Comparative study on the two testing methods to obtain the heat gain for flat-plate solar water heaters with vertical storage tanks

In this paper, the testing methods to obtain the useful heat gain for flat-plate solar water heaters with vertica1 storage tanks by the mixing-water method and by the draining-water meters are comparatively studied. The results show that the useful heat gain obtained by the draining-water method is slightly higher that that obtained by the mixing-water method. In addition, the experiments also show that in the mixing-water method the percentage of useful heat gain stored in the flat-plate solar collectors is small and hence when we conduct the testing on the useful heat gain for flat-plate solar water heaters the effect of the working medium in the flat-plate solar collectors can be assumed negligible