Life cycle performance evaluation of cascade-heating high temperature heat pump system for waste heat utilization: Energy consumption, emissions and financial analyses

Inspired by the principle of cascade energy utilization, the concept of cascade-heating is introduced, and five layouts of cascade-heating high temperature heat pump (HTHP) systems are proposed and optimized to utilize the waste heat. The energy consumption, carbon and pollutant emissions, life cycle cost (LCC) and payback period (PBP) models are established. Meanwhile, detailed comparisons are made with conventional HTHPs and boilers. The results indicate it is more positive for cascade-heating HTHPs in terms of energy consumption, carbon and pollutant emissions, LCC and PBP. The primary energy consumption of cascade-heating water cooled saturated suction system (CWSAS) is declined by 1.8–22.8% and 3.4–19.2% in contrast to conventional HTHPs and traditional boilers, respectively. The life cycle carbon emissions of CWSAS are reduced by 1.7–6.1% and 76.5% compared to conventional HTHPs and electric boiler. The pollutant emissions can also be prominently declined by adopting cascade-heating HTHPs. For life cycle economic performance, LCC of cascade-heating flash tank superheated suction system (CFSUS) can be reduced by 4.5–18.3% compared with traditional HTHPs. Furthermore, PBP of CFSUS is the lowest of 3.1 years, and 15.4–65.9% shorter than traditional HTHPs. CWSAS is the most recommended configuration on account of its remarkable overall energy, environment and economic performances.