Paper No 95 – Techno-economic optimization of high-temperature heat pumps using pure fluids and binary mixtures – 14th IEA Heat Pump Conference, Chicago, USA
Electrically driven high-temperature heat pumps (HTHPs) are becoming a promising and cost-effective technology to replace fossil-fuel driven boilers through residual heat recovery and revalorization. HTHPs are however often designed and optimized in terms of thermodynamic performance, neglecting financial aspects such as the levelized cost of heat (LCOH). In this study, the heat pump design and operating conditions are optimized by minimizing the LCOH. This is done for a wide set of working fluids and boundary conditions. Both subcritical, transcritical and supercritical cycles, as well as (zeotropic) binary mixtures, are considered. Depending on the boundary conditions, both pure fluids as well as (zeotropic) binary mixtures, mostly operating in the subcritical region, are financially attractive. The potential benefits of zeotropic mixtures are twofold: (1) more favorable operating conditions and (2) higher COPs. Transcritical cycles only showed to be attractive for large temperature glides at the heat sink side. The results also shows that the financial and thermodynamic optima differ in many cases. One reason for this is that working fluids with a high COP often induce high compressor inlet volume flow rates, resulting in high compressor costs.