The thermal performance of bikini solar combisystems is investigated for the Task 26 DHW profile for different H/D ratios of the tank. The insulation thickness is the same for all H/D ratios. The heat transfer area of the top and the bottom mantle is constant for all H/D ratios and the auxiliary set point temperatures are 55, 60 and 75°C for the low energy house, the house with medium space heating demand and the old houses. Fig. 7 shows net utilized solar energy for three different space heating systems with three different collector areas and H/D ratios of the tank. The H/D ratio of the tank does not play an important role when the heat transfer area is the same for all H/D ratios as long as the H/D ratio is higher than 2. For 3 m2 solar collector area a decreased space heating load results in an increased thermal performance of the system. This is due to the decreased set point temperature for the low space heating demands. For a collector area of 5 m2, the thermal performance in the house with the medium space heating demand is a little bit higher thermal performance of the system in the low energy house while the system has the lowest thermal performance in the old house. For a collector area of 8 m2, the thermal performance of the solar heating system in the house with medium space heating demand is a little higher than the thermal performance of the system in the house with low energy demand and higher than the thermal performance of the system in the old house.

Fig. 7. Net utilized solar energy versus H/D ratio for the bikini solar combisystem