A Practical Software for Hourly Energy Efficiency Simulation of U-Tube Ground Source Heat Pump Systems

Abstract

AbstractU-tube ground source heat pump systems (GSHPs) are widely used in China and other countries for building energy efficiency consideration. Because of the transient heat transfer in the ground heat exchangers, hourly simulation of GSHPs is important to the assessment of GSHPs scheme design. In this paper, proprietary simulating software is developed which includes a pretreating tool, a computing engine, and a post-treating tool. The preprocessing and post-processing tools are developed based on EXCEL and VBA. The computing engine is coded with C++ language. Text files are designed for data exchanging between modules. In the computing engine, the core model is an explicit one-dimensional transient numerical heat transfer model for the domain beyond the borehole and a steady-state heat transfer model within the borehole. Quadratic correlations for the performance of heat pump units are employed which are functions of the outlet temperature of the ground heat exchanger. Energy consumptions of the source-side pump(s), the load-side pump(s), and fans are all taken into account. Considering interactions between COP and EER, the thermal load and temperature of the ground heat exchanger, COP/EER of heat pump units is computed by an iterate algorithm. Based on hourly building loads, this software can present results of ground temperatures, fluid temperatures, energy consumptions, and energy efficiencies. One simulation case of one-year duration consumes no more than 1 min of CPU time on a common PC. Based on simulated results, one can quickly assess a GSHPs scheme or refine it if necessary. The novelty of this software is the transient numerical heat transfer model proposed by the authors. Flexibility in treating time-varying load, accuracy and fast computing speed make it a practical tool for GSHPs design and analysis.KeywordsGround source heat pump systemEnergy efficiencySimulationSoftware