A "HESCO"-type diffuser was selected as an example for the validation exercise in the IEA Annex 20 project (Air flow pattern within buildings). It consists of 84 small round nozzles that are arranged in four rows in an area of 0.71 m x 0.17 m. With the same effective area, the diffuser is simulated by 1, 12, and 84 simple rectangular slots and by the momentum method. In the momentum method, the supply air momentum is set to be that of the 84 small round nozzles. The simulation of the diffuser is incorporated in the airflow computation in a room.
Is it possible to translate a computed flow field to a design case with different physical dimension? - This and related questions must be answered when the results of the "air flow pattern atlasM, as proposed in the IEA Annex 20, should be applied to actual ventilation systems. Looking up a case in the atlas and transforming results to an actual application is like interpolating in a table. If geometries are similar, scaling laws may be applied. The interpolation problem also arises when numerical or experimental data from literature must be translated to a case at hand.
Knowledge of air movement within a building is often a condition for solving problems with the spread of pollution. The internal airflow paterns are mostly very complex and a survey of the airflow normally demands that measurements are carried out. Measuring equipment for defining air movement within buildings almost always uses the tracer gas technique. We have used two tracer gases and have kept a constant concentration of these in the polluted and the clean zones respectively. Thus enabling us to get a time history of the airflow between the two zanes.
Conventionally used thermal anemometers are able to measure velocity, but cannot determine direction. In the present study, a new kind of thermal anemometer is presented which consists of a 38mm-diameter sphere with 12 NTC resistances on its surface. Each of them is a single Constant Temperature Anemometer which takes measurements of the local heat transfer on the surface depending on the position on the ball.
A conference room has been converted to temperature- and carbon dioxide controlled ventilation. A number of tests have been conducted with the system in different load conditions. The variables that have been measured are air flow rate, temperature and carbon dioxide concentration. The activity in the room during the measurements has also been well recorded. The main purpose has been to evaluate the ability of a demand controlled ventilation system to maintain a good indoor air quality.
Tracer gas tests were conducted on a five-storey apartment building to determine the air and contaminant flow patterns within the building. The test method involves the injection of a small amount of tracer gas, SF6, into a selected location to create a single source and monitoring the tracer gas concentrations at locations throughout the building. Based on the rates at which the tracer gas concentrations change at various locations, the air and contaminant flow patterns within the building can be determined. Several such tests were conducted.
A new handbook, describing in details the measurement techniques which could be used to better understand the infiltration and ventilation in buildings is presented. This handbook results from the cooperation between Annex 20 and Annex 5 of the IEA ECB program. It presents the techniques for detecting and measuring as well the air leakages as the air flows in buildings and inventilation systems. Methods related to ventilation efficiency and effectiveness, like the measurement of the age of air, are also described.
The International Energy Agency (IEA) task-sharing project "Air Flow Patterns within Buildings" was initiated in May 1988 for a duration of 3,5 years. Twelve nations contribute work and expertise and "share the task" specified in the project's objectives. This project and the AIVC belong to the same Implementing Agreement: The Energy Conservation in Buildings and Community Systems Program. As "Attachments" to the Implementing Agreement, they are called Annexes.
The subtask 2 of Annex XX (Optimization of Air Flow Patterns Within Buildings) involved a research project called "Air Flows Through Large Openings In Buildings". The scope of this project was to test the range of validity of available algorithms, and where possible to develop new ones. This paper focuses on the new interzonal airflow studies which have been carried out in this frame.
Air is the main transport medium for contaminants in buildings. Minimizing source strengths has first priority, second is to control air flow rates, supply and exhaust, and directions between zones in buildings. Computer simulation models forventilation and pollutant spread in buildings have been proven to give useful predictions. Large measurement campaigns for optimizing ventilation and pollutant problems are complex and expensive. They are often jammed by too many vague parameters influencing the result. The computer models are an alternative and form a supplement to measurements.
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