A thermo-economic and emissions analysis of different sanitary-water heating units embedded within 4th-generation district-heating systems

Abstract

This paper presents the results of a thermo-economic, primary energy factor and CO2 equivalent (CO2 (eq)) emissions sensitivity analysis for sanitary hot water (SHW) preparation in 4th-generation district-heating systems. The annual required additional heat for SHW, which is provided by a local heating unit, based on an air-to-water heat pump, a natural-gas boiler and an electrical resistance heater was determined using a TRNSYS simulation. Additionally, the seasonal performance factor of the heat pump under consideration was determined. This study considered three possible supply temperatures, i.e., 35, 40 and 45 °C. The results show that a local heating unit based on an air-to-water heat pump is the most efficient in terms of the consumed primary energy and CO2 (eq) emissions. This unit is also the second best in terms of thermo-economics. The unit, based on a natural-gas boiler, is significantly more appropriate than the electrical resistance heater unit in terms of both the primary energy factor and the CO2 (eq) emission factors for an electricity generation mix that has values higher than the EU-28’s average. The heat generated by this unit is also cheaper in the case of the EU-28’s average or a higher electricity than the electrical resistance heater.