Consider Design Problem 1.3 and repeat the heat load calculations by employing the natural convection correlations presented in this chapter. In order to maintain the temperature at 20°C, it is necessary to provide a heating system; two options are available. One is an electric baseboard heater and the other is a hot-water system that circulates water through a thin tube on the inside of the building. The water is heated by natural-convection combustion from a temperature of 10 to 80°C with 80% efficiency. Natural gas in Colorado costs about 14 cents per cubic meter. Electric power for an industrial organization in Colorado costs about 5 /kW h. Recommend the preferred heating system on the basis of an economic analysis.

Data from in Problem 1.3

A furnace wall is to be constructed of brick having standard dimensions of 22.5 cm × 11 cm × 7.5 cm. Two kinds of material are available. One has a maximum  usable temperature of 1040°C and a thermal  conductivity of 1.7 W/(m K), and the other has a  maximum temperature limit of 870°C and a thermal  conductivity of 0.85 W/(m K). The bricks have the  same cost and are laid in any manner, but we wish to  design the most economical wall for a furnace with  a temperature of 1040°C on the hot side and 200°C  on the cold side. If the maximum amount of heat  transfer permissible is 950 W/m², determine the most  economical arrangement using the available bricks.