Life cycle assessment of Irish district heating systems: a comparison of waste heat pump, biomass-based and conventional gas boiler

This paper presents a life cycle assessment of heat supply scenarios towards replacement of fossil-based energy systems through a case study focusing on an existing gas-fired boiler supplying heat for buildings located in Tallaght, Ireland. The three replacement systems considered are a waste heat-fed heat pump district heating system, a biomass-based district heating system, and an individual gas boiler. Current study found both the district heating systems have lower environmental impact than the conventional boiler system, with the biomass-based system being superior to heat pump. However, using 2030 electricity data showed almost similar impacts for both the district heating systems. Human toxicity potential was found highest among all impact categories studied due to the large additional infrastructure requirement across all three systems, whereas the other impacts, global warming, fossil fuel depletion and eutrophication, were due to involving usage of natural gas and electricity in use phase. The heating system employing biomass as resource showed reduced greenhouse gas (GHG) emissions by 45% and fossil fuel depletion by 73% compared to the conventional boiler. However, using 2030 electricity data, the heat pump system decreased GHG emissions by 42% and fossil fuel depletion by 47%. Further, replacing biomethane with the natural gas decreased global warming by at least 11.4%. The present study concludes that the environmental benefit of a district heating system is largely dependent on the carbon intensity of the electricity it uses, thus recommending the district heating systems for large-scale retrofitting schemes in Ireland to reach Europe’s 2030 GHG reduction targets.