Positive energy districts in Sweden: The impact from heat pumps, photovoltaic systems, and energy recovery from district heating return pipe

The present study addresses the implications of positive energy district metrics, comparing heat pump and district heating solutions combined with PV systems. A methodology was developed to calculate energy system equilibrium using data available to city stakeholders during the initial stages of a planned residential area. The model requires 3 dimensional drawings and data from similar buildings. This was integrated with a validated physics-based urban building energy model to simulate the thermal demand and a novel calculation of operational, individual and PV produced electricity on an hourly basis. This allows planners to estimate whether a district would meet ambitions for positive energy district as well as account for peak electrical and thermal demand and electrical energy import and export. The study also examined energy recovery from the return pipe of the district heating system. The method is applied to a case study of a planned residential district in east-central Sweden. The findings indicate that achieving positive energy district status is not feasible with either district heating or heat pump solutions combined with PV systems. Heat pumps are preferred when a lower yearly energy balance is the sole metric, however heat pumps double the peak electricity import in the winter. Neither the positive energy district yearly energy balance nor the primary energy indicator differentiate between primary and return district heating sources. The results also indicate that while positive energy districts aim to enhance the local energy system, the yearly energy balance metric alone does not promote such improvements.