Energy, exergy and economic investigation of operating temperature impacts on district heating systems: Transition from high to low-temperature networks

District Heating (DH) systems, owing to their remarkable techno-economic benefits compared to decentral heat production methods, are getting more and more popular worldwide. Today, DH systems are much more efficient than in the past but investigations show that there is still much to explore for more benefits and higher efficiencies considering such systems, where lowering the operating temperature is one of the points with the highest potential advantages. This study evaluates the effects of using different levels of operation temperatures of DH systems. For making the assessments quantifiable, specific case study DH network with a CHP plant as the main tool of supply is considered for the analyses. Three different design scenarios for the system are considered for all of which the results of the energy, exergy, and economic analyses are presented for the subsystems and the whole heat grid. Through thermoeconomic analysis, the unit exergy costs of electricity and heat and unit exergy costs of Space Heating (SH) and Domestic Hot Water (DHW) are determined. The results showed that lowering the operating temperatures increased the overall energetic and exergetic efficiencies of the CHP-supplied DH system, while reduced the cost per exergy unit associated with the SH and DHW supply.