Homework Solution

TP 4-2

Given:

        12 gallons of water
        DT = 130 ^oF - 50 ^oF = 80 ^oF
        cost of electricity = $0.08/kWh

Find:

        heat energy required to change the temperature
        cost for the temperature rise

Science:

DQ = mc DT

Solve:

m = (12 gal)(8.3 lb/gal) = 99.6 lb

c = 1.00 Btu/(lb ^oF)

Q = (99.6 lb)(1.00 Btu/(lb ^oF))(80 ^oF)

Q = 7986 Btu

1 kWh = 3413 Btu

Cost = (7986 Btu)(1 kWh/(3413 Btu))($0.08/kWh)

Cost = $0.187