In Figure 7 the influence of store insulation and UA values of the heat exchangers is shown. The highest influence on fsax, ext can be seen for the side insulation of the tank, followed by the top insulation (with lower area than the sides). The high standard variation for the insulation comes from very different variation ranges for the insulation thickness

and reciprocal dependency of heat losses of the store to the thickness of the insulation. Above 15 cm insulation of the store there is nearly no more change for all systems simulated. This is due to the short storage characteristic of all systems (maximum of fsav around 50%). For long term seasonal storage the insulation should be thicker (Streicher, 2003a).

Figure 7 Dependency of fsav, ext on specific parameter change of heat exchangers and store insulation

The insulation of the bottom of the tank is not very significant on fsax, ext, because it should be cold there anyway. Nevertheless, a little insulation should be placed at the bottom in order to avoid condensate dropping on the floor.

Figure 8 shows the dependency of fsav on the insulation for system #4. The insulation of the whole store gives an increase of fsav up to 15 cm thickness; above this value the changes are very small (ref. Figure 8 left). Top insulation is less significant than side insulation, because the top area is smaller.

Figure 8 Variation of fsav with thickness of side and bottom insulation of storage tank, example of system #4 (Bony, Pittet, 2003).

Looking for the differences of top sides and bottom insulation it can be seen, that the bottom insulation is not significant above 5 cm, because the temperature at the bottom of the tank should be low anyway (ref. Figure 8 right). Only on hydraulic layouts that also heat up the bottom of the store this value becomes more relevant.

Nearly no influence can be seen for the heat exchanger variations. Of course they should not be sized too small.