The set point temperature of the auxiliary heater in both bikini and tank-in-tank solar combisystems is determined in such a way that the solar heating system can fully cover the space heating load and the DHW load. Table 1 shows the set point temperature needed for the tank-in-tank solar combisystem for three different houses and the Task 26 DHW profile. It can be seen that Model 6 and 7 have low set point temperature due to the large auxiliary volume of the hot water tank.

Table 1. Set point temperature of tank-in-tank system for three houses with the Task 26 DHW profiles

tank-in-tank solar

combisystem for three different houses with high, medium and low flow DHW profiles are shown. For the tank-in-tank system, the set point temperature is the same for the houses with low and medium heat demand and higher for the old house with a high space heating demand.

Table 2. Set point temperature of bikini solar combisystem and tank-in-tank solar combisystem for three
different houses and for high, medium and low flow rates DHW profiles for all seven models