A desuperheater can be installed on your refrigeration system to obtain free hot water. You estimate you can heat 150,000 liters of water per year from 15°C (city water entering temperature) to 60°C. This will replace a natural gas water heater that operates at 80% efficiency. You pay $10.00 per GJ for your gas. The unit has an economic life of 5 years. How much can you pay for that unit and obtain a return of 12%?
Hear energy required to heat 150,000 liters of water per year from 15°C (city water entering temperature) to 60°C = mass x specific heat x temperature difference = 150,000 x 4186 x (60 - 15) = 28,255,500,000 Joules = 28.2555 GJ
The natural gas water heater is operating at 80% efficiency.
Hence, energy consumed by the natural gas water heater = 28.2555 / efficiency = 28.2555 / 80% = 35.3194 GJ
Annual electricity bill saved = annuity cash inflow = C = 10 x 35.3194 = $ 353.1938
N= economic life = 5 years
Return, R = 12%
Hence, maximum we can pay for the new unit = PV of all the electricity bills saved over next five years
= C / R x [1 - (1 + R)-N] = 353.1938 /12%
x [1 - (1 + 12%)-5] = $ 1,273.1844
Get Answers For Free
Most questions answered within 1 hours.