Towards Sustainable Heating: An Energy–Economic–Environmental (3E) Analysis of an Air-to-Water Heat Pump System Integrated with Grid-Connected Photovoltaics for the Southern Romanian Climate

The electrification of residential heating through heat pumps represents one of the central directions of the European energy transition; however, evaluating these systems requires moving beyond classical approaches limited to purely energy-based indicators. This paper proposes an integrated 3E analysis (Energy–Economy–Environment) of a hybrid system composed of a split-type air-to-water heat pump (nominal heating capacity of 8 kW, R410A refrigerant) and an on-grid photovoltaic installation with a peak power of 6.02 kWp, installed in a single-family house with a usable floor area of 122.3 m2, located in climatic zone II with a conventional winter design outdoor temperature of text = −15 °C. Operational data, collected over two consecutive heating seasons (2024–2025 and 2025–2026) at daily resolution and aggregated monthly, were processed to determine the seasonal performance factor (SPF), the specific heat demand, the operating costs compared with a conventional natural-gas solution, and the climatic impact through the TEWI (Total Equivalent Warming Impact) indicator. The results show SPF values of 3.30–3.51 (±7%, standard uncertainty), a strong correlation between outdoor temperature and COP (at both the monthly and daily levels), average annual savings of approximately 2834 RON compared with the natural-gas solution, and a payback period of 15–16 years. The cumulative climatic impact over the equipment’s lifetime (TEWI ≈ 35.1 t CO2-eq over 15 years) is offset to a large extent (≈83%) by the emissions avoided through photovoltaic production (≈29.25 t CO2-eq). The results indicated a higher LCCP (Life Cycle Climate Performance) compared with TEWI, by approximately 4.0%, for the system presented in this paper. The study also identifies limitations associated with the local electricity grid infrastructure, which reduce the exploitation of photovoltaic production during periods of high solar potential, and proposes optimization directions such as battery storage and improvements to the building envelope. The results support the need for multicriteria, 3E/4E-type assessments to underpin decisions on the decarbonization of the residential building sector.