The aim of investigations carried out in this work is to optimise the use of small solar heating systems for domestic sector. Demonstration project has been realized to

determine the investment cost and expenditure for construction and mounting. In a dialogue with Bulgarian solar collector manufacturers and importers, a price for small solar heating systems was analysed.

For the installation investigated in this work full price of investment is 750 Euro. This price corresponds to the Bulgarian economical standards and includes solar equipment available on the Bulgarian market in its lower price level.

Solar heating economy has to only been analysed by comparing the investment costs to the value of the calculated solar production. Two-year exploitation of solar installation shows that it can be used both in summer and in winter periods, which improves solar heating economy. In table 1 are shown results for overall solar production of installation. Calculations are made by using the theoretical model, but most of results are approved by experiments.

Calculated yearly solar energy production for a typical climatic conditions in south regions in Bulgaria is 1220 kWh. If substituted energy is electricity, which price in Bulgaria is about 0.07 Euro, the cost of solar production can be assessed to the 85.26 Euro per year. This gives payback time 8.8 years.

1. Conclusions

The thermal stratification in domestic solar hot water systems has been investigated both experimentally and numerically. Special test module with monitoring system registers all needed parameters to analyse efficiency and physical behaviour of the system. Mathematical model for thermal accumulator was validated to wide investigation scope. The main purposes of experiments relate to investigate the influence of serpentine location in the tank on thermal performance of the system. Three different configuration of serpentine location have been investigated.

Serpentine location in bottom zone of the tank realizes unstratified thermal accumulation in solar installation. Thermal stratification can be arrived with serpentine location in the top zone of the tank. Results show that the stratification in tank improves thermal efficiency up to 15-20%. This can results in using smaller collector area to prepare hot water.

Thermal efficiency in solar installations is highest when thermal stratification is stable and it is formed with heat exchange in hot and cold zone. This ensures high thermal efficiency of solar collectors and delivers useful energy on demand.

References

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2. G. F.Csordas, A. P. Brunger, K. G.T. Hollands and M. F. Lightstone, Plume entraintment effects in solar domestic hot water systems employing wariable-flow — rate control strategies, Solar Energy 49 (6), 497-505 (1992).

3. A. Shahab, An experimental and numerical study of thermal stratification in a horizontal cylindrical solar storage tank, Solar Energy 66 (6),409-421 (1999).

4. Y. Hoseon, C. J. Kim, C. W. Kim, Approximate analytical solutions for stratified thermal storage under variable inlet temperature, Solar Energy 66 (1) 47-56 (1999).

5. Zurigat et al., A comparision study of one-dimensional models for stratified thermal storage tanks. ASME J. Solar Energy Eng. 111, 205-210 (1989)

6. Shtrakov St.,A. Stoilov, Solar hot water installation with stratified accumulation, 8th

Arab International Solar Energy Conference and Regional World Renewable Energy

Congress, Bahrein 2004