A HVAC system is installed to provide a comfortable and healthy indoor environment at a low carbon emission. It is not only a question about energy efficiency; but also on how effective a system can use renewable energy when available. Large surface radiant heating and cooling systems are using water temperatures close to the desired room temperature both for heating and cooling. Therefore the system is capable of any type of energy source (district heating/cooling, water pumps, ground source systems) with a high efficiency.