Solar thermal heating through a mechanical ventilation unit with heat recovery: energy performance, economic evaluation, and life-cycle assessment in a building-scale case study

Ensuring adequate fresh air supply while limiting heat losses remains a challenge in low-energy buildings. This study assesses an integrated system combining solar thermal collectors with mechanical ventilation and heat recovery to reduce space-heating demand while maintaining indoor air quality. A building-scale case study is conducted on a 100 m 2 timber building in Montpellier, France, equipped with four flat-plate solar collectors (5.11 kWth), a 743 L buffer tank providing 26 kWh of thermal storage, and a ventilation unit with heat-recovery efficiency exceeding 80%. Over three heating seasons, the solar thermal system supplied 46.2% of the total heating demand (2328 kWh), exceeding 90% during shoulder periods and reducing electricity use. Electricity savings reached 1064 kWh, avoiding 40.8 kg CO 2,eq despite the low-carbon French electricity mix. A life-cycle assessment per kilowatt-hour of useful heat was performed using the Environmental Footprint (EF) 3.1 method with Global Reference normalisation. While the solar configuration shows higher impacts in most climate, toxicity, and eutrophication midpoint categories due to manufacturing requirements, it significantly reduces ionising-radiation impacts. The EF 3.1 Single Score for both systems exhibits very similar environmental performance under the French context. A country-by-country sensitivity analysis highlights greater benefits in regions with more carbon-intensive electricity generation.