MAXIMUM THERMAL EFFICIENCY OF CONDENSING BOILER

Since 1970s, kinds of condensing boilers (CB) have been widely applied in HVAC engineering, theirexit flue gas temperature is very lower, even down to about 40?-45?, and their thermal efficiency isvery higher, even up to about 107%~109%, based on low heat value. The application of CBs in HVACsystem or hot water supply system can increase thermal efficiency and reduce the consumption of fuel,because of the utilization of latent heat of vapour in the exit flue gas. Generally, the higher the contentof vapour in the exit flue gas and the lower the temperature of return or make-up water, then the lowerthe exit flue gas temperature of CB and the higher the thermal efficiency of CBs. And then what is themaximum value of thermal efficiency of CBs theoretically? In this paper, from the thermal equilibriumand the definition of thermal efficiency based on low heat value, the maximum value of thermalefficiency of condensing boilers that burn different typical fuels have been educed, which arerespectively as follows: 107.1%( 0 # diesel oil), 110.4%( natural gas), 105.2%( bituminous coal) etc,which are useful to both the design of condensing boilers in heating system and the design of HVACengineering.