Study on the Hybrid Ground Coupled Heat Pump Systems with Borehole and Foundation Pile Ground Heat Exchangers for Cooling Load Dominated Buildings

When the ground coupled heat pump (GCHP) system is utilized for cooling load dominated buildings, the heat rejected into ground will accumulate and results in performance degradation. One of the available options to resolve this problem is to utilize hybrid ground coupled heat pump (HGCHP) systems. This thesis aims to overcome existing hurdles of the HGCHP system to make it more attractive for cooling load dominated buildings.;Firstly, a short time step simulation model of conventional HGCHP system is developed, and its accuracy is verified by on-site experiments. Parameter deviations between experimental data and simulative results are less than 10%. Case studies of the conventional HGCHP system for different types of cooling load dominated buildings are carried out. Valuable application recommendations of the conventional HGCHP system are proposed.;Secondly, in order to further reduce the initial cost and the land requirement of HGCHP system, a novel pile foundation GHE with spiral coils is proposed. The solid-cylindrical source model, ring coil source model and spiral source model with their respective analytical solutions are established for heat transfer analyzing. Temperature responds of the ground, the coil pipe wall, and the circulating water are predicted by computer program. The results show that the heat exchange capacity could be as high as 212W/m for a normal foundation pile.;Finally, a novel HGCHP system with nocturnal cooling radiator serving as supplemental heat rejecter is proposed to provide a new valuable choice for cooling load dominated buildings. The analytical model of the nocturnal cooling radiator is established. Compared with a traditional GCHP system, the novel HGCHP system can save 10.2% of the total cost during 10-years' operation for a sample building even located in humid subtropical area.;In summary, the experimentally verified simulation model for conventional HGCHP system provides a reliable tool for system analysis and optimal design. The proposed novel foundation pile GHE is a new contribution to decrease the initial cost and land requirement. The developed novel HGCHP systems provide new valuable choices for engineers. The outcomes of this thesis can prompt wide applications of the HGCHP technology for cooling load dominated buildings.