The quantity of hot water used by the dishwasher is sent to the water heating model, which calculates the energy consumed to supply this amount of hot water to the dishwasher.

Home Energy Saver

In HESaver professional and consumer versions the daily hot water usage (gallons) attributable to the dishwasher is calculated according to Equation 20 (Koomey et al. 1994).

 

           Equation 20

where

Use_day = hot water use (gallons/day),

Loads_week = number of loads per week,

Use_load = hot water user per average load (gallons/load)

7 = days per week

Energy consumed by the water heater in providing the necessary amount of hot water for the dishwasher is calculated by the water heating model and incorporated into Equation 18 to arrive at the total energy consumption for the dishwasher.

Scoring Tool

The scoring tool method is similar in outline to that of the Home Energy Saver, however, it does not take an input for washer loads, instead loads are estimated based on number of (occupied) bedrooms, using the Building America calculation method (Hendron, R. and Engebrecht 2010). Consistent with the asset rating approach the hot water use per cycle is invariant in Scoring Tool. The gallons per cycle estimate is from Parker, D., P. Fairey, and R. Hendron (2010).

                    Annual dishwasher hot water use = hot water use per cycle * cycles per year            Equation 1.

                    Where:

                        Dishwasher cycles per year = 88.4 + (34.9 * number bedrooms)

 Dishwasher gallons per cycle = 4.64 * (1/0.46) - 1.9295 = 8.1

Daily hot water use is passed to the hot water method, and is calculated as Annual dishwasher hot water use/365