Problem # p007

Heatpump, conservation of energy, COP

A heatpump is a device which extracts heat,QC, from a cool environment ( either the outside air , or ground water , or soil ) and transfers heat into the house, QH , to compensate for the heat a house looses in the winter to the outside air. To do so the heat-pump needs an electric motor ( work W ) .    

  1. Give the equation which relates above 3 quantities, QC QH and W, to each other.

  2. Which of the above 3 quantities would be identified with the benefit ?

  3. Which of the above 3 quantities would be identified with the costs ?

  4. The coefficient of performance (COP) of a heatpump is the ratio of benefits divided by costs. For a ground-loop based system (extracting heat from the soil ) it is fairly easy to measure QC and in general the power consumed by the electric motor driving the unit can be measured as well. If
    QC = 20,000 BTU and W = 3 kW hr
    during the course of an hour, how much heat is actually supplied to the house and what is the COP ?
    1 kW hr = 3413 BTU

  5. Use the COP to explain how much better/worse the heat pump is than an electric baseboard heater.