Abstract
This paper presents the results of a thermo-economic (TE), primary-energy-factor and CO2-equivalent (CO2 (eq)), emissions-sensitivity analysis for the preparation of sanitary hot water (SHW) in fourth-generation district-heating systems. The annual required additional heat for the SHW provided by a local heating unit, based on an air-to-water heat pump (AWHP), a natural-gas boiler (NG boiler), and an electrical resistance heater (ERH), was determined using a trnsys simulation. Additionally, the seasonal performance factor (SPF) of the HP under consideration was determined. The study considered three possible supply temperatures, i.e., 35, 40, and 45 °C. The results show that a local heating unit based on an AWHP is most efficient in terms of the used primary energy (PE) and CO2 (eq) emissions. This unit is also the second best in terms of TE performance. The unit based on a NG boiler is much more appropriate than an ERH unit in terms of both the primary energy factor (PEF) and the CO2 (eq) emission factors for an electricity generation mix (EGM) that has values higher than the average for the EU-28. The heat generated by this NG unit is also cheaper than the heat produced by an ERH based on the average price for electricity in the EU-28.
Highlights
District heating (DH) systems have been used all over the world for several decades because in conjunction with state-of-the-art combined heat and power (CHP) units it is possible to produce heat with a relatively low primary energy (PE) consumption and greenhouse-gas (GHG) emissions [1,2,3]
The results show that a local heating unit based on an air-to-water heat pump is the most efficient in terms of the used primary energy and CO2 emissions
The authors suggested that replacing a bypass pipe with an in-line supply pipe and a heat pump (HP) could reduce the heat losses by up to 39% compared to the conventional system and by up to 12% compared to the conventional system with a bypass
Summary
District heating (DH) systems have been used all over the world for several decades because in conjunction with state-of-the-art combined heat and power (CHP) units it is possible to produce heat with a relatively low primary energy (PE) consumption and greenhouse-gas (GHG) emissions [1,2,3]. During this period DH systems have been divided into generations based on their size, efficiency, complexity and flexibility [4]. Developments on going in DH systems could see even lower supply temperatures, with values as low as 35 °C being tested [7]
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