1.1. Conventional control by hot water adjustment

The conventional control strategy includes a three-way valve in the hot water circuit between solar field and chiller or storage tank and chiller to mix the return flow from generator with the supply flow from the hot water source. It can be necessary to decrease the hot water inlet temperature when solar irradiation is high as with rising driving temperature and constant cooling water temperature, chilled water temperature would decrease — constant flow rates of all external water circuits assumed. This for example could cause condensation of water at chilled ceiling panels. In case of a low chilled water temperature level (e. g. 6/12°C) a drop of the chilled water temperature can cause a shut down of the chiller due to the danger of ice formation in the evaporator. In Figure 2, a scheme of this control strategy is presented.

This control strategy can only prevent chilled water temperature from too low values. Cooling water temperature is kept constant.