Abstract
Laboratory measurements and analyses conducted in a wide range of changes of water temperature and mass flow rate for different types of radiators allowed to provides limitations and assessment of the current radiators heat transfer model according to EN 442. The inaccuracy to determinate the radiator heat output according to EN 442, in case of low water mass flow rates may achieve up to 22.3% A revised New Extended Heat Transfer Model in Radiators NEHTMiRmd is general and suitable for different types of radiators both new radiators and radiators existing after a certain period of operation is presented. The NEHTMiRmd with very high accuracy describes the heat transfer processes not only in the nominal conditions—in which the radiators are designed, but what is particularly important also in operating conditions when the radiators water mass flow differ significantly from the nominal value and at the same time the supply temperature changes in the whole range radiators operating during the heating season. In order to prove that the presented new model NEHTMiRmd is general, the article presents numerous calculation examples for various types of radiators currently used. Achieved the high compatibility of the results of the simulation calculations with the measurement results for different types of radiators: iron elements (not ribbed), plate radiators (medium degree ribbed), convectors (high degree ribbed) in a very wide range of changes in the water mass flow rates and the supply temperature indicates that a verified NEHTMiRmd can also be used in designing and simulating calculations of the central heating installations, for the rational conversion of existing installations and district heating systems into low temperature energy efficient systems as well as to directly determine the actual energy efficiency, also to improve the indications of the heat cost allocators. In addition, it may form the basis for the future modification of the European Standards for radiator testing.
Highlights
An additional range of quantitatively managed tests to determine the actual operational thermal characteristics of the T1 10-elements iron radiator is shown graphically in temperature of the radiator supply water 70.2 ◦ C + −0.4 K, return temperature from the radiator changed from 35.3 ◦ C to 63.4 ◦ C, the radiator water mass flow varies changed from 0.0034 kg/s (39.0% nominal value) to 0.031 kg/s (356.0% nominal value) the radiator heat output varies from 481 W to 924 W
Across a wide range of tests and measurements carried out, the discrepancy between the results obtained from simulation calculations based on the NEHTMiRmd and the actual values obtain from measurement’s had not exceed 2.5%
A revised New Extended Heat Trans f er Model in Radiators NEHTMiRmd is general and suitable for all types of radiators, both new radiators and existing radiators after a certain period of operation. It describes the heat transfer processes with very high accuracy in panel radiators, iron elements radiators, convectors in the nominal conditions - in which the radiators are designed, but what is important in the operating parameters when the radiators water mass flow rate changes from 10% to 200% of the nominal value and at the same time the supply temperature changes whole range of radiators operation during the heating season
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Conducted analyses of the actual heat consumption in more than 600 refurbished buildings showed that the vast majority did not achieve the expected reduction in actual heat consumption (and in some cases actual consumption increased) [7], due to unproperly operating conditions of radiators with very high supply temperature, low mass flow rate and the associated low energy efficiency of the heating systems In such facilities there is an urgent need to develop “Individual projects” for the thermal and hydraulic adaptation of existing oversized central heating systems to new actual heat demand of the rooms, which is not possible without knowledge of a good model describing the heat transfer in radiators under these conditions. In addition it will allow for an appropriate modification of the EU Standards regarding the scope and test conditions of the radiators
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