A Simulation Study of Renewable-Energy-Integrated Building Energy Systems

Abstract

Heating, Ventilation, and Air Conditioning (HVAC) systems account for a substantial portion of building energy consumption. Given the high energy use and associated carbon emissions, implementing solutions that improve energy efficiency, achieve carbon neutrality, and integrate renewable energy is crucial. Among renewable sources, geothermal energy provides a sustainable option, particularly in cold climates such as those in the Nordic countries. The primary objective of this thesis is to simulate an integrated building energy system for a representative office building to determine the energy required to meet the building's thermal load and to analyze the temporal temperature variations in boreholes over time. Optimization is also employed to evaluate how borehole depth influences the coefficient of performance (COP) of the Water Source Heat Pump (WSHP). For this purpose, an office building was selected for simulation. A lumped-zone energy model of the building was developed, and a three-dimensional model of the building was constructed in SketchUp and imported into TRNSYS using the multi-zone building component. The building’s envelope, thermal capacitance, infiltration rate, ventilation rate, and internal gains (including occupants, equipment, and lighting) were modeled according to ASHRAE standards and actual building documentation using TRNBuild. Simulations were conducted for one year to estimate heating and cooling loads, which were then linked to a water-source heat pump. Thermal performance in the boreholes was assessed to evaluate both short-term seasonal temperature variation and long-term thermal balance. The results indicate that the water-source heat pump and borehole system can effectively provide heating and cooling. The soil temperature decreases during winter and increases during summer, and the boreholes gradually reach a long-term thermal balance between heat extraction and injection after several years of operation. Overall, the building’s total simulated energy demand was slightly higher than the measured data. This study demonstrates that integrating geothermal heat pumps with borehole heat exchangers is an energy-efficient and environmentally sustainable solution for large buildings in cold climates. The findings highlight the importance of accurate modeling of building loads and ground interactions to ensure reliable long-term performance. KEYWORDS: BES, WSHP, BHE, TRNSYS, HVAC, COP, RES