Question

Consider a 2.4-kW hooded electric open burner in an area where the unit costs of electricity and natural gas are $0.10/kWh and $1.20/therm (1 therm = 105,500 kJ), respectively. The efficiency of open burners can be taken to be 73 percent for electric burners and 38 percent for gas burners. Determine the rate of energy consumption and the unit cost of utilized energy for both electric and gas burners.

Answer 1

Answer:

1.75 kW

$0.137 kWh

4.61 kW

$3.16 therm

Explanation:

Utilized power input of the burner is

P(ui) = total power input * efficiency

P(ui) = 2400 W * 0.73

P(ui) = 1752 W or 1.75 kW

Unit cost of utilized energy is

C(ui) = Unit cost of electricity/efficiency

C(ui) = $0.1 / 0.73 kWh

C(ui) = $0.137 kWh

Power input to the gas burner is

P(gi) = Utilized power input of the burner / efficiency of the burner

P(gi) = 1.75 / 0.38

P(gi) = 4.61 kW

Unit cost of utilized energy is

C(gi) = Unit cost of gas /efficiency

C(gi) = $1.2 / 0.38 kWh

C(gi) = $3.16 therm