Optimal Environmental and Economic Performance Trade-Offs for Fifth Generation District Heating and Cooling Network Topologies with Waste Heat Recovery: Article No. 118322

Michael Murphy, Amy Allen, Gregor Henze, Nicholas Long

Research output: Contribution to journalArticlepeer-review

Abstract

Network topology greatly influences both the economic and environmental performance of fifth generation district heating and cooling (5GDHC) systems. In this study the optimal trade-offs between the environmental and economic performance of 5GDHC network topologies for a five-building district with waste heat recovery were explored. A life cycle assessment method was used to calculate the total life cycle CO2 emissions (LCCO2) associated with the installation and operation of various network topologies. Twelve months of empirical data from a data center cooling system were analyzed to assess its suitability for integration into a 5GDHC system. The most suitable method for utilizing this waste heat was selected based on the ambient loop warm pipe setpoint, waste heat temperature, and district energy system configuration. A multi-objective optimization algorithm was used to select the 5GDHC network topology that provided the optimal trade-off between LCCO2 and life cycle cost (LCC). A trade-off parameter was employed to weigh the importance of each objective in the selection process. The results showed waste heat from the data center was suitable for integration into the 5GDHC system due to its availability and consistent temperature profile. When return temperatures of 25 degrees C or higher were available from the liquid-cooled system, direct pre-heating of the ambient loop warm pipe was found to be the most effective waste heat integration method. The selection of the network topology that provided the optimal trade-off between LCCO2 and LCC (optimal trade-off topology) was highly dependent on factors such as fuel prices, CO2 prices, electricity CO2 emissions factors, availability of waste heat, embodied CO2 emissions associated with network installation and network infrastructure costs. Optimal trade-off topologies produced substantial LCCO2 reductions relative to corresponding LCC increases. LCCO2 reduction to LCC increase ratios from 5.78 to 117.79 were identified with CO2 offset costs ranging from 4.77 to 60.08 ($/tCO2e).
Original languageAmerican English
Number of pages19
JournalEnergy Conversion and Management
Volume309
DOIs
StatePublished - 2024

NREL Publication Number

  • NREL/JA-5500-88423

Keywords

  • 5GDHC
  • district heating and cooling
  • life cycle assessment
  • multi-objective optimization
  • network topologies
  • waste heat recovery

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