This decentralised, year-round heating and cooling system consists of a two-pipe closed loop water circuit, through which non-refrigerated water circulates continuously throughout the building. A supplemental central heat source adding heat to the loop at the lower end of the range and heat rejecter equipment capable of removing heat at the high end of the range maintains the loop water temperature throughout the year in an approximate range of (20o to 45oC). Filled with water, this circuit provides both a “sink” and “source” of energy. These systems achieve energy conservation by pumping heat from warm to cold spaces whenever they coexist anywhere within the building. Since the temperature of the water circulating is close to the room ambient temperature, all the internal pipework does not require thermal insulation. On demand for heating a space, the conditioner will absorb heat from the loop circuit, whereas on demand for cooling a space, the conditioner will reject heat to the loop circuit. The system provides the essential benefit of decentralised and individual choice of heating or cooling. The occupant may select heating or cooling or may shut off the conditioner serving an individual space without affecting conditions maintained in other spaces. The occupant may realise this freedom at any time of the day or year.