tracer gas

Diffuse ceiling ventilation is a novel air distribution device that combines the suspended acoustic ceiling with ventilation supply. A diffuse ceiling distributes the supply air above the acoustic tiles and has proven performance in laboratory experiments. To study the performance in real conditions a classroom was retrofitted with mechanical ventilation and a diffuse ceiling. The employed ceiling comprises active panels penetrable to air and impenetrable passive panels.

Tracer gas measurements are an unparalleled means of measuring air recirculation, leakage, and air flow rates in air handling systems [1-5]. However, such measurements are subject to significant measurement uncertainty in field conditions. A common problem is imperfect mixing of tracer gas.

As a part of the development of a numerical method of close capture exhaust systems for machining devices, a test rig recreating a situation similar to a grinding operation, but in a perfectly controlled environment, was produced. The properties of the obtained spray of solid particles were initially characterized using particle tracking velocimetry (PTV), in order to obtain input and validation parameters for numerical simulations. The dispersion of a tracer gas (SF6), emitted simultaneously with the particle jet, was then studied experimentally.

Open fronted ventilated enclosures are commonly used in industry to control worker exposure to a wide range of chemicals. These enclosures tend to be of basic design and often consist of nothing more than a box like structure with an open front to allow worker access and extraction at the rear to remove contaminated air. This design forces the worker to stand at the face of the enclosure and by doing so presents a blockage to the airflow.

In this work the evaluation of indoor air quality in a classroom equipped with cross-flow ventilation is presented. A numerical methodology, based on comparison with experimental data, used in the evaluation of the air exchange rate, airflow rate and the age of the air, was applied in the first phase of this work. The evolution of carbon dioxide inside spaces, with different airflow typologies, was then predicted in the second part. The study was based on a school located in the South of Portugal. In the experimental methodology the tracer gas decay method was applied.

The approval of the Technical Building Code has meant major changes in the construction of multi-storey buildings in Spain. One of the most important revisions, with respect to the buildings erected prior to the Technical Building Code, has been the obligation to ventilate each one of its rooms. Depending on the use and occupancy a minimum flow rate of ventilation is required in each room.

For residential forced air heating and cooling systems conventional thinking is that air supply registers should be located under exterior windows. There were good reasons for this in the past (primarily to counteract the cold downdraught from the window) but new construction standards (well-insulated walls, better glazing and air tight wall/window interface) mean that there is now less downdraught. Positioning the supply air register away from a window could have a large impact for new construction as duct lengths could be shortened (saving materials and construction time).

An experimental study of the phenomenon of buoyancy driven natural ventilation through single-sided horizontal openings was performed in a full-scale laboratory test rig. The measurements were made for opening ratios L/D ranging from 0.027 to 4.455, where L and D are the length of the opening and the diameter of the opening, respectively. The basic nature of airflow through single-sided openings, including airflow rate, air velocity, temperature difference between the rooms and the dimensions of the horizontal openings, were measured.

High local concentrations of a pollutant can be the result of high local emission rates of the pollutant orinsufficient ventilation. Using tracer gases to map the ventilation in multi-zone buildings combined withmeasurements of the local pollutant concentration provide the means to discriminate between thesecauses.

The development of a new device for the injection of tracer gas is discussed with the objective of practical application in the field of HVAC airflow measurements. The uniform tracer gas dispersion for very short distances, when measuring airflow by the constant emission method is of great interest. This new injection device has a compact tubular shape, with magnetic fixation to be easy to apply to duct walls. After a preliminary study with an initial prototype already tested, further detailed experiments had been carried out, culminating in a second prototype.