Operational, economic, and carbon footprint feasibility of a moderately-high-temperature heat pump as an alternative to conventional boilers in various scenarios

Abstract

This article conducts a comprehensive theoretical analysis containing operational, carbon footprint, and economic aspects of a medium–high temperature heat pump (HP) employing R-1234ze(E) as working fluid. Different scenarios consider three types of heat pump connections with district heating and cooling (DHC) networks. The study contains a total of six scenarios, where the first (single stage/two stage cascade (SS/TSC)) and second (SS) scenarios use waste heat for district heating. The third (SS/TSC) and fourth (SS) scenarios produce heating and cooling for district heating and cooling. The fifth (SS) and sixth (TSC) scenarios use heat from the district heating network (DHN) for conventional boiler applications (process heating). Regarding the energy analysis, the internal heat exchanger (IHX) presents a positive impact across all scenarios, improving from 1.5 to 4.6%. Moreover, the TSC configuration exhibits a lower coefficient of performance (COP) than SS for scenario 1 (−20.1%), and for scenario 3 exhibits higher COP than SS (+3.7%). The R-1234ze(E) COP for most scenarios surpasses R-134a. The second scenario, characterized by a lower condensing temperature, results in the highest COP (5.94), due to presenting the lowest compression ratio among the six scenarios. From a carbon footprint perspective, all scenarios demonstrate lower emissions with R-1234ze(E) than R-134a, with the second scenario exhibiting the lowest emissions (358 tCO2e), which is attributed to its low energy consumption. Compared to a natural gas boiler, the second scenario achieves an 84.4% reduction in emissions. Regarding the economic analysis, TSC configurations exhibit higher costs than SS ones (+59% for scenario 1 and +51% for scenario 3). The first (SS) and second scenarios present the lowest capital expenditure (CAPEX), 35161 € and 37717 € respectively, with the second scenario having the least operating expenditure (OPEX), 25275 € due to its low energy consumption, making it a viable alternative to the boiler. Economic viability analysis reveals that only the first four scenarios with SS configuration are feasible, given their OPEX is lower than the boiler, in the case of scenarios 1 and 2 (−14% and −40%), and lower than boiler plus chiller in the case of scenarios 3 and 4 (−18% and −40%). For only heating, the second scenario exhibits the lowest payback period (PBP) (2.18 years), and for heating and cooling, the fourth exhibits the lowest PBP (1.94 years) over a fifteen-year life cycle.