Abuilding with the characteristics listed is located below where the annual heating season lasts 21 weeks. the inside design temperature is 70°f . the average outside air temperature is 30°f. the gas furnace has an efficiency of 75% . fuel costs $0.25 per therm. the building is occupied only from 8 a. m. until 6 p. m., monday through friday. in the past, the building was maintained 70°f at all times and ventilated with one air change per hour (based on inside conditions). the thermostat is now being set back 12°f and the ventilation reduced 50% during the unoccupied times. infiltration through cracks and humidity changes are disregarded . what is the annual savings? data;

internal volume: 801,000 ft3
wall area: 11,040 ft2
wall overall heat transfer coefficient: 0.15 btu/ ft2 -hr-°f
window area: 2760 ft2
window overall heat transfer coefficient: 1.13 btu/ft2 -hr-°f
roof area: 26,700 ft2
roof overall heat transfer coefficient: 0.05 btu/ft2 -hr-°f
slab on grade: 690 lineal ft of exposed slab edge
slab edge coefficient: 1.5 btu/ft-hr-°f