Energy Abstraction On Geo-temperature Field Of Groundwater Heat Pump

Groundwater source heat pump, as a sustainable way of low-grade thermal energy utilization, has widely been used in air-conditioning field in recent years. As a key factor to the efficiency and life-span of GWHP units, the geo-temperature field is not only in relation to the geological parameters, but also in relation to the design, operation mode, and other parameters.The main objects of this paper are investigating the influence affected by various parameters of the single(doublet) well system by numerical simulation. The main work and conclusions are mentioned below:1.Based on the basic theories of groundwater flow and heat transfer, the models of groundwater flow and the thermal breakthrough time for a production well have been established. Using the two models, the impact of heat transfer by means of conduction and convection, under different groundwater velocity conditions on geo-temperature field is discussed and the relationship of the thermal breakthrough time for a production well with the effect factors involved is analyzed. The results are as follows:(1) When the velocity of the groundwater is about 1×10-7m/s, the heat conduction can be neglected.(2) The breakthrough time is positive to the initial distance r0 2and the depth of aquifer, and is negative to the flow Q.2.Furthermore, a mathematical model of energy transmission in confined aquifer has been established. The influence of energy extraction using a single well system of supplying and returning water on geo-temperature field under different hydrogeological conditions, well structures and withdraw-and-injection flow rate was quantitatively simulated using the finite difference simulator FlowHeat. The simulated results of the single well system show that:(1) Taking some typical media for example, neither the permeability coefficient nor the porosity of a homogeneous aquifer has insignificant effect on the temperature of the production segment provided that the production and injection capability of each well in the aquifers involved can meet the designed value, but the temperature of the production segment will decrease with the increasing of ratio of permeability coefficient.(2) If other conditions are constant, with the increase of the aquifer thickness, the distance between the production and injection screens, and the decrease of the production-and-injection flow rate, the temperature changes of the production will decline.(3) If there exits a lower permeable interlayer, compared with the main aquifer, between the production and injection segments, the temperature changes of the production segment will decrease.(4) For an aquifer of a constant thickness, continuously increasing the screen lengths of production and injection segments may lead to the deceasing of the distance between the production and injection screens, and the temperature changes of the production segment will increase.3. According to the simulation results of the single well system, the simulated research has been presented for the doublet system. The simulation result shows that:(1) Using the alternating running mode with different seasons can improve the efficacy of GWHP system and save on the power cost of pumps. The results shows that the power cost of pumps can save about 50% when using the alternating running mode.(2) The temperature changes of the pumping well will decrease as the aquifer thickness, the distance of well pair distance and the screen lengths of the doublet increasing.(3) The higher the permeability coefficient and the pumping-and-injection rate, the greater the temperature changes of the pumping well.4.Based on the simulation research of the single system and the doublet system, the matching between aquifer thickness and constant load of the single system and the matching between well pair distances and constant load of the doublet system are quantitatively studied. For single system, the relationship of aquifer thickness and pumping temperature difference are fitted with various flow rate(load), getting the minimum aquifer thickness that thermal breakthrough does not happen. For doublet system, the relationship of well pair distances and pumping temperature difference are fitted with various flow rate(load), getting the minimum well pair distance that thermal breakthrough does not happen.