Research On Operating Characteristics Of Condensing Gas Wall-hung Boiler In Hot Summer And Cold Winter Area

Energy conservation is one of the effective measures to enhance the current socio-economic capacity for sustainable development. Not only does it relieve the pressure on global energy shortage, but also it reduces the pollution on the surrounding ecological environment. So using the efficient products, adjusting the energy consumption structure, and promoting the use of clean energy have a great significance to the conservation of resources and the environment improvement. The condensing boiler has been a trend of the current heating source because of it has advantages of high efficiency, energy saving and environmental protection. It uses the natural gas which is a clean energy as its gas supply, and uses the way of fully premixed combustion to reduce the emission of pollutants effectively and reducing pollution of the surrounding environment. By recycling the sensible heat of flue gas and the latent heat of water vapo to greatly improve the thermal efficiency of the boiler, it can finally achieve the purpose of energy saving.In this paper, through using the condensing gas boiler as the research object and the low-temperature radiant floor heating as the end, the operating characteristics are studied by experimental measurement and numerical simulation in Shanghai that is in the typical summer and cold winter areas. Firstly, it is introduced briefly that the structure and principle of condensing boiler and of the low-temperature radiant floor heating is designed. So it could be built that the experiment platform of condensing boiler-low temperature floor heating. According to the experimental measurement requirements, it’s completed that the software and hardware design of experiment data acquisition system. And the experiment data is collected like the supply and return water temperature and their flow rate, indoor temperature, outdoor temperature and humidity. Also the amount of natural gas and condensate water are recorded. During the typical heating season in Shanghai, it is calculated and analyzed that the thermal comfort of low-temperature radiant floor heating and the impact of flue gas temperature on the condensation rate and outdoor temperature and humidity on thermal efficiency. The results show that when the outdoor temperature is 8~15℃ and outdoor humidity of 30~70%RH, in the condition of the supply water temperature is 63℃, the heating room has a better thermal comfort. The condensation rate of boiler descreases gradually with the increase of flue gas temperature and eventually it falls to 4~5%. When the supply water temperature keeps constant, the outdoor humidity increases 10%RH and then thermal efficiency will increase 0.03%. So the impact of humidity on thermal efficiency is littlel. While the outdoor temperature rises, thermal efficiency increases obviously.Secondly, according to the relationship between the outdoor temperature and thermal efficiency during the experiment period, the control program is designed based on the principles of climate compensation control system program. Referring to the the relationship among the outdoor temperature, thermal efficiency and returnwater temperature and based on the relationship between return water temperature and valve opening ratio, the system will control the valve opening through the signal from PLC. So it results in the change of return water temperature and maximizes thermal efficiency.Finally, based on the condition that the condensing boiler is a little far away from windows, the numerical simulation has been done about the heat transfer process between the flue gas and air in the exhaust pipe whose length is 3m and the flue gas diffusion in the air. The heat process is analysized and compared with the experimental data and is verified the correctness of the simulation. The results of flue gas diffusion show that in the no wind condition, flue gas diffuses very far in the longitudinal direction and the concentration of the flue gas is low. When the wind velocity which is perpendicular to the pipe is above 2m/s, the concentration of the flue gas in the exit is high and even it will happen that the flue gas emission is difficult. It’s more likely happened in Shanghai whose wind velocity is 3.2m/s in winter. When the length of the outdoor section of the exhaust pipe is half of origianal, the diffusion of flue gas in the longitudinal direction is reduced by about 1/3. These conclusions will provide a theoretical basis for the optimization of the exhaust pipes in the future.