Modeling of high-temperature heat pump cycles for industrial applications using moving boundary heat exchangers and advanced cycle architectures

Supplementary materials for a journal paper (Applied Thermal Engineering) on "Modeling of high-temperature heat pump cycles for industrial applications using moving boundary heat exchangers and advanced cycle architectures". Contains results of screening and cycle comparison as .xlsx files and has the code necessary to produce all other results presented in the paper.

Abstract:
High-temperature heat pumps (HTHP) are essential for improving the efficiency of industrial heating processes. Increasing the HTHP supply temperatures can enable a broader impact of the technology on different industrial sectors, but also has challenges associated with cycle efficiency, compressor discharge temperatures, and material compatibility. This study presents a refrigerant screening and compressor isentropic efficiency sensitivity study for steam-generating heat pumps (SGHP) at a variety of operating steam supply conditions. Additionally, modeling efforts are presented for the design and development of a state-of-the-art test facility for a novel HTHP architecture, aiming to produce heat at 200 °C in a subcritical cycle. Specifically, the cycle features refrigerant economization coupled with internally cooled rotors in an additively manufactured twin-screw compressor for enhanced discharge temperature control and efficiency. Based on previous refrigerant screening, the refrigerant that produced the best results was pure cyclopentane. A key advancement is the use of moving boundary heat exchanger models, which calculate phase change regions based on local thermodynamic conditions. Compared to conventional fixed temperature difference models, the moving boundary models of the evaporator and condenser revealed pinch variations of up to 3 K over a 40 K range of condensing temperatures, resulting in variations in compressor power and heating capacity of up to 13% and 33%, respectively. The resulting system model predicts a COP of 2.85, a second law efficiency of 48.7%, and a heat sink outlet temperature of 201 °C. The modeling efforts presented in this work thus demonstrate the feasibility of this cycle architecture in maximizing HTHP efficiency for industrial applications.

This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Industrial Efficiency & Decarbonization Office, Award Number DE-0010864.