Computer simulation analyses for solar combisystems with solar collectors with different rate of evacuation, different types of collector-building integration and different types of heating systems have been performed and several result sets have been obtained. Fig. 3a-c show the performance characteristics of investigated solar combisystem configurations (heating systems, flat-plate collectors, type of installation) expressed by means of system solar fraction f and specific stagnation time bst dependent on collector area Ac as variable parameter.

Fig. 3b. Solar combisystem performance characteristics with different types of solar collectors and radiators

for space heating (55/45°C).

Fig. 3c. Solar combisystem performance characteristics with different types of solar collectors and floor

heating (35/25°C).

As illustrated in figures 3a to 3c the performance of the solar combisystem (solar fraction) generally increases with the decrease in operation temperature for the space heating system and higher degree of solar collector evacuation due higher efficiency. On the other side, increase in solar fraction by enlargement of the collector area of its efficiency is always coupled with increase in stagnation time. Direct integration of solar collectors into the roof (thermally coupled without air gap) when compared with facade collectors results in higher solar fraction but leads also to considerably higher stagnation levels and specific stagnation time due to an unutilisable summer irradiation peak. General comparison of the separate installation of solar collectors on the roof or formal roof integration (with ventilated air gap as major type of roof integration) with facade direct integration leads to a different situation. For most of the investigated configurations the facade solar collectors result in lower or equal collector area needed compared to separate roof installation, especially when solar fraction above 30 % is required. At the same time, considerably lower stagnation times are achieved for faqade collectors.

Fig. 4 shows the change of solar fraction Af [%] for usual combisystem collector area of 10 m2 for investigated configurations related to reference case (atmospheric collector, separate installation, 55/45 °C with fAS55 = 28 %). Integration of all investigated solar collector types into the roof and integration of atmospheric and evacuated solar collectors into the faqade results in higher solar fraction of solar combisystems, especially above > 8 m2 of collector area (in the graph 10 m2). Additionally, the diagram shows the influence on solar fraction of different supply temperatures for heating of the building. As previously mentioned in general, lower supply temperature leads to higher performance of the solar combisystems, e. g. using 10 m2 separate installed atmospheric flat — plate collector combined with a low-temperature radiant heating system (35/25 °C) leads to an increase of solar fraction by 3 % (/As, 35 = 31 %) compared to reference system. Contrary, higher operation temperatures e. g. for air heating system (75/65 °C) decreases the solar fraction by 3 % (/As, 75 = 25 %).

Fig. 4. Change of solar fraction for collector area (Ac = 10 m2) based on reference case (/As, 55 = 28 %).