Flow rate control in standing column wells: A flexible solution for reducing the energy use and peak power demand of the built environment

Abstract

Standing column wells offer a generous and flexible solution to improve the energy efficiency of the built environment. As these systems behavior is strongly affected by groundwater advection, the acute challenge of predicting their thermal evolution with both accuracy and computational efficiency has so far hindered the development of design tools and optimized control strategies. In this work, a powerful simulation algorithm is implemented and applied to the performance assessment of multi-borehole standing column well systems located in a heterogeneous geological environment and operating under various constant and dynamic flow rate control strategies. The iterative algorithm relies on the non-stationary convolution technique to simulate the underground components, and the EnergyPlus approach to represent the heat pump efficiency at full and part loads. The findings suggest that using higher flow rates in peak conditions is a key element that minimizes auxiliary assistance and power demand. Complementary variable flow rate control aiming to maintain a 2 °C temperature difference across the plate heat exchanger has shown to alleviate groundwater usage and generate at least 8%–11% annual energy savings compared with constant flow. This operating strategy allowed the systems to deliver 197–246 W/m with a heating seasonal performance factor of 3.59. These results were achieved through 34 annual simulations having hourly time steps that were performed with the proposed algorithm in a total of 4 h 17 min, compared to 11 days for a single simulation using a numerical reference model.