Issue 4/2026

The paper addresses the thermal analysis of an underground water reservoir and focuses on comparing the internal surface temperatures of structures located below ground level. The objective was to evaluate, using transient numerical simulations, whether a 1D heat conduction model can serve as an acceptable substitute for a 2D model, which is commonly used as a simplification of the full 3D reality. For this purpose, transient heat transfer simulations were carried out using CalA and DesignBuilder software. The results show that the 1D model does not accurately represent the stable deep ground temperature, with the error increasing with depth. In the analysed case, the deviation in internal surface temperature of the underground structure exceeded 2 K.

Maintenance of HVAC systems is a key operational activity that reduces failure rates and significantly influences the economic performance of building operation. The main challenge lies in determining optimal maintenance costs, which are directly related to the available capacity for maintenance execution. A simplified approach can be taken to address this issue, without considering changes in parameters over time. This typically involves standard maintenance planning. An alternative approach is to link the system for fault detection and elimination with the maintenance system, including both planned maintenance and the resolution of unexpected issues requiring immediate intervention. Staffing levels can then be adjusted accordingly. Based on this integrated approach, workforce capacity can be adjusted. The integration of all subsystems into a unified framework can be implemented using system dynamics. This approach ensures the ability to control the system and achieve the desired output parameters. The outputs of the model are time-dependent relationships between the number of defects and failures and the number of workers, for a given facility size and utilization intensity. The result of the work is the development of a dynamic model describing system behaviour, which enables the establishment of a maintenance strategy and leads to an understanding of the complex system beha viour.

This article presents a methodology for early detection of increased electrical energy consumption in an office building using a regression-based energy consumption model with an hourly time step. Model parameters are identified on the basis of historical data. The paper briefly introduces the model structure and parameter identification approach, and further discusses practical applications of the model for anomaly detection.

The paper addresses the sustainability of the operation of existing district heating systems in the Czech Republic, which historically used primarily fossil fuel sources and currently are under transformation. The system integration of heat with electricity sector through Power-to-Heat technologies allows for the efficient use of district heating systems thermal capacity to store surplus renewable energy and can also offer additional support services to the electricity transmission system. Simulation study was performed in TRNSYS for three typical typologies of district heating systems in the Czech Republic. Key performance indicators such as CO2 emissions, non-renewable energy or the cost of heat produced by Power-to-Heat technology were assessed.

Within the design of the complex energy system SYNERGYS, one of its subsystems was modelled in the TRNSYS environment. This subsystem combines a solar thermal system, an air-to-water heat pump powered solely by electricity from a photovoltaic system, and seasonal heat storage from summer to winter period. To design the optimal configuration of a borehole field for seasonal thermal storage, number of variants were analysed, including borehole length, number of boreholes, spacing, and borehole configuration (U-tube) using a simplified model in TRNSYS (Type 557). The applicability of the simplified model was verified by comparison with a high-resolution model in FEFLOW for a defined simulation case, indicating relatively good agreement. In the subsequent analysis for the SYNERGYS system design, storage efficiency together with the usable heat delivery to a low-temperature district heating system was evaluated. Based on the analysis, general recommendations for the design of borehole fields were derived.

From a building physics perspective, interior insulation is a risky strategy, primarily due to the potential for condensation and moisture accumulation. This study investigates the influence of capillary-active insulation thickness (50, 100, and 200 mm) on the hygrothermal performance of a 440 mm brick masonry wall. Numerical simulations were performed using the Delphin software, applying a non-linear coupled heat and moisture transport model under standardized climatic conditions. The results indicate that increasing insulation thickness leads to significant moisture accumulation and an elevated risk of frost-induced damage. In contrast, the 50 mm insulation variant exhibits the lo west moisture load and the highest structural safety .

The paper addresses wind-induced load on buildings using computational fluid dynamics (CFD). It focuses on comparing different modelling approaches for wind flow simulation and its effect on building envelope. Both steady-state and transient CFD simulations are compared. The influence of mesh resolution is also discussed. The objective is to compare numerical simulation approaches on simplified building geometries and demonstrate their relevance for non-standard façade elements, which are increasingly used in modern building design.

The article deals with a numerical study of the prototype geometry of a water radiant ceiling panel and the determination of its expected radiant efficiency. The efficiency determined on the basis of CFD simulation was compared with the efficiency determined by a testing laboratory in accordance with the standard ČSN EN 14037-2, which prescribes the methodology for testing the thermal performance of radiant ceiling panels. The article describes a numerical study of a panel in three operating conditions with different temperature gradients. The creation of the numerical models, the setup of the computational cases and the simulation of all the variants are described and compared with each other. The calculations were performed in Fluent software and ser ve to verify the methodolog y for further a pplications in CFD studies with a similar focus.