This research paper collects the outcomes of an experimental study focused on the energy benefits achieved by coupling an energy efficient building with a sunspace in winter season and Mediterranean climate.

Acting as passive Solar heating elements, sunspaces are intended to be a valuable tool among sustainable and energy-efficient constructive and/or retrofitting strategies.

In order to assess the energy saving potential of the above-mentioned coupling and relate it to the main design parameters, two operative steps were carried out: the numerical step allowed different simulated configurations to be evaluated in order to identify the optimal one from an energy perspective and physically realize it; the monitoring phase served the double purpose of calibrating the simulation model and provide on-site validated data for subsequent assessments and comparisons. Three main sunspace configurations were tested: irradiative single-glazed, irradiative double-glazed and convective double-glazed.

The convective double glazed configuration was found to outperform the others since the daily energy consumption reduction exceeded the 27% (compared to the irradiative, double glazed counterpart) for all weather conditions. Besides, the activation of a mechanical ventilation system was slightly counterproductive in terms of discomfort phenomena since a less stable indoor air temperature was guaranteed.

Comparing the two irradiative configurations, it was found that the addition of an extra glass layer was responsible of a quite constant reduction of 1 kW h/day, thus increasing the percent heating energy demand saving achieved through the insertion of the sunspace from approximately 3,3%–8,7%, while minimizing indoor air temperature fluctuations too.