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Research Papers: Energy Systems Analysis

A Thermo-Economic and Emissions Analysis of Different Sanitary-Water Heating Units Embedded Within Fourth-Generation District-Heating Systems

[+] Author and Article Information
Primož Poredoš

Laboratory for Refrigeration and District Energy,
Faculty of Mechanical Engineering,
University of Ljubljana,
Ljubljana 1000, Slovenia
e-mail: primoz.poredos@fs.uni-lj.si

Boris Vidrih

Laboratory for Refrigeration and District Energy,
Faculty of Mechanical Engineering,
University of Ljubljana,
Ljubljana 1000, Slovenia
e-mail: boris.vidrih@fs.uni-lj.si

Andrej Kitanovski

Laboratory for Refrigeration and District Energy,
Faculty of Mechanical Engineering,
University of Ljubljana,
Ljubljana 1000, Slovenia
e-mail: andrej.kitanovski@fs.uni-lj.si

Alojz Poredoš

Laboratory for Refrigeration and District Energy,
Faculty of Mechanical Engineering,
University of Ljubljana,
Ljubljana 1000, Slovenia
e-mail: alojz.poredos@fs.uni-lj.si

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received January 31, 2018; final manuscript received April 23, 2018; published online July 23, 2018. Assoc. Editor: Asfaw Beyene.

J. Energy Resour. Technol 140(12), 122003 (Jul 23, 2018) (8 pages) Paper No: JERT-18-1091; doi: 10.1115/1.4040102 History: Received January 31, 2018; Revised April 23, 2018

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.

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Figures

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Fig. 1

Schematic of the local heating unit used in a simulation with trnsys. This unit additionally heats the sanitary water, previously heated by the DH supply in the heat exchanger.

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Fig. 2

External air and SCW temperature variations over a 1 year period in Ljubljana

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Fig. 3

Weekday and weekend patterns of SHW usage, denoted as SHW load ratio. Note: cumulative SHW usage load ratio per day = 1.

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Fig. 4

Simulation-based calculation of an AWHP's COP for 1 year with a 5 min time-step

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Fig. 5

Relative share of final costs based on a fixed EU-28 average gas price for domestic consumers at 0.0974 €/kWh for three different values of required additional heat: 1330, 1075, and 821 kWh/a. The analysis considered the lowest, average, and highest electricity prices in the EU-28 for domestic consumers. Note: The EU-28's electricity and natural-gas prices are based on EUROSTAT and include all taxes and levies.

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Fig. 6

Relative share of the final costs based on the fixed required additional heat for SHW at 1075 kWh/a for the EU-28's lowest, average, and highest natural-gas prices for domestic consumers, based on EUROSTAT: 0.0272, 0.0974, and 0.2070 €/kWh, respectively. The analysis considered the EU-28's lowest, average, and highest electricity prices for domestic consumers. Note: The EU-28's electricity and natural-gas prices are based on EUROSTAT and include all taxes and levies.

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Fig. 7

Relative share of the final costs for the case of the Slovenian market for three different values of the required additional heat: 1330, 1075, and 821 kWh/a. Note: Electricity and natural-gas prices include all taxes and levies.

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Fig. 8

Relative share of used primary energy for the NG boiler and ERH compared to the AWHP. The analysis considered the lowest, average, and highest PEFs of the EGM and natural gas in the EU-28. All the PEFs were based on the GEMIS model, version 4.95.

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Fig. 9

Relative share of CO2 (eq) emissions for the NG boiler and ERH compared to the AWHP. The analysis considered the lowest, average, and highest CO2 (eq) EFs of the EGM and natural gas in the EU-28. All the CO2 (eq) EFs were based on the GEMIS model, version 4.95.

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