Development of Optimal Design of Solar Water Heating System by Using Evolutionary Algorithm

There are growing initiatives to promote renewable energy in Hong Kong, particularly for solar energy. In order to encourage wider application of centralized solar water heating system for high-rise residential buildings, it is important to pursue an optimal design to get significant energy saving potential. In this regard, system optimization would be useful, as it can relate to a number of design variables of the solar water heating system such as the tilt angle and surface azimuth of the solar collectors, the storage capacity of the hot water calorifier, and the flow rate of the circulation pump set for the solar collectors. The objective function is to maximize the year-round energy saving by using the solar heating instead of conventional domestic electric heating. For the methodology of optimization, evolutionary programming, one of the paradigms of evolutionary algorithm, was applied. This has been proven to be effective for optimization problems with a non-linear and multi-dimensional nature. To generate values for the objective function, a TRNSYS plant simulation model was developed and coupled with the optimization algorithm. From the optimization results, it is suggested that the solar collectors can be installed onto the external shading devices as an integrated architectural feature, since the optimal tilt angle is 21° and relatively flat. The optimal surface azimuth is southwest 16° instead of due south. For the engineering design, both the optimal values of calorifier storage capacity and pump flow rate show that the calculations from normal design practice may not achieve an optimal performance. Therefore, an effective methodology of optimization and simulation is essential to generate an optimal design in a holistic approach.