air distribution

The paper presents the results of the research on application of the equation describing the increase in the air volume flux in buoyant plume above a point heat source to calculate plumes in rooms with displacement ventilation.The tests carried out in test room have given information about practical defining of the distance from the origin, assuming entrainment coefficient values and possibilities of assuming equal widths of temperature and velocity profiles in order to determine the origin distance.

Condensation on the surfaces of diffuser and cold air dumping are the two major concerns in the application of cold air distribution brought about by the high temperature difference between supply air and room air. Condensation will form if the surface temperature of the diffuser is lower than the dew point temperature of ambient air. The presence of surface condensation can promote growth of unhealthy and smelly mold, and produce unwelcome damage of a structural and/or aesthetic nature. Cold air dumping is a major factor that detracts from thermal comfort in an airconditioned room.

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 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.

The principles of a new tracer gas technique is described in the paper. The new technique involves pulse injection of tracer gas and has the same advantages as the previously known homogeneous emission technique. It can for example advantageously be used in large buildings and buildings with many rooms and yields information on the distribution of ventilation air within the building. However, contrary to the homogeneous emission technique, yielding the average ventilation performance during an extended time, the new technique allows measurement during short term periods.

The ventilation effectiveness concept has been extensively used in research, where it has long been recognised as a good indicator of air quality. Also, there are many examples of its parameters having been measured as an aid to monitoring the air quality in completed buildings, usually to solve an air quality problem. However, despite their value as a predictor of the air quality to be achieved by an air distribution system, ventilation effectiveness parameters are rarely used in design.

This article describes a new and more efficient Vortex Air Distribution system for a soda recovery boiler house. Essentially th.e technology utilises directional air supply of up to 150 m3/s to compensate for beat gains of up to 2000 kW. Issues addressed include all stages of the design process from the Computational Fluid Dynamic (CFO) experiment and scale mock-up tests in the laboratory conditions to the field measurements after the system had been installed. The supply air is distributed into the building through specially designed air terminals.

A test room and measurement system were developed for the full-scale measurements of the active displacement air distribution. The room represents a 3-meter wide module of a larger hall. The requirements for the room included minimisation of the errors caused by air leaks, thermal conductance and flow obstacles. The measurement of the flow pattern is carried out with ultrasonic and thermal anemometers. Automated traversing system was built to move the sensors in the vertical symmetry plane of the room.

A new ventilated cooledbeam system concept with free cooling has been installed and monitored in a retrofitted office building in the Wartsila NSD Finland complex in Vaasa, Finland. Good indoor air quality and individual room temperature control has been achieved using ventilated cooled beams. Both cooling- and supplyair distribution functions were integrated in the same room unit. No extra costs were incurred for the low-energy system's freecooling loop.

An interconnection between a building energy performance simulation program and a Computational Fluid Dynamics program (CFD) for room air distribution will be introduced for improvement of the predictions of both the energy consumption and the indoor environment. The building energy performance simulation program requires a detailed description of the energy flow in the air movement which can be obtained by a CFD program.