Energy-saving potential of ground source multiple chillers in simple and hybrid configurations for Mediterranean climates

Air conditioning accounts for a large share of energy usage in residential and tertiary sectors. Renewable energy technologies offer promising solutions to reduce the environmental impacts of meeting buildings’ energy loads. The possibility of using the soil as a thermal reservoir for heating and cooling systems has gained growing attention in the last decade due to its high potential for energy saving. In this paper, the benefits achievable using ground source chillers for air conditioning in an office building located in Southern Italy are discussed. A multiple chillers system coupled with a borehole heat exchanger is investigated and compared to conventional air-cooled and water-cooled systems. The analysis relies on detailed modeling of the main plant components and exploits a novel approach to calculating the thermal resistance of the borehole. Results show that the ground coupled multiple chillers system achieves a 6.516 average energy efficiency ratio, which is 53.2% higher than the reference air-cooled system and 6.5% higher than the conventional water-cooled system. In addition, a hybrid scheme that integrates the borehole heat exchanger with a cooling tower achieves a 19.5% reduction in make-up water consumption. A sensitivity analysis demonstrates that increasing the borehole depth could lead to a significant variation in the system performance, with different trends for simple and hybrid configurations. The proposed study puts forth a reference for the design and operation of this technology for covering the space-cooling demand of buildings in Mediterranean climates.