Modeling and Optimization of Energy Pile Systems for Enhanced Efficiency in Sustainable Building Applications

Abstract

The energy crisis and climate change, is creating an urgent need for sustainable and energy-efficient solutions. A significant portion of global energy consumption comes from households. Within this sector, the largest share is used for space heating and cooling. Therefore, efforts to reduce energy usage and cut carbon emissions should primarily target heating and cooling systems. A promising solution to this challenge lies in harvesting shallow geothermal energy through technologies such as energy piles, which have a multifunctional role to the building.

Energy piles are a specialized form of Borehole Thermal Energy Storage (BTES) systems that utilize shallow geothermal energy by taking advantage of the ground's stable temperature throughout the year. They are gaining popularity as an efficient solution for both heating and cooling, primarily because they serve a dual function within a building. On the one hand, they act as heat exchangers, enabling the transfer of thermal energy to and from the ground. On the other hand, they provide structural support, as they are typically constructed from reinforced concrete. This multifunctional role makes them a cost-effective choice and reduces the initial costs investments. These systems are commonly integrated with Ground Source Heat Pumps (GSHPs), which facilitate the exchange of thermal energy between the energy piles and the circulating fluid within the system. Their high Coefficient of Performance (COP) and environmentally friendly operation contribute positively to the transition towards more sustainable energy solutions.

This research focuses on an existing energy pile system located beneath a building on the TU Delft campus, which is responsible for covering the building's heating and cooling demands. The main objective of this research is to assess how the efficiency and reliability of this system can be improved through the implementation of advanced control strategies. To achieve this, a precise simulation model was developed to capture the underlying physical processes and monitor key performance indicators. Energy balance is a key metric and evaluation point for the system that secures the efficiency and sustainability of it. Additionally, various scenarios with different operational parameters were designed to evaluate the system's capabilities and performance.

The main findings initially indicated that the heating load is higher than the cooling load, revealing a significant imbalance. By creating various scenarios with different temperature setpoints, heating and cooling months, and durations of heating and cooling modes, an energy balance was achieved. However, the system was still unable to adequately cover the energy needs of the building during winter. Scenarios that utilized solar gains —by opening the building’s sunblinds— enabled the heating and cooling system to supply the majority of the heating load during winter. This aligns with one of the main goal of the system while maintaining energy balance throughout the year. Among the scenarios evaluated, scenario 5 demonstrated the highest heating and cooling energy delivery. According to performance evaluations, it also consumed the least electricity among the compared scenarios. Additionally, Scenario 5 provided the highest levels of visual and thermal comfort for occupants, as the sunblinds remained open during non-operational months. The system was found capable of operating under loads 50% higher than normal, although these levels push its operational limits. Moreover, it was observed that the energy piles system can store surplus energy during summer and completely cover the heating demand of a neighboring apartment.

The thermal plume interaction is investigated thoroughly and shows the rate and the magnitutude of the expansion or contraction of those. It was observed that energy is lost due to the open boundary with the ambient air temperature but varies between the scenarios. More details will be discussed in the following sections.