Modeling the time evolution of geothermal boreholes during peak heating and cooling demands

A geothermal heat exchanger requires special care in its design when it comes to peak heating and cooling demands of the building as the installation may incur in material damages due to the extreme temperatures reached by the heat carrying liquid. The peak demands tend to last a few days at most and the theoretical model used to predict the thermal response of the geothermal heat exchanger has, therefore, to consider the thermal inertia of the heat carrying liquid, the grout, and the ground close to the boreholes. With this in mind, the present work discusses a theoretical model that provides, among other things, the heat injection rates per unit pipe length of the different pipes in the borehole in terms of the bulk temperatures of the heat carrying liquid during those peak heating and cooling demands.

Improving the Electrical Efficiency of the PV Panel via Geothermal Heat Exchanger: Mathematical Model, Validation and Parametric Analysis

Silicon based photovoltaic modules (PV) are a wide spread technology and are used for small and large PV power stations. At the moment, the most efficient method which can be used to improve the annual electrical energy production of PVs is solar tracking systems. However, solar tracking systems increase substantially the initial cost of the investment and insert maintenance costs. During the last few decades, alternative improving methods have been investigated. These methods are based on the reduction of the PV cell temperature, which adversely affects the power production. In the present study, a system with water based photovoltaic-thermal (PVT) collector paired with geothermal heat exchanger (GHE) is compared on the electrical energy basis with a conventional PV system. As the first approach on the topic, the aim is to find out in which extent the PVT-GHE system improves the electrical energy generation by cooling down the PV cells and which parameters influence the most its energy performance. With this aim in mind, the model of the system with the PV, PVT, and GHE was formulated in TRNSYS and validated via experimental data. Meteorological data for Athens (Greece) were used and parametric analyses were conducted. The results showed that the PVT based system can increase the generated electricity from 0.61 to 5.5%. The flowrate, the size of the GHE and the number in-series connected PVTs are the parameters which influence the most the energy performance of the system.

Use of vertical geothermal heat exchanger with nanofluid for heat supply systems

Future district heating systems need to be more flexible and move towards a carbon-neutral generation. Compression heat pumps are foreseen to be promising future tools for district heating systems in EU countries. The paper presents the simulation data or a vertical double-pipe geothermal heat exchanger with ethylene glycol-Al2O3 as a working fluid. To simulate the operation of the heat exchanger, the STAR-CCM + CFD application was used. It has been determined the optimal volume particle concentrations of nanofluid and enhance of heat exchanger performance.

Human-induced load on the environment when using geothermal heat pump wells

The research is aimed to study the process of change in temperature mode dynamics for the Earth subsurface layer when heat is extracted with geothermal heat pump systems, reveal and disclose specifics of effect on the ecology caused by technologies using geothermal resources and give practical recommendations regarding further development of methods for designing heat pumps using low potential heat energy of soil based on the long-term forecast and efficacy assessment. Mathematical statistics and mathematical model methods were applied for assessment of economic and environmental effects. Methods based on principles of the theory of thermal conductivity, hydromechanics, theory of differential equations and mathematical analysis were applied for calculation of proposed systems and review of field observation findings. The authors had developed for research purposes an experimental geothermal heat pump system consisting of four structurally connected geothermal wells, each with installed U-shaped twin collectors of 200 m overall length, and a heat pump of 14 kW capacity with a heat energy battery for 300 L connected to the building heat-supply system. They also created a computer data archivation and visualisation system and devised a research procedure. The paper provides assessment of the effect caused by changes in the process operation mode of the heat pump system on the soil temperature near the geothermal well. As a result, the authors have found that the higher the intensity of heat energy extraction, the lower the soil temperature near the geothermal heat exchanger, in proportion to the load on the system. Moreover, it has been determined by experimental means that at critical loads on the geothermal heat exchanger the soil temperature is unable to keep up with regeneration and may reach negative values. The research also determined relation between inservice time and season of the system operation and temperature fluctuations of geothermal field. For example, it has been found by experimental means that the heat flow from the well is spread radially, from the well axis to its borders. Additionally, it has been proved that depending on the heat load value, the bed temperature is changed after the time of the first launch. For example, the geothermal field temperature has changed from the time of the first launch during 1-year operation by 0.5 °С in average. The research has proved that depending on the heat load value, under seasonal operation (heating only or cooling only) of the system, the soil temperature has decreased for five years by 2.5 °С and switched to quasi-steady state, meanwhile, stabilisation of the geothermal field in the state under 1-year operation (heating and cooling) occurred yet in the 2nd year of operation. In conclusion, the paper reasonably states that geothermal heat pump systems using vertical heat exchangers installed into the wells put no significant human-induced load on the environment. At the same time, still relevant are issues of scientific approach to development of the required configuration of the geothermal collector, methodology for its optimal placement and determination of efficacy depending on operation conditions.