Issue 2/2025

Frost is a common problem in HVAC and refrigeration systems. It strongly affects the operational efficiency of the equipment and leads to a significant increase in energy consumption. Recently, effective passive and active techniques have been proposed for frost protection and de-icing of already formed frost. Thus, the authors have attempted a review article that focuses on active prevention and de-icing techniques in HVAC, heat pumps and refrigeration systems. Despite the mapping of extensive theoretical and experimental work on active de-icing techniques, it is not possible, in the authors’ opinion, to establish a firm general and all-encompassing basis for comparing different tech niques.

The paper deals with the supervisory control of residential heat pumps in the context of modern energy sector. It analyses the current state of the technology, identifies key barriers to the incorporation of heat pumps in implicit (automatic control of consumption based on price signals, e.g. dynamic tariffs) and explicit (direct participation in markets with flexibility, where consumption is controlled on the basis of instructions from the network operator or aggregator) response mechanisms on the demand side, and analyses ways for overcoming them. Discussion on the legal, technical and operational aspects that are currently restricting the use of heat pumps in explicit demand-side response is included as well. The aim of the article is to inform the professional and general public about the current state of the art and to open a discussion on the necessar y changes.

The paper is the second in the two-part series focussing on the development of a prototype water-based radiant ceiling panel produced using innovative 3D concrete printing technology. The previous paper focused on the experimental determination of the emissivity of the surfaces of concrete samples, each 3D printed from concrete with different material composition and surface finish. Based on the measurements, the most suitable concrete mix for the 3D printing of the radiant panel envelope was selected. This paper focuses on computer simulation of the innovative radiant panel prototype using the CFD method, with the goal of predicting its radiant efficiency. It describes a numerical study of two models in a variant with thermal insulation and a variant without insulation. The creation of the numerical models, the setup of the computational cases and the simulation of the two variants are described and compared with each other. The study was prepared on the basis of the test procedure for testing the thermal performance of radiant ceiling panels described in the standard EN 14037-2. The presented study was a first step to assess the potential of the concrete radiant panel for further development and possible use in practical applications.

Internal leakage is a common characteristic of rotary regenerative heat exchangers. Manufacturers strive to minimise this leakage, as it adversely affects the efficiency of the exchanger. The is sue of leakage in rotary regenerative heat exchangers, particularly from the perspective of measurement procedures, is addressed in the latest version of the ČSN EN 308 standard. The article deals in detail with the leakage of labyrinth seals used in modern rotary exchangers and presents experimental results from a sample of 12 exchangers. The findings indicate that the leakage of the perimeter labyrinth seal typically ranges between 0.5 and 1%. The overall leakage then depends significantly on the specific design of the exchanger and is mainly affected by the geometric accuracy of the rotor winding and the sealing of the transverse seal.

The paper deals with the comparison of measured and calculated hot water consumption and peak flow rates in two primary schools. The methods for determining the calculated flow rates according to different regulations are presented and hot water consumption curves are prepared according to the distribution of hot water consumption measured over the individual days.