Issue 2/2023

This paper discusses the current issues of one-dimensional modelling of storage tanks with integrated heat exchangers. For modelling of tanks with integrated heat exchangers, it is necessary to use appropriate correlations. There are not many of them currently available. Moreover, many of the available correlations are based on the geometr y of the stora ge tank tha t is almost never used in practise an y more.

The article describes the measurement of thermal conductivity of insulating materials and inaccuracy in the evaluation of measured data. While in the area of lower temperatures the published measurement results may meet the requirements of the published norms, some of the simplifications introduced have problematic consequences in higher temperature fields. The credibility of the considerations made is supported by specific examples, partial conc lusions and proposals for a ppropriate measures.

The paper presents the results of a statistical evaluation of climate data for Prague over the last 18 years. The dependence of wind speeds (quarter-hourly averages) on outdoor air temperature as the maximum occurring wind speed at a certain air temperature is evaluated. This dependence has a convex shape, with the highest wind speed occurring at outdoor temperatures around 10 °C and decreasing to zero for both positive and negative temperature extremes. The results are presented in both graphical and analytical (formula) form. As an example of the application of the results, the effect of the evaluated wind speeds on the functionality of the ventila tion heads is given.

The limit temperatures in our regulations, whether optimal or acceptable, are set on the basis of many years of studies of human perception of the thermal environment. Heating is an energy-intensive process, and it is understandable that, in the face of the current energy crisis, energy conservation will also impact this area. This paper outlines the new requirements for minimum temperatures in buildings required by the revised regulations of November 2022. These adjusted limit values can have a significant adverse effect on human health, but also on buildings and their structures.

Foul water stacks in buildings should be designed to prevent undesirable negative pressure or overpressure, and excessive vibration and noise do not spread from the drainage pipes. In addition to the correct design of stacks dimensions, other factors also influence pressure fluctuations, such as the change of direction of stacks, the method of ventilation of stacks, the fittings, and accessories used on stacks. Overpressure most commonly occurs above changes in the stack direction, negative pressure at connection points of branch pipes with the flow, or below a change in the stack direction. At high negative pressure, water is sucked out of the trap, which causes the spread of annoying smells in the building. Water bubbles in the traps at lower overpressure, and at higher values, water is ejected from the sanitary appliances. The paper deals with the simulation of the influence of pressure fluctuation in the stack on the water level in the trap in program Ansys 2021 Workbench R1. Selected values of negative pressure and overpressure in the range from -550 Pa to +1500 Pa are considered in the stack, which risks spreading unpleasant smells in the building or water ejecting from sanitary appliances. A standard trap with a water height of 50 mm was used in the simulation. The results of the simulated hydraulic conditions at different pressure in the stack are evaluated to ensure the trap function. The effect of water evaporation from traps on their pressure resistance was also assessed.

This paper focuses on boundary conditions and operational influences that are not commonly considered when determining heating curves for qualitative (equithermal) control of hot water heating systems. This type of control is performed in heating systems, in heat sources, or in independently regulated heating circuits, e. g. by means of three-way mixing valves. The purpose of the quality control is to adjust the inlet temperature of the heating water to the actual desired value. Nowadays, when the aim is to keep the operating costs of heating systems as low as possible, either due to the increasing price of primary energy or with regard to environmental impacts, this method of control is suitable for most heating hot water systems, and it is necessar y to deal with its design as accura tely as possible.