Price models for the district heating return water for Nordic new apartment building with different backup heating systems

• Customer-attractive price models for district heating return water utilization. • System performance with radiators and return water at two temperature levels. • Return water covers 66%–77% of total heating demand depending on its temperature. • Return water discounts suggestions for systems with three backup heating options. • Optimal discounts vary with temperature levels of return water and radiators. Improving the energy efficiency of district heating is a key strategy for enhancing sustainability and reducing emissions, which can be achieved through low-temperature district heating systems. However, given the extensive stock of conventional high-temperature district heating systems, a complete transition within a short period is economically unfeasible. A promising interim solution is utilizing return water from high-temperature district heating for buildings with low-temperature heating devices and auxiliary heating systems, though its economic feasibility for consumers remains underexplored. This study develops economically viable pricing models to make return water usage attractive to consumers. Three district heating return water systems with different auxiliary heating options were proposed for a Finnish apartment building, and their energy performance and economic feasibility were analyzed under the proposed pricing models. A scenarios analysis was conducted using district heating return water at two temperature levels, with building energy simulations performed in IDA ICE 5.0. Economic feasibility was assessed using discounted payback periods and internal rates of return. The results indicate that district heating return water can cover 77 % of the building’s annual heating energy demand and 91 % of its peak heating power demand. A 10 % discount on district heating return water energy prices and power fees ensures economic feasibility for district heating return water systems with electric heaters and supply water, with a payback period of less than 10 years, while a heat pump system requires a 30 % discount.