DITCHEV, S. The Heat Pump Systems – an Option for Energy Efficiency and Innovation of Technologies. The Journal of CIEES, [S. l.], v. 1, n. 2, p. 40–44, 2021. DOI: 10.48149/jciees.2021.1.2.8. Disponível em: https://journal.ciees.eu/index.php/ojs/article/view/13. Acesso em: 14 may. 2026.