June offered several days with exceptionally high temperatures close to 34°C and cloudless skies with high solar radiation. It allowed us to test the HyWin system under the most demanding circumstances. The “Process Chart” graph shows that under these extreme conditions, the indoor temperature was maintained at a comfortable 24°C. Compared to a real building, the test unit has a much larger surface to volume ratio and only a low thermal mass. Thus, the result is remarkable and proves that the HyWin concept ensures indoor comfort in hot summer conditions.