Numerical Simulations Of Dynamic Performances Of The U-tube Ground Source Heat Pumps System

In the background of energy conservation and emission reduction, U-shape pipe GroundSource Heat Pump (GSHP) has been a hotspot in the world in recent years for its high efficiency,energy conservation, stability and environmental protection.The key point for GSHP system is the performance characteristic of the undergroundheat exchanger (UHE).Many UHE models have been established for system design andperformance evaluation while there are differences on computing speed and results betweendifferent models. Most models are analytical models which have a relatively long computingtime and thus not conducive to practical engineering application..The heat transfer of underground pipe heat exchanger in present work will be dividedinto two parts, inside the hole and outside the hole. This thesis ignored the details oftemperature distribution inside the hole and assumed the released and absorbed heat is posed onthe borehole wall directly since the drill hole was so small and meaningless to research. Outsidethe drill hole, unsteady heat transfer numerical model was adopted. Control volume methodwas applied to build up implicit equation and TDMA method was used to compute the result inthis work. The coupling between interior and exterior of the borehole was realized bycontrolling the heat flux and temperature of the borehole wall. Meanwhile, this paper supposedthat the energy efficiency of the ground heat pump units were only related to inlet watertemperature and the relational expression between energy efficiency of heat pump units andinlet water temperature could be obtained according to the efficiency data of heat pump unitsupplied by manufacture. Given the hourly loads of a building, by analyzing thermodynamiccycle of heat pump units in summer/winter, the coupling calculation model of the ground heatpump units and UHE was established.Computing algorithm was realized in MATLAB.The cross-comparison between this numerical model and analytical model wasconducted. Results demonstrated that this model has high practical engineering value foraccurate and fast computing characteristics. It could provide long-term ground/watertemperature and system energy consumption information when using this model to make along time (e.g.30years) hourly analysis on a case.Based on these information we can assess adesign shceme of GSHP..