Hydrothermal challenges in low-temperature networks with distributed heat pumps

Low-temperature networks (≤60 °C) combined with heat pumps allow for efficient heating and cooling of buildings and thermal energy exchange between buildings. Thus, such networks are a key technology to reduce the carbon footprint of urban areas. However, they are far more complex in operation than traditional district heating networks at high temperatures (>60 °C). To simplify future network planning, we present various challenges of low-temperature networks and offer solutions. We study the dependency of heat pump efficiencies on flow rates across the evaporator and present methods to cope with flow variations through heat pumps during operation. We introduce the concept “agent authority” and show that for an agent authority >≈0.7, flow variations during dynamic operation are within ≈20%. In a first case study, the total electricity consumption of a thermal network is minimised by reducing the flow rates through the heat pumps by ≈ 14%, however having only minor impact (0.3%) on the total electricity consumption. In a second case study, a decision matrix for selected network types is developed. We show that apart from quantifiable parameters such as energy efficiency or costs, qualitative criteria such as control and resilience are relevant in decision making.