The chart above shows the temperature of both tanks when the compressor was running for 2 hours and 20 minutes and then turned off for the rest of the test. The hot side contained 189 L of water and the cold side contained 75 L of a water/antifreeze mixture (30% water and 70% antifreeze to minimize the freezing point). So while it looks like both tanks changed the same amount, the calculations will show heat is being added to the system.

Also note that the hot side started cooling down once the compressor was shut down. If the tank was insulated perfectly this line would be horizontal. I would say that I’ve insulated the tank adequately, with definite room for improvement.

OK, now for the calculations!

Before your eyes glaze over, here are a few helpful reminders: cp is a constant in this case, so don’t worry about that too much, dt is the change in temperature, and m is the mass of what is changing temperature.

Compressor on:

Hot Tank:

E = c_{p}dt m

E = (4.2 kJ/kg^{o}C) (17.3^{o}C) (189 kg)

E = 13745 kJ

Cold Tank:

E = c_{p}dt m

E = (4.2 kJ/kg^{o}C) (-22^{o}C) (75.7 kg)

E = -7134 kJ

Adding these together gives 6611 kJ (2388 kJ/hour) added to the system. This is the heat added from the basement floor warming up the cold tank.

But wait! There is more. Once I turned off the compressor the cold side kept warming up. I used the data from an hour after the compressor to find how much heat was added to the cold side.

E = c_{p}dt m

E = (4.2 kJ/kg^{o}C) (4^{o}C) (75.7 liter) (1 kg/liter)

E = 1310 kJ

So this setup can pull 2388 kJ/hour when the compressor is running and 1310 kJ/hour when the system is not running.