| Compared with the traditional mixing ventilation, displacement ventilation, a new concept in air-conditioning system, has showed several remarkable advantages: it improves indoor air quality, consumes less energy, and has better economical efficiency. Over 30 years' study and application has proved that it is a very good ventilation method.However, in China, the research of displacement ventilation system has just been carried out. There are a lot of problems are waiting to be solved before its extensive application. For such a purpose, the present work is conducted in the following aspects:(1) Study on the method of numerical simulation of displacement ventilation. Generally, the simulation of displacement system needs the knowledge of basic theory of fluid flow and main principles of such a system. It is not easy for ordinary designers. In order to help them to compute and design a displacement ventilation system correctly and effectively, the author developed a method based on his numerical simulation experience and recent external research results. A detail example was given to show designers how to perform the simulation and analyze the simulation result.(2) Study on the effect of humidity in displacement ventilation system. The weather in east China, hot and humid, is quite different from that in Scandinavia region. Since the indoor environment is closely related to the outdoor natural condition, many conclusions on displacement ventilation drawn in other countries may not be suitable for applications in China. Therefore, it is necessary to study further effect of the existence of water vapor on displacement ventilation and to analyze humidity control problems. The study of the indoor moisture distribution was done in this paper through a numerical simulation of a representative office. The result showed that the stratification phenomenon also exists for the moisture. Similar to heat pollutant, we consider only the humidity desire in working zone. This brings further possibility for energy saving in air-conditioning system.(3) Influence of supply air conditions on displacement ventilation. The study has showed that the adjacent zone of supply units strongly influences indoor thermal comfort. To satisfy the indoor human comfort, it is necessary to control the location and the dimension of the adjacent zone. Inthis paper, we have discussed the influences of supply air temperature, supply air quantity, supply air turbulence, as well as mixing ratio of supply unit. All of above parameters are important for the extension of the adjacent zone. Consideration of all the parameters is essential for a good system design which can ensure the advantage of displacement ventilation.(4) CFD Simulations of contaminant distribution in displacement ventilation. According to the conditions of our outdoor air which is more heavily polluted than that of European countries, we have investigated the contaminant distributions in an office equipped with displacement ventilation system under two different air supply conditions. The result showed that the contamination situation in the lower zone of the office, i.e. the zone of occupants, was affected by of that of supply air. The supply air contamination should be kept to a low level in order to provide a good indoor air quality. However, the variation of the supply pollutant concentration has no influence on the indoor contaminant distribution of such system.(5) Study on the practical design of comfortable displacement ventilation system. The application of displacement ventilation just arises in China. Till now, designers have not completely accepted it and are not ready to design it because of the lack of handbook or guideline of displacement ventilation system design. On the basis of the related results abroad as well as our local condition, we have developed and given in details a method and its procedures of displacement ventilation system design in commercial and high-rise buildings, which are suitable for our country. It can be served as the refe... |
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