An experimental study was conducted to examine the energetic and ergonomic impacts of an optimized mechanically controlled ventilation system, implemented on the partition wall between a hyper-insulated test building and the attached sunspace, to overcome most of the inherent limitations of a purely radiative heat transfer in presence of very low thermal transmittance envelope. The system comprised two vented holes (at floor and ceiling level), piloted by a smart controller on the basis of the temperature difference between the two air volumes. The threshold was progressively reduced from 2 degrees C to 0.5 degrees C to ameliorate the energy performance without trespassing the comfort boundaries. Calls for extra heating from the active technical system (electric radiators) were thus minimized, regardless of the climatic conditions: the energy consumption (normalized over the indoor-outdoor daily average temperature difference and over the daily mean solar irradiation) decremented by 36% and 66% respectively compared to the 1 degrees C and 2 degrees C configurations, which, in turn, exhibited similar performance. The ergonomic penalty due to thermal overshooting was statistically acceptable. The outcomes were compared to those of a previous monitoring run on the same case study, with 20% less glazed surface: the new configuration more than halved the energy expenditure. Finally, the albedo of the surrounding materials was shown to be a key-player: even under extremely cold and overcast conditions, the sunspace temperature rose up to 40 degrees C when fresh snow layered all around the perimeter. Further investigation could support broadening the spectrum of potentially efficient applications.