Development of a Loss Method for Energy and Exergy Audit of Condensing Hot Water Boilers

Condensing boilers are used in commercial and residential buildings extensively. In this article, a loss method is proposed to estimate the energy and exergy efficiencies of condensing hot water boilers. The presented method is based on the development of the method presented in ASME PTC 4.1. Energy loss terms consist of exhaust flue gas, carbon monoxide formation, radiation, and condensate outflow sensible heat. Exergy loss terms also include radiation losses, physical exergy of the exhaust flue gas, chemical exergy of the exhaust flue gas, increase in the chemical exergy of the flue gas due to carbon monoxide formation, condensate outflow exergy, boiler exergy destruction, and economizer exergy destruction. Energy and exergy efficiencies are calculated by estimation of these loss terms. To depict the method’s capability and compare results with the direct method, an experimental setup was designed and constructed. Results of energy and exergy audition of the boiler by applying the loss method are compared with the direct method. The results show that, although the condensing economizer improves energy efficiency, it does not improve the exergy efficiency significantly. The energy and exergy efficiencies were 98.65% and 5.14%, respectively.