4-19 A solar collector provides the hot water needs of a family for a period of 8 months except for 4 months of winter season. The collector supplies hot water

at an average temperature of 60°C and the average temperature of cold water is 20°C. An examination of water bills indicates that the family uses an average of 6 tons of hot water from the solar collector per month. A natural gas water heater supplies hot water in winter months. The cost of natural gas is $1.35/therm (1 therm = 100,000 Btu =105,500 kJ) and the efficiency of the heater is 88 percent. Determine the annual natural gas and cost savings to this family due to solar collector.