods. A total of 13 simulated tests were conducted.