Issue 5/2021

Carbon dioxide is attributed a major role in drying the landscape by raising the temperature of the atmosphere; this increased temperature then causes faster evaporation. It has been mentioned in the media as well as scientific publications how the atmosphere radiates towards the Earth due to the increased greenhouse effect. Summer temperature extremes are related to the increased greenhouse effect of the atmosphere. Science is focused on tracking the sources of greenhouse gases and how they are sequestered, i.e. bound and reduced within the atmosphere. Energy fluxes, incident and reflected solar (shortwave) radiation and heat flux (longwave radiation) between the Earth’s surface, atmosphere and radiometer, are a measure of the greenhouse effect. The data were recorded as a part of continuous measurement at the Domanín site near Třebon, on clear and cloudy days around the summer and winter solstice and on several other days during the growing season. The fundamental role of water vapour and clouds in the energy balance of the Earth’s surface is demonstrated on the examples of the basic components of solar energy measured with the standard net-radiometer Kipp&Zonen CNR1; i.e. incident solar radiation and heat radiation towards the sky at the constant CO2 concentration in the a tmosphere.

The paper debates results of researches into wall heating which are showed that placement of wall heating panels in interior walls results in a lower heat loss than placement in outer walls, and that wall heating can ha ve equal or better energ y-efficiency compared to floor hea ting and conventional radia tors.

The paper deals with the influence of pipeline heat losses of a two-pipe counter-flow heating system with forced circulation and the related cooling of heating water under the design conditions and under the operating conditions set by the quantitative local control. A reference heating system consisting of a group of three radiators is used to model and compare the individual physical parameters resulting from the quantitative local control, under different boundary conditions. The mathematical simulation indicated obvious differences in the parameters of the heating system when the heat losses of the distribution systems are/are-not considered in the calculation. The cooling of the heating water in the heating system, i.e. a lower inlet temperature of the heating water to the radiators than assumed by the standard design method, reflects in the radiator heating output decrease and therefore in the potential decrease of the indoor design temperature of the heated room. This problem can occur both under the design conditions and under the opera ting conditions of the quantitative control.

Elimination of thermal bridges and thermal coupling is considered in design process as an important measure to reduce the heat loss of the building. However, the design is only one aspect of the construction, the other is the actual execution of the building, which is usually done with many changes. These changes can significantly affect the economics of the building operation and can cause serious technical problems. This paper is devoted to the economic side of the thermal protection of buildings. It shows on several practical examples the possibilities of economic evaluation of imperfections of the building thermal envelope. Despite the diversity of the assessed examples, it is demonstrated that the correct design of the building thermal envelope results in the most economical way of building design, almost without exception. On the other hand, modification of the building structures after its construction tends to be very costly. Yet, it must be determined on a case-by-case basis whether it will be cheaper to carry out the modification or to accept the increased heating costs.

Continuous periods of several tropical days are being established during the summer more often than before. A model day with daily maximum temperature of 30 ° C is currently used in the Czech Republic for computational assessment of summer thermal stability of residential buildings. Change of climatic conditions in recent decades has raised the question of whether such a simple approach needs to be revised. The aim of this paper is to describe a simple method for determining the parameters of the model day. The identified relationships make it possible to determine the daily maximum and amplitude of the external air temperature from the altitude of the site, without the need to analyze historical tempera ture data.

The article focuses on the noise and vibration propagated from air-to-water heat pump, the most commonly installed type of heat pumps, to its surroundings and to the building structures. From a technical point of view, the topic is limited to heat pumps with electrically driven and hermetically sealed scroll compressors, as these are the most commonly installed type of heat pumps of smaller capacities (up to 50 kW). The paper covers the issue of ON/OFF control as well as the issue of inverter heat pumps. Only the heat pumps installed in the exterior of houses or apartment buildings are addressed. Several separate articles will be devoted to the topic due to its wide scope.

The paper deals with the refinement of the rotor blade row design of a low-pressure axial fan by applying the results of flow simulation. The design method is based on semi-empirical data for isolated profiles. In the case of rotor row with a high value of relative spacing of the blades s/c = 2.5 to 10, the methodology for plane cascades can no longer be used. Values of pressure increase in the designed blade row, respectively stage, obtained by the flow simulation, are about 20 to 35 % higher than the design values. Therefore, the refined fan design uses an iterative process to achieve the design target. In the end, the paper presents analysis of the design study results for the rotor row of a ventilation fan with diameter 4.0 m with NACA 65 series profiles.