Validations of a double U-tube borehole model and a seasonal solar thermal energy storage system model

Abstract

In order to predict the performance of seasonal thermal energy storage systems reliably, a validated simulation model is required. In this article, an experimental investigation of a seasonal solar thermal energy storage system was used for the validation of the simulation model. Details of the system components, validation procedures, operating modes and schedules, data acquisition system, and measuring instruments are described. Three TRNSYS project files are developed for validations of the double U-tube borehole model, and different modes of operation. The operational and performance data, as well as relevant weather data, are collected. Mean bias error, root mean square error and correlation coefficient (CC) are used to quantify the agreement between each simulated and measured temperature of interest. The CCs for the double U-tube borehole outlet temperatures are 0.99 and 0.91 for solar heat charging and space heating modes, respectively. The CCs for the outlet temperatures of the solar collector and buffer tank are 0.91 and 0.88 in the solar heat charging mode, respectively. The CCs for the leaving water temperature, leaving air temperature, and room temperature are 0.95, 0.97 and 0.83 in space heating mode, respectively. The simulated absolute temperatures are found to be within ±4% of those measured.