Experimental characterization of the energy performance of an Heat Harvesting Window integrating an air to PCM latent heat exchanger

Adaptive building envelopes can enhance building energy performance by dynamically managing ventilation, solar control, and thermal storage. This paper presents the experimental evaluation of a Heat Harvesting Window (HHW), that combines a ventilated triple glazing unit with an Air to Phase Change Material Heat Exchanger (a-PCM HEX) positioned at the cavity outlet. Unlike conventional windows or Double Skin Facades, which restrict fresh air supply in Outdoor Air Curtain (OAC) or Thermal Buffer (TB) modes, or cause overheating in Supply Air mode, the HHW continuously delivers fresh air at temperature closer to thermal comfort range, by exploiting the latent heat storage. In winter Supply Air mode, median pre-heating efficiency reached 0.7–0.8 and daily heat losses were reduced by up to 90% compared with the references, mainly by lowering ventilation heat losses. In mid-season Thermal Buffer mode, the cavity efficiency exceeded unity for nearly 40% of daytime hours, indicating frequent net heat gains from passive solar buffering. In summer Outdoor Air Curtain mode, dynamic insulation efficiency was positive for over 90% of the monitored period, with an average value of 0.75, and the HHW reduced daily heat gains by more than 40%. The a-PCM HEX provided additional air-temperature moderation, including early daytime pre-cooling of about 4 °C under peak summer conditions. The study demonstrates the potential of integrating ventilated façades with latent heat storage to develop climate-responsive envelope systems capable of ensuring continuous fresh air supply and improved thermal performance.