Life Cycle Assessment of District Heating Pipes; Comparing Polyurethane with Polyethylene Terephthalate Insulation

Abstract

District Heating (DH) system has proven to be a viable solution for delivering heating, hot water, and cooling services to the end-users, in that it represents the most suitable energy solution for satisfying urban heat and cold demands. So, in order to keep evolving, district heating must constantly develop in response to the growing demands of a society striving towards sustainability. By this, the sustainability of this system needs to consider further aspects of material use and deploy a large-scale material efficiency which could be a crucial factor in obtaining a variety of additional environmental and economic benefits. In a typical DH distribution system, the pipe is an integral part. The commonly used DH pipe is the pre-insulated bonded pipe with steel carrier pipe, rigid polyurethane (PUR) foam, and high-density polyethylene (HDPE) casing. However, PET foam has been suggested as a suitable substitute for PUR foam. This thesis therefore presents a comparative study to benchmark the environmental impacts for the manufacturing of polyurethane (PUR) foam insulated pipe and a conceptual polyethylene terephthalate (PET) foam insulated pipe based on Life Cycle Assessment methodology. The functional unit is taken to be “the production of 2.42 m length of a DN100 pre-insulated pipe”. The results of life cycle assessments show that the process of manufacturing PUR foam insulated pipe has the largest environmental impacts across the selected impact categories, while the emissions are mostly noticeable in climate change and fossil depletion, which is mostly influenced by raw materials extraction and refinement. An evaluation of material layers indicated that steel pipe gives off the highest emission of all the material components in the pipe and methylene diphenyl diisocyanate (MDI) in the PUR foam. A comparison of insulations materials also showed that virgin PET foam has 28% less impact and when virgin PET in the PET foam is replaced with recycled PET, the impact was further reduced by up to 60%, thereby confirming it to be a suitable alternative. Furthermore, a sensitivity analysis showed that Substituting virgin PET foam with recycled PET foam in the overall system achieved the highest environmental benefits by approximately 12% and this savings in impacts is noticeable across almost all impact categories.