Performance Comparison for Site-specific Heat Output Prediction of Solar Collectors Based on a Modified Collector Efficiency Equation Model

This study compares the performance of estimation methods for site-specific solar collector yield using two simplified collector efficiency equations-based models for training and testing of the model. Two different collector efficiency equations are used for comparative evaluation: One employs a first order collector efficiency equation defined in terms of collector inlet temperature, solar irradiance, and outdoor temperature, termed first-order equation model with constant Tci. The other equation model is a modified collector efficiency equation expressed with the terms of heating load, solar irradiance, and outdoor temperature, termed modified equation model with heat load input. In the approach with the first-order equation model, the collector inlet temperature term is treated as another parameter to be estimated as an effective collector inlet temperature. To evaluate the equation-based models, the Polysun simulation program is used for generating a data set of solar water heating system. For evaluation of daily solar collector yield estimation, two data sets were generated: training data set and testing data set. For evaluation of hourly solar collector yield estimation, training and testing performances were evaluated respectively. By using hourly simulated data, the hourly collector estimation performance was evaluated in terms of daily root-mean-squared error for the process of model training to compare the performance of fitness of the model for hourly estimation. The daily performance of two models showed quite similar estimation results. The comparison of the hourly performance of the two models resulted in a better performance of the modified equation model with heat load input.