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.
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.
Previous work by Linden, Lane-Serff and Smeed (1990) has developed a simple mathematical model for natural displacement ventilation of an enclosure. The work also introduced the experimental salt-bath technique, which uses salt solutions and fresh water to generate buoyancy forces that are analogous to those found in naturally ventilated buildings. The work claims that a good correlation exists between the predictions of the simple mathematical model and the results obtained using the salt-bath technique.
This paper evaluates the performance of traditional displacement ventilation systems for small offices, large offices with partitions, classrooms, and industrial workshops under U.S. thermal and flow boundary conditions, such as a high cooling load. With proper design, displacement ventilation can maintain a thermally comfortable environment that has a low air velocity, a small temperature difference between the head and foot level, and a low percentage of dissatisfied people.
Measured contaminant and heat removal effectiveness data are presented and compared for a 3: 1 scale model room, which represents a smoking room, lounge, or bar with a two dimensional airflow pattern. In the experiments, heat and tracer gases were introduced simultaneously from a source to simulate a prototype smoking room. High-side-wall and displacement ventilation schemes were investigated, and the latter employed two different types of ceiling diffuser, low velocity slot and low-velocity grille.
At present, Computational-Fluid-Dynamics (CFO) with the 'standard' k-e model is a popular method for numerical simulation of room airflow. The k-e model needs a lot of computing time and large a computer. This paper proposes a new zero-equation model to simulate three dimensional distributions of air velocity, temperature, and contaminant concentrations in rooms. The method assumes turbulent viscosity to be a function of length-scale and local mean velocity.
Contaminant dispersion and potential draft risk in a workshop with displacement venti.la tion were investigated with computational fluid dynamics (CFD) techniques. Three factors were considered: the location of the worker, the temperature of the supply air and the supply air flow rate. The capacity of CFD is demonstrated in optimizing the operation of a ventilation system by weighting two significant aspects, i.e., the indoor air quality and the worker's thermal sensation.
The concept of air exchange efficiency of ventilation, a quantity entirely determined by the spatial distribution of the local mean age of air, is discussed. A divergence-type conservation equation for the local mean age of air is derived. This equation is solved numerically for a room ventilated by the desk displacement ventilation concept, using a CFO-routine. The CFO-calculated mean-age-of-air pattern is compared with mean age results from tracer experiments in a corresponding laboratory configuration.
Login