Probably the simplest illustration of how a heat pump works can be found with any home refrigerators.

If you've ever wondered how a refrigerator works, the mechanics inside can vary, but the principals are the same. Refrigerators simply remove heat from the items placed inside - it moves heat from inside the compartment to the outside. The resulting effect is that anything inside the fridge gets cold.

Thermodynamic laws dictate that temperature in any environment tends to normalize amongst each object in that environment. In keeping with this, we can better understand - a warm object placed inside a refrigerator among cold objects will eventually equalize in temperature.

So a thermal heat pump - refrigerator in this case, works by transferring the warmth of objects inside to the outside. This explains why you may have noticed the back and sides of your refrigerator are warmer than the other surroundings in your home.
 

Source:  Air Source Heat Pump ,  Heat Pump

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