The effect of ambient temperature on dynamic energy–exergy analysis of a d-type boiler during cold start-up

The ambient temperature is one of the factors affecting the operation and the fuel consumption rate in boilers. In this article, a D-type boiler was transiently analyzed from the aspects of energy and exergy during the cold start-up at different ambient temperatures. For this purpose, dynamic modeling of the boiler has been demonstrated by using thermodynamic and heat transfer governing equations. The numerical model compared with experimental data indicates high modeling accuracy. The results show that as the ambient temperature increases, the fuel consumption rate declines and the boiler efficiency rises by about 1%; this is due to the higher temperature of the inlet water as well as fuel flow rate reduction. Also, as the temperature increases from 2 to 32 °C, the fuel flow rate decreases by 10%; this analysis reveals that the existing boiler performance can be improved by preheating the inlet air. Exergy efficiency increases with the elevation of ambient temperature during the start-up. The exergy efficiency of the boiler at a temperature of 32 °C reaches 42% at its maximum value and 38.2% in a steady state, while the energy efficiency is 72% in this condition.