The dimensioning method presented leads to a solar heating system with a comparably small collector area of 8.9 m2 and a storage device capacity of 0.67 m3; assuming a 60 kWh/m2 single family house located in Zurich with a hot water consumption of 3000 kWh/a. In Table 1 the optimal system configuration for these assumptions (called the base case) are summarised. To find the dimensioning parameters leading to the best cost/benefit ratio a number of simulation runs are necessary. The results of these runs — sorted by primary energy savings and

additional cost — are shown in Figure 2. Each dot in the chart represents a system with a different set of collector area and storage device capacity, leading to specific primary energy savings and additional cost. The quotient of these terms is the cost/benefit ratio which can be understood as the slope of a line through the origin meeting the respective point. The dimensions leading to the smallest gradient, which is also the tangent to a polynomial derived from all points, are the optimal dimensions (cf. [2]).