A heat pump uses solar heat energy stored in the ground, water or outdoor air. This is renewable and totally free! Energy usage is reduced to the electricity required to run the compressor and circulation pumps inside the heat pump which can mean an energy saving of up to 70% compared to a traditional boiler or all-electric heating. For a small premium you can choose to buy 'green' electricity which your utility company guarantees comes from renewable sources like hydro or wind. Alternatively the electricity used can be offset with electrical energy generated onsite via solar photovoltaic panels for example. Either way, you are actively reducing your carbon footprint.
The renewable heat energy in the ground, water or air needs to be harnessed, collected and delivered to the heat pump. There are a number of proven methods for doing this which vary dependent on energy source as well as building and site conditions.
How a heat pump works: inside the heat pump a refrigeration cycle takes place which is dependent on the delivery of heat energy to make the refrigerant evaporate. It changes from liquid to gas so that it can be pumped to the compressor where it is pressurised which increases the temperature exponentially. In understanding how a heat pump works it is important to highlight that the refrigerant has a very low boiling point, so even at low temperatures (as low as 20°C in the case of some outdoor air heat pumps) evaporation takes place.