Question

Consider a house in Blacksburg, Virginia. The typical annual space-heating load for this size of a house is 100 x105 Btu. That is, with no insulation in the attic, we lose about 100 x 105 Btu per year. With insulation in the attic the amount of heat lost each year will be reduced. The value of energy savings that results from adding insulation and reducing heat loss is dependent on what type of residential heating furnace is installed. Assume that an electrical resistance furnace is installed by the builder, and its efficiency is near 100%. The cost of electricity is $0.16 per kWh. The cost of several insulation alternatives and associated space-heating loads for this house are given in the following table. Which amount of attic insulation is most economical? The life of the insulation is estimated to be 24 years.

Answer 1

Answer:

Given

Cost of Electricity = $0.16 per KWh

1 Btu=0.293 Wh

Cost of Electricity per million Btu =0.16*0.293*10^6/1000=$46.88

For R11

Cost of Heat loss Per year = Heat loss* Cost of Electricity per million Btu=74*46.88=$3469.12

Cost of Heat loss for 24 years=Cost of Heat loss Per year *24=24*3469.12=$83258.88

	R11	R19	R30	R38
Annual Heating Load(Per year)	74*10^6	69.6*10^6	67*10^6	66.3*10^6
Investment Cost ($)	2200	3800	5200	6500
Cost of Heat Loss Per year ($)	3469.12	3262.848	3140.96	3108.144
Cost of loss over 24 years($)	83258.88	78308.35	75383	74595.46
Total Life Cycle Cost ($)	83258.88	78308.35	75383	74595.46