This article defines a new air-exchange efficiency that takes into account the occupancy in each zone.. Cases studies are then described and show that the new efficiency can better evaluate the ventilation effect of the room.
The efficiency of an air diffusion system consists of two factors. The first is the ability of the system to remove heat and contaminants out of the ventilated room. This is most often characterized using temperature removal and contaminant removal efficiency. The second, seldom considered, factor is the uniformity of the temperature and contaminant distribution within the ventilated space. This factor describes how much the maximum contaminant concentration or minimum temperature differs from the average value.
The contaminant removal efficiency and the uniformity of contaminant concentration in the occupied zone of a room were studied in scale model with the following varying parameters : occupied zone obstruction level, air distribution system, air change rate, cooling load, contaminant sources distribution.
Results show that obstruction level, air distribution system, air change rate and cooling load have a small influence on contaminant removal efficiency and uniformity of contaminant concentration.
There is a variety of different methods consulting engineers use to design room system, room air diffusion, such as assumption of perfect mixing, design methods employing the empirical relations determined through research, air jet theory and computational fluid dynamics (CFD) codes. The most common design methods based on air jet theory allows only for the prediction of extreme values of air velocities and air temperatures in the occupied zone.
This research evaluated the effectiveness of local supply ventilation in controlling air quality at or near workers’ breathing zones in livestock confinement buildings. Commercially available ceiling (box-type) diffusers and local supply ventilation syste
Seven air supply and return diffusion layouts were tested to determine their effects on air distribution, air change efficiency and ventilation efficiency for workstations in an open-plan office. This document describes and comments the results of these measurements.
This work, along with the experimental measurements on which it is based, was carried out in the framework of research undertaken by the French “Groupe de Pilotage sur la Qualité des Ambiances” (GPQA), whose task was to initiate and co-ordinate work on ai
In this paper, the normal ventilation system and the concept of all fresh air conditioning and ventilating system are presented. The 2 systems are then compared, with the use of a non-isothermal k-e turbulence model.Results show the wind velocity distribution , the temperature distribution and the Scale for Ventilation Efficiency distribution for each case.Their conclusion is that with the all-fresh air ventilation system, there is a high ventilation efficiency around the occupant zone.
The objective of this paper was to illustrate the potential of the CFD technique to compare the effectiveness of different general ventilation systems in reducing the workers' exposure to styrene vapour in a workroom. . Thanks to the CFD technique predicted airflow velocities and styrene distribution are shown for the 3 different ventilation arrangements at identical planes across the room. And predicted values of styrene concentration at workers'position are given.
The second part of the paper deals with the measurements of the indoor thermal environment and the ventilation performance of a commercial kitchen.Measurements were made with a tracer gas (SF6) which is non-toxic and odorless.A smoke machine (ROSCO) was placed on the floor of the middle of the kitchen while operating the ventilated ceiling system. Air inlets near the floor or at the lower parts of the walls brought fresh air in the lower part of the kitchen and pushed the smoke upward.The results almost agreed with the results of the previous numerical simulation ( in part 1).
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