Think of the way your fridge works, but your house is the outside of the fridge and the ground is the inside of the fridge. That is, the heat pump uses electric

Think of the way your fridge works, but your house is the outside of the fridge and the ground is the inside of the fridge. That is, the heat pump uses electrical energy to move heat from the ground (more specifically a deep hole that is drilled) into your house. It takes less than 1J of electric energy to move 1J of heat, therefore one can claim an efficiency >100%.