Preheating of domestic hot water using a PV installation in a dual-function district heating substation – local benefit versus operating parameters of the district heating network
DOI:
https://doi.org/10.17512/INSTAL.2026.09.02Keywords:
dual-function district heating substation, domestic hot water preheating, photovoltaic installation, district heating return temperature, building energy balanceAbstract
This paper quantitatively assesses the impact of using energy from a local photovoltaic installation to preheat the water supplied to a domestic hot water heat exchanger on the operating parameters of a dual-function district heating substation and the connected district heating network. The analysis was conducted at an hourly time step over thirty consecutive days in July 2025, using measured domestic hot water draw-off data from an actual multi-family building. The photovoltaic generation profile was based on measured data from a 6.56 kWp installation and scaled to the analysed capacity of 40 kWp. A surrogate heat-exchanger model developed from SWEP SSP™ sizing data was used. Four operating scenarios were compared in two pairs with identical consumer-side configurations: without a circulation loop, S1 (no preheating) and S2 (with preheating), and with a circulation loop, S1a (no preheating) and S3 (with preheating). In both pairs, 74.2% of the available photovoltaic energy was utilized. Preheating reduced the average network-side flow rate by 27.8% without circulation and by 21.7% with circulation, while heat drawn from the network decreased by 35.8% and 31.5%, respectively. The flow-weighted average return temperature increased by 5.4 K without circulation and by 5.2 K with circulation, whereas the flow-weighted sum of degree-hours above the reference temperature increased by 5.6% and 0.3%, respectively. The effect of preheating was therefore practically independent of the presence of a circulation loop, while its system-level cost remained small. The conclusions apply to a single district heating substation under summer operating conditions.
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[1] Arteconi A., Hewitt N.J., Polonara F.: State of the art of thermal storage for demand-side management; Applied Energy; 2012; 93; 371–389; https://doi.org/10.1016/j.apenergy.2011.12.045
[2] Averfalk H., Werner S.: Novel low temperature heat distribution technology; Energy; 2018; 145; 526–539; https://doi.org/10.1016/j.energy.2017.12.157
[3] Bloess A., Schill W.-P., Zerrahn A.: Power-to-heat for renewable energy integration: A review of technologies, modeling approaches, and flexibility potentials; Applied Energy; 2018; 212; 1611–1626; https://doi.org/10.1016/j.apenergy.2017.12.073
[4] Brand M., Thorsen J.E., Svendsen S.: Numerical modelling and experimental measurements for a low-temperature district heating substation for instantaneous preparation of DHW with respect to service pipes; Energy; 2012; 41(1); 392–400; https://doi.org/10.1016/j.energy.2012.02.061
[5] Brange L., Englund J., Lauenburg P.: Prosumers in district heating networks – A Swedish case study; Applied Energy; 2016; 164; 492–500; https://doi.org/10.1016/j.apenergy.2015.12.020
[6] Buffa S., Cozzini M., D’Antoni M., Baratieri M., Fedrizzi R.: 5th generation district heating and cooling systems: A review of existing cases in Europe; Renewable and Sustainable Energy Reviews; 2019; 104; 504–522; https://doi.org/10.1016/j.rser.2018.12.059
[7] Chmielewska A.: Characteristics of Domestic Hot Water Consumption Profiles in Multi-Family Buildings for Energy Modeling Purposes; Energies; 2025; 18(17); 4578; https://doi.org/10.3390/en18174578
[8] Fuentes E., Arce L., Salom J.: A review of domestic hot water consumption profiles for application in systems and buildings energy performance analysis; Renewable and Sustainable Energy Reviews; 2018; 81; 1530–1547; https://doi.org/10.1016/j.rser.2017.05.229
[9] Gadd H., Werner S.: Heat load patterns in district heating substations; Applied Energy; 2013; 108; 176–183; https://doi.org/10.1016/j.apenergy.2013.02.062
[10] Gadd H., Werner S.: Achieving low return temperatures from district heating substations; Applied Energy; 2014; 136; 59–67; https://doi.org/10.1016/j.apenergy.2014.09.022
[11] Hamburg A., Mikola A., Parts T.-M., Kalamees T.: Heat Loss Due to Domestic Hot Water Pipes; Energies; 2021; 14(20); 6446; https://doi.org/10.3390/en14206446
[12] Khamma T.R., Zhang Y., Guerrier S., Boubekri M.: Generalized additive models: An efficient method for short-term energy prediction in office buildings; Energy; 2020; 213; 118834; https://doi.org/10.1016/j.energy.2020.118834
[13] Li H., Svendsen S.: Energy and exergy analysis of low temperature district heating network; Energy; 2012; 45(1); 237–246; https://doi.org/10.1016/j.energy.2012.03.056
[14] Lund H., Möller B., Mathiesen B.V., Dyrelund A.: The role of district heating in future renewable energy systems; Energy; 2010; 35(3); 1381–1390; https://doi.org/10.1016/j.energy.2009.11.023
[15] Lund H., Werner S., Wiltshire R., Svendsen S., Thorsen J.E., Hvelplund F., Mathiesen B.V.: 4th Generation District Heating (4GDH): Integrating smart thermal grids into future sustainable energy systems; Energy; 2014; 68; 1–11; https://doi.org/10.1016/j.energy.2014.02.089
[16] Luthander R., Widén J., Nilsson D., Palm J.: Photovoltaic self-consumption in buildings: A review; Applied Energy; 2015; 142; 80–94; https://doi.org/10.1016/j.apenergy.2014.12.028
[17] Mohammadi M., Noorollahi Y., Mohammadi-ivatloo B., Yousefi H.: Energy hub: From a model to a concept – A review; Renewable and Sustainable Energy Reviews; 2017; 80; 1512–1527; https://doi.org/10.1016/j.rser.2017.07.030
[18] Rozporządzenie Ministra Infrastruktury z dnia 12 kwietnia 2002 r. w sprawie warunków technicznych, jakim powinny odpowiadać budynki i ich usytuowanie (Dz.U. 2022 poz. 1225, z późn. zm.), § 120 ust. 2
[19] Sajjadi S., Shamshirband S., Alizamir M., Yee P.L., Mansor Z., Manaf A.A., Altameem T.A., Mostafaeipour A.: Extreme learning machine for prediction of heat load in district heating systems; Energy and Buildings; 2016; 122; 222–227; https://doi.org/10.1016/j.enbuild.2016.04.021
[20] Sayegh M.A., Danielewicz J., Nannou T., Miniewicz M., Jadwiszczak P., Piekarska K., Jouhara H.: Trends of European research and development in district heating technologies; Renewable and Sustainable Energy Reviews; 2017; 68(2); 1183–1192; https://doi.org/10.1016/j.rser.2016.02.023
[21] Tol H.İ., Madessa H.B.: Return-Temperature Reduction at District Heating Systems: Focus on End-User Sites; Energies; 2024; 17(19); 4901; https://doi.org/10.3390/en17194901
[22] Tol H.İ., Madessa H.B.: Enhancing District Heating System Efficiency: A Review of Return Temperature Reduction Strategies; Applied Sciences; 2025; 15(6); 2982; https://doi.org/10.3390/app15062982
[23] Vandermeulen A., van der Heijde B., Helsen L.: Controlling district heating and cooling networks to unlock flexibility: A review; Energy; 2018; 151; 103–115; https://doi.org/10.1016/j.energy.2018.03.034
[24] Wei Y., Zhang X., Shi Y., Xia L., Pan S., Wu J., Han M., Zhao X.: A review of data-driven approaches for prediction and classification of building energy consumption; Renewable and Sustainable Energy Reviews; 2018; 82; 1027–1047; https://doi.org/10.1016/j.rser.2017.09.108
[25] Werner S.: International review of district heating and cooling; Energy; 2017; 137; 617–631; https://doi.org/10.1016/j.energy.2017.04.045
[26] Yang X., Svendsen S.: Ultra-low temperature district heating system with central heat pump and local boosters for low-heat-density area: Analyses on a real case in Denmark; Energy; 2018; 159; 243–251; https://doi.org/10.1016/j.energy.2018.06.068
[27] Yildiz B., Roberts M., Bilbao J.I., Heslop S., Bruce A., Dore J., MacGill I., Egan R.J., Sproul A.B.: Assessment of control tools for utilizing excess distributed photovoltaic generation in domestic electric water heating systems; Applied Energy; 2021; 300; 117411; https://doi.org/10.1016/j.apenergy.2021.117411
[28] Ziemele J., Gravelsins A., Blumberga A., Blumberga D.: Combining energy efficiency at source and at consumer to reach 4th generation district heating: Economic and system dynamics analysis; Energy; 2017; 137; 595–606; https://doi.org/10.1016/j.energy.2017.04.123
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