How does a heat pump work?
When a building gets warm, the heat pump pushes heat from the building into the ground (for cooling in summer). In the winter, the heat pump will reverse and take the heat from the ground and use it to heat the building. Buildings may also want to create hot water or heated floors using this heat.
The system has to be balanced and/or big enough so that the earth around the piping does not get too hot in the summer (because it will have a hard time dumping more heat in to make the building cooler) or too cold in the winter (because it will have a hard time retrieving enough heat to distribute into the building).
A basic residential heat pump
A comprehensive residential heat pump
To explain further, take a refrigerator, for example:
The air inside your fridge is cool, but if you feel behind your fridge, you’ll notice the air is warm. That’s because a pump is taking heat energy from inside the fridge and pushing it out the back and into the room. Think of it this way, if you filled your fridge with jugs of warm water, heat would be taken from the jugs to make them cool. The heat would be rejected into the kitchen through the coils at the back of the fridge. If you kept removing the cold water and replacing it with warm water, the fridge would heat your kitchen.
Note: A heat pump system can be referred to by a number of different names such as: ground source heat pump system, geoexchange system, earth coupled system, and earth energy system.