TECHNIQUE FOR EVALUATION OF HEAT LOSSES OF DISTRIBUTION HEATING NET PIPELINES USING AGGREGATED INDICATORS

Abstract

Heat losses from distribution net pipelines of a centralized heating system were computationally estimated. The data were generalized. Formulas that allow evaluating the thermal state of supply and return pipelines for heating net main branches using buildings aggregated indicators were obtained as a result of the generalization. The total thermal load of the buildings connected to the heating net, the material characteristics of heat pipelines, factors that consider the peculiarities of heat transfer medium flow distribution along the heat pipeline were taken as aggregated indicators. Specific (linear) heat losses of subsurface heat pipelines in non-accessible channels were considered to be standard. Heat losses for structural elements of net pipelines were also taken into account. Idealized groups of buildings with the same thermal load were used in the calculation technique proposed. The standard ambient air temperature for the cold period and climatic conditions forKharkovwas used in the calculation. The real stepwise law for net water flow rate change along the heat pipeline was approximated using a power function. The peculiarities of heat transfer medium flow distribution along the heat pipeline was taken into account with the exponent in flow equation and the ratio of the average heat transfer medium flow of the main pipeline and the total heat transfer medium flow of its branches. Heat losses of the branches, based on the material characteristics ratio for the branches and the main pipeline, make it possible to determine heat losses of the heating net as a whole. The accuracy of applying the proposed formulas was evaluated. The imprecision between the results of the calculations using the aggregated indicators of buildings and traditional calculations method results, taking into account the actual change of flow rate and net water temperature along the heat pipeline, was compared. This imprecision does not exceed 6 %, which can be considered acceptable when assessing net thermal state at the early design stages.