Determination of the circulation flow rate in the calculation of internal hot water supply networks

Abstract

Calculations of internal ring networks of buildings have always been, are and will be an urgent task. The schemes of internal hot water supply systems change, the number of floors of buildings changes, the location of heating points from which hot water begins its journey to the consumer changes, the definition of water consumption changes, and finally the calculations themselves change, but it is undoubtedly the calculation methods for centralised hot water supply systems that are a key part of creating reliable and economical hot water supply networks in buildings. Modern methods consist of three different calculations: the supply part of the system, the circulation part with the determination of pressure losses in the entire system, and the thermal disinfection mode of the system. The circulation flow rate methodology widely used in Ukraine is based on a 1985 regulatory document and borrowed part of the calculation from the 1992 Polish regulations. As a result, questions arise that are not answered in the DBN. In terms of determining the heat losses of individual sections of the hot water system, not everything is perfect either. A building is designed for a lifespan of 50 years or more with daily, round-the-clock use of heat energy, and the heat consumption for preparation and transportation of hot water is the largest in the building and requires a detailed calculation. The DBN "Internal Water Supply and Sewerage" provides two figures for all cases: 11 and 7 W/m (specific heat losses by pipes of the internal hot water supply network). The calculated surface temperature of the pipes in different parts of the network varies, the air temperature in the premises through which the pipes pass varies, and the diameters of the pipes in certain areas change, but the two figures remain unchanged. Moreover, it is recommended that, regardless of the insulation material used for pipe insulation, the insulation thickness should be at least 10 mm. This may have been appropriate in 1985, when there were no computer programs for calculations and fewer thermal insulation materials, but now it is 2023 and the situation is completely different. The article, after analysing the regulatory documents, proposes a methodology for determining the circulation flow rate and calculating the hot water supply network in the mode of passing this flow rate.