| Summary: | 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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>E</mi><mi>N</mi></mrow></semantics></math></inline-formula> 442. The inaccuracy to determinate the radiator heat output according to <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>E</mi><mi>N</mi></mrow></semantics></math></inline-formula> 442, in case of low water mass flow rates may achieve up to 22.3% A revised <em>New Extended Heat Transfer Model in Radiators NEHTMiR<sub>md</sub></em> is general and suitable for different types of radiators both new radiators and radiators existing after a certain period of operation is presented. The <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>N</mi><mi>E</mi><mi>H</mi><mi>T</mi><mi>M</mi><mi>i</mi><msub><mi>R</mi><mrow><mi>m</mi><mi>d</mi></mrow></msub></mrow></semantics></math></inline-formula> 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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>N</mi><mi>E</mi><mi>H</mi><mi>T</mi><mi>M</mi><mi>i</mi><msub><mi>R</mi><mrow><mi>m</mi><mi>d</mi></mrow></msub></mrow></semantics></math></inline-formula> is general, the article presents numerous calculation examples for various types of radiators currently used. Achieved the high compatibility of the results of the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>s</mi><mi>i</mi><mi>m</mi><mi>u</mi><mi>l</mi><mi>a</mi><mi>t</mi><mi>i</mi><mi>o</mi><mi>n</mi></mrow></semantics></math></inline-formula> calculations with the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>m</mi><mi>e</mi><mi>a</mi><mi>s</mi><mi>u</mi><mi>r</mi><mi>e</mi><mi>m</mi><mi>e</mi><mi>n</mi><mi>t</mi></mrow></semantics></math></inline-formula> 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 <em>mass flow rates</em> and the <em>supply</em> temperature indicates that a verified <em>NEHTMiR<sub>md</sub></em> 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 <em>low temperature energy efficient systems</em> as well as to directly determine the actual <em>energy efficiency</em>, also to improve the indications of the <em>heat cost allocators</em>. In addition, it may form the basis for the future modification of the <em>European Standards</em> for radiator testing.
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