Question 14.11: Calculate the energy as heat required to raise the temperatu......
Calculate the energy as heat required to raise the temperature of 150 kg of water (40 gallons, the volume of a typical home water heater in the U.S.) from 18°C to 60°C, assuming no loss of energy to the surroundings.
The energy in the form of heat required can be calculated from Equation 14.30:
q_{P}=\Delta H=nC_{P}\Delta T (14.30)
where 1\ MJ = 1\ megajoule = 1 × 10^{6}\ J. If natural gas provides the heating energy at a cost of about $1.50 per 100 MJ, it costs about 40 cents to heat 40 gallons of water from 18°C to 60°C, assuming that all the energy transferred as heat goes into the water. In practice, only about half the energy transferred as heat is absorbed by the water; the remainder is lost to the surroundings, so the actual cost is about 80 cents.