Numerical Simulation of a Shallow Geothermal Heating/Cooling System

Abstract

In recent years, sustainability concerns have played an increasingly important role in building design, leading to rapid adoption of shallow geothermal heating/cooling systems. Understanding the heat exchange with the ground and associated thermo-hydro-mechanical processes involved is critical to ensure safe, efficient long-term performance of these geothermal systems. The current study considers heating/cooling loads for a large office building in Chicago, based on recommendations for typical DOE Commercial Benchmark Buildings and solves the coupled thermo-hydro-mechanical response of different soil types using the Code_Bright program. The paper considers a closed-loop system comprising an array of 80 m deep vertical heat exchangers that operates on a seasonal cycle with zero net heat transfer to the ground and can supply a heating load up to 2440 kW. Using estimated thermal properties of the Chicago clays, the THM analyses show negligible drift in the temperature within the surrounding ground for long-term operation of the geothermal system. However, when thermo-elastoplastic properties are considered, the analyses show that thermal cycling induces long-term settlements of the building.