Energy saving if electric type of water heater replaced by gas heater

A facility uses 150 KL/Yr of hot water. If the hot water is set at 55 degree C and the input water averages 20 degree C, What is the annual energy required to heat the water?

Calculate the annual operating cost if the water is heated by an electric heater (Efficiency=0.90), and a gas water heater efficiency = 0.70. Electricity cost is Rs. 7/Kwh and gas is Rs. 1/Kwh.

Q = m x Cp x Delta T

    = 150000 L/Yr x 1 Kg/L x 4.186 KJ/degree C-Kg x 35 degree C

    

    = 21976500 KJ/Yr

Kwh/Yr = 21976500/3600 = 6104.58 Kwh/Yr

For the electric water heater:

Operating Cost, Rs/Yr = 6104.58 Kwh/Yr x Rs. 7/ 0.90 = Rs.47480/Yr

For the gas water heater:

Operating Cost, Rs/Yr = 6104.58 Kwh/Yr x Rs. 1/ 0.70 = Rs.8720.82/Yr

Savings = 47480 - 8720 = Rs. 38760

Examples of the first law of thermodynamics

       1) A 1000 Watt electrical heater uses 1000 J/sec of electrical energy.  If it is 60% efficient, then the heater converts 60% of the electrical energy into heating water and 40% is wasted by being transformed into heat.

-Electric energy transformed into light and heat energy

-This is the law of the conservation of energy. It states that energy can neither be created, nor can it be destroyed. This means that the total amount of energy in the universe always remains conserved, or constant. However, energy can be changed from one form to another.

         2) When an exothermic reaction occurs some of the molecular enthalpy (energy in the molecules) of the system is converted into heat or light. This energy is then released by the system to the surroundings. The total energy of the system decreases, but the energy of the surroundings increases by the same amount.

 Energy (system) = - Energy (surroundings)

For more click on below link...

Examples of the first law of thermodynamics