Research On Overall Performance Of Condensing Gas Instantaneous Water Heater

On the backgrounds of the fully support of national policy and energy consumption structure’s continual optimization, our country’s natural gas industry is in a splendid stage of development, which the natural gas’ s apparent consumption has been growing at the speed of more than 10% annually and the ratio of domestic gas consumption increases by years. Gas water heater by virtue of providing people with domestic hot water safely and conveniently has come into innumerable homes and has become a sort of household electrical appliance in our daily life. Along with the ever- increasing promotion of human ideological understanding level, the condensing gas instantaneous water heater regarded as the upstart in water heater industry at the advantage of high efficiency, energy conservation and environmentally friendly is considered as the trend of future development in water heater industry and has been widely recognized by community.The paper studies the overall performance of the condensing gas instantaneous water heater based upon large numbers of water heater experiments both in winter and in summer. Concerning about the main indexes of water supply system, combustion and heat transfer system, exhaust system, the research has made qualitative and quantitative appraisement about critical factors and indexes which lots of works have been done on the heat transfer characteristics of the main heat transfer exchanger and condensing heat transfer exchanger especially. Improvements have been put forward based on analysis and summary of the water heater’s key performance parameters and its variation, which can supply certain references for the condensing gas instantaneous water heater manufacturing industry. The main research works are as follows:① The water heater heat efficiency overall performance is figured out through the research on overall heat efficiency in winter and summer. In the process of analyzing the influence of heat load, excessive air coefficient, water flow on heat efficiency, the research finds that under the circumstances of water flow is 7.93L/min and low- medium heat load, the heat efficiency is optimum. The fan’s adjustable air velocity is relatively narrow. If the adjustable air velocity area could be broadened, the overall performance of the water heater would be promoted.② By the research on hydrodynamic characteristics of water supply system, the characteristic curve of the relationship between water flow and water pressure has been acquired.③ The complex heat transfer coefficients, convection heat transfer coefficients on the flue side and the efficiencies of the main heat transfer exchanger both in winter and in summer are figured out through the heat transfer calculations on the main heat transfer exchanger. The complex heat transfer coefficie nts and convection heat transfer coefficients on the flue side have the same change trend with different factors, which increase as water flow enlarges and become steady when water flow reaches 8L/min. The complex heat transfer coefficients increase as heat load increases and decrease as excessive air coefficients increase. In winter the complex heat transfer coefficient value can reach 0.12 k W/(m2·℃), otherwise, the value only reach 0.1k W/(m2·℃) in summer. However, under the same heat load and water flow situation, the values are nearly the same both in winter and in summer.④ The overall efficiencies tend to increase as the main heat transfer exchanger efficiencies increase. The main heat transfer exchanger efficiency values are above 83.9% on all working conditions, which are relatively lower under high water flow. And the mean values in summer are higher than in winter.⑤ The condenser’s performance in winter is better than in summer. The condenser’s mean efficiency value in winter is 34% higher than that in summer on the same water flow. The condenser’s efficiencies present a state of fluctuating as water flow increases, which are lower on slower water flow rate and higher when water flow rate in the condenser reaches 0.15m/s in winter. But the condenser’s performance is promoting as water flow rate increases and in order to keep the efficiencies above 30% water pressure must exceed 0.1MPa.⑥ The overall efficiencies tend to increase as condenser’s efficiencies increase, which are in high level when condenser’s efficiency values are in 65%~75% in winter and condenser’s efficiency values are in 32%~45% in summer.⑦ After lessening 1/5 of main heat transfer exchanger’s area on water side, the main heat transfer exchanger’s efficiency values decrease by an average of 3.1% and the ratios of condenser’s heat transfer proportion increase by an average of 1% and the condenser’s mean efficiency values increase by an average of 8.2% and the overall efficiencies of the water heater are maintained above 88%.