## 1 Introduction
[15] analysed various configurations for integrating HPs into DH systems incorporating gas-fired CHP units. They found that supplying HP-generated heat directly to consumers is more suitable for decentralised systems, whereas connecting the HP to the return pipe upstream of the CHP unit is better aligned with centralised system configurations. [PERSON] et al. [16] investigated the placement of a large-scale HP within a DH system and concluded that incorrect placement has the potential to negate the positive effects by up to 63%. [PERSON] [14] provided practical insights into the DH network in Stockholm, where high-temperature HPs have been integrated with CHP plants since the 1970s. The study highlights that the combination of large-scale HPs and CHP enables flexible heat production and optimisation based on electricity prices. [PERSON] et al. [9] examined the use of wood-biomass-powered CHP units and geothermal HP with photovoltaic (PV) power plants to achieve carbon dioxide (CO\({}_{2}\))-free heat and electricity production for a DH system near Milan, Italy. [PERSON] et al. [10] demonstrated that small-scale DH systems with CHP units offer greater potential for the integration of high-temperature HPs compared to medium- and large-scale systems. Their analysis of 12 different system configurations showed that the optimal integration method varies with system complexity, highlighting the need for configuration-specific research. [PERSON] et al. [11] performed an analysis on the implementation of booster HPs in ultra-low-temperature and low-temperature DH systems. The overall system performance improved when a central HP was utilised in the return flow of the DH system but also determined lower efficiency for the system when an HP was placed in parallel with a CHP plant. [PERSON] et al. [17] indicated that large-scale HPs in CHP-based DH systems, utilised during periods of low electricity prices, are economically viable and contribute to the reduction of CO\({}_{2}\) emissions. The implementation of such HPs has the potential to reduce operating costs by 8-12% compared to DH systems based on CHP units. While the literature has explored the integration of large-scale HPs either as replacements for, or in combination with, boiler or CHP-based DH systems, the potential of medium-scale HPs within existing third-generation DH networks that already utilize CHP and boiler technologies remains largely unaddressed. The modelling of HPs in these analyses also varies significantly, ranging from theoretical process models to data-driven approaches, both of which may not accurately represent commercially available products. Notably, research tends to focus on the operation of either CHP or heat pumps in isolation, with limited attention given to their synchronised operation within DH systems. Consequently, there is a clear research gap regarding the implementation and coordinated operation of medium-scale HPs alongside CHP and boiler units in existing third-generation DH systems. This paper makes several key contributions to the field of DH system optimisation and decarbonisation. Specifically, it addresses the integration of medium-scale HPs into third-generation DH systems that are already operated with CHP and boiler units. The main research question of this study is as follows: Is it viable to implement medium-sized HPs to cover a fraction of the heating load in the DH system? This study is based on a comprehensive dynamic simulation model of the DH system encompassing consumers, distribution, and production subsystems. Unlike many previous works that rely on theoretical or simplified representations, this analysis incorporates the operational characteristics of commercially available equipment, thus providing more realistic insights into system performance. The research investigates various sizes of implemented HPs and explores multiple operational strategies, including prioritisation of technology and synchronised operation of CHP and HPs, as well as the management of produced electricity.