EXAMPLE 2-15 Cost of energy for cooking with electric and gas stoves

The efficiency of cooking appliances affects the internal heat gain since an inefficient appliance consumes a greater amount of energy for the same task, while the excess energy consumed is manifested as heat in the surrounding space. The efficiency of the open burners is determined as 73 percent for electric units and 38 percent for gas units (Fig. 2-59). Consider a 2 kW electric burner at a location where the unit cost of electricity and natural gas is $0.09/kWh and $1.20/therm, respectively. Determine the rate of energy consumption and the unit cost of energy for both the electric and gas burners.

Please give explanations of the exercise and the illustrated image as to what is happening.

Schematic of electric heating unit with an efficiency of 73 percent and a gas burner with 38 percent, discussed in Example 2-15