The simulation analysis has revealed a number of interesting features for the system performance: (i) the collected energy is distributed to all users in a fair manner, irrespective of their distance from the collector field and the daily hot water consumption profiles (ii) an energy saving behaviour is most likely to evolve by most users, since the auxiliary energy consumptions are charged individually (unlike in large DHW solar systems with central water storage and delivery) and (iii) high values of solar fractions, comparable with those attained by thermosiphon systems, have been derived. The CCSS solar system presented can overcome the above problems by employing separate storage tanks for each family, more » thus being best suited for multistory buildings. This is due to the extensive lengths of pipework required for both the transfer of solar energy and the delivery of hot water. The common practice for large DHW solar systems, of employing a central storage and delivery facility, has been shown in the past to exhibit a rather poor performance and considerable heat losses. The thermal behaviour of a central DHW solar system, the design of which is based on a new Central Collection-Separate Storing (CCSS) approach, has been investigated theoretically. It appears that simulation work should begin to consider day to day variations in DHW =, number = , This goes against intuition, and it can probably be attributed to the fact that a modestly sized DHW system coupled to a constant DHW load never uses the diodes. TRNSYS simulations with modestly sized DHW systems with such a diode, using an identical DHW consumption day in day out, showed that contribution of good diode performance to the solar fraction was essentially zero. Tests confirmed the equation to within about 10 to 20%, and showed that under typical conditions the backup tank under solar heating conditions was only about 1/sup 0/C colder than the solar tank, an improvement of about a factor of 7 over the case with no diode. A simple equation has been developed to describe the performance. The chimney has a high conductance of heat for upflow, and a negligibly small one for downflow.
A double chimney device has been developed which acts as an effective thermal diode between a solar domestic hot water (DHW) tank and a backup heater mounted on top.