Research On Heat Transfer Performance Of U-type Vertical Pipe Ground Source Heat Pump In Servere Cold Area

With the development of society,human demand for energy also increases, constraints and social impacts of energy development on the environment has become increasingly evident, today fossil fuels gradually unable to meet the social needs for green energy.The ground source heat pump with a clean and environmentally friendly, non-polluting, renewable characteristics is used as a green air conditioning system, It is consistent with the general direction of the sustainable development of China’s energy and environment,and is the current research focus to solve the energy problem.In this paper, ground source heat pump ground heat exchanger is used as the research object, ground source heat pump for vertical borehole heat exchanger establishes geometric and mathematical models based on the practical applications,and using CFD modeling software for the simulation analysis and calculation of the established model. Secondly, several possible factors of the thermal short circuit of ground heat exchanger were analyzed using the model.next,against the adverse effects of the heat exchanger efficiency caused by the thermal short-circuit problem, Proposing single U-tube ground heat exchanger optimization schemes. Optimization of ground source heat pump single U-ground heat exchanger with an efficient use of geothermal energy is the main purpose of this study, the main aspects of the work are as follows:(1)This paper describes the background and significance of an engineering ground source heat pump vertical double U-tube underground heat exchanger in detail,the basic characteristics and development status,clearing the importance of optimizing the efficiency of ground source heat exchanger,and analyzing the impact of ground heat exchanger heat exchanger efficiency factors combined Hot short circuit problem. Drilling depth, backfill materials, fluid flow are all important factors for the efficiency of ground heat exchanger.The shorter Drilling depth,the shorter the heat transfer fluid and the surrounding medium by heat exchange time,the lower the temperature of the water.The faster the fluid flows,the more fully the heat exchange of the fluid with the surrounding fluid medium will be.the lower of the water temperature will be. Enhanced heat transfer efficiency backfill material favorable for ground heat exchanger.(2)A detailed analysis of the impact of a single change in the factors on the thermal short-circuit problem. With the increase in drilling depth, the thermal short circuit becomes more apparent. When the flow rate is low, the thermal interference significantly, depending on the flow rate should be carried out to consider the situation. The larger the thermal conductivity of the backfill material, the greater the heat exchange unit of depth, but the thermal short circuit phenomenon is more pronounced. Different concentrations of ethylene glycol antifreeze for hot short circuit is not too large, based on economic considerations, should try to choose a low concentration of antifreeze antifreeze in meeting the requirements of the premise.(3)The ground heat exchanger outlet manifolds without insulation and insulation were compared, obtained additional insulation on heat exchanger efficiency is beneficial. Different length, thickness, insulation materials are simulated, considering the construction, economy, efficiency on heat transfer capability analysis to identify the most suitable insulation.(4)Considering the economic, energy and environmental protection, a series of analyzes evaluated the direction of ground source heat pump systems, ground source heat pump system established to consider the direction of research, and future research directions are suggested. To evaluate the energy efficiency of the system by seasonal energy efficiency ratio, energy utilization factor. Economy by calculating the initial investment, operating costs, payback period evaluated. Evaluation of environmental benefits through greenhouse gases, soot emission reductions.In this paper, the numerical simulation of various factors on the thermal method shorted problems affecting ground heat exchanger efficiency, reasonable additional insulation depth study. Conclusions of research projects in cold regions GSHP technology application has a reference that can guide the healthy development of ground source heat pump, while the rational design of practical engineering ground source heat pump system also has some reference value.