If you’re using one of eTool’s default hot water system templates, the formula for calculating the operational energy use for the system pulls information from the ‘Water Inlet Temperature’ field in Site Attributes tab at the Project Level.

Below is the formula for calculating the Operational Energy demand for an electric instantaneous hot water system. ‘IWT’ = Inlet Water Temperature. Refer to this page for more eTool expressions.

The default Water Inlet Temperature is 15ºC but depending on where you are in Australia or the world, the water inlet temperatures may vary which could significantly affect the energy demand on the HWS.

For our users’ reference, below is a table of the assumed average annual temperatures by capital city (Australian) based on data from the Bureau of Meteorology and Water Services Association.