Typical March day is represented by relatively low outdoor air temperatures and moderate solar radiation, so generally there is no need for cooling. Nonetheless, if the direct global radiation is high enough, it can cause overheating of internal living and working spaces. In such cases the overheating can be avoided if shading is properly used. Desired result of automated regulation of solar gains during

early spring would be the prevention of overheating during day-time but at the same time enabling adequate heat gains from solar radiation to sustain internal air temperatures above the external ones during night-time.

Fig. 2. Experiment conducted during two early spring days (9th and 10th of March). The internal conditions in the test cell were regulated according to the set-point indoor air temperature, available global solar radiation and external air temperature. The indoor air temperature profile exhibits the effect of cooling induced by shading the window from solar radiation — evident in the shift between the peaks in external and internal air temperatures as well as in 3K lover day-time and 3 K higher night-time temperatures. The internal conditions were regulated only

by the positioning of the roller blind.

Both days are characterized by very changeable weather, where times of clear and overcast sky frequently exchange. This weather pattern can be distinguished from the “spiked” distribution of measured direct solar radiation. On both days during day-time external air temperatures reached maximum levels just below 14 °C, on the other hand night-time minimal values plunged just below 7 °C. During the first day direct solar radiation reached maximum value of 433 W/m2 at 11:00. In the afternoon much lover values were recorded and the roller blind was mostly open as there was no danger of the test cell overheating. Because available solar radiation was low the roller blind was never

completely closed during the first day. On the second day external air temperatures were almost identical to those on the first day, but the amount of available solar radiation was greater. Maximum value of 706 W/m2 of solar radiation was achieved approximately at the same time as on the previous day. During times of high solar radiation levels on the second day of the experiment the roller blind almost completely covered the window, although times of fully extended roller blind were very brief. During early spring experiment the system was able to regulate internal thermal conditions in the desired way. This means that by positioning the roller blind the interior was kept cool and at the same time enough solar gains were acquired as to heat the interior of the cell during evening and night-time.