A Numerical Model Of Spiral Pipe Pile Foundation Heat Exchanger

Ground source heating pump system is a new technology for heating and cooling, using thevast thermal storage capacity of soil. Pile ground source heating pump system has been thehotspot for its large heat transfer area, low investment cost and many other advantages. Heattransfer model of the pile spiral heat exchanger was established in this thesis aiming atproviding computing methods for the design of pile ground source heating pump system.For the time being, the existing analytical models of pile heat exchanger are built based onconstant heat flux assumption, which is not the real case. In addition, the thermal parameterdifference between the foundation pile and soil was not considered in former models and thecomputation is complex. However, the numerical model can handle variable heat flux andproperty difference of different regions flexibly. Thus, the attention was mainly focused onthe establishment of a transient value model of pile spiral heat exchanger.In this model, the pile heat exchanger is simplified as a solid cylinder and the pile-soilinterface is regarded as heat source face. The interior of the pile and the soil region havedifferent thermal parameters. Only heat transfer along radial direction is considered. Nodesare arranged uniformly in the radial coordinate direction. Every node represents a controlvolume which has a thermal capacity. Different control volumes are connected with thermalresistances. Time-varying heat flow is imposed on the pile-soil interface. The boundary whichhas infinite distance away from the center of the pile foundation is adiabatic, Applying energyconservation principle to every control volume，explicit discrete equations are built.A real pile foundation was simulated using the numerical model. The simulated resultswere compared to tested values and simulated values fit tested values well. It demonstratedthat the one-dimensional numerical model has a high accuracy and a significant practicalvalue on engineering application.The effect of pile foundation diameter on heat transfer was analyzed using one-dimensionalnumerical model. Results show that the smaller the diameter is, the greater the thermalresponse will be.A one-year-period simulation was conducted using the one-dimensional numerical modelto determine the amount of heat exchangers. This case study shows that this numerical modelis fast and is suitable for time-varying load cases.In summary, this numerical model for pile foundation heat exchanger is accurate, fast andflexible to treat time-varying loads. It can be used to analyze the design scheme of pilefoundation heat exchangers.