Dishwashers consume energy for both mechanical functions and water heating, with the majority of the energy used for water heating. Both machine energy and water heating energy are directly dependent upon the number of loads washed. To estimate the energy consumption of these appliances, Equations 18 and 19 use the calculation method described by Wenzel et al. (1997).
EC = ME + WE Equation 18
where
EC = Annual energy consumption in utility units
ME = Machine energy (kWh/year)
WE = Water heating energy in utility units (returned from water heater)
When ME and WE are in different units (e.g. for non-electric water heaters) the energy consumption is reported and tracked in terms of more than one fuel (e.g. 126 kWh and 23 therms).