In view of the influence of terminal temperature difference during operation of heaters in heating network and departure of extraction pressure loss from standard value upon the extraction pressure for heating system

two mathematical models to quantitatively calculate the vaviation of unit′s economic condition are obtained respectively by using the equivalent enthalpy drop theory and the calculation method of performance under variable conditions. The calculation results from the two said models have been compared through practical examples

it is found that the calculation model by using the equivalent enthalpy drop theory can meet the practical engineering requirements.