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displacement ventilation

Displacement ventilation environments with chilled ceilings: thermal comfort design within the context of the BS EN ISO7730 versus adaptive debate

The current design standard BS EN ISO 7730 is based upon the work of Fanger dated 1995, dealing with a steady-state human heat balance model that leads to a prediction of the sensation of human thermal comfort for a given set of thermal conditions. That model was then developed for "conventional" environments. But is the current standard still applicable to more sophisticated environments such as offices with chilled ceiling, in combination with displacement ventilation ? This paper presents findings from a study that sought to answer that question.

Measurements of air temperatures close to a low-velocity diffuser in displacement ventilation using an infrared camera

The authors have developed a whole-field measuring technique that allows the visualization of air temperatures and airflow patterns over a large cross-section. For that measurement, an infrared camera and a measuring screen placed in the airflow are used. Thanks to that technique, real-time images within large areas can be recorded and transient events can be captured. The method was applied to a flow from a low-velocity diffuser in displacement ventilation.

Validation of a CFD model for temperature and particulate concentration in a test room with mixed air and displacement ventilation

This study aims to validate a CFD model (Flovent) for calculation of temperature and particulate concentration in a ventilated room. Measurements were operated in a test room with a heat source and a cigarette source. Good agreement was found with the model for temperatures with a mixed ventilation system in the room as well as with a displacement ventilation system. For particulate concentrations, the model was validated for mixed ventilation and 'borderline validated' with displacement ventilation.

Displacement ventilation : smart way to deal with increased heat gains in the telecommunication equipment room

This paper gives information about the design of displacement ventilation systems for telecommunication equipment rooms, which need an increasing cooling load because of higher density and new generations of telecommunication systems.

CFD investigation into gaseous impurities in a workshop with displacement ventilation

A validated CFD model was used to generate concentration distribution data for CO2, radon and moisture in a Hong Kong workshop with displacement ventilation.Contaminant concentration distribution depends on the contaminant source type and location. A low concentration may be obtained in the occupied zone when the contaminant source is associated to a heat source whose thermal plume is sufficiently strong to reach the upper zone.

Whole field mapping of temperature pattern in the near zone of an elevated displacement diffuser

This paper deals with the effect of discharging the air from a diffuser elevated above the floor. The temperatures have been measured and the airflow patterns visualised close to a diffuser for displacement ventilation, results from the whole-field method (using infrared thermography) were images of different colours representing different temperatures of the air close to the diffuser.. The aim of the measurements was to see how the elevations of the diffuser above floor level and the thermal jet length of the supply could affect the near zone.

Quantification of the benefits of displacement ventilation in airborne disease control

A poor ventilation in buildings costs considerable amounts of money for hospitals and businesses.10 % of hospital acquired infections are directly due to an airborne route. The quantity and the quality of air supplied is important but also the way it is introduced into spaces. A change of the Wells Riley equation (establishing a link between the likelihood of infection, the infective agent production rate, the exposure time, the pulmonary and room ventilation rate) is proposed to take into account ventilation eefectiveness.

Performance of displacement ventilation in practice

This paper gives the results of a field study in Danish office spaces with displacement ventilation systems. Draught was identified as a serious problem. Half of the 227 occupants were not satisfied with indoor air quality. Occupants counteract draught discomfort in blocking air supply diffusers or asking the maintenance staff to increase the supply air temperature. So a very careful design for displacement ventilation is required in order to perform satisfactorily in practice.

Field survey of occupants thermal comfort in rooms with displacement ventilation

Thermal comfort for 227 occupants in 8 office buildings with displacement ventilation was investigated. The occupants' thermal sensation was close to the predictions by the PMV index. The main conclusion is that draught is the major local discomfort factor for the occupants, mainly at lower leg. The effect of vertical temperature gradients on occupants local discomfort did not appear as evident.

Particle filtration in a ventilated room

Several studies based on analytical models and numerical simulations have shown that it is difficult to control airborne particle movements in a ventilated room. However, more knowledge and information on particle characteristics and particle movements, in combination with new numerical simulation tools, have recently made it easier to estimate particle patterns. In the present paper new information is used to evaluate the role of filtration and ventilation in the particle elimination process.