Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.
Natural gas combi boilers are one of the most common branches of the household goods used for space and domestic hot water (DHW) heating. Although most of the combi boilers in the market have reached considerably high space heating efficiency values via condensing technology, there is still a huge demand on increasing their DHW comfort level and efficiency. Broad definition of the comfort level in the combi boilers is the expectation of an end-user to have hot water in a very short time and without fluctuations. DHW expectancy differs from market to market, therefore resulting in wide product diversity and a challenging competition between the manufacturers. The present study has mainly focused on the investigation of one of the parameters which are particularly effective on the DHW comfort level. As the first step, 1D mathematical model is constructed for DHW function with the transient energy equations of the concerning components. The differential energy equations of the model are discretized implicitly with Finite Difference Scheme in order to solve them numerically in Matlab. Boundary and initial conditions are defined as closely as possible to the exact working conditions. Thermodynamic properties of the flue gas mixture and water are obtained via open source software Cantera . Then, the numerical results are compared with the experimental data to validate the model. After obtaining a model for basic applications and rough results to estimate the behavior of an appliance, one of the software parameters affecting the comfort level of the end-users, late ignition time is investigated numerically.