TAKING INTO ACCOUNT THE DYNAMICS OF GROUNDWATER TEMPERATURE CHANGES AT AREAS OF COASTAL WATER INTAKES OF HYDROTHERMAL HEAT PUMP SYSTEMS

Abstract

Forecasting the dynamics of changes in groundwater temperature in areas where coastal water intakes are located is often of great practical interest, since the temperature of groundwater used should not go beyond the limits of conditions, due, for example, to technological features of production. The aim of the work is to experimentally and analytically evaluate the impact of groundwater temperature changes, as a result of mixing with waters filtered from a nearby reservoir, on the efficiency of a hydrothermal heat pump system. An experimental hydrothermal heat pump system developed and constructed at the Institute of Renewable Energy of the National Academy of Sciences of Ukraine, consisting of a heat pump and two wells, through which water is circulated from the Poltava aquifer to the heat pump, is presented. A feature of this system is that its wells are geomorphologically located on the territory of the remnant of the Kyiv forest plateau, limited from the west, from the south and from the east by beams. In addition, the Poltava aquifer is exposed by erosion and comes to the surface at a distance of 100 meters from the location of the wells. And 300 meters from the wells at the bottom of the beam there is a series of ponds. A description of the characteristics of the measuring equipment installed on the hydrothermal heat pump system and the developed interactive dispatching system, which was used to build a system for visualizing and archiving data obtained in the course of this research work, is presented. It has been experimentally determined that the water temperature in the well, which opened the aquifer, tends to decrease or increase depending on the time of year, and the obtained dependences of temperature change on depth are substantiated, taking into account the ambient temperature and other factors of exogenous impact. A mathematical model is presented that makes it possible to determine the temperature of groundwater during the operation of a water intake, which has the form of a linear row of wells located parallel to the riverbed. A solution of the heat transfer equation is given, which describes the process of heat transfer in a production aquifer. Based on analytical calculations, it was determined that in the case of a rise in the water temperature in the river according to a linear law, a continuous temperature increase occurs in the reservoir over time, and with an abrupt rise in the temperature of the water in the river, a stationary temperature distribution is established in the reservoir. From the data obtained, it was concluded that the determining factor in the heating of groundwater is filtration, that is, convective heat transfer. The conductive component entails only some scattering of the thermal front. The obtained theoretical and practical results make it possible to improve the construction of geothermal systems. There are prospects for further studies of the influence of geological, hydrogeological morphological and anthropogenic conditions of temperature change below the neutral layer, and their influence on the efficiency of geothermal heat pump systems.