Development of a tool to predict the transient behaviour of a combination boiler

In this master thesis a study is performed to investigate the possibility of the creation of a tool to predict the transient behaviour of the combination boiler.

An experimental study is performed to find a heat transfer correlation for one of the heat exchangers from the combination boiler. Two empirical relations were found, one for operating at conditions for central heating. the second for operating at conditions for domestic hot water demand. With these relations and some commonly used empirical relations for heat transfer, the transient behaviour of the combination boiler could be evaluated. This is done by using energy balances for the primary and secondary heat exchanger. To be able to evaluate the transient heat performances of the whole boiler, the delay that is caused by the pipes connecting the two heat exchangers, is implemented as well.

The tool will be used primarily to evaluate the heating up performance for different combination boiler configurations in domestic hot water mode. When operating in this situation, the temperature of the flue gas will normally be higher than the dew point of the water vapour inside the flue gas. For this reason, condensation is not included in the model. When it is desired to evaluate the performance of the boiler appliance for low central heating temperatures it is recommended to do further research on condensation and a way to implement it in the model.

The key conclusion of this project is that it is possible to generate a transient heat transfer model, which can quickly deliver reliable performance data using global dimensions available from 3D CAD software. The key benefit of this is that it is applicable to a large range of heat exchanger designs and is readily usable for CAD software engineers.