Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman Comparative performance assessment of a novel cogeneration solar-driven building energy system integrating with various district heating designs Amirmohammad Behzadi ⁎ , Ahmad Arabkoohsar Department of Energy Technology, Aalborg University, Denmark ARTICLE INFO Keywords: PVT District heating system Low- and ultralow-temperature heat grids Smart building energy system Heat storage tank ABSTRACT In the present study, a novel solar-based building energy system, which is integrated with both electricity and district heating grids, is proposed and modeled. The solar system uses photovoltaic-thermal panels and has neither a battery nor a heat pump. The elimination of the battery and heat pump is proposed to reduce the cost of the system to motivate the building owners to adopt the solution as a cheaper energy system for their buildings. In this way, the building energy system would be able not only to produce a major portion of the heat and electricity demands of the households but also to supply its excess production to the grids to decrease the energy bill of the building. As district heating systems are on the verge of a transformation to their next generations, it is important to know how this system would respond to the future designs and standards of district heating sys- tems. That is why the simulations are accomplished based on different district heating integration scenarios, i.e. existing, low-temperature, and ultralow-temperature district heating systems. For doing the simulations and comparative analysis on the performance of the system in various dynamic operating conditions, TRNSYS software is employed. The results show that the ultralow-temperature district heating model is the most suitable case for integration with the proposed system. In this case, the building energy systems will supply over 400 m 3 hot water to the heat network and about 1940 kWh surplus electricity to the power grid over an entire year. Due to a lower panel temperature, the system produces the largest amounts of electricity and heat (3647.4 kWh and 9118.5 kWh) compared to the other two cases. The maximum overall efficiency values of 74.51%, 62.35%, and 52.35% for ultralow-, low-, and the 3rd generation-district heating models are achieved. 1. Introduction Today, there is a unanimous emphasis on the necessity of increasing the share of renewable energies in the global energy matrix [1]. An example of this is the planned energy policy of Denmark, based on which the electricity and heat consumption in the residential sector is to be fully renewable-based by 2035 [2]. For successfully achieving this ultimate objective, highly integrated energy systems, known as smart energy systems, are required [3]. In a smart energy system, electricity grids, heat and cold distribution grids, gas networks, and the trans- portation sector, while supplied by renewable sources, come into strong synergies [4]. Increased security of supply, sustainable production/ distribution of energy, much higher efficiency of the energy production chains, better cost-effectiveness, etc. are the benefits of future in- tegrated smart energy systems [5]. On the other hand, since buildings are responsible for a remarkable portion of the energy consumption of national energy matrices, the widespread use of renewable-based distributed building energy systems could be significantly useful for achieving the desired smart energy system [6]. This will be especially more effective if the building energy systems are able and allowed to have two-way interactions with energy distribution grids [7]. That is why paving the path for further use of solar systems (including photovoltaic (PV), PV-thermal (PVT), and thermal panels) has become a policy of energy planners. 1.1. District heating systems As mentioned, district heating (DH) systems will be one of the key elements of highly integrated energy systems, especially when the share of fluctuating renewables increases [8]. DH systems are, even today, in service in many parts of the world, providing the space heating and domestic hot water (DHW) demand of end-users. Germany, Sweden, Denmark, etc. are some of the countries with vast implemented DH networks. At the moment, the third generation of DH systems is in service; however, it is well demonstrated that DH systems should up- grade to their next generation to be compatible with the standards of https://doi.org/10.1016/j.enconman.2020.113101 Received 5 February 2020; Received in revised form 20 May 2020; Accepted 10 June 2020 ⁎ Corresponding author. E-mail address: amirmohammadbehzadi1@gmail.com (A. Behzadi). Energy Conversion and Management 220 (2020) 113101 0196-8904/ © 2020 Elsevier Ltd. All rights reserved. T