The Feasibility Research On Passive Hybrid Downdraught Cooling For Public Buildings

Air quality problems in University classrooms and lecture halls are persistent due to the density of personnel, poor ventilation which lead to uncomfortable indoor thermal environment. In recent years, with the universalization of the multimedia teaching, classroom indoor thermal environment is deteriorating further. Central air-conditioning is the main equipment of cooling and ventilating closed public buildings in the middle and lower reaches of the Yangtze River. Since costs of investment and running of central air conditioning are high, lack of funds, shortage of conventional energy sources, the number of students in teaching classes is uncertain, and extreme season is holiday. It is unrealistic to use the central air-conditioning in a teaching building. The principle of Passive and Hybrid Downdraught Cooling system relies on the thermal buoyancy, the density of cooled air is higher than the inside air, which leads the heavy cooler air downdraught to cool the indoor space. By means of tube wells, double wall, patio, courts, the hot air rise and exit to outside without fans and piping. The PHDC system is completely different from the conventional air conditioning system in that it integrates cooling system with the building space. Without impact by building mass, building depth and openings in the wall, PHDC makes up the limitations of natural ventilation in deep-plan or enclosed buildings. Because of the reduction in equipment investment and lower energy consumption in operation, harmful gas emissions are greatly reduced, urban heat island is mitigated. Air conditioning piping is the medium of various diseases delivery, without using pipes, the PDC system can reduce the spread of the disease, and help create a healthy indoor environment. The advantage of PHDC is low power and environmental friendly. This dissertation will explore the application feasibility of this novel ventilation and cooling technology in university teaching building in the middle and lower reaches of the Yangtze River, take Wuhan city as an example.This dissertation discusses from five aspects as follow: (1) The classification and adaptability analysis of passive ventilation and cooling. Firstly, a brief introduction on the function and pattern of ventilation was introduced, the types of passive cooling techniques were summarized. After sorting out the types of passive cooling ventilation techniques, it was found that with the development of modern society, public buildings stepped into complex and large-scale. Application and research on natural ventilation in these buildings were changed from direct and single methods to indirect and multiple methods, from uncontrolled to organized way, from simple to systematize. This dissertation has put forward four cooling and ventilation types. According to case study, different types of ventilation and cooling technology were discussed and analyzed. It pointed out the disadvantage of direct natural ventilation, and suggested that indirectly and controlled ventilation and cooling is possible to solve the problems in the deep-plan, enclosed public buildings.(2) Theory of passive downdraught cooling. PDC is originated in ancient Egypt, which was got the attention in Europe in recent years. The origin of PDC technique, current research situation, the application of advantages and problems were literature reviewed and summaried. Combined with the latest research achievements in the field of air conditioning, PHDC technique which is fit in different climatic zones in our country is put forward.(3) Determination of indoor and outdoor design parameters. The indoor and outdoor parameters are only in HVAC standard, not for passive cooling buildings. After The collation and comparison of indoor thermal comfort studies in domestic and foreign passive cooling and natural ventilation buildings, design parameters based on PHDC in Wuhan is presented. A case study of a monolayer lecture hall in University in Wuhan is studied by calculations and simulations to demonstrate the feasibility of the design parameters.(4) Potential study of energy saving. After analyzing Wuhan typical year meteorological data, it revealed that potential of energy efficiency in public buildings with PHDC system is quite significant. Because the transitional season will be extended by the application of this technology, and cooling season is shortened from the usual four months to about one month in enclosed public buildings. There will be no cooling needs for university teaching buildings due to summer holiday during extreme temperature. Therefore, PHDC can not only solves the problems of ventilation and cooling for the entire school year, but also can greatly enhance the classroom indoor air quality.(5) Theoretical calculations and simulations of the typical teaching buildings based on PHDC. Type of space based on PHDC is presented after survey on spatial scales and combinations of University teaching buildings. Three typical types of teaching space are presented as examples. According to the most unfavorable outdoor parameters during Wuhan transition seasons, theoretical calculations and simulations are used to further verify the feasibility of PHDC system in different types of teaching space. According to case study, the relationships between ventilation types and architectural space, the floors are confirmed, and some relevant notes are clarified through the outlet size calculation.PHDC is a new aspect in passive cooling field in the future. The system is seldom used in our country. With the energy conservation and architecture sustainable development, study on this technology as an alternative to conventional air conditioning has a very important practical significance. The conclusions of this study are not only applicable in teaching buildings, but also provide design references and creat new idea for architects in building types such as conference rooms, theaters cinemeas, and some other enclosed public buildings.