Question

Consider a house in Blacksburg, Virginia. The typical annual space-heating load for this size of a house is 100 x 10 Btu. That is, with no insulation in the attic, we lose about 100 x 106 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, converted to dollars per 106 Btu is approximately $21.75/106 Btu. The cost of several insulation alternatives and associated space-heating loads for this house are given in the following table. Which amount of attic insulation is most economical? The life of the insulation is estimated to be 25 years R11 1,800 74 x 106 Amount of Insulation R19 2,700 R30 3,900 67.2 x 10 R38 4,800 66.2 x 106 Investment cost (S) Annual heating load (Btulyear) 69.8 x 106 Fill in the table below. (Round to the nearest cent.) R11 R19 R30 R38 2700 3900 4800 1800 Investment cost (S) Cost of heat loss per year (S) Cost of heat loss over 25 years ($) Total life cycle costs (S)

Answer 1