SOLAR ENERGY FOR WATER HEATING BROOKS 



165 



Figure 4 shows the performance of three enclosed tanks connected 

 in parallel. The tanks had been filled at 8 : 30 a. m. with cold water 

 (67° F.). The hot-water output per tank in the insulated box at 4 : 15 

 p. m. on September 12 is better than that from the exposed tank in 

 July (fig. 3). Furthermore, the exposed tank cooled nearly to air 

 temperature every night; and although the water temperature in the 

 enclosed tank dropped 25°, this drop was less than one-half the diflfer- 

 ence between the evening hot-water temperatures and the morning air 

 temperatures. It is unfortunate that usual methods of insulation will 

 not preserve a temperature the next morning at 8 : 30 a. m. high enough 

 for eflBcient clothes washing. 



The data for figure 4 were obtained with tin-plate reflectors under 

 each tank so curved that all the incident light was thrown onto the 

 tanks. The entire box appeared black from all angles except at the 

 east and west edges. In November these reflectors were removed, and 

 the entire box was painted black. The useful heat output with or 

 without reflectors was 724 B. t. u. per day per square foot of glass area. 

 The amount of solar energy received by the thin, flat absorber, was 

 1,020 B. t. u. during the day the triple tanks had reflectors, and 1,003 

 B. t. u. per square foot during the day the triple-tank box was plain 

 black. This indicates no advantage in using tin-plate reflectors in an 

 insulated box. The general results of all comparisons between the 



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FiGDRB 4. — Temperature of water drawn from enclosed triple-tank absorber, after one 

 day's heating, at 4 : 15 p. m. and 8 : 30 a. m., September 11 and 12, 1935 ; tem'perature 

 readings were taken of each 5 gallons as drawn. 



