Sequential heating arrangement

The heating that occurs as the solar thermal system heats the water before the conventional heat source provides any necessary additional heating.

This has already been touched on under 'Pre-feed cylinder'. Sequential heating occurs in all solar cylinders as the solar system heats the water to a temperature relative to climatic conditions and rate of draw-off, before the conventional heat source applies heating (if necessary) to ensure a usable temperature has been reached.

When two cylinders are fitted so that one is pre-feeding the other, it is most important to ensure the water leaving the cylinder and going to the taps has reached the minimum desired, usable temperature before heating the pre-feeding cylinder. This means that a sequence of priority applies to different, sometimes stratified volumes of water.

The priority is to achieve a usable temperature and eliminate bacteria growth. Once this has been achieved, the next step is to make best use of the available free energy in order to reduce fuel consumption and pollutants, and to save money. This is done by redirecting the solar energy from the initial priority volume to a “buffer/pre-feeding” volume where exchange can be achieved more efficiently at lower temperatures and also valuable benefits can be had more easily from low light conditions. This also allows available energy to be stored, which would be lost without the storage capacity. This stored hot water in the pre-feed cylinder will fill the primary cylinder when its volume has been drawn off: it could therefore be used, for instance, on the following day which might have a lower level of solar gain than the day before. When high demand is experienced and both the secondary/pre-feed cylinder and the primary/pre-fed cylinder have cooled, the focus of available solar energy is directed to recovering the temperature of the primary cylinder as the priority of service provision to the client’s satisfaction is paramount to an effective hot water system.