Energy performance and cost analysis of some borehole heat exchanger configurations with different heat-carrier fluids in mild climates

The results demonstrated that, for conventional heat pumps with dry evaporator, the use of anti-freeze additives in mild climates is convenient only in grid-shaped borehole fields with a heating-dominant thermal load. In all other cases, the use of pure water decreases the overall operating costs. In addition, flooded evaporator heat pumps using pure water as a secondary fluid on the ground loop proved to be the most cost-effective solution.