Lowering the pressure in district heating and cooling networks by alternating the connection of the expansion vessel

Low-temperature district heating and cooling networks, operated at water temperatures below 20 degrees C, substitute fossil-based heating systems with environmental heat or waste heat from industrial processes and additionally provide a source of direct cooling during the warmer months. These networks have the potential to reduce carbon emissions and are a key future technology in the strategy to combat climate change. However, large initial investments limit the diffusion of such networks. A large fraction of those investments, apart from trenching, goes to piping. Piping costs are highly dependent on pipe diameter, material and pressure rating. In this work, we focus on reducing costs by reducing the pressure in the system; thus allowing a reduced pressure rating. To reduce the maximum pressure in a hydraulic system, we present a novel technique based on alternating the connection of the expansion vessel. We explain our concept in a lab experiment and subsequently apply our method to the large-scale network at ETH Zurich, Switzerland. At ETH Zurich, we predict a pressure reduction of 8% from 6 to 5.5 bar. Lowering the pressure increases the economic viability and may thus promote the market dissemination of low-temperature district heating and cooling networks. (C) 2019 Elsevier Ltd. All rights reserved.