The CSHPSS plant analyzed (see Fig. 1) is designed to serve 500 dwellings of 100 m2 in the residential area called Parque Goya, located in Zaragoza. The whole system reaches a high solar fraction (69%) of the space heating and DHW demand. The system has been modeled and developed in the software TRNSYS [10,11].The system consists of three main parts: solar field loop, space heating and DHW circuits. The heat exchangers (ex1 and ex2) connect the solar field (primary loop) to the space heating and DHW circuits (secondary circuits), since the primer uses a water-glycol mixture (67/33 weight) as heat transferfluid to protect the solar field of freezing during the winter nights. The energy harvestedby the solar collectors is transferred either to the seasonal energy storage or to the DHW storage (preferably to this one). The seasonal storage tank is a cylindrical water tank built ofreinforced concrete. It is connected to thedistribution system through a third heat exchanger (ex3) which preheats the return water from the heating network. Due to its large size, the processes of loading and unloading of the seasonal storage tank are significantly slow, which facilitates its function of covering part of the space heating demand during the winter season with the solar thermal energy that has been stored during the summer period. The DHW storage is an independent tank much smaller than the seasonal storage tank, to get in a few hours of solar heating the temperature required (60º C) for the DHW daily service. This design approach together with the priority of loading of the DHW tank with respect to the seasonal storage tank, allows getting high solar fractions for the DHW. The space heating system produces hot water at 50° C for a district heating network of low temperature.DHW