Dual pressure condensation heating high temperature heat pump using eco-friendly working fluid mixtures for industrial heating processes: 4E analysis

To make better use of waste energy for the industrial heating processes, dual pressure condensation heating high temperature heat pump system (DPS) is proposed, to achieve the purpose of step heating. Meantime, environmental-friendly working fluid hydrocarbons are selected as the components of the mixtures. The energy, exergy, environmental and economic (4E) analysis models are established, and the system performance is optimized, compared with single-stage (SS) system and fossil fuel-fired boilers. There is an optimal intermediate water temperature corresponding to the highest system energy efficiency. The maximum COP of 5.29 is achieved when R600a/R601a (50/50) is adopted, improved by 18.23% and 24.18% compared with DPS and SS systems using pure working fluid. By using zeotropic working fluid, the irreversible heat transfer loss can be significantly reduced. The overall exergy loss with R600a/R601a (50/50) is 21.68–41.27% and 12.26–16.69% lower than pure SS and pure DPS systems, respectively. In terms of environmental and economic aspects, DPS with zeotropic working fluid shows excellent performance. In comparison with boiler, pure DPS and pure SS system, the reduction of carbon emissions through the whole lifetime is 81.22%, 15.35% and 20.04%, and the life cycle cost is decreased by 93.91%, 9.70–15.05%, and 27.89–38.07%.