Citation: Ochs, F.; Magni, M.; Dermentzis, G. Integration of Heat Pumps in Buildings and District Heating Systems—Evaluation on a Building and Energy System Level. Energies 2022, 15, 3889. https:// doi.org/10.3390/en15113889 Academic Editors: Targo Kalamees, Mark Bomberg and Antonio Rosato Received: 5 May 2022 Accepted: 23 May 2022 Published: 25 May 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Integration of Heat Pumps in Buildings and District Heating Systems—Evaluation on a Building and Energy System Level Fabian Ochs * , Mara Magni and Georgios Dermentzis Unit for Energy Efficient Buildings, University of Innsbruck, 6020 Innsbruck, Austria; mara.magni@uibk.ac.at (M.M.); georgios.dermentzis@uibk.ac.at (G.D.) * Correspondence: fabian.ochs@uibk.ac.at Abstract: The use of heat pumps in buildings is one of the best and often the only option for the decarbonization of the building stock. District heating seems a promising solution in urban areas and in existing buildings when the use of heat pumps is restricted and also technically and economically challenging (source exploitation, space restrictions, sound emissions, etc.). Heat pumps can be integrated in various ways in buildings and district heating systems: large central high-temperature heat pumps in district heating, medium-size heat pumps block- or building-wise or small heat pumps decentral apartment-wise. The best option depends on the individual district heating CO 2 emissions and the electricity mix as well as on the perspective of the building owner versus that one of the district heating system and its future development. Austrian examples of district heating systems and different variants of integrating heat pumps are investigated in a comprehensive way by means of an energetic and environmental simulation-based analysis. This assessment includes a detailed investigation of the capabilities of the booster heat pump to increase the PV own-consumption and is also expanded to include various scenarios for the development of the electricity mix and the decarbonisation of district heating. Keywords: decarbonisation; district heating; heat pumps; booster heat pump; renewables; PV own- consumption; CO 2 -emissions; energetic and environmental evaluation 1. Introduction The buildings sector is responsible for around 37% of global CO 2 emissions, of which 10% are caused by the building construction industry [1]. The current pandemic has led to a reduction in CO 2 emissions, but this is expected to be only temporary. The world’s population continues to grow and with the number of people inevitably an increase in CO 2 emissions is expected. To achieve the 2050 neutrality targets, it will be necessary to drastically reduce current emissions and offset the rising trend in CO 2 emissions due to population growth. This can be done, as the global report describes [1], 70% by increasing electrification and efficiency, and the remaining part by using district heating (DH) and other renewable sources and behaving responsibly. According to [1], it is expected that by 2050 over 85% of the buildings will be zero-carbon-ready leading to a reduction of 75% of the heating intensity of which around 50% will be covered by Heat Pumps (HP) and 10% by DH. There exist several scenarios for the development of DH in Europe. Exemplarily, two different studies, one for Austria and one for Germany, are presented to show the wide range of expected contributions of DH in a future energy system. According to [2] in Austria, the assumption is that the buildings will be deeply renovated, and, in contrast to a further extension of the DH system, the share and size in terms of energy remain rather constant, while, for Germany, the prediction according to [3] is that the role of DH will significantly increase with a share of 40% (see Figure 1). The share of large-scale HP in the DH in 2050 is assumed to be almost 50%. It is noteworthy that, according to [4], the current Energies 2022, 15, 3889. https://doi.org/10.3390/en15113889 https://www.mdpi.com/journal/energies