What is the January solar load fraction for a water-heating system in Washington, DC, using \(100 \mathrm{~m}^{2}\) of solar collector if the water demand is \(4 \mathrm{~m}^{3} /\) day at \(65^{\circ} \mathrm{C}\) with a source temperature of \(12^{\circ} \mathrm{C}\) ? No heat exchanger is used, and the solar collector efficiency curve is given in Figure 7.19; the solar collector is tilted at an angle equal to the latitude.

Figure 7.19

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ne collector efficiency 20 40 0 Symbol Fluid Covers Surface FRnopt FRU (W/mC) 80 1 Water 0 Black paint 0.68 34.0 50 60 23456 Water 1 Black paint 0.74 8.2 Air 1 Black chrome 0.52 4.8 Water 1 Black chrome 0.70 4.7 Water 2 Black chrome 0.61 3.2 Water Evacuated tube 0.54 1.4 3 5 0.1 0.2 Tin-Ta (km2 W Flow rates Water: 0.02 kg/s m(14.7 lb/h ft) Air: 0.01 m/s m(1.97 cfm/ft) 0.3 0.4