These have been measured and calculated in the BESA test regime. This is the VWART (Volume Weighted Average Return Temperature) calculation and is a good guide to the HIU characteristics. VWART calculations are provided for DHW, Space Heating and Standby operational modes. Then an overall average figure is stated for each tested HIU.

Heating takes up most of the operational mode, either by radiators or by underfloor heating, and returns the highest temperatures to the network and plant. It is very important therefore that the circuit is balanced and uses the most effective means of control, and no circuits left ‘open’. Underfloor heating by nature of its lower operating temperatures is particularly suited to HIUs.

Hiper HIU by nature of being electronically controlled has an ‘optimised heating’ feature. Temperature on both flow and return are monitored by the controller, and as the room temperature gets close to the comfort level of the room, the controller then reduces the temperature to the space heating circuit, preventing overshoot of room temperature and maintaining lowest return temperatures to the network and plant.

So the important trade off against the space heating VWART is the DHW and standby modes.

Standby, or ‘keep warm’ is temperature controlled and controls and limits the return temperature to 40°C (a programmable function).