PASCO ET-8782 Energy Transfer– Thermoelectric - Manual (Page 35)

Model No. ET-8782 Experiment 4: Coefficient of Performance
35 ®
Reversible Heat Pump
A certain kind of air conditioner, known as a reversible heat pump, can also be used to heat a
building. You will now use the peltier to model a reversible heat pump being used to keep a
building warmer than the surrounding air.
Place the heat sink on the cold block, and the foam insulator on the hot block.
Delete the data that you have previously recorded. (Click on the Experiment menu and select
Delete All Data Runs.)
Click the Start button. Make sure that the hot and cold blocks are within 0.1 °C of each other
before proceeding. (If they are not, remove the insulator, turn on the fan and wait for the
temperatures to equalize. Then turn off the fan, replace the insulator and proceed.)
Set the switch to Heat Pump mode. Allow the heat pump to run for 10 to 15 seconds, then open
the switch. Watch the temperature graphs; once the temperatures have peaked out, stop data
recording.
For a reversible heat pump heating a building, we are interested in the heat pumped into the
building, Q
hot
. (This is opposed to the previous case where we were interested in the heat pumped
out of the building.) Thus the Coefficient of Performance is
(for heating)
6) Use your values for the heat delivered to the hot block (Q
hot
) and the area under the Power
versus time curve (W) to calculate the Coefficient of Performance, k.
7) If you had used a simple resistor (rather than the peltier) to heat the aluminum block, and used
the same amount of energy (W), what would have been the maximum amount of heat
transferred to the block?
8) Compare your model to a building being heated by a reversible heat pump. What does the
peltier represent? What does the cold block represent? What does the hot block represent?
9) Why is it important for k to be greater than 1 for a reversible heat pump? Compare this to a
simple electrical heater. How much heat is delivered to a building using a simple heater
supplied with 100 J of electrical energy? How much heat is delivered to a building using a
heat pump, with k = 2, that uses 100 J of electrical energy to pump heat from outside to inside
the building?
Further Investigation
Think of a factor that you can vary in the experimental set-up. Predict how varying that factor
would affect the coefficient of performance in heating or cooling mode. Do an experiment to test
your prediction.
k
Q
hot
W
---------- =