Theoretical investigation of a novel high-temperature heat pump exploiting low-temperature waste heat and using two-phase machines with zero electric consumption

Abstract

A novel high-temperature heat pump (HTHP) exploiting low-temperature waste heat is presented, which is enabled by two-phase compressors and expanders without the need for any requirement of external electric power. The investigation involves a sensitivity analysis at the design point, considering the concurrent variation of five independent variables. The aim is to identify the best-performing conditions for a rubber manufacturer and a canning industry which have different temperatures of waste heat and required heating power. The COP of the overall HTHP system, which is the ratio between the output heating power and the input thermal power (coming from the heat source) is evaluated. The maximum COP values are 0.258 for the rubber manufacturer and 0.452 for the canning industry. The primary energy saving is assessed in terms of equivalent fuel consumption. For the rubber manufacturer, the resulting yearly cost saving is in the range of 129 ÷ 646 €/kWth of HTHP installed capacity, and 140 €/kWth for the canning industry. The economic viability of the HTHP is contingent upon achieving isentropic efficiencies of the expanders and compressors higher than 0.59 and 0.55, respectively, for the rubber manufacturer, and both higher than 0.45 for the canning industry.