# Homework Help: Heat pump cycle

1. Sep 19, 2004

### eku_girl83

Here's my problem:
A heat pump cycle whose coefficient of performance is 2.5 delivers energy by heat transfer to a dwelling at a rate of 20 kW.
a) Determine the net power required to operate the heat pump, in kW.
b) Evaluating electricity at 8 cents per kWh, determine the cost of electricity in a month when the heat pump operates for 200 hours.

I know that the coefficient of performance = Qout/Wcycle = Qout/(Qout-Qin).
But what is meant by net power? And more importantly, how do I calculate it?

eku_girl83

2. Sep 20, 2004

### Staff: Mentor

Power to operate the heat pump is Qin.

3. Sep 20, 2004

### CharlesP

Here's my problem:
A heat pump cycle whose coefficient of performance is 2.5 delivers energy by heat transfer to a dwelling at a rate of 20 kW.

a) Determine the net power required to operate the heat pump, in kW.
20 kw/2.5 = electrical power input = 8 kw This must be the "net power."
That is about typical for a freon based heat pump. I got one.

b) Evaluating electricity at 8 cents per kWh, determine the cost of electricity in a month when the heat pump operates for 200 hours.
8 kw x 200 hr = 1600 kwh. 1600 kwh x .08 $/kwh =$128.00
Looks like a typical bill to me. But natural gas is cheaper.

I know that the coefficient of performance = Qout/Wcycle = Qout/(Qout-Qin).
But what is meant by net power? And more importantly, how do I calculate it?