In order to validate the presented model and to analyse performance of solar installation with stratified accumulation numerous experiments and calculations have been made. After a thorough investigation, appropriate values and formulas for parameters in mathematical equations and parameters of simulation calculation were chosen. A satisfactory coincidence between experimental and theoretical results was achieved. in fig. 3 are presented results for theoretical calculation and measured data for utilised
energy in a typical day. Since there are difficulties to arrange all initial parameters in mathematical system with real parameters for tank, solar collectors and climatic conditions, we assume that the correlation between the theoretical predications and measured data is good.

In this study are presented and discussed some results related to the influence of serpentine location in tank on the system performance. All experiments are made in approximately equal conditions. Daily water consummation has a relatively regular distribution as it is shown in Fig.2. The water consumption is 200 l per day, which is water quantity, corresponding (or little smaller) to the collector area (2 m2) possibilities for energy conversion. The solar radiation (Fig. 3) has a typical summer distribution for Bulgaria latitude and varies for different experiments in very small range. Useful (utilized) energy has a typical

daily distribution as it is shown in Fig.3. Variations in useful energy is caused by different inlet temperature for solar collectors Fig.4 shows the daily temperature distribution of water in tank for 6 sectors (layers). These results are addressed to system performance with two serpentines, located in top and bottom zone of the tank. Middle serpentine element is turned off. This is a thermally stratified accumulator because there is a top hot zone (sensors D12 and D11), middle temperature zone (sensors D8,D9,D10) and cold zone

(sensors D1…D6). Lower half of tank is with cold water (30-35oC) and small variation in temperatures. This is because there is a big quantity of water with relatively uniform temperature. The top zone is also with small temperature difference because it is constantly charged with heat by top serpentine. The most sensible to the water consumption is middle zone (sensors 8…10). Because the collector area is a bit smaller than what daily consumption require, the middle zone is situated in the upper half of the thank (D8…D10). On the other hand, cold zone is with relatively high temperature (30- 35oC) because there is a serpentine element heating the water in bottom zone.

Fig.5 shows temperatures from 5 sensors in solar installation with one serpentine configuration. The serpentine element is located at the bottom part of the tank. This is a configuration, which realize practically unstratified thermal accumulator. It is because the heat is extracted at the bottom and is transferred regularly to the top by buoyancy force. In this case the consumption is not so effective and the necessity of bigger collector area is evident. The thermal efficiency of this configuration is about 15% lower than configuration with two serpentines.

the heat exchange area is small and big water quantity is isolated from heat exchange process.

Configuration with three serpentines has nearly the same efficiency as the configuration with two serpentines and here is not presented the results for it. Thermal efficiency is little higher, but it is not sufficient to compensate additional cost expenditure. Presented results show the physical behavior of installation at special condition — daily — consumed water and distribution, climatic conditions, collector area and so on. At other conditions and parameters the behaviour will be other, but main results will resemble presented above.