Question

100 60 W incandescent lamps will be replaced by 32 W fluorescent lamps. Compute the savings in air conditioning energy that this replacement will enable if the building air conditioning runs 4500 hours/year. The air conditioner has a COP=2.8.

Answer 1

Effect of bulbs on Air-Conditioning: When bulbs are glowing, most of the electrical energy is converted into heat and some amount of electrical energy is utilized to provide light. So when we use glowing bulbs in an air-conditioning room, the heat from bulbs will result in increase in room temperature and thus require air-conditioners to work more for maintaining colder temperatures. Therefore, glowing bulbs will increase load on air-conditioners.

Let me explain the question as a situation.

There are 100 incandescent lamps. Each incandescent lamp consumes power of 60Watts. Now we are replacing all these incandescent lamps by fluorescent lamps. Each fluorescent lamp consumes only 32Watts. Observe that there is a decrease in power consumption due to replacement of bulbs. The decrease in power consumption = (60 - 32) = 28Watts per bulb. As we are replacing all the 100 bulbs, the total decrease in power consumption is 28*100 = 2800Watts = 2.8KW.

• We can say that total KW savings = 2.8KW.

The decrease in heat generation by lamps will reduce work load on air-conditioners. Given Coefficient Of Performance (COP) of air-conditioner is 2.8

Now the air-conditioner savings are given by :

• Air-conditioner savings =
• = (2.8 * 4500)/(2.8) = (12600)/(2.8) = 4500 KWh per year

Therefore the answer is 4500 KWh/year.