A modification of the anti theta,f-chart method for solar domestic water heating systems with no mixing
Technical Report
·
OSTI ID:6522938
The importance of stratification to the performance of Solar Domestic Hot Water (SDHW) systems has been emphasized in the last several years. For a long time, the use of high collector flow rates (about 70 kg/hr-m/sup 2/) was thought to be the part of the optimum strategy for SDHW systems. Recent studies based on experiments and simulations have shown, however, that the performance of these systems may be improved significantly by reducing the collector flow rate to about 10 kg/hr-m/sup 2/. High flow rates permit higher collection efficiencies but prevent stratification in the storage tank. In addition to the gains in thermal performance due to improved stratification, a low flow strategy has other advantages such as a reduction in piping materials and parasitic power requirements. The preceding factors explain the increasing in designing SDHW systems to operate at low collector flow rates. Stratification can also be induced in the storage tank by the use of properly designed diffusers. The diffuser for the tank inlet flow is an important component since well designed diffusers prevent the momentum of the incoming fluid from destroying the stratification. Mixing in the storage tank is the main cause of the gains resulting from a decrease in the collector flow rate. A design method, based on the utilizability concept, has been developed to estimate the performance of SDHW Systems when there is no mixing in the tank. For this case, comparisons of the yearly solar fraction predicted by TRNSYS and by this new version of the anti theta,f-chart method result in a rms error of 1.5%. The method provides an upper bound for the performance of the systems studied and the original anti theta,f-chart method developed by Braun provides a lower bound. The actual performance of the system could be determined from the ASHRAE-95 standard test results.
- Research Organization:
- Wisconsin Univ., Madison (USA). Solar Energy Lab.
- DOE Contract Number:
- FG03-84SF15303
- OSTI ID:
- 6522938
- Report Number(s):
- DOE/SF/15303-2; ON: DE87010501
- Country of Publication:
- United States
- Language:
- English
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