Experiences from cleanroom installations has frequently shown that displacement ventilation has a much higher efficiency than mixing ventilation with respect to particle and CO2 reduction, cooling efficiency etc. Another cleanroom experience is that low particle concentration benefits asthma and allergy sufferer. Low particle concentrations reduces the impact of other pollutants and enhance the quality of life for everybody. In an office, the level of discomfort this means less tiredness, better concentration and lower absenteeism.
Airborne particle concentrations of 20 nm to 10 µm particles were studied in two similar classrooms in a school. One classroom was ventilated by mixing ventilation with supply air filtration and one by displacement ventilation without supply air filtratio
Multiple regression analysis is used to predict the mean room velocity and determine the most influencing parameters on the velocity. More than 120 experiments for four different heat source locations were carried out in a test chamber with high level mixing ventilation. The measured parameters, such as supply air momentum, room heat load, Archimedes number and local temperature ratio, were used as independent variables. These parameters are examined by two methods: a simple regression analysis incorporated into scatter matrix plots; and multiple stepwise regression analysis.
The performance of two personalized ventilation systems combined with mixing or displacement ventilation was studied under different conditions in regard to thermal comfort of seated occupants. The cooling performance of personalized ventilation was found to be independent of room air distribution. Differences between the personalized air terminal devices were identified in terms of
the cooling distribution over the manikins body. The personalized ventilation supplying air from the
This paper deals with a modeling approach that combines the classical heat and moisture balance differential equations along with the use of experimental time-series data. This approach provides an ideal form for advanced model-based control system design.
Air supply diffusers used in air-conditioning systems can be classified as ceiling diffusers, sidewall diffusers, floor diffusers, jet nozzles, and low velocity displacement diffusers. Fixed or adjustable slats are usually used to control airflow directions.
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.
Using results from dynamic simulations, the article compares the energy consumption for the air conditioning of an industrial building with mixing and displacement ventilation.
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