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displacement ventilation

Displacing air conditioning.

                   

Indoor air quality in rooms with cooled ceilings. Mixing ventilation or rather displacement ventilation?

Experimental investigations and practical experiences in Europe have proved that hydronic cooled ceilings are able to remove high cooling loads without impairing thermal comfort. As hydronic cooled ceilings cannot remove latent loads and pollutants, e.g., C02, VOCs, odors, additional ventilation has to be applied. Often, displacement ventilation is used, which is able to provide lower pollutant levels in the occupation zone than mixing flow systems, if the occupants are causing most of the pollution.

Measurement of personal exposure using a breathing thermal manikin.

When a person is located in a contaminant field with significant gradients the contaminant field will be modified locally due to the entrainment and transport of contaminated air in the human boundary layer as well as due to the effect of the person acting as an obstacle to the flow field, etc. In this paper personal exposure measurements are performed by means of the Breathing Thermal Manikin. Contaminant concentration is measured in a number of locations in the breathing zone and in the inhaled air.

Displacement ventilation forming at different air flow rates.

The paper presents the results of the tests of two-zone airflow pattern forming in a room with displacement ventilation where various heat sources and various airflow rates were tested. The position of the interface layer between the zones was determined experimentally - on the basis of tracer gas concentration measurement and on the way of calculation - on the basis of the plume model above a point heat source complemented with experiment. The following heat sources were used: a plume simulator, a desk lamp, a computer, a round plate and a human body.

Performance evaluation of a displacement ventilation system for improving indoor air quality: a numerical study.

To evaluate the performance of a ventilation system, the local mean age of air has usually been used to estimate how efficiently fresh air is diffused to a desired location. However, this index alone is often not sufficient to assess the local air quality that is also associated with the property of the contaminant source in a ventilated space. Several new indices have been proposed recently, which enable the use of numerical simulation and appear to be appropriate scales for assessing mixing ventilation systems.

The effectiveness of displacement ventilation.

The effectiveness of ventilation related to the two primary tasks of ventilation, (I) the supply of fresh air, and (ii) removal of contaminants, is investigated. To allow a quantitative description of ventilation performance, several effectiveness numbers are discussed, and their dependence on air flow characteristics is explained. The effectiveness of displacement ventilation regarding renewal of the internal air population is analysed both experimentally and by means of Computation Fluid Dynamics simulations.

A comparison study of the effectiveness of three ventilation systems in purging pollutant using CFD.

A three-dimensional mathematical model to solve the mixing, displacement and vortex ventilation systems in the removal of pollutants with a thermal source is described. The study carried out to investigate the effectiveness of each of the individual ventilation systems showed that the vortex ventilation system performed better than the other two systems in providing moderate occupancy thermal comfort but very effective in purging pollutants away from a typical office room environment

Field study on the ventilation effectiveness and thermal comfort in a concert hall with displacement ventilation system.

The purpose of this study is to identify the ventilation effectiveness of a displacement ventilation system in a concert hall with 501 seats, where a large amount of outside air is required for ventilation. Displacement ventilation was considered appropriate to reduce the amount of outside air. Light bulbs were placed on all the seats to simulate the heat source from the audience. From the measured concentrations, the local mean age of air at the breathing point with the displacement ventilation system was found around one third of that of the fully mixed condition.

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