Issue 1/2023

The paper deals with the evaluation of daylight illumination of a direct tube room illuminated by a light pipe with a direct tube. The typology of light pipes and their basic components are described. The main part of the paper deals with a possible method of determining the amount of daylight in a space illuminated by a direct tube light pipe. The method consists of the step-by-step determination of the daylight factor at the light pipe dome and consequent consideration of the tube characteristics. The path of the light rays reflected from the walls of the tube and incident on the centre of the diffuser is always in one vertical plane. This represents a significant simplification of the calculation compared to other locations on the diffuser. On this basis, the amount of light entering the diffuser and the consequent effect of light in the room can be determined.

The pressure loss of the rotary heat exchanger is an important parameter that influences the air transport energy consumption and the economics of the heat recovery operation. The available correllations for determining the pressure loss of rotary regenerative heat exchangers are summarized on the basis of a review of the literature. The research on rotary heat exchangers with different rotor geometries is presented in the paper. A correlation for determining the friction coefficient in a sinusoid-shaped channels with a small cross-sectional area and a correlation for calculating the pressure loss of a rotary exchangers have been proposed on the basis of the experimentally established dependencies. The presented correlations have been experimentally valida ted and can be a pplied in practice with sufficient accuracy.

The aim of the paper is to outline the two-phase flow phenomenon in fluid condensation in a tube heat exchanger in terms of the occurring flow regimes and heat transfer (calculation of the Nusselt number and heat transfer coefficient). This paper presents selected gas-liquid flow regimes that occur during condensation in a vertical pipe when the fluid flows downwards. A brief characterization of the flow regimes and methods for determining important flow parameters such as phase fraction, vapour quality, mass flow rate, fluid velocity, dimensionless numbers, etc., that affect heat transfer during fluid condensation in a heat exchanger are presented. In the paper, the correlation for the calculation of the Nusselt number for the prevailing annular flo w regime in the duct is presented.

The paper presents the effect of commonly used methods for reducing the family house energy consumption on the total energy demand. an analysis of the development of prices of electricity and natural gas and price of heat from district heating system is carried out. the following part of the paper targets the economic balance of three different heat sources (heat pump, gas condensing boiler and district heating system) with regard to the realistic payback period.

In this paper, realistic values of emission factors from woody biomass combustion are determined and three approaches are described for using these values in balance calcu lations.

Surface temperatures of various materials and grass plots of three different heights were compared on a summer clear-sky day. The aim of the work was to compare surface temperature of physical surfaces (metal sheets of different colour) with vegetation which has low reflectance (albedo) and cools itself by evaporation of water. For that purpose, experimental equipment was constructed, consisting of a pole 30 m height with 4 m long cross beam on which net-radiometer, thermal camera and shielded sensors for air temperature and air humidity measurement were fixed. Net-radiometer measured incoming and reflecting solar (shortwave) radiation and flux of heat (longwave radiation) between land surface and sky. Daily courses of surface temperatures were measured on 3 grass plots of different height and two reference plates made from aluminium sheet of white and black colour. Measured radiative temperature was compared with temperature measured by contact temperature sensors. The lowest surface temperature was recorded on the grass 30 cm high, which cool itself by evaporation of water (evapotranspiration). The surface temperature of grass was lower despite grass has lower reflectance than white metal sheet. The surface temperature of grass was lower than temperature of air.