An alternative to using a storage vessel to maximise the use of solar heat is to match the heat demand to the availability of solar heat. This can be achieved by allowing appliances like the dish washer or the washing machine to start operating only when sufficient solar heat is available. Instead of setting the start of the washing program, the latest allowable time of stop of the program can be set.

Simulations are carried out for the base case, which includes a 3 m2 vacuum collector and a 150 l vessel. Different DHW and hot fill patterns are compared, including the one described in chapter 3.2.3, a pattern with heating demand only during the day time, one with heating demand only during the night time and one where the daily heating demand for DHW and hot fill is ‘smeared out’ over 24 hrs.

The results show a difference in primary energy savings between the different patterns in the order of 1%. This small figure is due to the fact that even a rather small 150 l storage vessel is an efficient way to match the heating demand to the availability of solar heat. The results suggest that rather than implementing complicated control devices, that may result in delays and therefore annoyance on the part of the occupant, the use of a storage vessel is a better way to maximise the use of solar heat.