Page 358 - Handbook of Energy Engineering Calculations

The annual water consumption for this building is 1 gal (3.79 L) per person
per day (12 people) (250 days per year) = 3000 gal/yr (11,370 L/yr). The
energy required to heat this water, H Btu/yr = (gal consumed/yr)(required
temperature rise, °F) 8.3, where the constant 9.3 converts gallons to pounds.
Or, H = 3000(100)(8.3) = 2,490,000 Btu/yr (2627 MJ/yr).

The usable energy from the solar water heater, S = (percent annual
2
sunshine)(solar insolation on collector surface, Btu/yr · ft )(solar collect
2
heating absorbing area, ft ); or S = 0.59 (732,000)(6) = 2,591,280 Btu/yr
(2734 MJ/yr).
Comparing the heat required to warm the domestic water for this building,
2490.000 Btu/yr, versus the heat available from the solar water heater,

2,591,280 Btu/yr, shows that the solar water heater could be substituted for
the existing water heater in this building. The energy costs saved in heating
the water can be used to pay for the solar collector. Figure 16 shows a
possible arrangement for a solar water heater used as a booster heater to

reduce water heating costs in an occupied building.