Analysis of water heater standby energy consumption from ELCAP homes

The Bonneville Power Administration (Bonneville) routinely prepares forecasts of future energy demands in the Pacific Northwest region of the United States. Bonneville also implements conservation programs to reduce load demands. Results from the End-Use Load and Consumer Assessment Program (ELCAP), undertaken by the Pacific Northwest Laboratory for Bonneville, indicated that single-family homes with electric space-heating equipment consume more than 4700 kWh/yr to heat water for domestic uses. This energy use amounts to about 23% of the total electricity consumed. Additionally, the peak consumption for water heating coincides with regional system peak demands. Detailed analyses of the water heating end-use data acquired for residential buildings in ELCAP reveal that the average standby load for existing homes is 1200 kWh/yr, while homes built as part of the Residential Standards Demonstration Program averaged 1100 kWh/yr. These figures are consistent with the current figure of 1300 kWh/yr that is being used in the regional energy forecast. We also determined that standby loads for some of the participants were behaviorally driven. The data indicated the occurrence of vacancy setbacks in which the participant appears to lower the thermostat to save energy while the house is vacant. Anecdotal evidence from interviews revealed that this does occur. Reasons for setting back the thermostat ranged from not thinking about using the breaker, to fear that the tank would freeze in cold weather. These types of activities also appear to create the occurrence of dueling thermostats where the upper and lower thermostats, after the vacancy period, are not returned to the same temperature. This leads to additional energy use in an attempt to maintain a uniform temperature in the tank.