Issue 3/2021

The revision of ČSN 73 0601, which came into effect in October 2019, concerns the protection of buildings against radon. However, it also has a more general overlap. It distinguishes whether the radon concentration measured in the indoor environment (in general, the concentration of any pollutant can be considered) is intended to assess the health risk to building occupants or to evaluate the building quality. The article shows that it is not possible to conclude whether the building as such is sufficiently protected against the excessive occurrence of the pollutant in the indoor air only on the basis of its measured concentration. Other changes brought about by the revision of ČSN 73 0601, such as a new way of selecting radon protection measures and a new procedure for the design of radon protection insulation, are briefly mentioned as well. Currently, it is sufficient to choose an insulation product with radon resistance grea ter than the minimum value of radon resistance.

The article targets the issue of pressure loss of flexible air ducts. The friction factor related to the declared roughness of flexible air ducts and the effect of air duct compression were analyzed on the basis of available literature. Pressure loss of flexible air ducts was verified and the effect of compression on the pressure loss of air ducts with small diameters was examined by experimental measurements. Commonly used flexible air ducts a vailable on the Czech market were selected for the study.

This paper deals with a vertical green garden attached on the external side of a light external wall, typical for industrial and storage buildings. The influence of greenery on the heat balance of the building depends on the local climatic conditions, thermal properties of the building enclosure, requirements for the indoor environment and the type of greenery. The experiment includes three different real-scale test walls. The experiment includes three different real-scale test walls. Two reference test walls represent a current standard technical solution designed as a steel frame filled with thermal insulation. Trapezoidal steel sheets are attached to the external side of the core wall, either in direct contact with the core wall or with a ventilated air cavity between the sheet and the core wall. The third test wall replaces the external metal sheets by the system of wire baskets filled by soil substrate and greenery with integrated plastic irrigation pipes. The article presents and discusses some results of the first two years of measurement in the period 2019–2020. The measured data from green walls are compared with both reference walls. The measured data made it possible to estimate cooling power due to evapotranspiration, which subsequently has an impact on lowering the external surface temperature and reducing heat flux through the internal side during gro wing period of the year.

The first part of the article describes the design and development of an experimental system for water extraction from outdoor air in desert conditions. The core of the device is a sorption unit with a desiccant exchanger, which operates in a partially circulating mode and is equipped with heat recovery from cooling for desiccant regeneration. The unit has been designed and tested in laboratory conditions to verify the mathematical model, which serves for the further design of the energy system for autonomous operation. It has been shown that in case of sufficient energy for operation, the unit can produce on average around 200 litres of wa ter daily in the extreme desert conditions of Riyadh.

the article deals with the issue of controlled heating of water in the storage tank by an electric heating element. it describes a co ntrol method based on a numerical model of a storage tank and the prediction of hot water consumption and variable price of electric energy. in the presented example of the hot water preparation for the household, the influence of the basic parameters of the system on the annual cost of electricity is demonstrated by sensitivity analysis. the results also indicate the possible savings of energy costs of around 10 % achieved with the use of predictive control, considering energy prices in the year 2019.

The increase of energy prices encourages the interest in economizing measures not only for the thermal equipment, but especially for the piping. Among the most effective measures, and rather cheap and easily realizable, are the thermal insulations. It is a good level of professional knowledge that is the condition needed to provide production, usage, design and assembly as well as the maintenance of thermal insulations. The aim of this paper is to inform about the current state of legislation for the insulation foam made of polyurethane and polyisocyanurate, the modern materials with the high thermal efficiency. The procedures as given by the legislation are not always fulfilled by the certification process. As a consequence, there may be a larger hea t loss in practice then the value calcula ted by the designer.

The efficiency of heat recovery (HR ) fluid circuits is in most cases lower than the efficiency of systems with rotary regenerative heat exchangers. However, it is possible to achieve the opposite by coupling of HR fluid circuit systems with heat and cold production and distribution systems and thus transfer energy between individual HVAC systems. This study was prepared for the EPC project that was carried out at the Prague Congress Centre. As a result, for example, at outdoor air temperatures from -20 to +20 °C, the heat necessary for air heating is obtained mostly from the cold production system with relatively little pumping work.