System effects of lowered district heating supply temperatures

Abstract

Lowering temperature levels of a district heating (DH) system may offer several advantages such as reduced distribution losses, increased efficiency of flue gas condensation equipment and increased electricity generation in combined heat and power plants. In a broader perspective this can result in more efficient use of natural resources as well as reduced climate-impacting emissions. This study examines how decreased DH supply temperatures influence the power-to-heat ratio and thereby electricity production and fuel use in a combined heat and power plant. Carbon dioxide equivalent (CO2-eqv.) emissions and primary energy use were calculated with three different marginal electricity perspectives. A regional DH system situated in mid-Sweden was used as a case study and the energy system cost optimization modelling tool MODEST (Model for Optimization of Dynamic Energy Systems with Time-Dependent Components and Boundary Conditions) was used. The results show that decreasing the DH supply temperature results in increased electricity production as well as increased fuel use within the system. Further, there is a significant difference in CO2-eqv. emissions and primary energy use for the studied marginal electricity perspectives.