Areas of application and limitations of fabric air distribution systems

Status:

completed 07/2012

Aims:

In the area of comfort ventilation (for example in laboratories, conference rooms, supervisors' offices in factory shops) and also to some degree in the area of industrial ventilation, air distribution systems involving fabric air hoses are employed. These fabric air hoses are generally fitted to the ceiling. Essentially, they have the function of distributing fresh air cost-effectively in rooms from which air is evacuated. Little is known of the climatic factors (air velocity, temperature, efficacy of the ventilation, local air-exchange rate) in rooms employing ventilation systems of this type. The manufacturers of these systems publish only basic design ratings.
Consultancy activity has revealed frequent complaints of draughts in rooms in which fabric air hoses are used for the supply of fresh air.

Activities/Methods:

Computational fluid dynamics (CFD) simulations were used to study the thermal conditions and the flow situations arising through the use of fabric air distribution systems. Studies were performed for a range of room geometries and room functions in five applications (laboratory, office, open-plan office, waiting room and production shop). Several load scenarios were simulated for each of the applications. For each scenario, the temperature profiles, air velocity profiles and profiles of the local air exchange rates were calculated in a number of planes. In addition, the PPD and PMV values were calculated as profiles in several planes for the purpose of climatic assessment in accordance with EN ISO 7730.
The PMV (predicted mean vote) value serves as an index of the perceived comfort which predicts the average value for a given climate.
The PPD (predicted percentage of dissatisfied) value is an index representing a quantitative prediction of the percentage of persons dissatisfied with a certain ambient climate owing to their finding it too cold or too hot.

Results:

Based upon the results of the simulations, load limits can be stated for the various scenarios above which fabric diffusers can no longer be used without an adverse effect upon comfort. At the same time, critical areas can now be identified which can be examined by measurement on a case-by-case basis.

Two studies are planned for the laboratory area for verification of the results of the simulations. The measurements to be performed are currently being formulated.

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