Chapter 19, Problem 6P

Replacing incandescent lights with energy-efficient fluorescent lights can reduce the lighting energy consumption to one-fourth of what it was before. The energy consumed by the lamps is eventually converted to heat, and thus switching to energy-efficient lighting also reduces the cooling load in summer but increases the heating load in winter. Consider a building that is heated by a natural gas furnace with an efficiency of 80 percent and cooled by an air conditioner with a COP of 3.5. If electricity costs $0.12/kWh and natural gas costs $1.40/therm (1 therm = 105,500 kJ), determine if efficient lighting will increase or decrease the total energy cost of the building (a) in summer and (b) in winter.

Determine the luminous efficacy of the following lamps having comparable illumination outputs:a. A 300 W incandescent lamp that emits 5820 lmb. Two 32 W linear fluorescent lamps that emit 2950 lm per lamp in a luminaire that consumes 70 W including the ballastsc. A 70 W metal halide lamp that consumes 88 W, including the ballast and emits 5500 lm