Problem 91P

Analyzing Thermodynamic Cycles

A heat pump maintains a dwelling at 68°F. When operating steadily, the power input to the heat pump is 5 hp, and the heat pump receives energy by heat transfer from 55°F well water at a rate of 500 Btu/min.

(a) Determine the coefficient of performance.

(b) Evaluating electricity at $ 0.10 per kW · h, determine the cost of electricity in a month when the heat pump operates for 300 hours.

a.)

Step 1 of 2

We have to determine the coefficient of performance for the heat pump.

The coefficient of performance is given by the expression

Where,

= is the energy discharged by heat transfer from the system

to the hot body

= heat energy the pump receives by heat transfer from the well

= 500 Btu/min

= net work input = 5 hp

So,

Now,

Hence, the coefficient of performance is

Thus, the coefficient of performance is 3.3.

b.)