Heat pumps are the ideal solution for powering new passive and low-energy buildings, as geothermal resources provide buildings with heat and electricity almost continuously throughout the year. Among geothermal technologies, heat pump systems with vertical well heat exchangers have been recognized as one of the most energy-efficient solutions for space heating and cooling in residential and commercial buildings. A large number of scientific studies have been devoted to the study of heat transfer in and around the ground heat exchanger. The vast majority of them were performed by numerical simulation of heat transfer processes in the soil massif–heat pump system. To analyze the efficiency of a ground heat exchanger, it is fundamentally important to take into account the main factors that can affect heat transfer processes in the soil and the external environment of vertical ground heat exchangers. In this work, numerical simulation methods were used to describe a mathematical model of heat transfer processes in a porous soil massif and a U-shaped vertical heat exchanger. The purpose of these studies is to determine the influence of the filtration properties of the soil as a porous medium on the performance characteristics of soil heat exchangers. To study these problems, numerical modeling of hydrodynamic processes and heat transfer in a soil massif was performed under the condition that the pores were filled only with liquid. The influence of the filtration properties of the soil as a porous medium on the characteristics of the operation of a soil heat exchanger was studied. The dependence of the energy characteristics of the operation of a soil heat exchanger and a heat pump on a medium with which the pores are filled, as well as on the porosity of the soil and the size of its particles, was determined.

The thermal performance of windows is an important area of research to reduce the energy consumption of buildings and improve indoor comfort. The application of innovative glazing technologies can improve the energy performance of windows and transparent facades, resulting in significant energy savings. This paper presents research results on the energy performance of electrically heated windows. A comprehensive CFD and experimental analysis of the heat transfer processes in a window space depending on the size, power, and location of an electric heater was performed. The convective gas flows in the gas gaps and in the boundary layer were also analysed, and it is shown that a window with an electric heater can reduce the energy consumption of a room by 10–12%. This study is a pilot study to assess the feasibility and cost-effectiveness of electric local heating of a window or facade to minimise heat loss before full-scale implementation. The results of numerical modelling and experimental studies confirm the potential of the new technologies.

In this paper, heat transfer and airflow in the gap between the panes of a central part of a double-glazed window were investigated using mathematical modeling. It has been shown that the cyclical airflow regime, in the form of ascending and descending boundary layers, loses stability and changes to a vortex regime under certain conditions depending on the gap width, transverse temperature gradient, inclination angle and window height, as in Rayleigh–Bernard convection cells. The study made it possible to determine the critical values of the Rayleigh number (Ra) at which the air flow regime in the gap between the panes of a window changes (in the range of values 6.07 × 10³ < Ra < 6.7 × 10³). As a result of the modeling, the values of the thermal resistance of a central part of double-glazed window were determined as a function of the width of the gap between the panes, the angle of inclination and the transverse temperature gradient.

CFD Simulation of Heat Transfer Through a Window Frame

This study investigates, both experimentally and theoretically, the impact of incorporating window shutters on the thermal resistance of double-glazed window units, employing computational fluid dynamics (CFD) modelling. The integration of shutters, whether installed internally or externally, introduces an additional air layer that significantly influences heat transfer between indoor and outdoor environments. This effect on the thermal performance of the transparent structure was analysed through experimental measurements under real operating conditions and numerical simulations involving fluid dynamics and energy equations for the air gaps, alongside heat conduction equations for the solid components. Fourth-kind boundary conditions, considering both radiative and conductive components of the total heat flux emanating from the building’s interior, were applied at the solid–gas interfaces. The simulation results, comparing heat transfer through double-glazed windows with and without shutters, demonstrate a substantial increase in thermal resistance, ranging from 2 to 2.5 times, upon shutter implementation. These findings underscore the effectiveness of employing shutters as a strategy to enhance the energy efficiency of windows and, consequently, the overall energy performance of buildings. This research contributes to the advancement of sustainable materials for engineering applications by providing insights into the optimisation of thermal performance in building envelopes.

The results of theoretical and experimental studies of heat transfer through the window structures of the building are presented, the thermal characteristics of the windows are established and the level of heat loss realized through them is estimated. To determine the heat transfer resistance of two-chamber double-glazed units, numerical modeling of radiative-convective heat transfer is performed, taking into account the thermal conductivity of the gas layer between the glasses. Natural free convection of the gaseous medium in the double-glazed chambers occurs as a result of the temperature difference between the side glass surfaces of the chamber. Modeling is performed by numerically solving the system of fluid dynamics and energy equations for the air layer and glass. On the inner surfaces of the chambers, conditions of the fourth kind are set, which take into account the radiation and conductive components of the total heat flow coming from the glass surface. The results of simulation of heat transfer through double-glazed windows with ordinary glass indicate that about 60 % of heat is transferred by radiation. Therefore, an effective measure to reduce heat loss through windows is to reduce the radiation component of the total heat flow by applying a low-emissivity coating to the inner surfaces of the glass unit. This makes it possible to reduce the total heat flow (and, accordingly, heat loss to the environment) by 20–34 %, depending on the number of glass surfaces with this coating. Conducted independent experimental studies confirm the modeling results. In order to comply with the current requirements of state building regulations and to achieve the energy efficiency class of type C buildings (specific heat consumption for heating 1 sq. m of usable area is less than 75 kWh), for the climatic conditions of Kyiv, it is recommended to use double-chamber windows with two low-emission coatings with the formula of the glass unit: 4M1-10-i4M1-10-i4M1. Bibl. 22, Fig. 8.