Water Heater Energy Consumption

Two main types of water heaters are modeled in the Home Energy Saver, separate “stand-alone” units, and cases where the home’s heating system (boiler) provides the domestic hot water supply. When the hot water is supplied by a boiler, water heating energy is calculated in the DOE-2 building simulation model. All other water heaters are modeled according to the methodology outlined in this section. For homes with a clothes washer and/or a dishwasher, the required gallons of hot water per day is provided as an input to the hot water model (described below) by the clothes washer and dishwasher models.

This module calculates energy consumption for heating water in three steps[1]. The first step is to estimate average daily hot water use. This calculation is based on number and ages of people living in the house, presence or absence of a dishwasher and a clothes washer, the water heater temperature setting and tank size, and the local climate (Lutz, et al, 1996).

Once the average daily hot water use has been estimated, a simple calculation is performed to determine the daily energy use by the water heater. The calculation uses the energy consumption characteristics of the water heater as determined by the DOE Energy Factor test, ambient air and inlet water temperatures, and how much hot water is used on an average day. The last step is to convert the daily energy use into annual consumption of specific fuels.

Originally the Home Energy Saver addressed only storage and combined boiler water heating, however starting with the v.2013 further types of water heaters were added:

Notes:

[1] Methodology for water heating provided by combined space and water heating systems is described in Warner 2005.